The Stellar Heavens

M ed u m 8vo h e 1 05 . 6d . i . , clot xtra, F L A M M A R I O N ’S P O P U LA R A S T R O N O M Y

Tr nslated m the e c . ELLA G E a fro Fr n h by J RD OR ,

With 3 Plates and 288 Ill ustrations . The six books into which the b ook is d ivid ed give a very lu cid and accu rate d esc ription of t he knowledge whi ch has be e n acquired of the m v b od e o f c e b h e ec he m and h c c i o ing i s spa . ot as r sp ts t ir otions p ysi al onst in e m of f t he a we can e e . N ot tu rions. O transl tion only sp ak t r s prais

d e it e e e e the a b u t M r . e has dd ed u efu e only o s w ll r pr s nt origin l , Gor a s l not s f r t he u e of b t he f m u d e and has o p rpos ringing in or ation p to at , also — — increase d the nu mber already very consid e rable o f t he e xc e lle nt illustra t ha t he is l e bec m e ul in E d it has tions , so t work ik ly to o as pop ar nglan as ' — i F A tlzene u m . bee n n rance . ‘ h M r E G e has ed E h has m The wh c . . d e work i . J or translat into nglis a for itself a nam e and re pu tation in Franc e and has gone into general f hu d ed h u d c e Th f c c ircu lation t o the nu mbe r o a n r t o san opi s . is last a t is proof how well within the bou nds o f possibility it is to make t he latest d is c e e of c e c e c m ehe b e and f sc t o the c m m m d ov ri s s i n o pr nsi l a inating o on in . M Flam m ar ion has e d h u m h h u h the of his w . attain t is tri p t ro g grasp kno ed e t he u c d of his e and his e o f b i h m e t he m l g , l i ity styl , pow r ring ng o ost stu pe ndou s and c omplicated o f the things re vealed to u s in the d epths of ' ac e M Flam m ar ion s e h u d fi nd m r e cc e ce sp . . pag s s o l al ost as g at a ptan in h u in his o wn S m c o f e m e and of e me ar e t is c o ntryas . i pli ity arrang nt stat nt i f s u c c ss —Seotsm an part o f h s c harm and o hi s e f . ' me if d e not d E M . Fl m m a e v u ce its h a rion s lat st ol , it o s ispla nglis rivals , a he t o wh c I i f m ay well take a high pl c e in t rank i h they b elong . t s u ll ' M r e c a e fu e d u c d and ha . e u e . l i , , t nks to Gor s r l r vision , w ll p to at ’ r r e ed c e fu b u h ab e o f the l e d c e i e M . Go s ition is so ar lly ro g t r ast at st is ov r s that the English stu d ent m ay now congratu late himself on be ing in an eve n ' ' f M Fla -Da zl l e a h m e . m mar i n Chr oni be i h t e c u o o . c e tt r posit on t n o ntry n y . You ng stu d e nts o f astronomy who wish t o obtain a general id ea o f the most wond erfu l and fasc inating of all sc ie nces will fi nd prec isely what they ’ M m m u e and e c T in F e c h e . he r see k . la arion s loq nt po ti apt rs re a e u r h e and c e t r t J- eaker many ill st ations in t is abl attra tiv ea ise Sfi . I is f sc e e d t o e e e hu d ed e and t a a inating work , xt n ing n arly s v n n r pag s , d ealing in popu lar langu age with som e of the most interesting of t he d is ' ver ies and f m e s — Dail N ews co spe cu lations o astrono r . y . M F mm is u d c c m e he has e de ed od . la arion a so n pra ti al astrono r ; r n r go and l b u e v c e the c e c e and he e e u b e f cu of a orio s s r i to s i n , poss ss s a val a l a lty u l e The u m e fu e and wel u ed me pop ar xposition . vol is pro s ly l ill strat , so ' f the be m h fi s — at u r d a R o e he e e e ce . S ev iew st plat s aking r t ir r t app aran y . ' A h h ac e m u be c c d ed t o Flam m ar ion s P u A m ig pl st a or op lar strono y. Never be fore has the science o f the heave ns b ee n treate d with su ch fu lness and interest as in this fascinating book ; for Flammarion is a m an of lette rs e m an of c e ce—a m an o f e e t oo e d wed w h the as w ll as a s i n l tt rs , , n o it wondrou s gifts of lu cidity and charm which d istingu ish the best French ’

i e . F m m i b is mu c h m e b b h m e wr t rs la ar on s ook or a sor ing t an ost nov ls , m e m c h m m c e m e e c h m e m et or ro anti t an ost ro an s , or po ti t an ost po s , y ' c and c e ﬁ c c — u d l r c u e . L ate M onth st i tly s i nti ally a rat g y . I m u be c fe s ed h M F am m h . not e s t e e t st on s t at l arion only arr st att ntion , — b u t assists the read er to grasp astronom ical theories a task in whic h le ss ’ ’ u a e s f e fa he he m ak e t h m —Lzfem ¢ or ld e e W . pop l r writ r o t n il w n t y att pt. y The b is m f c o ne and h d t he e d e f m t o ook a ost as inating , ol s r a r ro start h As m u f r h ﬁnis . a an al o t ose who wish t o obtain a good gener al know ' ed e of m h l be f u d u e — i S c enc Goss . l g astrono y t is work wil o n nsu rpass d . i e p ’ L N D N CH ATT W N DU S 1 1 1 ST MART N S LAN E W O O O I , . I , . C. TH E STELLA R H EA V EN S

' ‘ A N I T RO U CT IO T O T H E Sf TUDY O F N D N , T HE ST A RS A ND NEBU LZE

L E L L ARD GORE

H onor ar y [Member of Me Liv erpool A str onom ic a l Soc iety A ssoc iate of Me A str onom ical Soc iety of Wales ; Cor r esponding ( t/ze lo t a t y Tor on A s r onom ic l S ocie y,

A U T H O R O F ‘ ’ ‘ T H E SCEN ERY OF T H E H e A VE N s H E VI SI B LE N IV ER E , T U S , ’ ’ ' ‘ T H E WORLDS OF SI ACE S A R G ROU Ps E TC. , T ,

L O N D O N C H A T T O WI N D U S ‘ I 9O 3

P R E F A C E

STE LLAR or S I DE RE AL A STRO N O MY is that branch of the

science which deals with the n umber , motions , distances ,

. of . The etc , the stars term may be extended to include the nebul ae .

The following pages contain descriptions and details

, of the most interesting objects among the stars and

The f f nebul ae . in ormation has been care ully brought

and f f to u p to date , will , it is hoped , be ou nd use ul the beginner , as well as to the more advanced student f o the stellar heavens .

J. E . G ORE .

F ebr uar y: 1 90 3 .

C O N T E N T S

C H A P T E R I

T HE ST ARS

PA G E — — The Constellations Number of Stars Star Magnitu de s — Colours of Stars— Spectra— Parallax and Distance — Absolute Size— Proper Motions— The Sun’s Motion in Space

C HAPTER I I

A N D B N T DOUBLE, MULT IPLE, I ARY S ARS

' — - — Dou ble Stars Naked eye Dou bles Te le sc 0 pic Doubles — — — Triple Stars M u ltiple Stars Discovery of B inary Stars Orbits of B inary Stars Spe ctroscopic B inaries

C HAPTER I I I

VARIABLE ST ARS

Variable Stars— Classes of Variables—Temporary or New — — Stars Long-Period Variables Irregu lar Variables — Short Period Variables - A1gol Variables Cl u ster — — Variables Suspected Variables Method of Ob se r vation CONTENTS

CHAPTER IV

ST AR CLUST ERS AND N EBU LIE

PA G E — — Glob u lar Clusters Irregu lar Clusters Irregular Nebul ae — Spira1 Nebul ae Planetary Nebulae Annular — N eb u lae N eb u lo u s Stars

C HAPTER V

T HE ST ELLAR UN IVERSE The Milky Way— The Stellar Universe—The Nebular Hypothesis TH E STE LLA R H E AV E NS

CH APTE R I T H E S T A R S — The Constellations -N u m ber of St ar s Star Magni — — t u des Colou r s of St ar s Sp ect r a Par allax and — — — Distance Absolu te Siz e Pr oper Motions The ’ Su n s Motion in Space .

— The V a The Constellation s, stars isible to the n ked

a a . eye have been divided into groups , c lled constell tions

T r e fl f r of f hese a now chie y u sed o the purpose re erence , but in ancient times they were associated with the figures of a a The of men and nim ls , etc . origin these constella a f tion figures is somewh t doubt ul , but they are certainly ’ of 8 great antiq uity . Ptolemy s constellations were 4 in

ff f B . C . n umber , but di erent writers , rom the first century , ’ a f 6 2 B give various n umbers , r nging rom 43 to . ayer s 1 6 0 a 6 0 1 2 a Atlas , published in 3 , cont ins , new constell tions in the Southern H emisphere having been added T ’ Th by heodorus to Ptolemy s origin al 48 . e present B ’ n umber is 84 . ayer s Atlas was the first to show the S outhern sky , and the first to designate the brighter

a of a a a st rs by the letters the Greek alph bet , ( lpha) , 2 THE STE LLAR H EAVEN S

e 8 B (b ta) , 7 (gamma) , (delta) , etc . (see Appendix , K Fl m a st ead A 1 2 . Note ) . publishe d an tlas in 7 9 Maps and catalogues of the n aked -eye stars have been a A B published in recent ye rs by rgelander , ehrmann , H H Of H ’ eis , ouzeau , Proctor , an d others . these eis s —at a far as a a is , perhaps , th e most reliable le st , so ccur te T star magnit udes are concerned . h ey ex ten d from th e ° ’ f E B e hr m nn s North Pole to 3 0 south o the quator . a maps are conﬁned to the Southern H emisphere between 0 ’ an 20 f E H u z e u the Sou th Pole d south o the quator . o a s

A both all a tlas shows h emispheres , th e st rs having O f A been bserved by himsel in Jamaica an d South merica . ’ Th Of U e maps the ranometria Argentina , by Gould , show all the Southern stars to the seventh magnitude of E of ar e (an d some north the quator) , but man y these beyon d the reach of ordin ar y good eyesight . A n opera

all . glass will , however , show them

The ﬁgures representing the constellations were originally S ar e drawn on pheres, or celestial globes, as they now called .

They are therefore reversed, the stars being supposed to be viewed from the centre of the sphere . The ancient astronomers attributed the invention of the sphere to Atlas . It seems certain that a celestial sphere was constructed by Eudoxus so

B . far back as the fourth century C . Strabo speaks of one made

Kr ate s 1 0 B . C. t o by about the year 3 , and , according Ovid, Archimedes had constructed one at a considerably earlier period . None of these ancient spheres have been preserved . r There is , however, in the Vatican a fragment in ma ble of a - Greco Egyptian planisphere , and a globe in the museum of

Arolsen, but these are of much later date . Our knowledge Of the original constellation ﬁgures is derived u from the acco nts given by Ptolemy and his successors , and from a fe w globes which only date back to the Arabian period of astronomy . Among the Arabian globes still existing, the most famous is that preserved in the B orgia Museu m at Vel

. C u letri in Italy It is made of opper, and is s pposed to have TH E STARS 3

be en made by a person called Caisar, who was executed by the

1 22 . S u ltan of Egypt in the year AD . 5 The most ancient of all is one discovered some years ago at Florence . It is supposed

A . D. 1 08 1 . to date back to , and to have been made by Meucci

There is also one in the Farnese Museum at Naples , made in

A D. 1 22 . 5. Of modern celestial globes, the oldest is one made o by Jansson B laeu in 1 603 . This shows all the c nstellations ’ of both hemispheres . Ptolemy s ﬁgures of the constellations Diir e r N u r e m were restored by the famous painter Albert , of in 1 1 berg , 5 5, and the ﬁgures on modern globes and maps have ’ Dii r e r s been copied from this restoration . maps are now very rare . A list of the constellations , with the Arabic names of the principal stars , will be found in the Appendix (Note A) .

r — The Of N u m ber of the Sta s , n umber stars visible to the n aked eye is much less than might be supposed

f To d a rom a casual glan ce at the sky . or in ry good eye ar e whole a sight about stars visible in the he vens , f and there ore only at any given time and place . The tot al n umber visible in the largest telescopes is probably about

u In the famous catalog e of Hipparchus, formed in the year ’ - ‘ 1 2 B . C. 7 , there are only stars . Al Su ﬁ s Description of ’ the Heavens, written in the tenth century , includes stars , bu t he refers to many others , without, however, giving their — exact position . The famous German astronomer Heis who — had keen eyesigh t shows in his Atlas stars visible to the naked eye north of the Equ ator and more between the ° 20 u Equator and so th declination, or a total of stars ° e 20 u b tween the North Pole and so th declination . If we

suppose the remainder of the sky to be of the same richness , this would gi ve a total of stars visible to the naked eye in

. B both hemispheres ehrmann, in his Atlas of the Southern ° s heavens , hows stars between 20 south declination and

the South Pole . This gives stars for the whole sky . t B Adding all hose seen by Heis and ehrmann , we have for the e whol sky stars . The average of these thre e results is B t z wh The elgian as ronomer Hou eau , o Observed the I — 2 4 THE STELLAR H EAVEN S s tars in both hemispheres , shows a total of for the whole 6 - sky . These observers noted all stars down to 7 magnitude , o or slightly below the sixth magnitude , which is supp sed to be about the limit of ordinar y eyesight . Persons with exceptionally keen vision may perhaps see a slightly larger number . For m stars to the seventh agnitude, Gould found a total of ° stars between the South Pole and 1 0 north of the Equator . This gives for the whole sky a total of stars to the

. B s e venth magnitude Mr. Gavin J . urns ﬁnds from the Harvard photometric measures a total of stars down to magnitude

in the whole sky, and the present writer finds from the ’ Harvard Photometric Durchmusterung a total of stars ° from 6 0 to 6 9 9 between the North Pole and 40 south declina for o 6 0 tion , which would give the wh le sky stars from 1 ’ 6 . . B to 9 9 magnitude Adding this to Mr urns result, we have a total of stars down to magnitude There are , probably, not very many people , however, who could see a star of the seventh magnitude without optical aid . of As we descend in order faintness , the number of stars rapidly increases, but until the photographic charts of the heavens, now in progress , have been completed, it is not easy to estimate the probable number visible in the largest telescopes . ‘ ’ Sir William Herschel , in his gauges of stars in the Milky Way, e 1 8 made with a reflecting tel scope of 7 inches aperture , found 00 about 5 stars to the square degree . As the whole star sphere n e B contai s square d grees (see Appendix , N ote ) , this u B u t wo ld give a total of about for the whole sky . u in the Milky Way is of co rse exceptionally rich small stars , and does not represent the whole heavens . Taking the area covered by the Milky Way as one -fourth of the star-sphere — a very lib e ral estimate and its richness as five times that Of the remainder of the sky (on an average) , I find a total of about A photograph of a rich Milky Way spot in the

e . 1 8 8 const llation Cygnus , taken by Dr Roberts in 9 , shows

stars in a space of three and a half square degrees . This would give a total of about B u t another photo e graph , taken near the pole of the Milky Way with the sam

1 ou r nal B r itish A str onom ical A ssociation 1 0 2 j , January, 9 . TH E STARS 5

o telescope, w uld indicate a total of only We may therefore conclude that a total of about will not be u very far from the truth . This is the n mber now usually assumed by astronomers .

— The e St ar Magnitu des, most casual obs rvation will Show that the stars differ considerably in their apparent t ‘ O ff f brightness . S . Pau l says ne star di ereth rom ’1 ar e of another star in glory . I n deed , there stars all of — f S degrees brightness rom irius , the brightest star in

a fa the he vens , down to the intest visible in th e largest ’ The ‘ telescopes on the clearest nights . term magnit ude , a a a when applied to the st rs , mean s their pp rent bright a a ness , not their bsolut e size , which in most c ses is unknown . Ptolemy divided those visible to the naked a eye into six cl sses , the brightest being called ﬁrst mag nit u de fa ; those considerably inter , the second ; those fa and much inter still , the third ; so on to the sixth fa magnitude , which were su pposed to be the intest , j ust n visible to the naked eye o a clear an d moonless night .

T f . hus , the larger the n umber , the ainter the star

Ptolemy only noted whole magnitudes , but the Persian

Ai-Su ﬁ u astronomer , in the tenth cent ry , divided these

a for . T m gnit udes , the ﬁrst time , into thirds hus , a star slightly fainter than an average star Of the ﬁrst magni

1 -2— 1 a 2 one t ude he called that is , nearer to th n ; a 2 - 1 or a little brighter than the second he called , ne rer 2 2 a 1 and on T has f th n ; so . his method been ollowed a B a H in modern times by Argel nder , ehrm nn , eis , an d H a a of H ouze u , but in the photometric c talogues arvard , f Ox ord , and Potsdam th e magnitudes are measured to f T f t wo decimals o a magnitude . his has been oun d

1 1 . 1 Cor. xv . 4 2 line not o o A short between the ﬁgures a c mma or p int, as sometimes stated . 6 TH E STE LLAR H EAVE NS

n a for a a as the ecess ry gre ter ccuracy , h eaven s contain of all of stars degrees brightness . Although the ancient astronomers included all the very

brightest stars in the first magnitude , there are in reality several stars brighter than a standard star of the first magni A a tude , such as ldebaran ( Tauri) . These are Sirius, which is nearly eleven times brighter than Aldebaran (according to the a a u revised me sures at Harvard) Canopus ( Arg s) , the second brightest star in the heavens and about two magnitudes brighter a than Aldebaran ; Arcturus, Vega, Centauri , Capella, Rigel, a 3 a B Procyon , Eridani , Altair, [ Centauri , and Orionis ( etel a a geuse) . Of these , Canopus , Centauri , Eridani , and B Cen d o tauri are Southern stars , and not rise above the English - 1 horizon . Al Su fi noted thirteen stars of the first magnitude

visible at his station in Persia, and Halley enumerated sixteen h in the whole sky . According to the Harvard p otometric

measures, there are thirteen stars in both hemispheres brighter

1 0 Se e . than Aldebaran , which is rated 7 ( Appendix, Note C) For the study of the stars and constellations Proctor’s large

A tlas is perhaps as good as any other . The meaning of the ‘ ’ term magnitude is the ratio between the light Of any star

and that of another exactly one magnitude fainter . This ratio ff has been variously estimated by di erent astronomers, and f 1 8 1 0 6 ranges from 5, ound by Johnson in 5 , to 3 , assumed 1 8 8 by} Peirce in 7 . The value now universally adopted by astronomers is (of which the logarithm is This

number is nearly a mean of all the estimates made , and agrees with the value found by Pogson in 1 854 by means of an Oil

Z Ollner 1 8 0 . ﬂame, and by Rosen with a photometer in 7 It simply m eans that a star of the ﬁrst magnitude is 2 51 2 times the brightness of a star of the second magnitude a star of the

second times brighter than one of the third , and so on . This makes a star of the ﬁrst magnitude j u st a hundred times

brighter than one of the sixth . Thus , Aldebaran is equal in

1 9 is Inclu ding the star Eridani , which now only of the S third magnitude , and has probably faded in brilliancy ince ’ - Al Su ﬁ s time . TH E STARS 7

n 1 00 x bright ess to stars of the si th magnitude , and Sirius would be equal to a close cluster of about sixth -magnitude stars

(see Appendix, Note I ) . The following may be taken as examples of stars of the different magn itudes ; they are derived from the Harvard m : easures First magnitude , Aldebaran and Spica ; second u 3 a magnit de, { Aurig e and B Canis Majoris ; third magnitude, c a O hiu chi u 9 Aurig e and B p ; fo rth magnitude , Herculis and

e a w . Draconis ; ﬁfth magnitude , p Urs e Majoris and Sagittarii

Stars of about the sixth magnitude are, of course, numerous,

- and lie near the limit of ordinary naked eye vision , although on clear moonless nights still fainter stars may be ‘ glimpsed ’ by - keen eyed observers . The sun’s stellar magnitude is the number which represents the sun’s brightness as seen from the earth on the above scale e e of star magnitudes . Various estimates of its valu have b en 26 - 2 made , ranging from to 7, and it may be taken at about

° 26 5 (or abou t times brighter than Sirius) .

— m a Colou r s of Star s , As y be noticed with a little a of ff attention , the st rs visible to the naked eye are di erent

of . S ar e or shades colour ome white , even slightly bluish ,

S or a . like irius Veg Some are distinctly yellowish , as

a . S A C pella ome have an orange h ue , like rcturus , an d m a n so e are notably reddish , like Aldeb ra , Antares , and B a etelgeuse . Perh ps the reddest star visible to the ‘ a . of Sir n ked eye is p Cephei , the garnet star William

H as a f erschel ; but it is only bout the ourth magnitude , - a its colour is hardly perceptible without an opera gl ss . ‘ a H ae Red B Other reddish stars are ydr , called the ird

7 by the ancient Chinese , 7 and p Geminorum , p. an d v U a M a 8 A O hiu c hi ae rs joris , an d Draconis , ﬂ p , y A quil ,

H e etc . I n the Southern emisphere Crucis (in the 2 S r M ae 8 outhern Cross) is decidedly red , an d p usc , an d -1 71 T Gruis , and others , are very reddish . here is some — reason t o think that Sirius which is now a white star ot was red in ancient times , but the evidence is n concl u 8 TH E STELLAR H EAVEN S

The A sive . variable star lgol is , however , distinctly Al- u ﬁ described as red by S in the tenth cent ury . It is a now white , an d there can be little or no doubt th t it has ’ l- u ﬁ s e T of ch anged in colour since A S tim . his change colour in Algol seems to lend su pport to th e su pposed A t h change of colour in Siriu s . mong e telescopic red stars t here ar e several which have been suspected of T being variable in colour . here is no star visible to the

a o f - or n ked eye a well marked bluish greenish colour , although among the telescopic double stars almost all colou rs seem to occur . A catalogue of red stars was published some years ago by B u Mr . John irmingham , of T am , Ireland . This was revised and extended by the Rev. T . E . Espin , in the year 88 B u 1 8 . oth these catalogues were p blished by the Royal Irish

Academy . Red stars are remarkable from the fact that their ff su n u spectra di er considerably from that of our , th s showing A a different physical constitution . m ong them are many of the most remarkable of the variable stars, an interesting class of

Objects which will be considered in another chapter . A list of the most remarkable red stars at present known will be found in the Appendix, Note D .

-The of Sp ectr a, of the Star s. spectrum a star is the narrow rainbow-tinted ban d of light which is formed by ’ the st ar s light when it is passed through a narrow slit and m a a prism . Spectra y also be Obtained by placing f Of - of T a prism in ront th e object glass a telescope . hese S a pectra are crossed by d rk lines , an d sometimes by Th f a ff a bright ones . e spectra o st rs di er consider bly ; some being very simil ar to the spectrum shown by ou r o wn and ff su n , others of quit e a di erent character , th u s ff indicating a di erent ph ysical constitution . The spectra of the stars have been divided into different classes or types, according to their character . The following is ’ Vogel s classiﬁcation

1 0 TH E STELLAR H EAVEN S

a helium , and prob bly carbon and magnesium . Sir William Huggins ﬁnds that in stars whose spectra show strong lines of B helium , such as Rigel and ellatrix , there are dark lines which probably coincide with the lines of nitrogen . These and some I ‘ others belong to a subdivision of Class . , known as the Orion ’ type . Professor Pickering divides each class into subclasses designated by capital letters . Class I . is divided into sub B classes A, , C , D , Class I I . into E to L, Class I I I . is called M , and Class IV. N . — r a l x and i n f h The d of Pa l a D sta ce o t e St ar s. istance a a f f st r rom the earth is ou n d by measuring its parallax . The parall ax of a star is the small angle subten ded at ’ Of the star by the radius the earth s orbit round the sun , or , in other words , the mean distance between the earth T f r and su n . his is the astronomical unit o all sidere al

T f n e i measurements . his small angle is ou d by m asur ng the apparen t change of place in the position of a star ’ caused by th e eart h s change of place in its an nual The motion roun d the su n . measurements , which are f c very di ﬁ ult and delicate , are usually made at intervals of Six a of months , when the e rth is at opposite points its

The a a r orbit . par llax is alw ys ve y small , showing that li f the stars e at a vast distance rom the earth .

There is no star known with a parallax ’ of even one second

a of arc . The parallax of the nearest fixed star , Centauri , is only of a second . From this the distance of the star in -fi v e miles is easily computed, and comes out about twenty and — -fi v e a half billions of miles that is, twenty and a half millions e of millions of miles (see Appendix, Note E) . The gr at majority of the stars are at such a vast distance from the earth that the parallaxes of only a few have hitherto been deter mined with any approach to accuracy . The following are, perhaps, the most reliable parallaxes yet found TH E STARS 1 1

a Centau ri .

LI. 2 1 6 1 Cygni Sirius A O . . Procyon 7' Ceti Cordoba Z one V 243 ” Cassiopei a Altair

For the ten brightest stars in the Northern Hemispheres , the following parallaxes have been recently found at the Yale University Observatory

P ar allax.

1 ’ 2 See under Proper Motions . Variable. 1 2 TH E STELLAR H EAVEN S

Sir David Gill thinks that the parallax of Rigel Orionis) ’ is not greater than Hence the star s distance is at least m ’ twenty illion times the sun s distance from the earth , or a — journey for light of about 3 26 years l and yet it is one of the brightest stars in the heavens l — Absolu te Size of the Star s AS the stars show n o — — perceptible disc like the planets even with th e largest 1 is telescopes , it impossible to determine their act ual size , f even when their distance rom the earth is known . I n

some cases , however , it is possible to make a probable

. T of a w estimate h us , in the case Centauri , we kno that ou r if a u sun , placed at the same distance as th e st r , wo ld appear somewh at fainter than th e st ar does to u s (see ’ A of a ppendix , Note F) an d as the spectrum th e st r s a m a light is very simil r to the solar spectrum , we y con c lu de with much probability that it does not differ very widely from the su n in size and physical constit ution . h or f T e star is a binary , revolving double star , an d rom its orbit and p arallax it has been comp uted that the mass T of the system is about twice t he mass of th e sun . his conﬁrms the conclusion derived from its apparent bright n ess an d spectrum . I t is now known that stars of the ﬁrst or Sirian type are much brighter in proportion to their mass than those of the

o . second or s lar type Thus , Sirius, which is also a binary star , has (with its faint companion) a mass of about three and a half ’ times the sun s mass (the mass of the bright star being 2 3 6 ’ times the sun s mass) . B u t Sirius is very much brighter than the sun would be if placed at the same distance . The sun would, I ﬁnd, if placed at the distance of Sirius , shine as a e star of below the s cond magnitude, or nearly four magnitudes fainter than Sirius . Stars of the Sirian type are therefore probably of larger size and less density than ou r sun . With

1 a ar ent A small pp disc is visible in a telescope, but this is ‘ ’ ff o . merely an optical e ect, and is called the spuri us disc TH E STARS 1 3

of reference to stars of the other types spectra , we have no means of judging of their absolute size, as the distances of very few, if any, have been determined with any approach to certainty.

— M of W Pr ope r Motions, any the stars have hat is e — a or called a prop r motion that is , motion , apparent

of . The real , on the background the sky motion may ’ a a and be only pp rent , due to the su n s motion in space , f or it may be due to a re al motion of the star itsel . Probably in most cases both causes combine t o produce T of the observed motions . hese motions are , course , very small , an d can only be detected by telescopic

O a a o f a bserv tions but they accumu l te in the course ges , and in some cases the ch ange since ancient times has been so considerable as to become appreciable to the The of naked eye . proper motions the stars were ﬁrst H a 1 1 1 1 8 f detected by lley in 7 5, and J. Cassini in 7 oun d that while Arct urus had moved with reference t o the a of ecliptic since e rlier observations , the position th e star

1 B o i w as ) Ot s unchanged . The star with the largest proper motion known was for m any ’ ‘ 1 8 0 G r oomb r id e s the years the star 3 of g catalogue , called ’ w ‘ runaway star by Profe ssor Ne comb . It has a proper ’ B u t motion of about seven seconds of ar e per annu m . a star with a still larger proper motion has recently been discove red by M r. Innes and Professor K apte yn . It is a star of the eighth in magnitude the Southern constellation Pictor, and has a proper motion of about per annu m . Other stars with large proper : L 2 motions are the following acaille 93 5 ( 75 magnitude) , 8 u 6 1 Cordoba ( 5 magnit de), Cygni magnitude), Lalande (73 magnitude) , e u 86 Indi magnit de) , Lalande ( magnitude) , z o o 4 ( ) Eridani magnitude) , ,u Cassiopeia ar e magnitude) , There several others with proper " motions of 3 7 to and a large number with moti ons of less than 1 4 TH E STELLAR H EAVEN S

m e m As entioned above, the prop r motion has in so e cases accumulated to such an extent in the course of ages as to become perceptible to the naked eye . An interesting case of l- u fi 6 1 . A S this kind is that of the star Virginis , the Persian ’ astronomer, in his D escription of the Heavens , written in the 6 1 tenth century, speaks of Virginis as a double star of the fifth b u t e magnitude, it is now a single star, as seen with the nak d ’ - eye . This is due t othe fact that it was in Al Sufi s time close 6 bu t to the star 3 Virginis , has since moved away about one - degree towards the south west . This interesting fact was pointed out by Professor Moye in the Obser v atory for Decem b e r 1 00 , 9 .

1 a 9 a The star 1 Cassiopei , which lies near Cassiopei , has a " o of proper moti n of about 3 7 arc per annum , and about years ago must have been close to the star a Cassio i e a . p , and might have been so seen by the ancient astronomers Of Among telescopic double stars , one the companions of the 1 1 6 triple star Struve 5 , which was to the west of the primary star 1 8 1 — of in the year 3 , is now owing to the proper motion the — of C . brighter star to the east it (see Appendix, Note )

I n addition t o the proper motion s across th e line of in sight , which we have j ust considered , motion th e lin e of o r f sight , either towards th e earth away rom it , has been observed in man y st ars by mean s of the spectro f f f scope . This motion produces the effect o a S hi ting o ’ the dark lines in the star s spectrum from their norm al

. If a a position th e st r is moving tow rds the earth , the f of lines are shi ted towards the blue end the spectrum, and if f f the star is receding rom the earth , they are shi ted of towards the red end . From the measured amou nt this shift t he velocit y in miles per second at right angles to of the line sight can be easily computed . The following large motions in the line of sight have been observed , among others TH E STARS 1 5

STARS APPROACH I N G TH E EARTH .

H Cassiopei a 1 830 Groombridge e Andromeda it Sagittarii 1 Pegasi 1) Cephei

C . Nebula C . 4373

S TAR S R ECEDI NG FROM TH E EARTH . 9 Canis Majoris 96 B Le por is 95

A motion of approach is indicated by the Si gn and r e cession by Professor Campbell ﬁnds the av er ag e velocity of the stars u 2 1 abo t 3 4 kilometres , or miles a second so the above high velocities se em to be exceptional .

’ —An of The So n s Motion in Space . examination stellar proper motions has le d astronomers to the inter esting conclusion that the sun and solar system are a moving through space with considerable velocity . This is a result which might h ave been anticip ated f T rom a consideration o f stellar proper motions . homas

of a 1 0 r a Wright D urham , writing in the ye r 75 , em rked ’ ‘ a and that the sun is star , the stars are suns ; and as of a a most the st rs are pparently in motion , the su n is

. The of most probably moving , too reality this solar motion has been placed beyond doubt by the fairly ao f ir cordant r esults o all computers . S William H erschel

1 8 H e in 7 3 was the ﬁrst to investigate the matter . found that the sun was moving towards a point in the 1 6 TH E STE LLAR H EAVEN S

a H n A constell tion ercules , ear the star , a result which ff u f n does not di er m ch rom moder determinations . Calculations in recent years place the point a little to ’ - of H e r sc he l s osition f r f the north east p , an d not a rom the bright star Vega (a L yra ) The point towards which the sun ' is moving is termed the ’ ’ solar apex , or apex of the solar way . The following position ‘ ’ of the apex will Show the general accordance of the results found

t A cen i lina Ri k s s on Dec tion. g . Sir William Herschel Rancken 3 2 L . Struve 73 3 + 2 73 3 1

O . Stumpe 287 9 + 3 9

Newcomb 2 77 5 3 5 Campbell 2 77 ' 5 20 Kapte yn 29 5

The actual velocity with which the sun is speeding throu gh space has been variously compu ted in recent years from about f u 6 to 1 4 miles a second . Pro essor Campbell ﬁnds abo t 1 2 m 3 iles a second , and from a recent investigation of stellar motions Professor Kapte yn considers that a velocity of ‘ 1 8 s 45 kilometres, or miles , a econd is the most probable ’1 value that c an at present be adopted . This is about four times ’ the — radius of the earth s orbit per annum that is, four times ’ the earth s mean distance from the sun .

Eberhard, Keeler , and Vogel have found a motion of reces

1 1 e sion in the great nebula in Orion of about 7} kilom tres , or ’ 1 0 8 . 5 miles , a second This probably represents the sun s motion in nearly the Opposite direction .

1 r ceedin s o tile o al A adem o mster dam 1 0 1 P o g f R y c y f A , 9 ,

6 6 . pp 74, 75

1 8 THE STE LLAR H EAVEN S

saw a a 1 1 8 V a Cent uri double , and in 7 y irginis w s L B . a doubled by radley an d Pound Condamine , during

i a h s . 1 journey in Peru , saw an d f Crucis double 6 Cygni 1 and 8 1 was seen double in 753 , , Cygni in 755. - b m a N aked eye Dou le Star s. Among these y be mentioned the following : Mizar (referred to above as a telescopic double) has near it a small star known to O A a a as A T the ld r bi n astronomers lcor . his c an be

a on a seen with ordin ry good eyesight . 1 and 2 Cancri are

The or easily seen . star Capricorni consists Of two st ars a M which , although closer th n izar an d Alcor , are more

equal in brightness , and can be easily seen with the n aked

‘ n n eye o a clear ight . g Ceti has n ear it a small star

v S a (! Ceti) easily visible . agitt rii has been already 9 Ta H mentioned . uri , in the yades , is another p air which some eyes can see without optical aid , and also f K T o H a . auri , a little north the y des o Cygni is another a L a of a ex mple . N ear y eonis is star th e sixth m gnitude h which some can see wit the n aked eye . Perh aps the

f for - e L a most di ﬁcult obj ect naked eye vision is yr , the northern of two sm all stars which form a little triangle T with the bright star Vega . his to some eyes appears

- f . O a double , but it is a di ﬁcu lt test A n pera gl ss will a O S . T how it distinctly his is a very remark ble bject , as , of viewed with a good telescope , each the components l f is a close double star , and there are severa aint stars between the pairs . T n of Telesc opic Dou ble Star s. here are thousa ds n and telescopic double stars now know , the list is being M f const antly added to . an y o these may be seen in of f W small telescopes two to our inches in apert ure , hile man y others are SO close as to require the highest powers of the l argest telescopes to Show them as anything but single st ars . Among these latter are included man y L B 1 D OU B LE , M U TI PLE , AN D I NARY STARS 9

r c on binary o revolving double stars , which will be Th f sider e d further on . e position angles o double stars ar e measured from the north point of the ﬁeld of a and V iew rou n d by e st , south , west , back to the north

i a point aga n . I n an stronomical telescope , in which the

a of im ge is inverted , the north point is , course , the lowest ’ point in the ﬁeld .

Among double stars visible with small telescopes of, say, three to four inches in aperture , the following may be men io d t ne . They are given in order of right ascension, and the 1 00 positions are for 9 . ° ’ a 8 m . o a : o . . 6 2 Cassiopei h 34 , N 5 ; magnitudes , , 9 ; u position angle, distance , Yellow, bl ish . A very u wide do ble star, but the companion is faint in small telescopes 6 m 6 ° 6 6 " 6 : 1 . . . Eridani h 3 , S 5 , ; 77 3 ° 8 m . 1 8 : 1 . . y Arietis h 4 , N

White, yellow . ° a 6 m . . 2 Pisc iu m 1 . 2 8 : h 5 9 , N ,

- Greenish white , bluish . ° Andr m da 1 . 8 m . 1 1 o e : . 0 y h 5 , N 4 3 , 5 ; 3

Gold and blue . One of the ﬁnest double stars in the heave ns . The companion is double ; b u t it is a binary or e has r volving double star, and now closed up and become a very diffi cult object in rece nt years . ° " 9 : 2 m 0 . . 8 2 1 Eridani h . 545 , S 4

White, light yellow. A splendid double star one of the ﬁnest

n . in the sky, but not visible in E gland ° i . Pe r se : 8 m . 2 Z . 1 3 h 47 , N 3 7 , 9 3 ; - - u Greenish white, ash colo red . Three other distant companions . ° " i : . P r se m . e e . 1 8 3 h , N 39 3 , 3 ; 8 8 1 - Greenish, bluish white . °

m . 8 . . 1 8 B Orionis (Rigel) 5 h 97 , S , ;

White . The colour of the compan ion has been variou sly stated . ° ' 8 m . 2 : h . 0 2 Z Orionis 5 3 5 , S . ,

White, olive .

1 Date of measure . 20 TH E STE LLAR HEAVEN S

a. : 2 8 . . 2 m . 2 Geminorum (Castor) 7 h , N 3 3 7 ; 2 2 ° 6” 57 5 This is in reality a triple star, the spectro e S scop howing the brighter star to be a close double . ° : 1 0 . m . 20 1 . 2 y Leonis h 4 4 , N ,

Yellow . ° 1 2 0 m . . : . 6 8 7 Centauri h 3 , S 4 4, 4 ;

1 0 2 . B . ( 9 , Innes) inary ° . 6 . : 1 2 6 m . 0 y Virginis h 3 , S 3 , 3 ;

Yellowish . ° ' V n ic r u m 1 2 m . 1 2 e at o . 8 2 Canum (Cor Caroli) h , N . 3 5

2 . 3 , White ° a : 1 . 1 m . . Z Urs Majoris (Mizar) 3 h 9 9 , N 55

Greenish , white . The brighter star is a spectro scopic double . °

8 m . . 60 1 1 . 2 2 a Centauri : 4 h 3 , S , ; — 1 0 2 . ( 9 Innes) Nearest star to the earth , and a binary period - about eighty one years (See) . ° " a i 1 . 8 m . . 2 6 2 8 1 B o Ot s : 4 h 3 , N 7 3 , 3

Yellow , blue . A beautiful object, and a test for telescopes of moderate power. ° ° ' 1 . 1 1 2 B Scorpii 5 S 9 3 , 5 Orange, B f pale yellow . urnham ound the brighter star to be a close e doubl . °

. 0 m . 1 a : 1 1 1 . Herculis 7 h , N 4 3,

Orange, green . ° ' m . 2 2 0 hi hi 1 8 . 0 . 7 Op u c h 4 , N 3 45 , - Yellow, purple . A well known binary star. °

a m . 8 1 1 0 a : 1 8 . . Vega ( Lyr ) h 34 , N 3 , 5 ;

’ " 51 s ( 1 892) °

9 1 . m . . Serpentis : 8 h , N 4 4 5, 47

Yellowish , white . A ﬁne wide pair. ° ' 6 6 a 1 8 . m . . I 2 1 8 y Coron Australis h 597 , S 37 , ; 5

A binary ; period about 1 54 years angle decreasing. ° " 6 : 1 . m o . 2 1 Cygni 9 h , N 7 3 , 53 ; 34 m

Yellow, blue . A ﬁne object for a small telescope . ° 8 m . . 0 : 1 . e D raconis 9 h 4 5 , N 7 4 , 7 5;

Yellow, blue . ° - " : 20 . 2 m . . 1 1 1 2 7 Delphini h 4 , N 5 4, 5 ; - Gold and bluish green . B L B 2 1 D OU E , M U LTI PLE, AND I NARY STARS

° " 8 2 2 : m . 6 1 Cygni 2 1 h . . , N 3 5 3 ,

The nearest star in the Northern H e misphere . ° ° 6 u u : 2 1 . 6 m . . 1 0 2 2 Eq lei h 9 , N 9 ; 7 4 — The bright star is a close binary one of the most rapid known . ° " : 2 1 . 6 . . 2 8 2 11 Cygni h 39 m N 4, 5 ; 5 9

- u . White, bl ish white

° ° °

m . . 0 2 o 1 : 2 2 . 2 Z Aquarii h 37 , S 4 , 3 4 ; 3

d . Pale yellow . Perhaps a binary star with a long pe rio

° ' °

5 2 2 h m . . 1 2 o Cephei : , N 57 9 ; e e - Y llow , blue . The brighter component is a w ll known variable star . The nu mber of known dou ble stars now amo u nts to several

u s . tho sands , and are being con tantly added to Most of the recent discoveries are , however, very close, and only to be seen with large telescopes . — T Tr iple Star s . hese are very interesting obj ects , and f of a a o . consist three st rs close together , inste d two I n some cases there is a physical con nection between the a an st rs . I n others the connection seems to be only f far optical one , the ainter stars probably lying behin d the brighter stars in space .

The following are some interesting examples of triple stars 2 ° 0 0 d . 0 m . : 1 . (4 ) Eri ani 4 h 7 , S 7 " u e 1 0 8 A L 9 again do bl 2 6 binary . arge common proper motion of about per annu m . ° 1 e 6 h m . . 1 0 6 8 : . 8 5 Monoc rotis 3 55 , N , ,

Green , blue , orange . °

1 L . 2 : 6 . m yncis h 37 4 , N . 59 u Greenish , white, bl ish . The close pair is a binary long period . ° a u : 1 2 . m . . 6 2 2 2 6 Cr cis h , S , , ; the This is brightest star in the Southern Cross . ° u u : 2 1 . 1 8 m . . 6 1 1 5 Eq lei h , N 5, 4, 5 ; 86 ° A good test for a four-inch refractor ; 1 4 is again double .

—T n of f Mu ltiple Star s . hese co sist our or more com 2 2 TH E STELLAR H EAVEN S The following are good examples 9 ° ' . 2 m . 8 6 . 2 8 Orionis 5 h 9 , S 5 , 7,

- AC , D C , This is the well known ‘ ’ trapezium in the great nebula in Orion . Near A is a faint o star (Struve) , and near C is an ther (Herschel) , and there are e oth r fainter stars in the group . The four bright stars can be easily seen with small telescopes . I have seen them with one -a- and half inch (reduced aperture) in the Punjab Sky.

' ° ' 0 : . m . . 2 Orionis 5 h 3 37 , S 39 63 6 8 and 6 3 : B urnham found the bright star to be a close double and rapid binary . A second - group and other faint stars are in the ﬁeld . With a four inch f refractor in the Punjab , I saw ten stars in all , our in each group, and two faint stars between the groups . ° 80 : . m . 1 8 1 2 1 1 h 3 7 5 h 34 , S . 7 7, 9, , , ; ° I o4 ' 5 ; A beauti ful object for small telescopes . B urnham ﬁnds that two of these are close double stars in a large telescope . I have seen the six

- stars given above with a three inch refractor in the Punjab . - They lie about 6 m . to the east of the fourth magnitude star a s Leporis, which is itself a wide double tar, 4 ,

° e a : 1 8 . 1 m . . 7 Lyr h 4 , N 39 45, 41 ; - Visible in an opera glass as a double star, and to some with the - -a- naked eye . Each star is again double with a two and half or 1 " 2 - £ 6 5 three inch telescope ; , 4 , 3 4 ,

° ° 1 3o 5 ; Between the pairs are three fainter stars , and other faint stars are near . ° 8 a : 2 2 . 1 m . . 6 1 0 2 8 A B Lacert h 3 , N 3 9 , , 5; , B C B D , , Espin sees a faint companion to D .

i — The of D scov er y of Binar y Star s. credit the dis c ov e r y of binary or revolving double st ars seems to be M a of Rev . d ue to the Joh n ichell , who bout the middle the eighteenth cent ury deduced from abstrac t reasoning The the probable existence of these revolving su ns . tr u th of this h ypothesis was proved from direct observa ir H tion by S William erschel , by whom they were acci B L L B 2 D OU E , MU LTI P E , AN D I NARY STARS 3

’ dentally disc ov e r e d t owar ds the end o f the eighteenth centu r y while carrying out researches with a view to a finding the distance of some double stars from the e rth . ‘ a f a a flu c t u a I nste d o finding , as he expected , th t n nual tion to and fr o of one component of a double st ar with — respect to the other th at altern ate increase and decre ase ’ of their dist ance an d angle o f position which the earth s — annual motion would produce he observed in man y cases a regular progressive change ; in some cases bear fl a ing chie y on their dist nce , in others on their position , and a a one as adv ncing ste dily in direction , so clearly to ’ f indicate a real motion of the stars themselves . Care ul measurem ents during a period Of twenty-fi v e ye ars con of a firmed the correctness this discovery , an d est blished the fact that in man y of the double st ars the components a a revolve roun d e ch other in periods v rying in length , — — and in orbits differing in most cases widely from the f m circular or ; indeed , in some instances in such elon gated ellipses as to bear more resembl ance to the orbits of comets than to those of planets .

r bit s of in -The a O B ar y Star s, ﬁrst ttempt at comput ing the orbit of a binary star was made by Savary in 1 8 0 a f o U a M . 3 , in the c se 5 rs ajoris I n the same year of 0 O hiu c hi E the orbit 7 p was comp uted by ncke . A n orbit for y Virginis was computed by Sir Joh n H erschel 1 8 and one for a in 3 3 , Castor in the same ye r . Since th at time a considerable n u m ber of orbits h ave been com u t e d for p binary stars by various comp uters , including

B am a Ce lor ia Dober c k me a Aitken , urnh , C sey , , , Du r , Fl m

a H H K linke nfu e s m rion , Glasenapp , ind , ussey , Jacob , , L M Se e Villar c eau and ewis , ann , Powell , , , the present Th writer . e calcul ation of a binary star orbit is a matter of f and considerable di ﬁculty and trouble , cannot be The described here . most important elements are the 24 THE STE LLAR H EAVEN S

- a of f period and the semi axis m jor the orbit , as rom ’ of t he f if a these the mass system can be ound , the st r s

parallax is known .

An accou nt of the principal results arrived at by astronomers

may prove of interest to the reader. The binary stars described

are given in order of right ascensi on . Recent measures of e position are given wh n these are available . ° ' 1 a : R A . 0 . 2 m . 1 8 ; Cassiopei . , h 4 9 . , N 57 magnitudes 4

and 7. D iscovered by Sir William Herschel in 1 779. Since s that year numerou measures have been made , and several 1 6 orbits have been computed , with periods ranging from 7 years

Du né r 22 2 Dob e r ck . . 1 6 by to years by Dr See ﬁnds 957 years , with an eccentricity of 0 5 1 42 and an apparent mean distance " " a 0 1 ( ) of 8 2 between the components . A parallax of 54 was ’ found by Otto Struve . This combined with See s elements gives ’ the mass of the system about four times the sun s mass (see

Appendix , Note H ) . Comstock , however, ﬁnds a period of about 00 a - 1 u 1 6 2 5 years , and This gives a mass abo t times the ’ " . 2 1 8 sun s mass Position 5 ( 99, at Greenwich Observa 8 tory) . Spectrum, second type (F G) . 2 ° R . . A 1 8 m 1 . a : . . . 7 Andromed , h 57 , N 4 7 This - is the companion of the well known double star 7 Andromeda . A complete revolution has been described since its discovery by 8 . 1 8 2 . B O Struve in 4 urnham found a period of 54 years, See — 0 e . 54 years, and Hussey 55 years results in close agr ement u 0 8 The eccentricity of the orbit is very high, abo t 57 according " Se e . 0 0 1 00 . to Position 4 ( 9 , Greenwich) ° R 88 . A . . 1 m . . 1 6 55 Tauri . , 4 h 4 3 , N and " 2 1 : 0 Hussey ﬁnds a peri od of 00 years . Position 39 1 8 ( 99, Greenwich) . ° 82 R . 1 0 . . : A . m . . 1 O Struve . , 4 h 7 , N 4 and 9 f 1 8 Glasenapp ound a period of 5 4 years , Hussey 97 94 years , " : 0 1 and the present writer years . Position 5

1 8 . ( 99, Greenwich) ° ’ . . 6 a R A. 6 0 m 1 Sirius ( Canis Majoris) . , h . 4 4 , S 34 brighter

1 1 0 . than , and Some irregularities in the proper motion of

1 ’ v 1 0 1 . 8. Publications of the Lick Observatory , vol . . , 9 , p 5

26 TH E STELLAR H EAVEN S

than the distance of Uranus from the sun . As in the case of

Sirius, the faint companion has about the same mass as the sun ,

and must therefore be a comparatively dark body . The spectrum of Procyon is of the second type (F 5 G , Pickering) . Schaebe r le Position ( , Angle and distance i ncr asm e g . A r ﬁ ° s : . 1 m . . 1 6 . B . 9 g 7 h 47 , S 3 57 , 3 oth yellow B 1 D iscovered by urnham in 873 . A close and diffi cult double

. 0 B 2 star Glasenapp found a period of 4 % years , urnham 3 3 2 2 0 years , and See years , with an eccentricity of The

. shorter periods seem to be nearer the truth The spectrum , is ” . o : 0 2 of the second type (E , Pickering) P sition 3 1 8 ( 99, Greenwich Observatory) . ° A B 2 m 1 6 2 B : 8 . 6 . . . t . Z Cancri ( ) h , N 7 o h yellow m Discovered by Sir William Herschel in 1 78 1 . Nu erous orbits e 2 6 2 have be n computed, the periods ranging from 4 5 to 5

. 60 years See ﬁnds years, and this is probably not far from the truth . Professor Seeliger has investigated the motion of this

system (which is triple, or perhaps quaternary) , and ﬁnds that to make the observations agree with theory it is necessary to assume t dou ble the tha the third star is in reality a very close , components u of which revolve ro nd their centre of gravity , and both round the centre of gravity of the components of the close pair. This

u B . hypothesis is , however , disp ted by urnham The spectrum

8 . is of the second type (F G , Pickering) Position

1 00 . ( 9 , Greenwich)

° ° w 6 . B Le oni . 2 I m . . . s 9 h 3 , N 9 , 7 oth yellow Dis

1 82 . covered by Sir W . Herschel in 7 Various orbits have been 8 2 2 o 2 . computed , with peri ds ranging from 1 to 7% years See

1 1 6 2 0 . ﬁnds years , with an eccentricity of 537 The spectrum

t . : is of the second ype (E , Pickering) Position

1 00 . ( 9 , Greenwich) ° B ! a o : . m . . p Urs Maj ris 9 h 4 53 , N 54 55 oth 1 8 2 1 1 yellowish . Discovered by O . Struve in 4 . A period of 5

f 1 2 . years was ound by Casey, and 9 9 years by Glasenapp See

ﬁnds 97 years . Spectrum ﬁrst type (A, Pickering) . Position " 0 2 1 00 . 7 ( 9 , Greenwich) ° : 1 1 . 1 2 m . . 2 . . 6 Urs a Majoris h 9 , N 3 4, 5 Yellowish - Discovered by Sir W . H erschel in 1 780 . A well known binary B A N D B 2 D OU LE , M U LTI PLE , I NARY STARS 7

star, for which a number of orbits have been computed , with 60 periods from 581 to years. See ﬁnds years , with an eccentricity Of 0 397. The spectrum is of the second type (G,

1 00 w . Pickering) . Position ( 9 , Green ich) ° e 2 : 1 1 . 2 m . . 1 . O . Struv 34 h 54 , N 4 7, Yellowish An orbit computed by the present writer in 1 886 gave a period

i . of years . See ﬁnds 77 years . Spectrum second type (E )

° " 0 1 8 . Position 34 99, Greenwich) ° ' 6 . 6 1 8 6 8 . . . u 2 1 1 . 2 m . O Str ve 3 5 h 7 , N 3 , 7 Yellowish Dob e r ck e 80 found a period of y ars , See ﬁnds years , and

u 66 . . H ssey years Spectrum second type (F, Pickering) Posi

1 00 . tion ( 9 , Greenwich) ° 8 ' 6 1 6 B 1 2 . 1 m . . 26 Struve 39 Coma erenices h 9 4 , N 7 , 1 80 79 . Lewis ﬁnds a period of years , with an eccentricity of u The Spectr m is of the ﬁrst type (A) . Position

1 00 . ( 9 , Greenwich) ° ' m . 2 . . : 1 2 . 6 . 8 y Centauri h 3 , S 4 5 4, 4 Yellowish An orbit computed by the present writer gave a period of

88 0 8 00 . P years See ﬁnds years , with an eccentricity of osi

1 02 . tion ( 9 , Innes) ° '

: 1 2 . 6 6 m . . 0 . y Virginis h 3 , S 54 3 , Yellow This famou s binary Star was discovered by B radle y and Pound in 1 1 8 u the year 7 , and it has been freq ently measured since by u observers of d ou bl e stars . N umero s orbits have been com — u te d 1 1 6 2 8 . p , with periods ranging from 4 1 to years Calcula

1 1 Se e . tions in recent years vary from 75 to 94 years , found by e e 0 8 0 The eccentricity is very high , b tw en and 9, according to In all computers , and is the largest known among binary stars .

e . fact , the orbit is more lik that of a comet than a planet An u e e entire revol tion has be n nearly completed sinc its discovery , so the orbit is now well determined . The component stars are

at present nearly at their . greatest distance apart , and the pair forms a fine object for small telescopes . From spectroscopic B e lo olsk measures of motion in the line of sight , p y finds a parallax of and a combined mass equal to 1 5 times the u mass of the sun . The spectr m is of the first type (A, Picker ing) . Position ° ' 2 a B 1 . 1 m . 1 8 6 6 . 4 Com erenices 3 h 5 , N . 4 , . Orange

1 M ntlz oti o l N ces 1 0 2 . y , January , 9 2 8 TH E STELLAR HEAVE N S

- 2 A fast moving binary, the period being about 531 years . The

plane of the orbit is in the line of sight , so that the apparent e motion is wholly in the distanc , the position angle remaining

nearly constant . Spectrum of the second type (F) . Position

° °

z o o 1 00 . 5 ( 9 , Greenwich)

° °

8 m . 26 : 1 . 2 . O . Struve 9 3 h 3 , N 3 5 7 3 , 7 7. Yellowish . This close and diffi cult binary star has pe rform ed a complete

revolution since its discovery by Otto Struve in 1 844 . A n orbit computed by the present writer in 1 89 1 gave a peri od of 477 B 8 88 — years urnham ﬁnds 4 4 , and See 4 , years results in fairly

o . close agreement . Spectrum f the ﬁrst type (A) Position

1 00 . ( 9 , Greenwich) °

1 m . . . 2 V e natic o r u m : . 6 8 5 Canum 3 h 33 , N 3 5, 5 b e r ck 1 20 h . Do W ite , blue found a period of about years , and

1 8 . See 4 years The eccentricity of the orbit is very high , about

Spectrum of the ﬁrst type (A) . Position :

1 00 . ( 9 , Greenwich) ° a . 6 m . 60 1 2 . B Centauri : 4 h 3 , S oth — orange yellow. This famous binary star the nearest of all the stars to the earth— was discovered by Richand in India in

e 1 68 . Dec mber, 9 Numerous observations of it were made in u the eighteenth and nineteenth cent ries , and the orbit has now been well determined . A number of orbits have been computed, 1 with periods ranging from 75 to 883; years . From a recent a investigation , See ﬁnds a period of years , which c nnot r be far from the truth . The appa ent orbit is very elongated . ’ Assuming Gill s parallax of See ﬁnds that the mass of t he ’ u . system is twice the s n s mass (see Appendix, Note H) The mean distance between the components is a little greater than o f e c c e n the distance Uranus from the sun, but owing to the t r icity of the orbit (0 ° 52 8) this distance varies to a considerable ff d e al extent . Although the components di er a good in bright

e . ness , their masses are ne ly qual Spectrum of the second ar " ° 6 1 2 . : 2 1 0 . type (G) Position 3 ( 9 , Innes)

° ° 2 8 : 1 . 1 m . . 2 6 . O . Struve 5 4 h 4 7 , N 4 7 5, 7 Yellowish ,

f . 1 1 8 whitish . A close and di ﬁcult double star A period of 5 1 8 B years was found by the present writer in 93, but urnham

6 2 61 . o : ﬁnds years, and See 7 3; years Positi n

1 00 . ( 9 , Greenwich) B 2 D O U B LE , M U LTI PLE , AN D I NARY STARS 9

° ’ 6 . . B o o tis 1 . 68 m . . 1 1 8 4 h 4 , N 9 3 5 Yellow, purple al Discovered by Sir William Herschel in 1 780 . Sever orbits u have been comp ted for this ﬁne pair, the periods ranging from

c 1 28 . e c c en 1 1 7 to 1 72 years (Comsto k) . See ﬁnds years The ’ tr icit 0 2 1 . y is high , 7 according to See s orbit Spectrum second o type (G) . P sition °

m . 0 6 B a B l 1 . . . 71 Coron orea is 5 h , N 3 oth u yellowish. Several orbits have been comp ted, with periods of 1 6 0 6 . 4 to 7 years Comstock and See both ﬁnd 4 years, which mu st be very near the truth ; Nearly three revolutions have now been described since its discovery by Sir W . Herschel in ° 1 u I ° 1 78 . Spectr m of the second type (F) . Position 3

1 00 . ( 9 , Greenwich) 2 ° ' 6 B B O is 1 . 20 s. 8 . o t : . M 5 h 7 , N 37 43 5, oth white . 1 6 1 Several orbits have been computed , with periods of 4 1 to 3 4

. B years See ﬁnds years . Spectrum ﬁrst type ( ) . Posi

1 00 . tion ( 9 , Greenwich) ° u 8 1 m . 0 . 2 : B O Str ve 9 5 h . , N . 4 7, oth

. B oOtis . 1 yellowish A small double star, near Periods of 5 88 u 6 2 . to years have been comp ted . See ﬁnds 5 years A complete revolution has now bee n described since its d iscovery

1 8 . 1 00 by Otto Struve in 45 Position ( 9 , Green wich) . B ° ' a 1 8 m . 26 6 . y Coron orealis 5 h . 3 5 . , N 3 4, 7 Yellow, u bl e . Orbits have been computed with periods of 73 to 953. years . The inclination is very high, and the apparent orbit very e elongated . Sp ctrum of the ﬁrst type (A) . Position : 1 00 ( 9 , Greenwich) . ° 5 : 1 . m . . 1 1 B o Scorpii 5 h 59 , S 5, oth yell w. A remarkable triple star. Several orbits have been computed for 1 0 the close pair, with periods of 49 to 55; years . The longer period seems more correct . The eccentricity is small, but the inclination of the orbit plane is high, and the apparent orbit rather elongated . A fu ll revolu tion has been completed since

. 1 8 1 All its discovery by Sir W Herschel in 7 . three stars have e a common prop r motion , and probably form one system , but the h motion of the t ird star is very slow. Position

° ° 0 a B a 1 6 . 1 1 m . : . 6 . Coron ore lis h , N 34 , 7 Yellow, 30 TH E STELLAR H EAVEN S

1 bluish . Various periods have been found , ranging from 95 to

0 . 846 years . See ﬁnds 37 years Spectrum of the second type 1 8 (E) . Position ( 99, Greenwich) . ° ' m 1 . 1 6 . . 6 Z Herculis h , N . 3 47 3 , 3 Yellow , bluish

- s . m or reddi h This is a fast oving binary, and a number of 0 6 orbits have been computed, with periods of 3 to 3 3 years . 0 See ﬁnds 3 5 years . A period of years was found by o 1 8 all D o little in 99, and from a careful discussion of the 1 00 observations to 9 Lewis ﬁnds periods of to 3 years . He computes the probable parallax of the star at and the

combined mass of the system that of the sun . He thinks there is evidence to Show that the companion varies in brightness

° ° 1 6 o . from 5 to 7 5, and its c lour from red to blue He also thinks

that the primary star may possibly be a close double . Three c omplete revoluti ons ha v e been performed since its discovery 1 82 by Sir W. Herschel in 7 . The spectrum is of the second

. 1 00 type (G , Pickering) Position ( 9 , Greenwich) . ° 1 6 1 . m . . 6 8 . B . B 4 7 h , S 34 4 , 7 oth yellowish f - o B A ast m ving binary, discovered by urnham , who ﬁnds a

o 2 . peri d of 47 years Glasenapp ﬁnds and years,

° o . See 33 years , and the present writer years The longer periods seem to be near the truth . Position :

1 8 . ( 95, See) °

m . 0 6 B 6 . 2 1 : 1 . 2 . . Struve 73 7 h 53 , S , oth yellow - This is another fast moving binary, the period being about

6 . 4 years The eccentricity of the orbit is comparatively small , but the inclination of the orbit being high , the apparent orbit is ° sec ond e ° very elongated . Spectrum Ztyp ( F Positi on 3 29 5

1 00 . ( 9 , Greenwich) ° ° m . . 8 B . h hi 1 6 6 . O iu c : . 1 p 7 h 57 , S 5, oth yellowish f 8 2 0 Several orbits have been computed , with periods o 7 to 3 years . The longest period seems to be the best . Spectrum ’

. : 2 1 00 . second type (F) Position ( 9 , Greenwich) ° ' iu c hi 1 2 2 . 0 O h 8 . 0 m . . 6 7 p h 4 , N 3 Yellow, purplish . - This well known binary star was discovered by Sir W. Herschel

1 w ell . in 779, and has been observed since that time Numerous of 8 orbits have been computed, with periods 735} to 9 years .

1 M ontlzl N otices b 1 00 . y , Decem er, 9 L AN D B 1 D O U B LE , MU LTI P E , I NARY STARS 3

An orbit computed by the present writer in 1 888 gave a period u of years , and this has been conﬁrmed by the s bsequent u calculations of B u rnham and Mann . See fo nd years . u The orbital motion seems to be somewhat dist rbed, possibly by 0 1 62" the attraction of an invisible body. With a parallax of

e . found by Kru ger, Dr See ﬁnds that the combined mass of the system is about times that of the sun . Spectrum second 1 00 type ( K) . Position ( 9 , Greenwich) . ° ' . . 0 6 1 1 . : 1 8 2 m . 99 Herculis h 3 , N 3 3 3 , 7 Yellow, u f p rple . For this close and di ﬁcult pair the present writer

u . d and fo nd a period of years See ﬁn s years , Aitken

6 . u 3 years The eccentricity is very high , abo t according

u . : to See . Spectr m of the second type ( F) Position

1 8 . ( 99, Greenwich) ° ’ 8 . m . 0 1 . B : 1 6 . . Z Sagittarii h 5 3 , S 3 4 4 oth yellow In the year 1 886 the present writer computed an orbit and found

. Fr ole 1 8 u a period of years y, in 93 , fo nd years ,

See ﬁnds and Aitken years . Position

Tu nis) . °

m . . a 1 8 . B y Coron Australis h , S 37 oth yellowish . Several orbits have been compu ted for this Southern binary star, with periods from 55 to years . The latter u 1 8 2 period was comp ted by the present writer in 9 . Dr. See e 1 2 ﬁnds a very similar orbit, with a p riod of 5 7 years , and these orbits represent the measures satisfactorily. Position :

° ' 20 m . . 1 1 B B Delphini h . , N 4 5 oth yellowish .

D iscovered by B urnham in 1 873 . Several orbits have been computed , with periods ranging from years , found by Celor ia , to years by the present writer. See ﬁnds years. Spectrum second type (F 5 G) . Position :

1 00 . ( 9 , Greenwich) ° ' : 20 . 6 1 m . 6 o . 8 . 6 B 4 Aquarii h 4 , ; , 7 oth yellow. Dob er ck 1 2 8 1 2 ﬁnds a period of 9 years, and See 9 years .

. o : 1 Spectrum of the ﬁrst type (A) Positi n ( 899,

Greenwich) . 3 ° ' : 2 1 . 6 m . . 6 B Equulei h 9 , N 9 oth yellow. Wr ou ble wsk A very rapid binary , for which y found a peri od of 1 1 years , and See years . Hussey thinks, however, that 3 2 T H E STELLAR H EAVEN S

o or the peri d is probably only one half of this, about 57 years, 1 and he has computed an orbit with this period . Several r e v olu tions have been described since its discovery by Otto Struve in

1 8 2 . 5 Spectrum second type ( F Pickering) .

x 2 1 . 0 1 m . . 2 0 . B o Pegasi h 4 , N 5 5 th yellowish . B Another very rapid binary, discovered by urnham in 1 880 . 6 Dr . See ﬁnds a peri od of years . This and Equulei have the shortest periods at present known among binary stars , the c an components of which be separately seen in large telescopes . ‘ ’ I n the so -called spectroscopic binaries (see next section) the — components are not visible with the possible exception of

Capella , which has been elongated at Greenwich . The spectrum of 1c Pegasi is of the second type ( F 5 G) . ( I t is also a spectro : 1 00 scopic binary . ) Position ( 9 , Greenwich) . ° ' 8 26 6 1 0 2 6 m . . . Y 5 Pegasi 3 h . 5 9 , N 34 , ellowish , fﬁ B bluish . A close and di cult double star, discovered by urn in 1 8 8 Schae b e r le ham 7 . found a period of years, Glasenapp

2 0 B 2 . years, See 4 years , and urnham 57 years The pair have a large proper motion , for which the present writer foun d in the direction of position angle The spectrum is of the second type (E , Pickering) . Position " 0 7 5 ( 1 895)

Mr. Monck ﬁnds that , of the binary stars for which orbits have th e been computed , those showing solar type of spectrum are much more nu merous than those with the Sirian type . This would suggest that the solar stars are nearer to the earth than the Sirian .

— A new of Spect r oscopic Binar ies. class binary stars has been discovered in recent years by the aid of the T s e c t r OSCO ic spectroscope . hese have been termed p p ’ of bin aries , and are supposed to consist two component stars so close together that the highest powers o f the largest telescopes fail t o S how them as anything but single stars . I ndeed , th e velocities indicated by the

1 ’ 8 . v . 1 0 1 . 20 Publications of the Lick Observatory, vol . , 9 , p Recent measures by Ai tken seem to conﬁrm the short period found by Hussey .

34 TH E STELLAR HEAVEN S — component stars is a dark body as is the case in some — of of e these systems there will , course , be on ly on set o f the and lines in spectrum , the lines will then be merely f f shi ted rom their normal position , not doubled . This of f occurs in the case A lgol , the amou s variable star , and of A T in some other stars the lgol type . h ese will be

con sidered in the n ext chapter . Professor Campbell thinks that these spec t r osc 0pic binaries ar e probably quite as n umerous in the sky as those in which the com onents in p are visible the telescope . The following are some stars which have been found double with the spectroscope = d . . . 2 1 . 2 1 . The Pole Star Period, 3 d 3 h 4 m s The existence of a third star is suspected . The orbit is nearly c ir cu ’ lar, and about the size of the moon s orbit round the earth .

a a 1 0 . Capella ( Aurig ) Period, 4 days Orbital velocity, about

1 8 6 miles a second . Attempts to see the star visually double L with the great ick telescope have failed, but several observers at the Greenwich Observatory have seen the star ‘ elongated ‘ - - with the twenty eight inch refractor. The observed changes in the relative position of the components agree well with the peri od of 1 04 days found with the spectroscope . The orbit is nearly circu lar . Assuming that the plane of the orbit passes through the earth , Vogel ﬁnds that the mass of the system is ’ about times the sun s mass , and the distance between the 1 components about miles . Professor Cam pbell ﬁnds of that one component has a spectrum the solar type, and the other seems to show the hydrogen line H 7 and the principal lines of iron .

6 : o . 2 i Orionis Peri d, days Orbital velocity, 4 m les a

m B . second . Spectru

a : . . B Aurig Period, days Velocity, 74 miles a second

D istance between components, about miles . Mass of

o . o the system , ab ut times that of the sun Spectrum sec nd type (G)

1 A str o lz sical ou r nal 1 00 . 8 f o . p y j , June, 9 , p 3 9, o tnote B B D OU LE , MU LTI PLE , AN D I NARY STARS 3 5

‘ - i Geminorum A well known variable star. Period of r e volu 8 o . tion , days . Velocity , ab ut miles a second The time of periastron passage does not coincide with the time of minimum brightness . Spectrum second type (G) .

a : . Castor ( Geminorum) Period, days Companion a dark body . Mass of the system very small . Spectrum ﬁrst type (A) .

Le onis : . E Period , days Velocity, 34 miles a second .

Spectrum I I (H) .

' 3 Ursa Majoris (Mizar) : The brighter component of this wide dou ble star was discovered to be a spe ctr osc 0pic double at 1 8 o Harvard Observatory in 8 9. The peri d was found to be u about 1 04 days ; but Dr . Eberhard has since fo nd a period of 1 u about 20 6 days . Spectr m ﬁrst type (A) .

a ir inis . Spica ( V g ) Period, about 4 days Velocity , 55 miles a second . Companion dark or nearly so . Vogel ﬁnds the mass ’ 2 6 of the system about times the sun s mass, and the distance a u between the components bo t miles . The system is

° approaching the earth at the rate of 9 2 miles a second . Taking ’ the most probable view of the star s parallax, the angular separa tion of the stars would be a quantity far too small to be ’ detected by the most powerful telescopes . Spectru m ﬁrst type B 2 ( A) .

f 8 02 . B 2 Centauri Period , 4 days Spectrum I ( A , Peculiar,

Pickering) . 3 Libra This Algol variable is a spectroscopic binary with a high velocity . Spectrum A .

71 . B 2 Scorpii Period , days Spectrum I ( A , Pickering) .

0 : . 1 Draconis Period , 9 days Velocity, 5 miles a second . 8 Spectrum F G .

: 28 1 8 . 8 x Draconis Period, days Spectrum F G .

u. . 1 2 , Scorpii Period, days Velocity, 4 miles a second . ’ 1 4 . B Mass about times the sun s mass Spectrum I ( 3 A ,

Peculiar , Pickering) . L - 5 a . yr The well known variable star Period , days . 1 1 2 Velocity , miles a second . Keeler and Vogel agree that the su pposed orbit is incompatible with the occurrence of eclipses

A str o li sical ou r nal 1 0 1 p y j , June, 9 36 TH E STE LLAR H EAVEN S

‘ as in the case of Algol . Vogel , however , is convinced that 8 a s , Lyr represents a binary or multiple ystem , the fundamental

u 1 2 . 22 revol tions of which in d h . in some way control the light u change , while the spectral variations , altho gh intimately asso ’ c iat ed u with the star s phases , are s bject to complicated disturb ’ o u an es, running thro gh a cycle perhaps measured by years .

G . W . Myers ﬁnds that the mass of the larger component is 2 1 probably times that of the sun , and that of the smaller

95times the solar mass . The mean density of the system is ou r om about the same as that of atmosphere, so that the c ‘ ’ po ne nt s are in a nebulous condition . They revolve nearly in contact, and are probably surrounded by extensive atmospheres .

Spectrum B 2 A ( Composite) .

7 a : . 1 2 ) Aquil Period , days Velocity, miles a second . - 8 a This is also a well known variable star, and , like , Lyr , the times of observed minima of light do not agree with the times of supposed eclipse in the computed orbit . Spectrum G . K Pegasi This short -period binary star has been fou nd to be also a close spectroscopic binary, but it is not possible to say at present which of the two components is the spectroscopic binary . Spectrum F 5 G .

l. : . 2 Pegasi Period , days Velocity, 7 miles a second .

u . I t is a Suspected variable . Spectr m F 5 G a Cephei : This well -known variable star is also a Spectro a 7 a scopic bin ry , with a period of days , and, like ) Aquil , the or bital motion does not account well for the light changes.

Spectrum G . 8 8 8 1 . 8 77 Pegasi : Period, days Velocity, miles a second .

Spectru m G .

: 1 2 . A Andromeda Period about 9 days Velocity, about

e . . 55 mil s a second Small mass Spectrum I I (K, Picker ing) . ° m . . 8 o 1 0 R A. . Lacaille 3 5 7 h 5 , S 4 Peri d, about

3 days . Magnitude, One component slightly brighter 80 ! than the other. Relative velocity about 3 miles a second and mass about 70 times that of the sun . This is a very remarkable object, and its distance from the earth is probably

I a . . r very great , is the Algol v riable V Puppis (which see) B 1 Spectrum A . B L A N D B D O U E , M U LTI PLE, I NARY STARS 3 7

Per se i Variable velocity from 24 kilometres to 1 2 kilo B metres . Spectrum , Peculiar . 77 Geminorum Variable velocity from 1 4 kilometres to —2 u 5 kilometres . Spectr m Ma . a Equulei : Variable velocity from 2 6 kilometr es to 2 kilo

. 8 . metres Spectrum F G , Composite 0 - Out of 3 5 stars examined by Professor Campbell , forty one b i proved to be spectroscopic inar es, and he thinks that eventually ‘ it will be found that a star which is not a spectroscopic binary ’ is a rare exception . C H APTE R I I I

VARIABLE STARS — — Var iable Star s Classes of Var iables Tem por ar y St ar s — Long-Per iod Var iables Ir r egu lar Var iables — — Shor t -Per iod Var iables Algol Var iables Clu ster — — Var iables Su sp ect ed Var iables Method of Obser

v ation .

— To d of Var iable St ar s, or inary observation the light

the stars seems to be constant , and in most cases the

— - a . T brightness is apparently , at le st invariable here

and are , however , n umerous exceptions to this rule , these are known as ‘ variable stars - a most interesting class of o f stell ar obj ects . I n some these curious objects the

light varies to a very considerable extent , the star being and at at times visible to the naked eye , others invisible

except in a powerful telescope . I n some the variation

a in . is sm ll , others irregular Some have long periods between their maxima or minima of light ; in others the fe w a fe w of period is on ly a d ys , or even hours . Very

a a S or the v ri ble stars how an y parallax proper motion , and therefore probably lie at a great distance from the earth . C — The f lasses o f Var iables. ollowing classiﬁcation of the variabl e stars has been proposed by Professor k of H Pic ering , the arvard College Observatory A — n CL S S I . Temporary or ew stars . [ 3 8 ] VARIAB LE STARS 39

— of l CLA SS I I . Stars undergoing large variations ight in periods of several months . A — a CL S S I I I . I rregul rly variable stars undergoing but

c as a B . slight hanges of brightness , Orionis ( etelgeuse)

ASS — a of 6 CL I V . Vari ble stars short period , like Cephei ,

a L a . n A quil , B yr , etc ’ AS S V — CL . Algol stars those which , like Algol; undergo at r eg u lar intervals a dimin ution of light lasting

a fe w for ho urs only . Secular variation is a term which has been applied to the supposed increase or decrease of light in certain stars of m a a of in the course ages . So e prob ble c ses this kin d will be considered in the section on Suspected V ariables . — Tem r r or T ar e at po a y N ew Star s, here stars which intervals in the history of astronomy h ave s u ddenly blazed ou t w a or , sometimes ith a brilliancy riv lling , even sur f passing , the brightest st ars in the heavens , and , a ter remaining visible for some d ays or weeks (or in some a or c ses months) , have either entirely disappeared become f i a very aint objects n the telescope . I n some c ses the a f T st r has aded into a small pl anetary nebula . hese ’

s nova or . extraordinary obj ect are termed , new stars ’ T a al ‘ hey are lso c led temporary stars , to express their of short duration brilliancy .

The following are some details of these remarkable objects . The ﬁrst temporary star of which we have a reliable accou nt is one recorded in the Chinese annals as having appeared in the

1 B . C . a u s year 34 in the constell tion Scorpio . Pliny tells that it was the sudden appe arance of a new star which led Hipparchu s e s the to form his catalogu of star , the ﬁrst ever formed . As date ’

e 12 B C . e of Hipparchus catalogu is 5 . , it s ems very probable that the star referred to by Pliny was identical with that mentioned by the Chinese as having been seen nine years previously . B A temporary star is said to have appeared in the year 76 . C. 40 TH E STELLAR H EAVEN S

6 h ’ t a. t e b between the stars and in Plough (Ursa Major) , u no

details are recorded . ‘ - ’ 1 0 1 A . D o I n the year . a small yellowish blue star is re c rded ’ e - a in the w ll known sickle in Leo , but the description le ves its

exact position uncertain . ‘ ’ 1 0 A D. 5 e In 7 . a strange star is recorded near , , and

7 1 2 A D . : 7 Canis Majoris , and another in 3 . near a Herculis a O hiu chi and p . A bright star is recorded in the Chines e annals as having 1 0 1 b r i t a appeared on December , 73 , between the gli stars and 3 u 1 Centauri in the So thern Hemisphere . It is said to have remained visible for seven or e ight rihed as resembling a ‘ large bamboo mat ’

very vague, seems to imply that brilliancy .

Close to the spot indicated is a variable star, 1 R Centauri , which may possibly be ith the star of

the Chinese annals . ’ 2 0 0 Strange stars are mentioned in 9 . 3 4, and

6 . A . D 3 9 , but the accounts are very their position

. 6 A D e A t 8 . uncertain In the year 3 . a s en near , i , h and 30 Sagittarii . As t e place the position of a star which was observed by chi— now o missing, it has been thought p star may

have been a return of the star r annals .

D . I n the year 393 A . a st

6 1 A D. no and another in 5 . A known variable and

— - red star R Crateris lies close to ter position .

8 2 A D . In 9 . the Chinese annals a star somewhere near

Procyon (a Canis M inoris) . ‘ An extraordinary star is recorded as having appeared near ° d 1 20 1 0 1 1 A . D. n 5 Sagittarii in the year , a another in 3 near ? a Scorpii . The number of these 5 recorded in this part

of the sky is very remarkable . H epidannu s mentions a star i ies in 1 0 1 2 as being of astonishing size and dazzling the Temporary stars are 5 having been seen in

1 i See section on LongPe r io d Variables .

42 TH E STELLAR HEAVEN S

In 1 670 a star of the third magnitude was observed by

’ Anthelm 3 near 1 Cygni . It remained visible for about two years, and increased and diminished several times before it

ﬁnally disappeared . A star of the eleventh magnitude has been observed near its place at Greenwich Observatory, and variation was suspected in this small star by Hind and others . — — There is a known variable star S Vulpecu la near the place ; ‘ a o An but, cc rding to Hind, this variable is distinct from l ’ ’ ’ R the m s . A 1 00 A . The po sition of nthe lm s star for 9 is . ° . 8 1 . 2 s. 2 9 h 43 m , N . 7 A small temporary star was observed by Hind in Ophiuchus

2 8 1 8 . on April , 48 When ﬁrst noticed it was about the ﬁfth

o . magnitude, but very s on faded to tenth or eleventh magnitude

This curious object has become very faint in recent years . In 1 866 1 8 1 8 it was twelfth magnitude, and in 74 and 75 not above

o 1 00 R. A . 1 6 . . thirteenth magnitude . Its positi n for 9 is h 53 m ° s . 1 2 54 . , S o 2 8 1 860 A new star was disc vered by Pogson , May , , in the globular cluster 80 Messier in Scorpio . When ﬁrst seen it was 6 7 magnitude, and bright enough to obscure the cluster in 1 0 which it was apparently situated . On June it had nearly o disappeared , and the cluster again sh ne with great brilliancy ’ Po s n and with a c ondensed centre . g o s observations were c on u ﬁrmed by Auwers and L ther. It (or another star in the cluster)

1 86 . was again seen as eleventh magnitude by Pogson on June 9, 3 1 0 1 86 On February , 4, he estimated it at ninth magnitude , and 1 on March 5 and it afterwards rapidly faded again . Its ° R A . 1 . 1 . . 2 o 1 00 . 6 1 s . 2 positi n for 9 is h m 5 , S Near

t wo i i . the cluster are known variable stars, R and S Scorp

A very interesting temporary star, sometimes spoken of as ‘ B ’ B the laze Star, suddenly appeared in Corona orealis in

1 866 . B May, It was ﬁrst seen by irmingham , at Tuam , Ireland, m 1 2 about idnight on the evening of May , when it was about o the i the sec nd magnitude , and equal to Alphecca, br ghtest

- ‘ ’ star in the well known coronet . It was shortly afterwards noticed by several observers in various parts of the world . It seems to have blazed out very suddenly, as Schmidt, the

1 A st a 2 r o lt sic l ou r nal 1 02 1 6 . 1 . p y j , 9 , April , p 7 VARIAB LE STARS 43

h ob » Director of the At ens Observatory , stated that he was serving the region about two and a half hours before B ir ming ’ ham s discovery, and felt certain that no star of even the ﬁfth magnitude could possibly have escaped his notice . The star 2 rapidly diminished in brightness , and on May 4 of the same f year had faded to 8 5 magnitude . I t a terwards increased to about seventh magnitude, but quickly diminished again . I t was w soon discovered that the star as not really a new one , but had been previously observed by Schonfeld at B onn in 1 855 and

1 8 6 e n . 5 , and rat d as 9 5 mag itude on both occasions A few days after its discovery its light was examined by Dr . Huggins

with the spectroscope , and it showed the bright lines of hydro gen gas in addition to the ordinary stellar spectrum . D uring the years 1 866 to 1 876 Schmidt detected variations of light

which seemed to show a certain regularity, and he deduced a

probable period of about 94 days . This was conﬁrmed by o ’ Sch nfeld, who observed changes in the star s light from

about the seventh to the ninth magnitude . It would therefore u nov a seem to be an irreg lar variable star, and not a true . It is e a B s for situated a little south of Coron orealis , and its po ition °

0 R. A . 1 . 2 . 1 1 0 15 s. 26 9 5 h 5 m 9 , N . 2 1 8 6 On the evening of November 4 , 7 , a remarkable tem

or ar . p y star was discovered by Schmidt at Athens , near p Cygni

When ﬁrst seen it was about the third magnitude . Schmidt observed the region on several nights between November 1 20 and , and was certain that no star of even the ﬁfth magnitude 0 2 could have escaped his notice . B etween November 2 and 4

the sky was cloudy, so that the exact time of its appearance is w unkno n . It rapidly diminished in brightness, and on Novem be r 0 3 had faded to the ﬁfth magnitude . It afterwards de

~ u u 1 8 . s ec t r osco i creased very reg larly to Aug st , 77 I t was p p u cally examined a few days after its discovery, and its spectr m

showed bright lines similar to the star in Corona B orealis . 1 8 u In September, 77, it was fo nd to have faded into a small

planetary nebu la . I t was only ﬁfteenth magnitude in Septem

1 88 1 1 02 . ber, 5, and about 55 in 9 It is now known as QCygni . ° i 1 00 R. A . 2 1 . . 2 and its posit on for 9 is h 3 7 m 47 s. , N . 4 u 1 88 Towards the end of Aug st , 5, a small star made its appear ance close to the nucleus of the Great Nebula in Andromeda 44 TH E STELLAR H EAVEN S

(Messier The new star was independently discovered by

several observers . Its magnitude was estimated by Engel

1 2 . . hardt on September , and on September Mr Maunder at Greenwich Observatory found its spectrum ‘ of precisely

i . e . the same character as that of the nebula ; , it was per fe c tl y continuous, no lines , either bright or dark , being visible , ’ and the red end was wanting . Dr . Huggins , however, on September 9 thought he could see from three to ﬁve bright

lines in its spectrum . The star gradually faded away, and on a 1 886 Febru ry 7, , was estimated only sixteenth magnitude with

- - the twenty six inch refractor at the Washington Observatory . Professor Asaph Hall found ‘ no certain indications of any ’ u parallax . Auwers pointed o t the similarity between this out 1 860 80 burst and the new star of in the cluster Messier, and he thought it very probable that both phenomena were due to a physical changes in the nebul in which they occurr ed . A small temporary star of the ninth magnitude appeared

1 88 . in the constellation Perseus in 7. It was found by Mrs Fleming on photographs of stellar spectra taken at Harvard

Observatory . A remarkable and interesting temporary star was discovered

1 8 2 . in January, 9 , by Dr Anderson , in Auriga . He announced

. of its discovery to Dr Copeland , the Royal Observatory, Edin

‘ on 1 burgh, February , but seemed certain that he had seen it 2 2 on the morning of January 4 (but mistook it for 6 Auriga ) .

It was then about ﬁfth magnitu de . After this annou ncem e nt was published an examination was made of photographic plates

taken at the Harvard Observatory , and it was found on photo

1 6 1 8 1 1 1 8 2 . graphs taken between D ecember , 9 , and January 3 , 9 These photographs showed that the star was fainter than the 2 1 8 1 r eleventh magnitude on November , 9 , and Professo ‘ Pickering says it probably attained the seventh magnitu de 2 within a day or two of December , and the sixth magnitude

on December 7. The brightness increased rapidly until Decem 1 8 20 ber , attaining its maximum about December , when its o magnitude was It then began to decrease sl wly, with u 20 slight ﬂ ctuations until January , when it was slightly below the ﬁfth magnitude . All these changes took place before its

discovery , so that it escaped observation nearly two months . VARIAB LE STARS 45 During half of this time it was probably brighter than the ﬁfth ’ e magnitude . The star rose to anoth r maximum of light in e u 1 e n F br ary, for on February 4, wh n ﬁrst see by the present e d e . e writ r, he stimate it magnitude Aft r this it rapidly 1 8 the diminished, and on March of same year it was about

1 e . ninth magnitu de . On April it had faded to about the ﬁft enth A u 1 8 2 u I n ug st, 9 , it brightened up again to abo t ninth magni e e tud , and then diminished to about tenth or el venth, and 1 8 S remained in this state to the end of 94 . I t then lowly d e 1 0 1 u iminished, and in F bruary, 9 , it was fo nd to be a very faint and minu te nebu la . Soon after its discovery its spectrum was found to contain bright lines accompanied by dark lines . The observe d shift in these lines indicated enormou s velocities and suggested the theory of a collision between two dark bodies .

However this may be, there seems to be no doubt that it has now— like several other temporary stars— changed into a plan

R. . A 2 s . ar f r 1 00 . e t u . o . y neb la Its position 9 is 5 h 5 m 34 , ° 20 N . Another small nov a of about the seventh magnitude appeared 1 in the Southern constellation Norma in 893 . The spectrum a was similar to that of Nova Aurig , and, like that star, it seemed 1 00 to have faded into a planetary nebula . Its position for 9 is °

R. . 1 . 22 . A 1 1 s . 0 5 h m , S . 5 Another small temporary star of about the eighth magnitude was discovered by Mrs . Fleming in the Southern constellation A e e e rgo . It se ms to have appeared b twe n March 5 and A 8 1 8 u 1 1 8 pril , 95. On J ly , 95, it had diminished to the eleventh The magnitude . spectrum seems to have been the same as that of the new stars in A u riga and Norma . Another object of the same kind was also found by Mrs . Fleming on photographs of the constellation Centaurus . It was about the seventh u e magnit de at its brightest, and appeared some time b tween

1 8 1 8 . J u ne 4 and July , 95 It was observed visually on

1 6 1 8 0 . December , 95, by Professor . C Wendell and had then fade d to the eleventh magnitude . The spectrum was not similar th e A to those of temporary stars in Auriga, Norma , and rgo . - e . . 2 . I t was clos ly north east of the nebula N C C. 5 53 On 22 2 1 8 u December and 9, 95, Professor Campbell fo nd that the spectrum was continuous but peculiar, and quite unlike that of 46 TH E STE LLAR H EAVENS

. 1 1 1 8 6 the nebula near it On June , 9 , Professor Hussey found ‘ the star magnitude, and surrounded by a faint irregular nebula which seemed to extend continuously to the nebula south ’ preceding . On July 9 it had faded to the sixteenth magnitude, and the nebula surrounding it was seen to be continuous with ’ 1 8 the adjacent nebula . On January 4 , 97, Hussey failed to ﬁnd the star, and it must have been then below the sixteenth magni 1 of tude . Chandler is opinion , however, that the star may - o of possibly be merely a long peri d variable , with a period ‘ ’ 0 R. . 1 1 0 A . 3 74 days, or irregular. Its position for 9 is 3 h ° 1 s . 1 34 In . 7 , S . 3 1 8 8 of 1 8 Early in the year 9 , or possibly towards the end 97, a h new star appeared in t e constellation Sagi ttarius . It was found by Mrs . Fleming on photographic plates taken at Harvard in 8 1 8 . March and April , 9 These showed that it was about 47 8 8 2 magnitude on March , and had diminished to 4 on April 9. 1 It was observed with the telescope by Wendell on March 3 , 1 8 99, and estimated magnitude . A photograph of the 1 1 8 8 spectrum taken on April 9, 9 , shows the hydrogen lines and bright , some other lines which seemed to be identical with lines in the spectrum of Nova Auriga . When observed by

Wendell, its light was found to be nearly monochromatic (that ‘ ’ is, of nearly one colour) , showing the chief nebular line and a

r . m faint continuous spect um It would, therefore , see that this ’ star, like other new stars, has changed into a gaseous nebula . ° ' . 8 R. A 1 8 . 6 . 1 2 8 s . 1 1 1 00 . Its position for 9 is h 5 m , S 3

nov a . Another small , also discovered by Mrs Fleming , appeared 1 8 o u - in April , 99, in the c nstellation Aquila, a little so th west of 5 a . n 2 1 the star Aquil I t was about seventh mag itude on April , 1 8 2 1 8 1 00 99, tenth magnitude on October 7, 99, and in July, 9 , it ’ was found to be a nebula of the twelfth magnitude . Its place °

R. . 1 . 1 6 s. . 0 1 00 A 1 . for 9 is 9 h 5 m , S The discovery of so many of these small temporary stars in the last few years suggests that the phenomenon may not be so B u t rare as is generally su pposed . unless a new star became clearly visible to the naked eye it might very easily escape detection .

1 A str o lt sical ou r nal 1 8 p y j , April, 97. VARIAB LE STARS 47

we Lastly , come to the very remarkable and brilliant new — star- the brightest of modern times which suddenly blazed out

2 1 1 0 1 . in the constellati on Perseus on the night of February , 9

I t was discovered by Dr . Anderson (the discoverer of Nova Auriga ) at Edinburgh about on the morning of February 2 2 2 as a star of about 7 magnitude , and was independently detected u 2 2 on the following evening (Febr ary ) by several observers , including the present writer. It rapidly increased in brilliancy , and on the evening of F e bruary 2 3 it was slightly brighter than

Capella, and was then probably the brightest star in the Northern

Hemisphere Its rise in brightness must have been very rapid . e — Gr im mle r Thre German astronomers , Plassman, and Schwab — stated that they were observing the region on February 2 1

. m from 7 to p . , and think that no star brighter than the third magnitude could possibly have escaped their notice. A photograph of the region taken by Mr . Stanley Williams , the - 20 1 1 . m well known English astronomer, on February , about p . , or only twenty-eight hours before the discovery of the nov a by Dr. Anderson, shows no trace of the new star, although stars to about the eleventh magnitude are clearly visible . After 2 the February 3 new star gradually diminished in brightness , and on the night of Febru ary 2 5 it was redu ced to about the 1 ﬁrst magnitu de . On March it had decreased to about the

e d 6 . s con , and about March to the third From that date it d 1 8 fa ed with some small fluctuations of light until March , when it had descended to abou t the fourth magnitude . From that date a seri e s of the most remarkable fluctuations of light 1 set in . On the evening of March 9 it had fallen to a little 20 below the fifth magnit u de . On March it had risen to 2 2nd u and on the it was again below fifth magnit de . It was u 2 again about fo rth magnitude on March 3 , and below five on

2 . 26 March 5 I t again rose to above four on March , and these u o e u c rious ﬂuctuations c ntinued with more or less r g larity, and with a longer period of variation , until the third week in May, o when the star became so low on the Northern h rizon , and the

so f . twilight strong, that observations became very di ﬁcult During the month of June the observations show considerable

a . ﬂuctuations , and to a sm ller extent in July also In August the variation of light was small , the estimates of magnitude 48 TH E STE LLAR H EAVEN S

° 6 . 1 0 1 ranging from 57 to 5 During September and October , 9 , ’ the star s light seemed to fade slowly, with no violent ﬂuctuations , u 2 from abo t 6 to 67 . At the end of the year it had fallen to

u . 1 0 2 about seventh magnit de In the beginning of March , 9 , it 1 02 had faded to the eighth magnitude in June , 9 , to the ninth , 0 1 2 . and in November, 9 , to about the tenth magnitude

When the new star was ﬁrst seen by Dr . Anderson , he thought blu ish ~white e its colour was , and it r mained of a white or slightly yellowish colour on February 2 3 and 24 . It was of a pale yellow 2 26 on February 5 and , and became orange at the beginning of

March . During the remarkable oscillations of brightness the colour seems to have been orange at m aximum and red at minimum light . Early in 1 90 2 Professor B arnard found it ’ - greenish white .

According to Professor Pickering, the spectrum of the new ‘ 22 2 star was on February and 3 of the Orion type, nearly ’

. 2 continuous , with narrow dark lines On February 4 there S m was a remarkable change, the pectru having then become — like that of other new stars that is, crossed by dark and bright bands , the principal dark lines being bordered by bright lines on the red side of the spectrum . The observed displacement of the hydrogen lines from their normal position in the spectrum seemed to indicate a relative velocity of 700 to miles a u second, th s suggesting the collision of two bodies with high of velocities . B u t these enormous velocities colliding bodies seem to be contradicted by the fact that measures of the dark lines of calcium and sodium by Adams, Campbell , Stebbins , and Wright in America indicate a velocity in the line of sight of only some three miles a second . The observed high velocity

s t may have been , however , due to an outbur of hydrogen gas a from the body of the star . Remark ble changes were also observed in the spectrum during the sudden ﬂuctuations in the ’ A r il 1 0 1 . star s light which took place in March , p , and May , 9 An examination of photographs of the star’s spectrum taken at 1 0 1 the Harvard Observatory in July, 9 , showed that, like other ‘ S u new stars , it was lowly changing into a gaseous neb la , the ’ chief nebular line being very bright . The nebular spectrum

o 1 1 . became m re marked in August and September, 90 i 0 1 . I n September, 1 9 , D r Max Wolf, while examin ng the new

50 TH E STE LLAR H EAVEN S

of photographs taken in the years 1 890 to 1 900 Professor Pickering ﬁnds that this small star was variable to the extent

of about one magnitude, and that its position closely agrees with

that of the new star . The same small star was also found by

. B la k M S . j o on a photograph taken by him on January 30 , 1 ‘ 899. Professor Pickering says We may there fore conclude that a star whose light varied from the thirteenth to the four t e enth magnitude was visible for seve ral years within o ne or nov a ff two seconds of arc of the , the di erence in position being ’1 less than the errors of measurement .

0 R. . . nov a 1 0 A . 2 2 s . The position of the for 9 is 3 h 4 m 4 , ° ' . x u Pe r se i N 43 3 3 I t lies between the stars and , a little

nearer to the latte r star . Several theories have been advanced to explain the pheno sat isfac mena of temporary stars , but none of them are very i

. o r ne ar l u tory The rush of a dark, y dark, body thro gh a gaseou s nebula is perhaps the most probable cause of these outbursts . The friction produced by the rapid motion of a body through a nebulous mass would , of course, produce u enormous heat, and this intense heat might , again , prod ce an explosion of gases imprisoned in the interior of the dark , or B nearly dark, body . oth causes may possibly combine to produce the obs e rved phenomena . A collision between two r da k bodies would produce a somewhat similar result, but such an event is e vidently not so probable as the passage of a dark body throu gh a gaseous nebula .

- — In of Long Per iod Var iables. this class variable stars — the variation of light is generally very large usually — several magnitu des and the length of the period c on sider able a f 0 6 1 0 f , r nging rom about 9 to days rom maxi d o f mum to maximum . Several seem to have perio s

a T of about a ye r . here are a large n umber these long

period vari ables known . The following are among the most remarkable and interest - d ing of the long peri od variables. Most of them can be observe

1 ir cu lar . 66 1 Harvard College Observatory C , No , October 3 ,

1 90 2 . VARIAB LE STARS 51

- o at maximum with an opera glass . They are given in rder of 1 00 right ascension . The positions are for 9 ° B R . o 1 . s . . : A . T Cassiopeia . , h 7 m 49 , N 55 etween

8 A a . , and Cassiopei , nearer the latter star D iscovered by 8 u Krueger in 1 870 . It varies from 7 to magnitude at maxim m bu t 1 2 . to 1 1 to at minimum Mean period about 445 days ,

u . with some irreg larities The star is red , and Grover has seen ’ it surrounded by a ruddy haze . A maximum (magnitude 8 1 0 1 was observed by Grover, August , 9 (interval since last u o 0 maximum 437 days) , and another magnit de) , Oct ber 3 ,

1 902 (interval 448 days) . ° . 1 8 a : o 8 . s . . R Andromed h m 4 5 , N 3 Closely north

B 1 8 8 . a . of p Andromed Discovered at onn , 5 M aximum

6 8 6 1 2 8 . 5 to ; below at minimum Mean period, about

1 1 . . e 4 days A maximum was observed by Dr K lly at Kingstown , 1 1 0 1 is Ireland, on December 5, 9 . The spectrum a remarkable t he 1 88 one of third type . In September, 9, Espin found the

F line very bright . °

. 8 s . . 2 a : 1 . 1 2 1 S Cassiopei h m , N 7 Discovered at

B 1 86 1 . 0 a . onn, A little to the west of the star 4 Cassiopei 6 1 0 6 8 6 . e 1 . Max . 7 to min b low 3 Period about days, one of u the longest known . Peek saw a bluish nebulosity ro nd the star 1 00 u in March , 9 . A maximum magnit de) was observed at e 2 1 0 1 Harvard on S ptember 3 , 9 . Espin found the F line very

2 8 1 88 . bright on November , 9 ° o 2 8 . . . 1 s (Mira) Ceti h I 4 m . , S 3 A very remark abl e and interesting variable star . D iscovered by Fabr ic iu s in 1 596 . It varies from 1 7 to 5 magnitud e at maximum to 8 to

° u . u 1 bu t ir r u 9 5 at minim m Mean period , abo t 3 3 days , with eg l r i i a t e s . This is perhaps the most interesting variable in the

. u heavens Its brightness at maxim m is very variable . At the maximum of 1 779 Warge ntin fou nd it equal to Aldebaran on 0 2 he u u n October 3 , and on November tho ght it had f rther i i e n . e u creas d brightness On the other hand , H is fo nd it only

1 868 . ﬁfth magnitude at the maximum of November 7, At the minimum it never descends below magnitude, so that it a m - lways re ains visible in a three inch telescope . At the minimum 1 0 1 t of December, 9 , it was estimated by Nijland (A s . — 4 2 52 TH E STELLAR H EAVEN S

N aeli 0 . f , N The ollowing maxima have been observed in recent years

Date. Obser ver .

1 8 2 m 97, December 3 4 Fla ery . 1 8 8 9 , October 5 Harvard . 1 8 8 2 6 9 , October 9 Gore . 1 8 8 1 9 , October 5 Flanery . 1 8 99, September Harvard Observatory .

° i1 8 2 o . 99, September 3 4 Flanery 1 00 1 9 , July 3 Harvard Observatory . 1 0 1 1 9 , July 4 Harvard Observatory .

The hydrogen lines of the spectrum were seen bright by

Secchi in 1 869 and by Espin in 1 888 . ° 2 . 2 8 . 6 s . . 1 U Ceti h m 5 , S 3 Discovered by Sawyer

68 . 1 2 . in 1 885. Max . to min about Period about m 1 1 1 . 0 . 2 36 days A aximum was observed February , 9 ° Tr ian u li : 2 . 0 . s . . R g h 3 m 59 , N 3 3 Discovered by

1 8 0 . . . 1 1 . Espin , 9 Max to min 7 Mean period about

268 days . A maximum magnitude) was observed on

2 1 0 1 . January , 9 ° H or olo ii : 2 . 0 . s . . 0 R g h 5 m 33 , S 5 Discovered at 6 2 M . 2 . 1 0 . 1 8 . ax Harvard , 9 4 to min 7 A very remarkable

08 . m variable . Period about 4 days A aximum (4 magnitude)

1 0 1 00 . was observed July , 9 °

: 0 . s . . 2 T Eridani 3 h . 5 m 57 , S 4 Discovered at

1 8 . . 2 . 1 1 . o 2 H arvard , 95 Max 7 ; min Mean peri d, 53 days

(H . M . Parkhurst) . ° 0 . . 6 . 2 . s R Reticuli 4 h 3 m 3 , S 3 Discovered by the Ra oonathi 1 86 Indian astronomer g Chari , in 7, at the Madras

. 8 t o 8 . Observatory (conﬁrmed by Roberts) . Max 7 5; min

2 0 . below 1 3 . Period 8 days °

L : . . s . . 1 R eporis 4 h 55 m 3 , S 4 Discovered by

1 . 6 t o . 8 . 8 . 6 Schmidt in 55 Max 7 ; min about 5 Period, 43 ’ ‘ ’ . s . days, but with an inequality This is Hind crimson star 1 It is very red on a scale of 0 to 0 . ° °

a : . . 1 s . . R Aurig 5 h 9 m 3 , N 53 About 3 north

of a . B 1 862 . . 8 east 9 Aurig Discovered at onn , Max to 7

° . 1 2 1 2 . o 60 ir r e u lar i min 5 to 7 Period , ab ut 4 days , but with g VARIA B LE STARS 53

‘ ’ c ties . There is a stand still in the light urve at about 9 magni u and t de from two to four months before maximum , the star remains at this brightn e ss for about 48 days . The spectrum is a ﬁne one of the third type . A maximum was observed by 2 1 00 Grover magnitude) on July 3 , 9 , and another 8 o 2 1 0 1 . magnitude) Oct ber 4, 9 (interval 45 days) ° s . 20 U Orionis 5 h . 49 m . 53 , N . D iscovered by Gore 1 1 88 on December 3 , 5. I t was at ﬁrst thought to be a tem or ar nov a - p y star or , but afterwards proved to be a long period

6 . 1 2 variable . Max . to min below . Mean period about

375 days . A maximum was observed by Grover on 1 1 0 1 26 1 0 1 April 3 , 9 , and at Harvard on April , 9 (magnitude ’ Krueger calls its colour a peculiar copper red 1 (8 4 on e 0 a scal of to It has a ﬁne spectru m of the third type . 7 ° G . 8 1 . 22 6 . s . 7 eminorum h m 5 , N D iscovered by

1 86 2 . 2. Schmidt in 5. Max . 3 min 3 7 to 4 Mean period u 2 1 abo t 3 days . The star was found to be a close and difﬁcult — - dou ble by B urnham a featu re very unusual among long period i var able stars . Professor Campbell ﬁnds a variable velocity in the line of sight . ° 6 . 1 . 1 s . . 2 V Monocerotis h 7 m 4 , S D iscovered by

o 1 88 . 6 6 1 0 Sch nfeld in 3 Max . 3 to 9 min . about 7 . Period, 2 about 3 3 days . ° ° e : . 1 . 20 s . 2 2 R G minorum 7 h m , N . About 3 west 6 G 6 6 of eminorum . D iscovered by H ind in 1 848 . Max . to 8 . e 1 . 0 . 7 ; min b low 3 Period , about 3 7 days According to

Schonfeld , the light curve is very variable at maximum , when the star ofte n remains for a week without any perceptible change . Vogel saw the hydrogen lines of the spectrum bright

1 86 . in February, 9 A maximum was observed by M . Esch 1 1 about middle of September, 9 1 . L ° : . 1 0 . 2 s . 2 Puppis 7 h m 9 , S . 44 Discovered by u 1 8 2 . . 6 8 6 2 Go ld in 7 Max to 4 min . 5 to . Period, about 1 0 4 days . Variation rapid at maximum and comparatively slow

. at minimum Red in all phases of its light, and especially so

. S of at minimum It has a plendid spectrum the third type . ° . . 1 0 s. . 2 2 U Geminorum 7 h 49 m , N Discovered by

1 A str o n sical ou r nal 8 1 1 8 . p y j , August, 95, p . 4 54 TH E STE LLAR H EAVEN S

1 8 . . 8 . 1 . od Hind in 55 Max 9 to 97 min below 3 Mean peri ,

o 86 . ab ut days, but with large irregularities Although this

star cannot be observed without a telescope , it is inserted fu here, as being, perhaps, the most wonder l variable star in f the heavens . For most o its period the star remains about

the thirteenth magnitude . It then suddenly brightens, and after remaining near a maximum for a few days it diminishes

again in a fe w hours . Sometimes it rises to a maximum with

. 1 86 astonishing rapidity I n February , 9, it was observed by Schonfeld to increase three magnitudes in twenty -four hours ! u Some marvellous fl ctuations of light were observed by Pogson . 26 1 8 6 u On March , 5 , he says The variable s bject to strange u fluct ations at intervals of six to fifteen seconds, quite to the e xtent of four magnitudes when the adjacent stars were quite steady and not at all twitching, like the variable . At times it surpassed the [comparison] star 8 9 ; at others it had quite vanished . A new phenomenon to me Watched it for half an 6 ’ hour, with powers 54 , 5, and 95, on the equatorial (at Oxford, 1 . 2 1 8 6 England) On the following evening (March 7, 5 ) he says L b u t as ight very unsteady , not subject to such pulsations were ’ ‘ 66 u e . 1 6 1 8 se n last night On April , , Pogson fo nd it of the

thirteenth magnitude . The following day it had attained its maximum brightness (ninth to tenth magnitude) ’ ! 1 The spec 1 8 8 B to . axe n trum is said be continuous At a maximum , in 5 , ‘ dell found that this extraordinary object had a s omewhat hazy ’ or nebulous appearance .

° ° ' ° : 8 . 1 1 . s . . 1 2 2 o . R Cancri h m 3 , N About 3 north 8 1 82 . . 6 0 of , Cancri . D iscovered by Schwerd in 9 Max to

8 . 1 1 . 3 min below 7 Period, about 3 53 days , but lengthen

ing . A maximum magnitude) was observed at Harvard

1 1 00 . Observatory about December 4 , 9 ° B x 0 8 . a : . 2 . s . . 62 2 R Carin 9 h 9 m 44 , S etween and

a 1 8 1 . . l Carin . Discovered by Gould in 7 Max to 57 ;

. 2 t o 1 0 . 0 . min 9 Mean period, about 3 97 days A very inter 0 8 esting variable . Roberts ﬁnds that the period varies from 3 5 1 2 8 u - to 3 days , and that a f ll cycle is completed in thirty seven

1 ’ . B xen Quoted from Mr . Pogson s Journal by Mr Joseph a

in A str o lt sical ou r nal 1 6 1 0 2 . 1 2 . dell the p y j , April , 9 , p 7 VARIAB LE STARS 55

- 1 H h 20 or . e thirty eight years observed a maximum on Marc ,

1 0 1 . 9 . The star is red ° R L . . s . . eonis Minoris 9 h 39 m 3 5 , N 34 D iscovered

8 . 1 . 6 . 6 1 S 1 8 . by chonfeld in 3 Max to 7 ; min 3 Mean period,

0 ir r e u lar ite s . about 37 5 days , but subject to g Spectrum third

type . ° 1 1 he o : . 2 . 1 1 s . . t R Le nis 9 h 4 m , N 5 Closely south of 8 1 1 2 . . 2 star 9 Leonis . D iscovered by Koch in 7 Max 5 to A 6 . 1 0 . u 1 . 7 min 9 4 to Mean period , abo t 3 3 days very interesting variable and e asily found with an opera -glass at

u . maxim m I t is red in all phases of its light, and has a ﬁne 6 u Spectrum of the third type . A maximum (5 magnit de) was e b m 1 1 00 n obs rved y Fla ery, April 3 , 9 , and a other at Harvard

2 1 0 1 . Observatory magnitude) , February 7, 9 Espin saw

1 88 . the hydrogen lines bright in March , 9 ° 6 1 e a : 10 . 6 . 1 1 s . . S Carin h m , S D iscov red by Gould ,

6 6 . 2 . 1 1 . 1 8 1 . . 7 Max to min 9 to 9 Mean period, 49 days — Increase of light slower than decrease an unusual feature

a . among variable stars . The st r is reddish

° ° ' ° 8 . a 1 0 . . s . . 6 1 o R Urs Majoris h 37 m 34 , N 9 About 3

1 8 . north of 38 Ursa Majoris . D iscovered by Pogson in 53

6 8 2 0 2 . . 1 2 6 1 2 . u Max to min . to 3 Mean period, abo t 3 days ‘ b u t The star rises with astonishing rapidity to the maximum , ’ fades away very slowly . The spectrum is of the third type. A m 6 u 1 6 maximu (7 magnit de) was observed by Grover on March , 1 0 1 and H u 2 1 0 1 9 , at arvard magnit de) on March 3 , 9 , G u e u 20 1 02 and another by rover magnit d ) on Jan ary , 9 l 1 0 d 0 1 0 2 (interva 3 ays) , and (77 magnitude) on October 3 , 9 l 28 1 1 (interva 3 days) . At the maximum of 90 Peek fou nd that ‘ its colour changed in two months from deep dull ruddy to w ’ nearly hite .

° ° ’ ° 1 2 . 1 . 1 8 2 o : . 2 s . u R Corvi h 4 m 7 , S 4 . Abo t 33 south

e . Kar linski 1 8 ast of 7 Corvi Discovered by in 67. Max . 6 8 to

. 1 1 1 8 77 ; min below 5 . Period, 3 5 days . Increase of light

quicker than decrease . Spectrum of the third type . ° a : 1 2 . 1 0 s. 60 T Urs Majoris h 3 m . 5 , N . D iscovered

1 M ontlzl N otices 1 0 y , June , 9 1 . 56 TH E STE LLAR H EAVENS

M 6 8 . 1 8 6 . ax. 1 by Hencke in 5 to 5 ; min . to 3 Mean

2 . . m period, 57 days Spectrum of the third type A maximu 1 1 0 1 v (79 magnitude) was observed on August 5, 9 , by Gro er,

who says . This was the faintest maximum of this star since

° 1 886 . The light at the three previous maxima was 6 3 magni ’ u . t 2 1 0 2 t de He observed ano her maximum on May 3 , 9 , when

° the brightness was again 6 3 magnitude (interval 2 8 1 days) . ° : 1 2 . . 26 s . . v R Virginis h 33 m , N 7 Disco ered by

8 . . 1 0 8 0 . d Harding in 9 Max to ; min 97 to Perio ,

u 1 u . A m axim u m abo t 455 days, but with some irreg larities /

magnitude) was observed at Harvard , May ° ‘ a : 1 2 . . s. . 6 1 S Urs Majoris h 39 m 34 , N , Discovered

° ° 1 8 . . 6 8 2 . 1 0 2 1 . by Pogson In 53 Max 7 to ; min to 1 5 Period , 2 2 ° ° about 6 5 days . M axima were observed by Grover ( 7 7 mag nitu de 2 6 2 1 0 1 ) on May 4, and (7 magnitude) on December 7, 9 2 1 8 1 0 2 (interval 7 days) , and (77 magnitude) on August , 9 2 (interval 2 4 days) . v ° a : 1 . 2 . 1 s . . 2 2 R ( ) Hydr 3 h 4 m 5 , S Discovered

M ar al i 1 0 in . . by d in 7 4. Max . 3 5 to 5 5 ; m 97 Mean 2 e period, 4 7 days , but with irregularities . A remarkabl and

. , interesting variable The period has diminished since its dis c ov e r 00 1 0 8 8 s 1 8 y, having been about 5 days in 7 , 4 7 day in 7 5,

6 1 1 82 1 8 0 . u 4 days in 5, and 437 days in 7 The minim m occurs

about 1 90 days before the maximum . The spectru m is a very ‘ ’ et ﬁne one of the third type, which Dun describes as d un é ’ x beaut tout a fait extraordinaire, the bands being e tremely 1 88 wide and perfectly black . At the maximum of 9 Espin

found the hydrogen lines bright in the spectrum . The star is

. laner Ma 1 8 reddish Maxima were observed by F y on y 5, 97 8 1 8 . (4 magnitude) , and July 4, 9 magnitude) ° . h . . 60 B t e 1 2 s . S Virginis 3 h 7 m 47 , S etween stars

. M . 72 and 8 1 Virginis . Discovered by Hind in 1 852 ax 57 to

8 0 . m 6 . ; min Mean period , 37 4 days Spectru of the

third type . A maximum (6 8 magnitude) was obse rved by

m 22 1 8 . Fla ery on July , 99 ° Di o r ed : 1 . 6 2 s . . sc v T Centauri 3 h 3 m . , S 33 c by ’

M r k . M r iod a wick 1 8 . 2 1 . e an e in 94 Max to 6 ; min . 7 to 9 p , i

90 4 days . An interesting variable star . ° R V e n tic or u : 1 . . s . . 0 Canum a m 3 h 44 m 39 , N 4 Dis

58 TH E STE LLAR H EAVEN S

1 860 . . t o 1 . Hencke in Max 7 9 ; min . to 2 7 Mean 0 period, 4 9 days . A maximum was Observed by M . Esch 1 1 0 1 02 . January , 9 (79 magnitude) ° 1 6 . 2 . 2 s . 66 R Draconis h 3 m 3 , N . D iscovered by G e e lm u d e n 1 8 6 . . 8 1 . y in 7 Max to 7 ; min . 2 t o 1 3 Mean

2 6 . e period , 45 days Maxima were observ d by Grover on

2 8 1 0 1 2 1 0 2 u July , 9 magnitude) , March 5, 9 magnit de), 6 ° 1 0 2 u . and November 3 , 9 ( 3 magnit de) ° : 6 . 2 . 1 . 1 s . 1 S Herculis h 47 m , N 5 Discovered at

B 1 8 . 6 . . 1 onn in 5 Max to min to 3 . Mean period ,

0 2 u . 3 9 days , but with large irreg larities The star is reddish , u - and the spectr m of the third type . It lies closely south west 6 of the star 49 Herculis ( 1 magnitude) . A maximum mag nit u de 1 6 1 0 1 ) was observed by Grover on May , 9 (interval 2 0 since last maximum , 9 days) , and at Harvard ( 7 magnitude)

6 1 0 1 . about June , 9 At some minima Grover has seen it sur ’ rounded by a bluish nebulosi ty . ° 1 6 0 . 1 s . 0 RR Scorpii h . 5 m 5 . , S 3 Discovered by

1 8 2 . . 6 2 1 0 . Thome in 9 Max to 7 min . 9 3 to Mean period ,

2 82 7 days . hi h i ° O u c i h . 8 8 . . s . X p 3 3 m 3 5 , N Discovered by

88 . M x . 1 6 a . 6 8 . Espin in to 7 min 9 Period, 33 5 days . ° ° A : . . a 1 1 . s . 8 R quil 9 h m 3 3 , N About 3 south of

B . . 1 8 Aquila . Discovered at onn in 1 8 56 Max to

. 6 1 0 0 . min 9 to Mean period , 3 5 days The increase of light from ninth mag nitude to seventh magn itude is very rapid .

The star is reddish , and its spectrum of the third type . A

. . 2 2 maximum was Observed by H M Parkhurst on September ,

1 0 1 . u 28 9 magnitude) , and another by Dr Kelly abo t July ,

1 902 . °

: 1 . . 8 s . . R Cygni 9 h 34 In , N 49 Discovered by 1 2 2 Pogson in 852 . It lies about seconds of time to the east of 0 c an u u the magnitude star Cygni , and th s be easily fo nd

~ with an ope r a glass when at its maximum light . Max . to

1 . 2 . 8 ; min . below 4 Mean period , 4 57 days The star is B reddish , and the spectrum of the third type . right lines were 1 8 c on seen in the spectrum in 8 8 . The existence of these were

1 en N . A str onom isclte N aclt r iclzt , o VARIAB LE STARS 59

G e and was ﬁrmed by Maunder at re nwich , one of them found 1 to coincide with the F line of hydrogen . Peek has seen a bluish n u nebulosity at mi im u m . A maxim m magnitude ) was 1 1 1 0 1 8 observed at Harvard on June , 9 , and another ( magni u d 1 2 0 . t e) by Grover on September 3 , 9 °

6 . . . 2 1 . s x Cygni 9 h 4 m 44 , N 3 Discovered by Kirch

° 1 686 . 6 d 06 in Max . 4 to 5 min . Mean perio , 4 days , but with some irregu larities . A most remarkable and interesting variable . Distinctly visible to the naked eye at a bright maxi h m u m . T e e light variation is normous , amounting to nearly, u u e ! if not q ite , ten magnit d s This implies that the light at a bright maximum is nearly times the light at minimum A maximu m (4 2 magnitude) was observe d by G rover on A 1 1 0 1 1 0 2 ugust 4, 9 , and another on September 4 , 9 mag 2 ni de — r d tu 86 . The e ) interval 3 days star is , and shows a e e u magniﬁc nt sp ctr m of the third type, in which bright lines D 1 8 ( 3 very plain) were seen by Espin in May , 99. It is the u B tr e x Cygni of ayer, and is often confused with Flamsteed 1 fﬁ 7 Cygni , to which Flamsteed a xed the letter x by mistake , ’ the variable having been faint at the date of Flam st e e d s ob 2 . e an . servation It is sometimes call d x Cygni , but this is error 6 ° - 8 1 s . 8 : 2 1 . . . T Cephei h m 3 , N A little south west

k 1 . 6 8 e Ce r as i 8 8 . of B C phei . D iscovered by in 7 Max to 8 1 0 . d 6 . 8 . min to 7 Mean perio , 3 7 days The increase of light e e is slow r than the decrease . The star is r ddish, and has a ﬁne e d spectrum of the third typ , with dark ban s of considerable

intensity . A maximum magnitude) was obs e rve d by Grove r e ua 6 1 0 1 and 1 1 0 2 on F br ry , 9 , another February , 9 (interval

60 . D . M . 1 2 1 3 days) The star is 9 . ° : 2 1 . 2 . 1 s . . W Cygni h 3 m 4 , N 44 Closely south G 1 8 . 8 . of p Cygni D iscovered by ore in 5 Max . 5 to 6 3 ;

. 6 . I I min 7 to 7 Mean period, 3 5 days . Sawyer ﬁnds that

1 M onthl N otices 1 8 8 . y , March , 9 According to n Mrs . Flemi g, bright hydrogen lines are characteristic of the - A str o /z sical ou r nal long period variables ( p y j , N ovember, 1 898 , P 2 A maximum was observed by Dr . Kelly on September 7,

1 902 magnitude) . 60 TH E STELLAR H EAVEN S

‘ a o m c the light curve exhibits rather rapid and unif r in rease, ’ with a somewhat less rapid and irregular decrease . Its colour

is reddish , and the spectrum a remarkable one of the third type , ‘ ’ ’ Dunér d u é which escribes as d un bea t extraordinaire, with very w . . 0 1 0 1 ide and very black bands Max about August 3 , 9 ° 8 1 0 : 2 . 1 . s. . R Pegasi 3 h m 3 , N Discovered by H ind 8 1 8. . 6 1 in 4 Max 9 to 7 9 ; min . below 3 . Mean period, about 80 u b t . 3 days, with considerable irregularities A maximum was 1 0 1 0 2 observed by D r. Kelly on August , 9 magnitude) . ° °

2 . 8 m . . 1 1 : . s R Aquarii 3 h 3 39 , S 5 About south 2 0 1 8 1 1 west of Aquarii Discovered by Harding in . Max . 58 t o 8 1 1 . 8 5 min . about Mean period , 3 7 days , but with some

irregularities . The increase from tenth magnitude is rapid .

u of . The colour is reddish, and the spectr m the third type A maximum magnitude) was observed at Harvard on De c e mb e r 1 00 on 2 9, 9 , and another magnitude) December 7, 1 0 1 9 . 2 8 2° 1 . s . . V Cephei : 3 h . 5 m 44 ; N D iscovered by 6 8 ° I 1 882 2 6 . . Chandler in . Max . 6 to 4 ; min to 7 Mean 60 period, 3 days . °

a 2 . In . 1 s. . 0 R Cassiopei : 3 h 53 9 , N 5 Discovered by

1 8 . 8 6 . 1 2 . Pogson in 53 Max . 4 to 7 ; min 97 to Mean period ,

days, with some irregularities . The colour is reddish . ’ ‘ c Peek alled it ﬁery red , and says There is a slight hazy look ’ round the star , as if seen through an atmosphere . A maximum 6 2 1 02 (7 magnitude) was observed by Grover on December , 9

1 . (interval since last maximum , 4 4 days) Spectrum of the third I D H . n 1 8 type September, 99, Espin found the lines 3 and 7

bright . a I n ddition to the above , there are many other known

variables of long period , but they are mostly faint , even at of maximum , and not well within the reach amateurs with small

telescopes . It will be noticed in the preceding list that in some cases the observed interval between two maxima does not agree well with the mean period found by previous observations . In these cases the observer should add the mean period (or multiples of the

period) given to the observed date of maximum , and then watch the star at the next maximum to see whether it is before or after VARIAB LE STARS 6 1

its time . In this way much useful work may be done by amateur observers— work which does not come within the province of t he professional astronomer . I T of r r egu lar Var iable Star s. here are a n umber a stars which are certainly v riable in light , but which

e a a f se m to h ve no regul r period . I n most o these the

of a a a and nOt a amount v ri tion is sm ll , sometimes e sily

. T detected here are , however , some interesting objects in this class .

The following are among the most interesting of the irregular variables °

a. R . o . . 0 s . . a : . A Cassiopei , h 34 m 5 , N 55 Discovered by B irt in 1 83 1 conﬁr med by Sir John Herschel and others . ‘ 2 2 2 Variation from to 8 magnitude . Chandler says : Varia ’ tion only occasionally evident . Colour reddish . Spectrum of the second type (K , Pickering) . °

. 6 s . . Pe r se i : 2 8 . 8 p h 5 m 4 , N 3 D iscovered by A Schmidt in 1 854 while using it as a companion star for lgol . u Du nér Max . min . The colo r is yellowish, and calls ’ u . the spectrum s pe rbe . Third type °

a . . s . . 6 Aurig 4 h 54 m 47 , N 43 Suspected by Fritsch 1 82 1 1 8 in ; conﬁrmed by Schmidt 43 , and independently by

1 . . . Heis in 847. Max 3 min Colour nearly white Spec trum of the second type (F , Pickering) . ° a B : . . s . . Orionis ( etelgeuse) 5 h 49 m 45 , N 7 D is covered by Sir John Herschel in 1 840 . It varies from about

0 2 1 . to magnitude , with no regular period The star is very 1 reddish , and the spectrum a ﬁne one of the third type . I found

u 1 6 1 26 1 02 . the star nusually bright on October , 7, and , 9 I t

and . was then brighter than Procyon , equal to Capella ° 7 : 1 0 . 1 . 1 1 s . . 7 Argus h 4 m , S 59 Discovered by

B urchell in 1 827. This famous variable star is one of the most remarkable objects in the heavens , varying as it has done s f through all grades of brightnes , rom that of Sirius to below ! 1 6 the seventh magnitude It was observed by Halley in 77,

1 Al-Su ﬁ 1 -2 (tenth century) rated it magnitude , and called

Aldebaran ﬁrst magnitude . 62 TH E STELLAR HEAVEN S

f a and rated ourth magnitude . L caille estimated it second 1 1 B magnitude in 75 . urchell saw it fourth magnitude from 1 8 1 1 to 1 8 1 5. I t seems to have bee n of the second magnitude 1 822 1 826 1 1 8 2 B from to , but on February , 7, urchell found it a 1 8 2 8 first magnitude and equal to Crucis , and in February, , 1 82 1 between the first and second magnitude . From 9 to 83 3 e e u Johnson and Taylor rat d it second magnitud , and it was abo t m e this agnitud , or rather brighter, when Sir John Herschel commenced his observations at the Cape of Good Hope in 1 8 1 6 1 8 34 ; and so it remained till December , 37, when Herschel ‘ ’ was surprised to find its light nearly tripled . I t was then ‘ o . brighter than Procyon, and far superi r to Aldebaran I t

(1 exceeded Orionis , and the only star (Sirius and Canopus ’ excepted) which could at all be compared with it was Rigel . 2 8 Its light continued to increase, and on December it was nearly equal to a. Centauri . The maximum seems to have been 2 1 8 8 h reached about January , 3 , w en Sir John Herschel found it exactly equal to a Centauri . After this its light began to ‘ 1 1 8 8 decrease, but it was not until April 4 , 3 , that it had so far faded as to bear comparison with Aldebaran , though still some ’1 what brighter than that star . I n 1 843 it again increased in brightness, and in April of that year it was observed by Maclear to be brighter than Canopus and nearly equal to Sirius ! It f then aded a little, but seems to have remained at nearly the 1 8 0 S brightness of Canopus till February, 5 , ince which time it has gradually decreased . I t was still of the ﬁrst magnitude in 1 8 6 o 5 , according to Abb tt, but was rated by Powell in 1 8 58 ; third magnitude in 1 860 by Tebbu tt ; in 1 86 1 by Abbott ; ﬁfth magnitude in 1 863 by Ellery ; and sixth mag 1 8 nitu de in 1 867 by Tebb u tt . In 74 it was estimated 6 8 at 1 8 1 8 M w k 8 . 8 ar k ic Cordoba, and only in November , 7 In 7 ’ estimated it Tebbu tt s observations from 1 877 to 1 886 Show that it did not rise above the seventh magnitude in those 1 8 6 . 8 6 years In March , , it was rated 7 by Finlay at the Cape ‘

. 1 888 Te bb u tt of Good Hope In May, , thought that it had ’ 1 88 increased fully half a magnitude since April , 7, and might

1 8 . . . . s be rated as seventh magnitude . In 96 Mr R T A Inne

1 ’ Cape Observations, p . 34 . VARIAB LE STARS 63

u 1 00 1 0 1 found its mean magnit de in 9 , in 9 , e 1 0 2 and in January and F bruary , 9 , Schonfeld thought

u u that a reg lar period is very improbable, altho gh a period of

6 u 6 L . 4 years was s ggested by Wolf, and about 7 years by oomis The star is situ ate d in the densest portion of o ne of the most

e a the . r markable nebul in heavens I t is reddish , and the

( spectru m very Similar to that of the temporary stars . I t may perhaps be considered as a sort of connecting link between - long period variables and temporary stars . ° B a a 1 . . s . . 2 8 R Coron 5 h 44 m 47 , N etween and

. 1 . 8 . 1 . a Corona D iscovered by Pigott in 795. Max 5 ; min 3 A e e remarkabl but very irregular variabl , sometimes remaining e for a whole year at a maximum , with little or no perc ptible

e . 1 862 1 86 chang In the years and 3 it remained , according the u e to Schmidt , of about sixth magnit de for a y ar and a half The present writer found it visibl e to the naked eye in he 1 1 8 u 1 1 8 t u . P njab from April 4, 77, to Aug st , 77 At times , however, it descends to a minimum with great rapidity. A bright minimum of 7 4 magnitude was observed by Sawyer on u h 1 1 88 . t e u October 3 , 5 The colo r is nearly white , and spectr m

. B e of the third type, according to Pickering right lin s have e been s en by Espin . °

0 u 1 2 . 2 1 s . 2 6 6 . e 3 (g) Herc lis ; h 5 m . , N 4 Discover d

B ax n ll . . . by e d e in 1 857 Max 47 to min to 6 . The u spectr m is a ﬁne example of the third type . ° a. u : 1 . 1 0 . s . . 1 Herc lis 7 h m 5 , N 4 D iscovered by Sir

1 . William Herschel in 795 Max . min . 3 9. Variation u often scarcely perceptible . Vario s periods have been assigned ; ‘ : e Chander says Two or thr e months , with wide ﬂuctuations h ’ t e . ﬁ ne u from mean Colour reddish , with a spectr m of the third type . °

u a : 1 8 . . s . . V Aq il h 59 In 4 , S 5 Detected by several 1 8 1 1 8 2 Safar ik 1 88 w e observers Knott, 7 Schmidt, 7 , 4 Sa y r, 8 1 8 2 . . . . 9 Max min I t is a very red star, and is No . 483 ’ of B irmingham s Catalogu e (584 Espin) and lies a little south of

A Aqu ila .

i i : 1 . 1 0 . 1 s. . RV Sagittar 9 h m , S 3 3 Discovered by

Mar kwick . 1 1 Variation from to below magnitude . ‘ According to Roberts , there is apparently no regular period , 64 TH E STELLAR HEAVEN S

’ although there is evidence of a rough cycle of eighteen months . Professor Pickering found the spectrum peculiar and with bright 1 lines . ° A : 2 1 . 0 . 2 s. . 8 Cephei h 4 m 7 , N 5 D iscovered by

1 8 8 . . Hind in 4 Conﬁrmed by Argelander This is Sir W . ’ ‘ ’ Herschel s garnet star, perhaps the reddest star visible to the naked eye in the Northern Hemisphere . Numerous observa tions by the present writer in the years 1 883 to 1 899 show that 8 the star is certainly variable from about 3 7 to 4 magnitude , B but with apparently no regular period . right phases were

1 1 1 1 88 . observed on February 3 and May , 5, when B was very

° little inferior to 3 Cephei . The spectrum is a very ﬁne one of ‘ the third type, the separating spaces being sharp , dark , and ’ very broad . ° : 2 2 . 8 . s . . 2 B Pegasi h 5 m 55 , N 7 D iscovered by

1 8 2 2 2 . Schmidt in 47. Variation from to 7 magnitude

- i — T Shor t Per iod Var ables, his is a most remarkable f a M of and interesting class o vari ble stars . ost those hitherto discovered may be followed with the n aked eye o r a binocular ﬁ e ld -glass through all their changes of The f fe w brightness . periods range rom a hours to fe w s several days . I n a ca es the periods are longer, an d f Th of extend to twenty to ﬁ ty d ays . e increase light is usually more rapid than the decrease , but there are some exceptions to this rule . The following list includes the most interesting of the short period variables now known . They are given in order of right 1 00 ascension , and the positions are for 9 ° : 6 . 8 . 1 1 s . . 20 ( Geminorum h 5 m , N Discovered by

° 1 8 u . Schmidt in 47. Variation from 3 7 to 4 5magnit de Period = days 1 0 d . 3 h . s . I t was found to be a spectro — b u t 7 a scopic binary by Campbell and Wright , like 7 Aquil — and 6 Cephei the variation does not seem to be due to an eclipse . Spectrum of second type (G) .

1 A st r o h sica l ou r nal 1 8 6 . 1 0 . p y j , August, 9 , p 4

66 TH E STE LLAR H EAVEN S

1 8 1 . 6 m n covered at Cordoba , 7 Varies from 7 to ag itude .

. . 5 . Period, days , or 3 d 9 h Light curve regular . ° Tr n li 1 ia u . 2 2 s . : . 1 . 6 S g Australis 5 h 5 m , S 3 D is

at . 6 covered Cordoba Variation from 4 to magnitude .

Period, days . T i 8 ° ian u l 1 . . 2 . r : s . 6 2 U g Australis 5 h 5 In 5 , S Dis 8 covered by Roberts in 1 93 . Variation from to 8 4 magni

68 . . 2 tude Period , 5 3 days Almost stationary at its maximum

for about twelve hours (Roberts) . °

8 a : 1 6 . 1 0 . s . . Norm h m 3 5 , S 57 Discovered by

Roberts . Max . min . to Period, days . ‘ According to Roberts , it departs considerably from the ordinary - type of short period variation , the ascending period being almost ’ of the same duration as the descending peri od . ° ! 1 1 . 1 6 s . . 2 (3) Sagittarii 7 h . 4 m , S 7 D iscovered 8 6 1 66 . . by Schmidt in Varies from 4 to magnitude Period ,

days, but this requires a small correction . The spec

trum is of the second type (K, Pickering) . ° hi chi 1 . O u : . 1 s . . 6 Y p 7 h 47 In 7 , S D iscovered by 88 2 1 8 . 6 8 . Sawyer in Variation from to magnitude Period,

days . 1 ° i i 1 . 8 . 8 s . 2 W (7 ) Sagittar 7 h 5 m 3 , S . 9 Discovered

1 866 . 8 8 . by Schmidt in Varies from 4 to 5 magnitude Period ,

7 59460 days . ° . . 0 . 1 8 : 1 8 1 s . Y Sagittarii h 5 m 3 , S Discovered by

w 1 886 . o 8 u . Sa yer in Variati n 5 to magnit de Period,

days . The colour is white, and the spectrum of the

second type (G , Pickering) . °

d 1 8 . 2 2 . 6 s . . 0 59 ( ) Serpentis h m , N Discovered by

Miille r and Kempf in 1 891 . Varies from 5 to 57 magnitu de .

Period, days . The spectrum is of the ﬁrst or Sirian type . ° 6 . o s . . 1 : 1 8 . 2 U Sagittarii h m , S 9 Discovered by

1 866 8 . Schmidt in . Variable from 7 to 3 magnitude Period,

67 446 days . ° a : 1 8 . 6 . 2 s . . B Lyr h 4 m 3 , N 33 Discovered by

1 8 u . Goodricke in 7 4 . Variation from to magnit de Mean

1 2 . 2 1 . 6 . 8 5 . . period, d h 4 m 5 3 (Reed) A remarkable and

interesting variable . There are two maxima of magnitude, and two minima, one and one (the chief minimum) mag VARIAB LE STARS 67

i d . r a n tu e Situated as it is near a good comparison star, 7 Ly , the ﬂuctuations in the light of B Lyra are very evident and

c an v the a . interesting, and be well obser ed with n ked eye In recent years the star has been found t o be a spectroscopic binary, a fact which seems to be in some way connected with ’ the star s variation (see Spectroscopic B inaries in last chapter) .

u . The spectr m is of the second type (G , Pickering) °

6 s. . 6 1 x 8 . 1 . 8 Pavonis : h 4 m 3 , S Discovered by

1 8 2 8 . Thome in 7 . Variation from 3 to magnitude Period ,

days . A very interesting variable star, as all the light ‘ changes can be observed with the naked eye . Light curve ’ a r oxi regular . Period seems to be constant . There is an pp mate equality between the ascending and descending rates of

variation . °

a : 1 . 2 . 1 s . . 20 m U Vulpecul 9 h 3 m 5 , N Varies fro

7 to magnitude . Period, 7 97997 days . °

: 8 . . . u 1 . 8 s U Aq arii 9 h 3 m 5 , S 7 Discovered by

6 1 n . 1 886 . o Sawyer in Varies fr m 4 to 7 mag itude Period,

° 7 o 24o days . The star is white . °

7 a : 1 . . 2 s . . 0 7 Aquil 9 h 47 In 3 , N Discovered by Pigott

1 8 . . e in 7 4 Variation from 3 5 to 47 magnitude Mean p riod ,

. 1 m . 7 d 4 h . 4 , with oscillations of a few hours in the time of L maxima and minima, according to Dr . W . J . S . ockyer . From spectroscopic observations B e lopolsky ﬁnds evidence of orbital

motion in a period of 7 days 4 hours , but he thinks that the variation of light cannot be produced by an eclipse (as in the d case of Algol) , as the times of observe minima do not agree e with the tim of an eclipse in the compu ted orbit . The colour

of the star is yellow, and the spectrum of the second type (G) . °

1 0 a : 1 . 1 . 2 s . . 1 6 S ( ) Sagitt 9 h 5 m 9 , N Discovered

1 88 . 6 . d by Gore in 5 Variation from to 4 magnitude Perio , = 8 . 1 1 8 . days d . 9 h m . 4 s The minimum occurs d ays before the maximum . Owing to its proximity to a good — 1 1 a — comparison star Sagitt the ﬂuctuations of light, although

comparatively small, are very evident and interesting when - u ﬁ eld - observed with an opera glass or binoc lar glass, with e which instrument the variability was discov red . At the maxi it I 1 a mum is slightly brighter than Sagitt , and at the minimum o considerably fainter. Espin remarks that the star is ab ut four — 5 2 68 TH E STE LLAR HEAVEN S

’

V f . The days isible to the naked eye, and our days invisible colour is white . ° - 20 . . 2 s . . X Cygni h 39 m 9 , N 3 5 A little south west

A . 8 6 6 of Cygni Discovered by Chandler in 1 8 . Max . 4 min . to 77 . Period , days . An interesting variable .

The increase of light occupies four days, the decrease ten days , h l ’ with a a t in the latter about midway of its course . There are bright and faint minima , but regularly alternating . The colour

- is white . Can be well Observed with an opera glass . °

a 20 . . 1 s . . 2 T Vulpecul h 47 m 3 , N 7 Closely north

of 2 . 1 88 west 3 Vulpecula Discovered by Sawyer in 5. Variable

. o . 1 0 . from to magnitude Peri d , days , or 4 d h 2 0 7 m . 5 s . The minimum occurs about days before the c an ob maximum . A very interesting variable, and be well - served with an opera glass . The colour is white , and the o spectrum of the sec nd type (F, Pickering) . 6 ° : 22 . 2 . 2 s. . Cephei h 5 m 7 , N 57 D iscovered by

1 8 t . Goodricke in 7 4 . Variation from 3 7 to 49 magni ude

8 . . s . . Period, 5 d . h 47 m 393 , with some irregularities A very h an interesting variable . All t e light ﬂuctuations c be observed u with the naked eye . The colour is yellowish , and the spectr m s e ctr osc0 ic b u t of the second type (G) . It is a p p binary, , like 7 a ) Aquil , the light changes are not well accounted for by the orbital motion of two components .

The f a t o f ollowing h ve longer periods , an d seem orm a connecting link between the short -period and long period variables

° °

6 . 1 . s . . 2 1 T Monocerotis h 9 m 49 , N 7 About 5 west

8 6 . 8 2 . 1 . . of 3 Monocerotis Max 5 to 4 ; min to Period , 0 1 2 2 c an 2 7 days (Yendell) . It be followed through all

- its changes with a binocular ﬁ eld glass . The spectrum is of the second type (G , Pickering) . Maxima were observed by

1 02 1 2 . Yendell , 9 , January 3 , March 3 , and March 9 °

6 . 1 s . . : . 2 U Monocerotis 7 h m , S 9 D iscovered by

8 . i 6 1 1 8 . . . G ould, 73 Max to min to Per od, 4 days , but with some irregularities . The spectrum is of the second - type (K, Pickering) . Can be well observed with an opera glass . ° 2 1 . 8 m . 6 s . . Cygni h 3 4 , N 43 Discovered by Miss VARIAB LE STARS 69

1 Wells at Harvard . Variation from to magnitude (photo

u 0 . graphic magnitudes) . Period , abo t 4 days The variation is unusually large for so short a period . Mo st of the short -period variable s lie in or near the M ilky - r Way . The only well ma ked exception to this rule seems to be 1 o . W Virginis , a faint star with a period of ab ut days

— The fa i A Al gol Var iables. mous variable star lgol

(B P e r sei) is the type of this interesting class of variables . The a a of a a a and ch r cter the vari tion is peculi r one , is

ff f a All fl u c t u a quite di erent rom other vari bles . the light a a of fe w for tions t ke pl ce in the course a hours , while m a and of the re inder , much the longer portion , the The period the light remains constant at a maximum . n umber of these variables known at present is com a of par tively small , but since the discovery spectroscopic binaries it has become probable th at they m ay be much more n umerous than is generally sup posed . Owing to a of a the ch racter the variation , their discovery is matter f f f f o no small di ficulty . A minimum o a star o this class m a a f of y be observed by ch nce , but , rom ignorance its a a period , we c nnot tell when to expect nother minimum , and consequently a long tim e m ay elapse before th e f suspicion o variabilit y can be confirmed . I t seems certain now th at the variation of light in st ars of this a an a r cl ss is due to eclipse by dark o bright comparison .

The following list includes , I think, all the variables of this 2 class hitherto discovered . Some of them are faint, and can only be observed with a good telescope . They are given in

R. order of A . °

0 2 s . 8 1 U Cephei h . 53 m . 3 , N . D iscovered by Ce r a ki 1 880 s . . . 2 1 1 . in Max min to Period, d . h

. 8 49 m 3 s . The light ﬂuctuations occupy about ten hours ,

- or about one sixth of the period . The light is stationary for nearly two hours at the minimum . Decrease of light more

1 2 . 1 02 See Appendix, Note M December, 9 . 70 TH E STE LLAR H EAVEN S

’ . b ut rapid than the increase The colour is white , turns ruddy

. of or near the minimum The spectrum is the ﬁrst Sirian type , a feature usual in variables of this class . ° Pe r s i = D ° e I 0 : 2 2 s . 1 M + 4 , 5 4 h . 33 m . 3 , N . 4 1 0 2 o t o Discovered by Stanley Williams , 9 . Varies fr m

1 2 . 1 2 1 nearly magnitude Period , 3 d . h . m . s . P i ° e r se : . 1 . 0 s. . 0 Algol (B ) 3 h m 4 , N 4 D iscovered by 1 66 1 82 Montanari in 9, and independently in 7 by Goodricke , who determined its period . Max . min . 3 5. Mean period 2 20 8 s e at present , d . h . 4 m . 5 . , but subj ct to a secular variation of a few seconds . The light changes occupy a little u over nine ho rs . Schmidt found that the brightness of Algol is equal to that of 6 Per se i about forty -seven minutes before and - after minimum ; to that of e Pe r se i about sixty two minutes before and after the same ; and to that of B Tr iangu li ninety

ﬁ v e f u . minutes be ore and after minim m Vogel found, from 1 888 1 88 observations with the spectroscope in to 9, that the — variation of light is caused by a dark eclipsing satellite a ’ theory originally sugg e sted by Goodricke . Vogel s observa tions show that the distance between the components is about

miles from centre to centre , and their diameters about

and miles respectively . From this it follows - that the combined mass is abou t two thirds that of the sun .

The star is at present white, but is recorded as red by the Persian astronomer Al-Su ﬁ in the middle of the tenth century a remarkable instance of change of colour in a star . The spectrum is of the ﬁrst or Sirian type (A, Pickering) . ° A B x n s . . 1 2 a e Tauri 3 h . 55 m . 8 , N D iscovered by

i . . dell n 1 848 Varies from to magnitude Mean period,

. 2 2 . m . 3 d h , but with inequalities sometimes amounting to

. e B . 3 hours The spectrum is of the ﬁrst typ ( 3 A, Pickering) 6 ° 6 . 1 : . 1 . s. R Canis Majoris 7 h 4 In 5 , S Discovered

1 88 6 . by Sawyer in 7. I t varies from to 7 magnitude Period , 1 . . 1 In 6 . d 3 h 5 . 4 s The light ﬂuctuations occupy about ﬁve hours . The spectrum is of the second type (F , Pickering) . °

: m . 1 s . . 1 RR Puppis 7 h . 43 3 , S 4 Discovered by

f 1 0 1 1 . . . . 1 8 R T A Innes in 95. Variation rom to magnitude

6 . . 1 0 1 In 2 5 . Period , d h . 9 . 5 Variation regular The light

ﬂuctuations occupy abou t fourteen hours, and at minimum the light is stationary for about eight and a half hours . Roberts VARIAB LE STARS 71

‘ says : The light changes are accounted for by the revolution the e in plane of sight of two stars , one thre and a half times larger than the other, the smaller star being, however , one and l a ha f times brighter than its larger companion . On this supposition , a secondary minimum would be practically inap ’ r e c iabl 1 p e . He ﬁnds that the density of the component stars ’ = 1 2 cannot be greater than (sun s density ) . = ° Pu 2 2 . . 8 is Lacaille 1 0 . . s V pp 3 5 7 h 55 m , S 4 Dis covered by Williams in 1 886 . Max . min . to

1 1 0 . . 26 . . Period , d . h 54 m 7 s (Roberts) Light curve of the same type as U P e gasi . Variation continuous and symmetrical ’1 on either side of minima . There is no stationary period at Th minimum . e spectroscope shows the star to be a close ‘ : binary. Professor Pickering says The period days satisﬁes the observations of the changes , and of the varying ’ e separation of the lines in the spectrum . Sp ctrum of brighter

B 1 h B . component appears to be class A, t at of the fainter 3 A ‘ The separation is very large, and micrometer measures give ’3 the relative velocity of the two components as 6 1 0 kilometres 8 (37 miles a second . This gives a mass of over seventy times su n the mass of the According to Roberts , the density cannot ’ u be greater than of the s n s density, and he thinks that ‘ the two component stars revolve round one another in actu al ’ contact . (The italics are ° ! . 8 a : 8 2 . s . . Carin h 9 In 7 , S 5 Discovered by

1 8 2 . . . 1 2 . Roberts in 9 Max 7 9 ; min to Period , h ‘

. 2 . e e 59 m 99 5 Light variation very regular . Th r is no ’ o stationary phase at minimum (Roberts , who thinks the peri d o may p ssibly be dou ble that given above) . 1 ° B 6 . 8 . 1 . : 8 s . S Cancri h 3 m 4 , N 9 etween 7 and

. e 1 8 8 . 8 2 8 Cancri Discov red by Hind in 4 Variation , to 9 mag

nitu de . . 1 1 . . Period , 9 d h . 3 7 m 4 5 s The light ﬂuctuations u - occ py twenty one and a half hours . Argelander remarked that e u he aft r minim m the light begins to increase very rapidly, and was incline d to think that the descent from the maxima is even still more rapid . It was once obs e rved very faint at minimum .

1 A str o h sical o r al u n 05 . 1 2 1 0 1 p y j , N 49 , 49 ( 9 , February 2 . 88 . Mid 1 0 1 p , April , 9 . 3 A nnals o H a a d olle e r v r C . . . 1 f g , vol xxviii , part ii , p . 77. 72 TH E STELLAR H EAVE N S

a : 2 6 ° . . s . 2 8 S Antli 9 h 7 m 5 , S . D iscovered by Paul

1 888 . . 6 6 in Varies from 7 to magnitude . Period , 7 h . 4 m 8 4 s . The light ﬂuctuations occupy about three and a half

hours . Pickering ﬁnds that the light curve does not re semble L those of B yra and U Pegasi . The period is one of the shortest u h known , the star going thro gh all its ﬂuctuations of lig t three times over within twenty-four hours °

: . 2 . 1 s . . v S Velorum 9 h 9 m 7 , S 44 D isco ered by

° 1 8 . 8 . Woods in 94 Variation from 7 to 9 3 magnitude Period,

. 2 2 . 2 m . 5 . 5 d h 4 . Variation very regular The light

ﬂuctuations occupy about ﬁfteen hours, and the light is stationary ‘ 6 1 8 at minimum for h . m . Roberts says The passing into and from the stationary phase is abrupt the form of the light

curve at these two points being practically a right angle . The explanation that naturally suggests itself is that in stars of this type of variation we have two bodies, one bright and small ,

the other dark and large, revolving round one another, the ’ darker body eclipsing the brighter each revolution . ° 1 0 1 6 s 1 Velorum h . m . 44 . , S . 4 D iscovered by

1 0 1 1 0 1 0 . Roberts in 9 . Varies from to 9 magnitude Period , 1 20 0 2 20 d . h . 3 m . s . The light changes occupy 3 h . m . No stationary period at minimum . Ascending and descending phases equal . °

u 1 . s. . RR Centa ri : 4 h . 9 m 55 , S 57 Varies from

1 6 . o . to magnitude . Peri d , 7 h m . s I t seems to be a sort of connecting link between the short -period variables and those of the Algol type . Variation within narrow limits , usually ’ half a magnitude, very rapid and very regular (Roberts) . 8 ° 6 a : 1 8 s . Libr 4 h . 55 m . 3 , S . Discovered by Schmidt

1 8 6 2 2 . . in 59. Variation from 5 to magnitude . Period, d 7 h

1 2 2 8 3 . . 5 m . Light ﬂuctuations occupy twelve hours The u e spectr m is of the ﬁrst or Sirian typ . ° o a : 1 1 s 2 U Cor n 5 h . 4 m . 7 . , N . 3 D iscovered by Winn k e c e 1 86 8 . o in 9. Varies from to 9 magnitude Peri d ,

. 1 0 . 1 s . 3 d h 5 m . . , with some irregularities The light

ﬂuctuations occupy nearly ten hours . A r a : 1 6 ° o . 1 2 6 6 s . . R h 3 m . , S 5 D isc vered by 8 1 1 . 8 . Roberts, 9 Variation from 6 to magnitude Period,

. 1 0 . 1 2 . L . 1 2 . 4 d h m 79 5 . ight ﬂuctuations occupy 9 h m o No stati nary phase at minimum .

TH E STE LLAR H EAVENS

° a : 1 . 1 2 2 s. . 2 Lyr 9 h m . 3 , N 3 D iscovered by

1 02 . 1 1 1 2 8 . Stanley Williams, 9 Variation from to magnitude

. 1 . 2 2 2 7 Period , 3 d 4 h m . 3} 5 . Light ﬂuctuations eight hours . °

1 1 26 s . . 1 3975 9 h . 4 m . , N 9

1 0 1 . . Discovered by Schwab , 9 Max . min . nearly 9 Period,

: days 3 d . 9 h . 7 m . Variation unusually large for an Algol

star. °

1 . 2 s . . 2 Cygni 9 h 4 m . 7 , N 3 Discovered by Madame C e r aski. o 1 1 1 Va iati n about to 3 . Period , r . magnitude 6 . 0 . 8 8 d h 111 . ° ' 20 m . I . . 6 Cygni h , N 4 . Discovered by Madame r Ce aski. 8 6 1 1 . d Varies from to below magnitude Perio ,

. 1 4 . . 2 . u e e d 3 h 4 5 m s , The variation amo nts to about thr

magnitudes, and therefore exceeds that of any other known

Algol variable . Light ﬂuctuations occupy about thirteen hours .

Spectrum ﬁrst type . ° 20 1 m . . 2 . s . Cygni h 9 39 , N 4 D iscovered by Stanley

1 0 1 . 1 0 1 2 . Williams, 9 Varies from to magnitude Period ,

. 1 0 3 d h . 49 m . Decrease of light takes three and a half

1 0 111. hours, increase 4 h . Light constant at minimum for ﬁfty

minutes . ° : 20 s . . 1 W Delphini h . 3 3 m . 7 , N 7 D iscovered by

° Miss Wells at Harvard Observatory 1 895. Max . 9 5

° . 1 2 . . 1 z 1 2 m . . min below Period 4 9 . ) , d h . (Pickering ° : 20 . 8 . s . . Y Cygni h 4 m 4 , N 34 D iscovered by 8 d b u t 1 86 . Chandler, Variation from to 79 magnitu e ,

. 1 d . 1 1 . . variable at minimum Period for even minima, h 57 m

2 6 s . . . et . 1 1 . 1 2 . 7 , and for odd minima d 1 h 57 m 5 s (Dun )

The light ﬂuctuations occupy about eight hours . An investiga of B e tion the elliptic elements of this variable by Dr . un r leads him to the following result The variable star Y Cygni consists u of two stars of eq al size and equal brightness , which move u abo t their common centre of gravity in an elliptic orbit, whose major axis is eight times the radius of the stars . The period of 2 6 an anomalistic revolution is 99 933 days , and the eccentricity 0 is 1 4 5. A minimum occurred while the stars were at peri i . 8 . 2 1 26 . . 8 1 8 helion ( ) at h m G . M T . on December , 5 The line o of of apsides of the orbit, which then c incided with the line 1 1 sight, completes one revolution in the plane of the orbit in 4 ’ A str o h sical ou r nal tropical years ( p y j , April , VARIAB LE STARS 75

° f 2 1 . m . o . Cygni h , N . 45 A little north f Cygni Discovered by Madame Ce r aski from photographs

1 2 . Variable from about 1 1 to magnitude Period , probably b 1 8 a out days . ° — = far m . . C ni M 1 0 1 2 1 . yg D 4 h , N 43 Not n 8 1 1 6 from the variable SS Cyg i . Variation from 9 to magni 1 0 — a tude . Period, about 3 3 4 days very long period for a variable of this class . Duration of minimum about two days . °

2 2 s . . 1 U Pegasi : 3 h . 5 m . 53 , N 5 Discovered by d e 1 8 . Chandl r in 94 . Variation from 9 to 9 7 magnitude Perio ,

8 . 1 e u . 5 . . h 59 m . 4 (Pick ring) The colo r is white f and I t has been shown by Dr . Roberts, of South A rica , inde pendently by Professor Russell, of Princeton that the density of the Algol variables is very small , ranging from in the case of V P u ppis to 07 28 in Z Herculis

—A of Clu st er Var iables. large n umber variable stars have recently been found in the globu lar star clusters . Professor B ailey found 1 3 2 in the cl uster Messier3 a V enatic i 2 2 of in C nes I n the cluster No . 5 7 the N ew 1 1 General Catalogue of Nebul a he fou nd 3 . I n the M 8 ou t of 0 cluster essier5, 5 have been detected 75

a and 1 2 2 u 6) st rs , in the great So thern cluster Cen

V a a f tauri . ari bles h ave lso been oun d in some other - H clusters , but in the well known cluster in erculis , M if 1 fe w . essier 3 , there are very , an y

The mean period of forty of the variables is the cluster 0 6 2 d . 1 2 . m . Messier 5 is 5 , or h 37 4 , the longest period being

1 6 . . m 0 8 1 . 8 4 h 5 , and the shortest h 4 m . The range of varia 0 u e tion is between 7 and magnit d . The light curves are all very similar, showing a rapid decrease of light, but a much ’ more rapid increase . This has been called the cluster type . u There is probably no d ration of maximum . In some cases e the light at minimum seems to r main constant, or nearly so, ‘ to for a few hours . In the cluster Centauri no such uniformity ’

of . was found, but it contains many variables the cluster type 76 TH E STELLAR H EAVEN S

Professor B ailey divides the whole period of variation of this type as follows Duration of maximum Duration of minimum phase D uration of decreasing phase Duration of increasing phase

o w . 1 w The shortest peri d kno n is that of No 9 in Centauri , 6 1 1 m . which is h . , but possibly there may be some with even str sica l ou r nal 1 8 2 A o h . shorter periods ( p y j , November, 99, p

i — T of a Su sp ect ed Var ables. here are a n umber st rs h of whic have been suspected being variable in light , but which have n ot yet been admitt ed into the ranks of ’ T f f r known variables . hey orm good obj ects o observa

tion by amateur astronomers . The following are some of the most remarkable and interest ing cases 6 Urs a Majoris This is the faintest o f the well -known seven ‘ ’ ’l u Wain stars forming the Plo gh , or the Churl s , and has long

been suspected of variation in light . It was rated second magnitude b y Tycho B rahe and the Prince of Hesse ; Al-Su ﬁ B d 0 and Argelander made it ra ley 3 , and Heis It was u chOnfeld meas red at Harvard . S thought that variation

was established, with a long period . The spectrum is between

o 2 . the ﬁrst and sec nd types (A F , Pickering)

a. a : Hydr This reddish star, called by the ancient Chinese ’ ’ ‘ ’ ‘ B A al- ar a the Red ird , and by the rabians f the solitary one , ’ owing to its isolated position in the sky, south of the Sickle

c . in Leo, was suspe ted to be variable by Sir John Herschel I t 20 was observed to be very bright by Gemmill on February , 1 882 1 88 , and again unusually bright on May 9, 3 , when he thought it nearly equal to Pollux . It was rated second magni Al-Su ﬁ u tude by Ptolemy, , Argelander , and Heis, but Houzea 1 8 estimated it third magnitude in 75. I t was measured at

Harvard . I ts spectrum is between the second and third types

2 . (K M , Pickering) A Draconis : I have long suspected this star to be variable

1 ’ ’ Popularly , but erroneously, called Charles s Wain . VARIAB LE STARS 77

own o f 1 8 6 1 8 1 in light. My bservations rom 7 to 9 show decided

ﬂuctuations to the extent of nearly one magnitu de . It was d Al-Su ﬁ rated thir to fourth magnitude by Ptolemy, , Argel

- 1 8 . ander, and Heis , but Houzeau made it 4 5 in 75 The star is

hu e . of an orange , and the spectrum of the third type 0 S e rpentis : This star was rated fou rth magnitude by Al-Su ﬁ B e i h o Ptolemy, , Ulugh g , Lacaille , and Pig tt, but e B e B third magnitud by Tycho rah , Hevelius , ayer, Flamsteed, B Z radley, and De ach . Piazzi and Smyth made it and

Montanari called it ﬁfth magnitude . The Cordoba estimates 6 e range from to 4 magnitude, and Gould thought ther were strong indications of variability in one of the components (it is a double star) . He gives the magnitude as and 47 , but on one occasion at Harvard a difference of magnitude was noted e the b tween components . 6 : n Pegasi This star, which is usually rated about mag i u f u u m t de, was o nd nusually faint by Sch idt in a perfectly clear e 1 8 n sky on Novemb r 5, 47. Sig s of variation were also noted ’ at Cordoba . Seidel believed it to be variable, and Schwab s

Observations indicate a period of about 26 days .

‘ 8 a : a 3 Urs Majoris This star , which lies near 3 Urs Majoris B 6 a (in the Plough), was seen by irmingham as bright as Urs

u 6 1 868 . Majoris on Aug st , I t was fainter on the following e u night , and gradually decreas d to its sual brightness . I t was 6 -6 rated 5 magnitude by Argelander, and 5 by Heis and Ob se r Houzeau . It was measured magnitude at Harvard . v at ions by the present writer seem to indicate some slight variation . I t has a spectrum of the third type . Piscis Au stral is : This star was rated ﬁfth magnitude by -6 Al-Su ﬁ u B e i h L Ptolemy ; 5 by ; sixth by Ul gh g , acaille, and 6 - B Harding ; and 5 by ehrmann , Argelander , and Heis . I t u 1 was estimated sixth magnitude by Ho zeau in the year 875. u 6 Gould fo nd it to 7 from observations at Cordoba . It was measured with the photometer at Harvard . From e a consid ration of the various recorded estimates, C . H .

F . Peters concluded that the star is probably variable . The fact of its having been seen at all by Al-Su ﬁ proves beyond reasonable doubt that it must have been brighter in his time than it is at present, and the estimates of Argelander and Heis seem to conﬁrm the variability . 78 T H E STE LLAR H EAVEN S

7) Crateris : This star was rated 4 -3 magnitude by Ptolemy ; -6 Al-Su ﬁ B e i h B e 5 by fourth by Ulugh g , Tycho rah , and Hevelius ; sixth by Argelander and Heis at Cordoba and 6 - only 7 by Houzeau . It was measured at Harvard . It seems to be certainly variable to a considerable extent ; other wise it seems impossible to explain how a star which was seen S u only ixth to seventh magnitude by Ho zeau , or barely V isible f n to the naked eye, should have been rated ourth mag itude by B e Tycho rah , who was an accurate observer . The period of

o . m variation may, h wever, be very long The spectru is of the

first or Sirian type . ‘ The Story of 0 Eridani ’ has been already told in a most K nowled e 1 8 . s interesting paper in g (July, 93) by D r Ander on , o P r i the disc verer of Nova Auriga and Nova e se . I fully agree 0 with Dr . Anderson that Eridani is identical with the Last in ’ A cher nahr of Al-Su fi the River of Ptolemy and the , and that, consequently, the star has undoubtedly diminished in brightness from the first magnitude to about the third since the tenth ’ Al- h . t century I t was one of Su s thirteen first magnitude s ars , and his clear description of its position places its identity beyond all doubt . It was also rated of the first magnitude by Ulugh B e i h 0 g , and his position agrees with that of Eridani . In recent years it has been s uspected of variation in its light . It is a — splendid double star one of the finest in the heavens . The spectrum is between the first and second types (A 2 F) . o Pe r sei : This star and 3° Per se i form a conspicuous pair ° - o 8 . Al Su fi ab ut north of the Pleiades , in his Description of ’ the Heavens , written in the tenth century, expressly states that the two stars were exactly equal in brightness (third to fourth magnitude) ; but 0 is at present about one magnitude fainter

' ‘ o . than i , and the superior brilliancy of i is n ticeable at a glance 0 It seems certain , therefore, that has diminished in brightness , “ as the present magnitude of I agrees very well with what AI-Su fi - l . made it . A Su fi was a most accurate observer The spectrum o Pe r se i of B 1 of is the first type ( A) . 7 Geminorum This star was rated third magnitude by Al-Su fi 5 Ptolemy and , or equal to Geminorum but it is now n 6 is of the second magnitude, and its superiority in bright ess to

a . noticeable at glance Spectrum, ﬁrst type (A) VARIAB LE STARS 79

a Ophiu chi and B Canis Majoris were also rated third Al- Su fi magnitude by , but they are now about the second magnitu de . ° m 0 1 6 . . a i i : 1 . Sagittar 9 h 9 , S 4 This star was rated - - fi 2 u b Al Su . L 3 magnit de by Ptolemy, but only 4 5 y acaille estimated it Th e Harvard measu res make it thus ’ - of agreeing well with Al Su fi s estimate . The spectrum is the B first type ( 8 A) . L : u B eonis This star was rated first magnit de by Ptolemy , Al- Su fi B e 1 -2 lam st e e d bu t , and Tycho rah ; by F ; only second

u L . A o magnit de by alande, Argelander, Heis , and Houzeau cording to the Harvard photometric measures , it is now below u the second magnit de and the measures are discordant . V ariation was suspected by Sir William Herschel , and the present writer has seen signs of flu ctuation in its light . The spectrum is between the first and second types (A 2 F) . There are some telescopic objects which have been suspected of variation . The famous variable star Algol has several faint 1 8 Schr ot e r companions . One of these was discovered in 7 7 by , N atu who strongly suspected it to be variable . A writer in r e u 20 1 8 se e (Febr ary , 79) stated that he failed to any trace of the 1 8 star on several fine nights in the early part of 74 , using a seven -inch refractor ; but on September 9 of the same year he saw it very distinctly with the same instru ment . I t was L 2 measured by Talmage at the eyton Observatory on October , 1 8 e e e e 1 74 , and estimat d el v nth to tw lfth magnitude , and in 878 B u u e by rnham , who fo nd thr e other fainter companions, one ’ Schr ot e r s not far from companion , and forming with it a wide ’ u ’ do ble star . Franks fo u nd Schr ot e r s star easy enough with - -a- - 1 1 1 88 an eleven and quarter inch reflector on January , 5, and ’ B u about two magnitudes brighter than rnham s companion . Sadler thought it variable from about tenth to fou rteenth mag nitu de in some short period . If variation is confirmed , it would be very interesting, as a variable companion to a known variable u b e u star wo ld a rather nique object . f Ursa Majoris It was stated by Madler1 that he found the

t 1 8 1 8 1 . companion to his bright star invisible on April , 4 About an hour afterwards it was again visible, and he suggested that

1 Com tes Rendu s . . 8 . p , vol xiii , p . 43 80 TH E STE LLAR HEAVEN S

it is a variable of the Algol type . His account leaves it some what uncertain whether Alcor (the naked -eye companion) or the telescopic companion is referred to ; but as he seems to

have been using a telescope at the time , probably the close

companion is intended. Alcor has also been suspected of varia

tion in brightness . 7 Virginis : The components of this well -known binary star

were thought by Struve to be alternately variable in brightness . H is observations in 1 8 51 and 1 852 Showed that sometimes the

stars were exactly equal , and sometimes the southern star was 0 2 0 from to 7 magnitude brighter than the other . The period o of variati n would seem to be short , for Struve found the southern star half a magnitude brighter than the other on 1 8 2 on 2 th f April 3 , 5 , whereas the 9 of the same month he ound ‘ ’ e them perfectly equal . The suspicion seems to be support d ‘ ’ by the recorded measures of position angle, some of which the have been measured from one star, and some from other, the brighter star being usually taken as the primary in measures of u do ble stars .

A remar kabl e fact about variable stars in general is th at very fe w of them S how an y parallax or proper lie n f motion , so that they probably at a great dista ce rom

the earth . —Va f an Met hod of Obser v ation , riable stars orm

interesting subject of st udy for the amateur Observer .

The method of observation is exceedingly simple . No instru ment except a good opera-glass or binocular ﬁ eld glass is necess ary for the observation of the brighter

variable stars when at or ne ar their maximum brightness . few A L a I ndeed , a like lgol , B yr , an d Z Geminorum may be observed with t he naked eye through all their ﬂ M of . uctuation s light ira Ceti , when at a bright

m a s an . maximum , y be be t observed without y optical aid F or the those variables , however , which do not rise above ﬁfth magnit ude at maximum an opera -glass or binocular

is necessary .

8 2 TH E STELLAR H EAVEN S

or ff n the estimated known di erence is smaller , six , seve , or fﬁ The of the eight steps will be su cient . light variable and is then estimated , the observation recorded in the f w a : If a and b a ollowing y we call the comp rison stars , ff one and V a a di ering about magnit ude , the vari ble , a b and if V being brighter th n , is j udged to be midway b V b If a a . in brightness between and , we write 5 5 V

t o a b a V6b. is slightly nearer in light than to , we note 4 If V b a6V b. is slightly nearer to , we write 4 We may a b b V d V . also write 3 7 , or 7 3 , etc , as the case may f h o t e a . If be , the sum steps being alw ys ten we esti

a ff a at sa m te the di erence between th e comp rison stars , y, — seven steps a more desir able difference w e may write 1 a2V b or a V b o r d V 2b 5 , 3 4 , 5 , as the case may be , the f If sum o the steps in this case being always seven . th e variable be estimated exactly equal to one of the a V = a or V = b comp rison stars , we simply write , , as the

as m a . S a V or a c e y be ome observers write > , < V , but f this method should be care ully avoided , as it leads to M ’ f a . A con usion and mbiguity oreover , it is not rgelander s If of f method . a little map is made the vicinity be ore

a a b 0 . hand , an d the comparison st rs marked , , , etc , an

- observation may be entered in the observing book th us ,

a a V b e D te ; 4 6 3 ; clear sky , no moon ; and The of the record is complete . exact magnitude the variable may then be easily fou nd when the magnit udes of the comparison stars are known . I n most cases the magnitudes of the comparison stars c an be ascertained from the photometric catalogues of H arvard Observatory . of a I n making these estimates magnitude , comp rison

’ 1 Flam stee d s If the comparison stars used are or others, the ﬁgures representing the star should be placed in brackets to : 2 0 distinguish them from the steps . Thus (7 Cygni) 3 (7 ) 3

m 1 0 1 0 1 . Dece ber , 9 VARIAB LE STARS 83 stars should be taken (at the time of observation) having about the same altitu de (if possible) above the horizon f i a a ‘ as the variable . Pro essor Picker ng st tes th t two stars apparently equ al Show a difference when pl aced ’ one one above the other , the lower being apparently the o f brighter . When comparing the relative brightn ess a S two stars ne r each other , no attempt hou ld be made to t E observe bo h stars simultaneously . ach should be looked

dir ectl and a f one at y, the eye p ssed rapidly rom to the r of a of t he othe a number times , so th t the light star fa n f a a may ll o the same portion o the retin . Gre t stress is laid on this point by Argel ander in his original p aper on this method of observing ‘ th e comparative brilliancy ’ o f a 1 st rs , and as some observers seem to disregard ’ Argelander s instructions , I will quote his words here . H e says : L ook alter nately at the two star s which ar e to c be ompared , and endeavour to receive th e image on

th at part o f the eye in which it is seen the brightes t . i a On the other hand , exerc se the most ze lous care not to for a look at both stars at once , in such c se the two can ’ never be seen at once in their full brightness . Only very clear nights should be used for making these a of observations , and care should be t ken that none the ﬂe e c companion stars are dimmed by small y clou ds ,

which are often present in an otherwise clear sky . A : ‘ a rgelander says When the we ther is misty , when ar e ﬂ o r clouds ying , in bright twilight , too close prox im it a y to the moon , such Observ tions should not be

u ndertaken . It is especially important to avoid the of impression any other light , and when the moon is u p to place one ’s self in such a position that the moon will

. B f be hid by some object e ore observing, the eye should 1 ’ Silliman s A mer ican ou r nal 1 88 j , vol . xix . , 5, p . 344 ; and ’ ahr bu ch for 1 8 1 1 Schumacher s j 44, p . 9 . 84 TH E STELLAR H EAVENS

for a be some time accustomed to the d rkness, in order ’ that the pu pil may be dilated as m uch as possible . The m agnit udes of the comparison stars may in most cases be obtained from the catalogues of photometric measures m ade at H arvard Observatory ; but for ﬁnding the time of maximum of a variable star the advantage of ’ Argelan der s method is that there is no necessity for the observer t o know th e act ual magnit ude of the comp arison

stars . B y noting th e difference in light between the a h vari ble an d comparison stars eac night , the act ual time of maximum may be ascertained very accurately . A n d

this is the most important thing to ﬁn d in variable stars , for it enables us afterwards to ascertain the length of the f a a period rom m ximum to m ximum , which is th e most a import nt element to be determined . Some observers imagine th at to observe variable st ars accurately some form of photometer is n ecessary ; but this is q uite a All a mist ake . the best vari ble star observers now agree

that for this work the eye itself is the best photometer . of I ndeed , a skilled observer can estimate the brightness a st ar by the aid of good compar ison stars with greater

accuracy than can be obtained with an y photometer .

B u t of , course , to obtain such a result considerable

experience is n ecessary . Some observers in estimating star magnit u des by the method above described put the opera-glass or telescope

u t f f slightly o o ocus , an d consider that in this way the ’ effect of a star s colour on the eye is t o a great extent

h f . eliminated . Wit re erence to this method , Dr Gould ’ ‘ 2 t o remarked ( U ranometria Argentina , p . 45 , note l a : The f w Carin ) results are not very satis actory , o ing in part to the circumstance that man y of the comparisons - u t of f were made by putting the opera glass o ocus , a method which ou r experience shows not to give res u lts VARIAB LE STARS 85 in accordance with estimates by the method of sequences or by comparisons with artiﬁcial stars of measurable ’ The f brilliancy . present writer ully agrees with this O f pinion , and has always ound that the best results are f obtained by accu rately ocussing th e instrumen t used . For all the brighter stars n o instrument whatever is

a - necessary , n ked eye observations being in this case

of all. T a th e best his pplies to all stars down to , say , f a the ourth m gnitude . C H APTE R IV

STAR CLUSTERS AND NEBULJE

Globu lar Clu ster s Ir r egu lar Clu ster s Ir r egu lar N ebu lae Spir al N ebu lae Planet ar y N ebu lae nn — A u lar N ebu la N ebu lou s Star s.

C The ‘ is Globu lar lu ster s. term globular cluster applied to th ose clusters of st ars which evidently occupy of or f T a space more less globular orm . hey have been ’ ‘ a of aptly termed b lls stars , an d are among th e most T interesting objects in the heavens . here are some ﬁne

and a examples in both h emispheres , they usually cont in in of h un dreds , and some cases even thousands , small

stars .

The following are among the most remarkable globular

clusters . They are given in order of right ascension , and the positions are for 1 900 0 °

o 6 m . 2 Tou c ani : h . 1 . 47 9 , S 7 I t lies closely west of ‘ ’ the smaller Magellanic Cloud in the Southern Hemisphere, w and , with the exception of Centauri , is, perhaps , the ﬁnest

globular cluster in the sky. It is thus described by Sir John

Herschel : A most magnificent globular cluster. It fills the o field with its outskirts , but within its m re compressed part I ” u 0 can ins late a tolerably defined circular space of 9 diameter, o m wherein the c mpression is uch more decided, and the stars seem to run together ; and this part I think has a pale pinkish or rose colour which contrasts evidently with the white 86 l STAR C LUSTERS AN D NEB U L/E 87

th u light of e rest . The stars are equal , fo rteenth magni com tude, immensely numerous and compressed . I t is ar ativ el i nsu ate p y l d . After it has passed , the ground of the sky is perfectly black throu ghout the whole breadth of the sweep condensation in three distinct stages . A ’ ‘ u im st pendous object . Dr. Gould called it one of the most and pressive, perhaps the grandest of its kind , in either hemi ’ c B the sphere . A cording to Professor ailey, who photographed A u cluster at req ipa , Peru , the number of stars it contains is u about Among these he fo nd three variable stars, and three more were found by Mrs . Fleming . w m 6 ° 1 20 8 . . Centauri}: 3 h . , S 4 A magnificent — V globular cluster the finest in the heavens . Clearly isible to m the naked eye as a hazy star of the fourth agnitude . It was ‘ described by Sir John Herschel as beyond all comparison the riche st and largest object of its kind in the heavens . The stars are literally innu merable . All clearly resolved into stars of e two magnitudes , viz . , thirteenth and fifteenth , the larg r lying in lines and ridges over the smaller. The larger stars n h form rings like lacework o it . Altoget er this object is ’ u n tr ly asto ishing . This marvellous object has been photo graphed by Sir David Gill at the Royal Observatory , Cape of

u B . Good Hope, and also at Arequipa, Per , by Professor ailey On the latter photograph the individu al stars c an be distinctly seen and counted . The enumeration has been made by Pro fe ssor B and Mrs . ailey, and the result is Professor

Pickering thinks, however, that the actual number in the cluster is abou t some of those counted being really ou tside the u e cl st r itself. Two variable stars have been found in this cl u ster . ° . 6 . 2 8 : 1 m . Messier 3 3 h 3 7 , N 5 A ﬁne globular cluster ° V e nat ici 1 2 - with outliers, in Canes , about north west of

- Arcturus . Sir William Herschel with his twenty feet reﬂector ’ ' ’ u 6 fo nd it a beautiful cluster of stars 5 or in diameter . Sir

John Herschel described it as very large and very bright, with u stars of eleventh to ﬁfteenth magnit de . A photograph by i . 1 8 1 d e sc r Dr Roberts (taken in May, 9 ) conﬁrms the general p ’ 1 2 tion of previous observers . No less than 3 variable stars

have been detected among the outlines of this cluster. 88 TH E STELLAR H EAVEN S

° m . 1 . . 2 o u i Messier 5 5 h , N A gl bular cl ster ly ng e Sir close to the ﬁfth magnitude star 5 Serp ntis . William 200 Herschel estimated the number of stars at , but it contains m . he many ore A photograph by Dr . Roberts shows t stars to f n N o the ﬁ teenth mag itude . less than 8 5 variable stars out of 0 u 75 have been detected among the outliers of this cl ster. ° 1 1 6 8 1 m 6 - . . o Messier 3 h 3 , N . 3 This is the well kn wn

” 7 globular cluster in Hercules . It lies between the stars 7 and i u Herc les, and is considered to be one of the ﬁnest of its class . 1 1 m It was discovered by Halley in 7 4 . Sir Willia Herschel described it as a most beautiful cluster of stars, exceedingly ’ compressed in the middle , and very rich . H e estimated the number of stars at but the real number is probably not b so large . From a photograph taken in America y Mr . H . K . the Palmer, with an exposure of two hours , he ﬁnds number to ‘ ’ ‘ ’ L be of which are bright and faint . ord

Rosse found three dark streaks or lanes , which were also seen B u ff h m by a . The existence of these dark lanes is conﬁrmed

. 1 88 1 8 by photographs taken by Dr Roberts in 7 and 95, and ’ b they are also visible in Palmer s photograph . Dr. Ro erts thinks S n that the cluster was probably evolved from a piral ebula . ° 2 : 1 . m . . t Messier 9 7 h , N 43 In a ra her blank ° 6 W u . . space in Hercules, about north of Herc lis Sir W ' ' 8 . Herschel found it a brilliant cluster, 7 or in diameter Sir

John Herschel described it as a globular cluster, very bright and large , and well resolved into small stars . Webb says it is a ‘ h . 1 very ﬁne cluster, t ough not equal to M 3 less resolvable , ’ inte nsely bright in centre . It has been photographed by D r .

Roberts. °

m . . 2 u 22 1 8 . 0 Messier : h 3 3 , S 3 Abo t midway between a i p. and Sag ttarii . S ir John Herschel describes it as a globu ' lar cluster, very bright, very large, very much compressed, 7 u diameter . The stars are of two magnit des , ﬁfteenth to six t e enth and twelfth and what is very remarkable, the largest of ’ ‘ the latter are visibly reddish . Webb found it very interesting V h n from isibility of components , tenth and elevent mag itude, m which makes it a valuable object for co mon telescopes, and a ’ u clue to the structure of many more distant or diffi c lt nebula . Observing with a three -inch telescope in the Punjab the present

90 TH E STELLAR HEAVEN S

- — naked eye cluster probably familiar to most people . Viewed - with an opera glass, it forms a good example of the appearance of a bright telescopic cluster as seen in a telescope . A photo ’ 1 88 graph taken at the Paris Observatory in 5, with three hours

' exposure , shows about stars down to the seventeenth

. o magnitude M re recent photographs, however, show that the surrounding sky is qu ite as rich in f aint stars as the cluster itself. We may therefore conclude that most of the faint stars apparently connected with the Pleiades do not really belong t o c on the cluster itself, but probably lie behind it in space . The e lusion to which some astronomers have been led , viz . , that the ff Pleiades cluster contains stars di ering enormously in real size, seems, therefore , quite fallacious . Most of the faint stars, which a ar entl it pp y contains, have probably no connection whatever with the brighter stars which form the group visible t o the naked eye . The existence of a considerable amount of nebulous matter apparently involved in the cluster has been disclosed by photography in recent years . Of 9 1 stars observed with the spectroscope at H arvard Observatory, 59 were found to be of

8 1 1 8 1 . type A, of E, 4 of F, of G, of H , and of type K ° h m . 2 Messier 37 5 . 457 . , N 3 About midway between K o and p Auriga . Sir J hn Herschel describes it as a rich m a nifi cluster, with large and small stars . Smyth called it a g cent object, the whole field being strewed as it were with spark - 00 f o ling gold dust , and the group is resolvable into 5 stars r m ’ the tenth to the fourteenth magnitude besides the outliers . These descriptions are confirmed by a photograph taken by

Dr . Roberts, in which the stars are shown down to about the sixteenth magnitude . The surrounding region is pretty rich in stars . ° - m . . 2 6 . 2 M essier 3 5 h 7 , N 4 A little north west of

7 the star 7 Geminorum . Just visible to the naked eye in a clear sky . It is a large rich cluster of stars about ninth to sixteenth ‘ ’ L magnitude . Lord Rosse called it magniﬁcent, and assell ’ spoke of it as a marvellously striking object . On a photograph ‘ 1 8 6 20 taken by Dr. Roberts in February, 93 , he counted stars ’ ' B u t in the cluster within a circle of 26 of ar e in diameter. a glance at the photograph sh ows that it is not nearly so rich in stars as the globular clusters . STAR C LUSTERS AN D NEB U L/E 91

° °

m . . 20 1 6 . Messier 4 h , S About 4 south of

Siri us . Just visible to the naked eye . Messier described it as

a mass of small stars . Webb says Superb group . ’ u Larger stars in curves with r ddy star near centre, which Espin susp ects to be variable . °

6 . m . . 1 Messier 4 7 h , S 4 A little west of the star ‘ r 2 Puppis . Sir John Herschel described it as a supe b cluster ’ of stars , twelfth to sixteenth magnitude . I t includes a plan i e t ar . y nebula ( Herschel) , wh ch Lassell , Lord Rosse, and Dr u u Roberts found to be ann lar. The cluster is abo t half a degree

the . in diameter , or the apparent size of full moon A photo 1 8 graph by Dr . Roberts , taken in February, 94, shows it to be a rich clu ster with stars down to the seventeenth magnitude in a ’ region densely crowded with stars . ° . 2 Pr : 8 . m . 0 a se e Messier 44 h 34 3 , N This is the p Old e of the astronomers in the constellation Cancer . A scatter d 6 cluster to the naked eye 3 stars were counted in it by Galileo,

but, of course , there are many more . x ° : 1 2 . m . . Crucis h 479 , S 59 A reddish star of the sixth magnitude near B Crucis (one of the bright stars in the u So thern Cross) , accompanied by a ﬁne cluster of small stars . It is described by Sir John Herschel as ‘ a most vivid and u 0 1 00 beautif l cluster of 5 to stars. Among the larger there are one or two evidently greenish ; south of the red star is one e o of thirte nth magnitude , als red , and near it one of twelfth u magnitude, bluish no neb la is perceptible in any part of u the extent of this cl ster, which, though neither a large nor u a rich one, is yet an extremely brilliant and beautif l object when viewed through an instrument of su ffi cient aperture to S ff how distinctly the very di erent colours of its constituent stars, f ’ which gives it the ef ect of a superb piece of fancy jewellery . ° ° 1 1 2 . 8 2 : 8 . 6 m . 2 Messier 4 h , S I About north of

u . , Sagittarii Sir John Herschel described it as pretty large and 1 very rich , with stars of eleventh to twentieth magnitude . Lord u Rosse saw some nresolved nebulous light, but a photograph

o . by Dr. Roberts shows the stars free fr m nebulosity On this

1 Sir John Herschel’s ‘ twentieth magnitude ’ stars are really i much br ghter . Probably not fainter than ﬁfteenth magnitude . 92 THE STE LLAR H EAVEN S photograph the streams of stars surrounding the centre seem s to be arranged in spirals, and suggest the idea that the clu ter r has been evolved f om a spiral nebula . ° 1 1 1 8 m . . 6 u a Messier h . 457 , S J st visible to the n ked ’ so - m eye in the called Shield of Sobieski , which for s the

of 1 68 1 . southern portion Aquila . It was discovered by Kirch in Sir William Herschel saw it divided into ﬁve or Six groups of n c stars of about the eleventh mag itude . Admiral Smyth om ‘ ’ ‘ u n pared it to a ﬂight of wild d cks , and says it is a gatheri g of minute stars , with a prominent eighth magnitude in the ’ middle, and two following . A photograph taken by Dr. Roberts r ag ees well with the descriptions , and shows that the cluster is free from nebulosity. ° 6 1 1 m . . 1 8 : . B Messier 7 9 h 49 3 , N etween 7 and

a . Sagitt Sir John Herschel describes it as a very rich cluster, with stars of eleventh to sixteenth magnitude . A photograph by Dr . Roberts shows a cluster in which the curves and arrange ‘ ment of stars closely resemble those in a spiral nebula . The surrounding region is densely crowded with stars down to the seventeenth magnitude, arranged in remarkable curves and ' of lines, which are very suggestive having been produced by ’ the effects of spiral movements . u Under the head of irreg lar clusters, we may mention the of Magellanic clouds, which are two spots Milky Way light visible to the naked eye in the Southern Hemisphere . These nu becu la m a or nu becu la m inor spots, also known as the j and , are f m ‘ ’ roughly of a circular or . The larger cloud covers over

- forty two square degrees, and when examined with a telescope is found to consist of upwards of 600 stars of the sixth to the f 00 tenth magnitude, with numerous ainter ones , and nearly 3 a a nu becu la clusters and nebul . The smaller Magell nic cloud, or minor , is fainter to the eye , and not so rich in the telescope . It Sir ohn covers about ten square degrees , and it is described by J 1 ‘ s Herschel as a fine, rich, large cluster of very mall stars of w t elfth to eighteenth magnitude, which fills more than many o fields, and is broken int many knots, groups , and straggling whole ) branches, but the the whole of the clustering part

1 Ca e b e tions 1 O s r v a . p , p 4 5.

94 TH E STELLAR H EAVEN S

“ 1 6 1 8 1 6 . , and a drawing of it was published by Huygens in 59 al Galileo does not mention it, although he paid especi attention - . V to Orion It is isible in an opera glass as a spot of milky light, and its general outline may be seen with a good three -inch telescope . Near the centre are four stars close together, which ‘ ’ form the trapezium of telescopists already r eferred to under the head of Multiple Stars . Numerous small stars are scattered over the surface of this great nebula, which was at one time considered by Lord Rosse to show symptoms of being resolvable into small stars when seen with his large telesc ope . The spectroscope , however, shows it to be glowing gas, consisting of hydrogen and some unknown substance . From his spectro sc 0 ic p observations of this nebula, Sir W . Huggins thinks that the ‘ stars of the trapezium are not merely optically connected w ith the nebula , but are physically bound up with it , and are very probably condensed out of the gaseous matter of the ’ nebula . There appear to be no grounds for considering this nebula to be an external galaxy . The nebula has been fr e o quently drawn , and it has been successfully ph tographed by

o . C mmon , Roberts, and others °

0 m . . Dor adu s : . 6 3 5 h 39 , S 9 Situated in the larger ‘ Magellanic cloud . Sir John Herschel describes it as one of the most singular and extraordinary objects which the heavens ’ ‘ ’ . u present It is sometimes called the looped neb la, from the curious convolutions formed by its nebulous rays and streams . ' ‘ ’ a - Near its centre is pear shaped opening , like the keyhole vacuity in the Great Nebula in Argo . - ° ' 6 . 2 m . . o 1 2 N . G . C . 22 : . o o . 3 7 39 h 7 , N 5 Near Mon cer tis ' A large extent of nebulosity, measuring about 77 by which ‘ is described by Dr . Roberts from a photograph as a cloudy mass broken up into wisps, streams, and curdling masses densely dotted over with stars, which also extend widely over the regions surrounding . There are many dark areas with few, if any, stars in them . Some remarkable black tortuous rifts meander through the nebu losity in the nor th pr eceding half of ’ the nebula . °

: 1 0 . m . . The Great Nebula in Argo h , S 59 A

1 of 7 The position is that the variable star ; Argus, which is involved in the nebula. STAR CLU STERS AN D N EB U LZE 95

magniﬁcent nebula , which covers a space in the heavens about ‘ ﬁve times as large as the full moon . It has a curious keyhole n e shaped vacuity ear the centre , and the wonderful variabl star 77 Argus (already described) is apparently situ ated in the densest

part of the nebulosity. The nebula shows , no signs of being

resolvable into stars , and, like the Great Nebula in Orion , the

spectroscope shows it to consist of glowing gas . ° iﬁ d a . 6 m . 2 Tr 20 : 1 . . Messier 7 h 5 3 , S 3 The Nebul

I t lies closely north of the star 4 Sagittarii . A very curious

object , with three dark lanes radiating from the centre . I t has

been well drawn by Sir John Herschel and Trouvelot, and it 1 e L has been photograph d by Dr . Roberts and at the ick ’ Observatory . Dr. Roberts photograph shows the dark rifts it very distinctly, and these rifts are free from stars . Although not has a very nebulous appearance , the spectrum seems to be

gaseous . A triple star seen by Sir John Herschel in the middle of one of the dark lanes is now in the edge of the nebu la itself. ’ It seems , therefore , that the nebula has moved since Herschel s

time . ° 8 1 . : . 6 m . 2 Messier 7 h 57 , S 4 A very ﬁne object in Tr iﬁd the Milky Way, in Sagittarius ; a little south of the

u . u r Neb la Visible to the naked eye . A bea tiful d awing of it ,

showing nebulous streaks and loops , is given by Sir John ‘ Ca e Obser v ations Herschel in his p , and he calls it a superb ’ 8 u . e . 1 neb la Ther are many stars in the ﬁeld Tempel , in 77, d found marke changes in the nebula compared with the stars , which are ne arly in the same relative positions as when observed

by Herschel . A photograph taken by Dr . Roberts in July , 1 8 ‘ 99, shows that there are many stars of between the eighth and seventeenth magnitu de either involved or seen in proj e ction u u pon the neb la , and on the following side they resemble a ’ ‘ u b u t cl ster of bright stars , he does not think they are physi cally connected with it ; they are probably between the earth ’ and the nebula . The present writer found it plainly visible to

the naked eye in the Punjab sky, and a glorious object even - with a three inch refractor. I t is followed by a ﬁne cluster

which lies between two eighth magnitude stars . Secchi found

the spectrum that of a gaseous nebula .

1 K now led e 1 00 g , February, 9 . 96 TH E STELLAR H EAVEN S

° ’ 1 1 m . . 1 1 6 : 8 . 2 o So ie ski s Messier h 3 , S 3 S uth of b

Shield . Sir John Herschel describes it as a cluster containing

1 00 . t at least stars, but a photograph by Dr Rober s shows that ‘ it is really a large bright nebu la with a cluster apparently ’ involved in it .

— Spir al N ebu la . These are among the most marvellous T and interesting objects in the heavens . hey were discovered by the late E arl of Rosse with his giant six f S a a oot telescope , and their piral ch r cter has been fully

conﬁrmed by photograph y in recent years . I ndeed , photograph y has shown man y nebul a to be spiral which had not previously been recognised as belonging to this

interesting class . A very l arge number of new nebul a were discovered by the l ate Professor K eeler at the Lick

-f ﬂ H e Observatory with the Crossley three oot re ector . f one - f of l and oun d that probably hal these are spira , that ‘ s l of any ma l , compact nebula not showing evidence ’ - The spiral str u cture appears exceptional . spectroscope t T shows that these wonderfu l objects are no gaseous . hey are probably partly condensed into the liquid or solid f orm .

The following are some remarkable examples of spiral nebu ka

1 o . m . . 0 Messier 3 h , N 4 This is the Great Nebula in Andromeda . It is plainly visible to the naked eye near the s v a tar Andromed , and forms quite a conspicuous object even - Al-Su ﬁ with a binocular ﬁ eld glass . It is mentioned by , the

Persian astronomer, as a familiar object in the tenth century .

It is of a very elongated form , and much brighter in the centre . Although the most powerful telescopes have failed to resolve it

not . into stars , the spectroscope shows that it is gaseous

Photographs by Dr. Roberts seemed at ﬁrst to show that it o r i n s c nsisted of a nucleus surrounded by g , but his later photo ’ ‘ - graphs prove that it is really a left hand spiral, and not annular. a n Two small nebul lie near it , o e completely separated from

98 TH E STE LLAR HEAVEN S

nd a . nebula, the larger with a nucleus a ring round it Admiral ‘ Smyth thought it r esembl e d a ghost of Saturn with its ring in ’ a vertical position . Its spiral Character was discovered by Lord u Rosse, and his drawing agrees well in general o tline with photographs taken by Dr . Roberts and D r . W . E . Wilson . ‘ D r. Roberts ﬁnds both nuclei of the nebula to be stellar, e u surrounded by d nse nebulosity, and the convol tions of the n S a spiral in this , as i other piral nebul , are broken up into star ’ like condensations with nebulosity around them . Sir William n t Huggins ﬁnds that the spectrum is o gaseous . This seems to u a be the case in all the spiral neb l , and shows that they are in a more advanced stage of evolution than the Great Nebula in

Orion and Argo . ° ° m . 1 0 1 : 1 . . Messier 3 h , N 54 About 5 east of

’ i U r sa Majoris . Sir John Herschel described it as pretty bright , very large , and irregularly round . Lord Rosse found ’ 1 it to be spiral , 4 in diameter , and his drawing agrees fairly ‘ well with a photograph taken by D r. Roberts , which shows a -d ﬁ ne d well e stellar nucleus, with the usual convolutions and ’ starlike condensations . — Planet ar y N ebu lae Th ese are a remarkable an d T m interesting Cl ass of n ebu l a . hey were so na ed by Sir William H erschel from their resemblance to pl an

u a e tar y discs . This s pposed resemblance pplies only to their gen eral uniformity of brightness and to the absence o f — at a an y deﬁnite n ucleu s or brighter portion le st , f T when seen with telescopes o moderate power . heir of far f of intrinsic brilliancy is , course , in erior to that the a a fa pl nets , being usu lly int objects , and only to be seen f n A well with telescopes o co siderable power . bout three fourths of the known plan etary n ebul a ar e situ ated in S H the outhern emisphere , but there are some interest f E A ing examples north o the quator . bluish colour a a of a r seems to be char cteristic these pl neta y nebul a . The following are some of the most interesting examples of this Class STAR C LUSTERS AN D NEB U LE 99

° B e h 1 8 m . . a . h 3 1 63 : 9 h . 7 , S 57 etwe n g and Carin ‘ Sir John Herschel says : B eau tifully rou nd and sharp ; just ’ ’ like a small plane t 3 or 4 in diameter The ﬁnest plan e tar y nebu la I ever remember to have seen for sharpness of ’ termination . ° ° m . . 1 8 2 . 2 : 1 0 . 20 H IV 7 h , S About south of the

u. H a . star , ydr Described by Admiral Smyth as resembling ‘ ’ u u u . J piter in size, eq able light , and colo r Sir John Herschel ‘ u speaks of its colo r as a decided, at all events a good, sky ’ e blue . H u ggins finds a gaseous sp ctrum . As a star it was measured magnitude at Harvard . ° ° - m . : 1 1 . 2 Messier 97 h . 9 , N 55 About south east of B Urs a Majoris . I t was described by Sir John Herschel as e u a remarkable planetary n b la , very large and round , about " 1 60 of arc in diameter . Lord Rosse compared it to the face of u an owl , on acco nt of two holes in the centre, and it has since ‘ ’ u . been known as the Owl Neb la . A photograph by Dr Roberts ” u 20 e shows it of an elliptical shape, abo t 3 in diam ter, with e no a fift enth magnitude star in the centre , but other star ‘ u The L in the neb la . He says : star seen by both ord Rosse ’ and Dr . Robinson has disappeared . Sir William Huggins finds the spectru m gaseous . ° 6 : 1 1 6 B i r h 33 5 h . S . 5 etween Centauri and 6 — Crucis nearer the latter . Sir John Herschel says Perfectly u u e -d fi n round , very planetary colo r fine bl e ; a v ry little ill e e d “ ” e e e u at the dg s ; has no satellit stars very like Uran s , only u about half as large again and bl e . It is of a most decided u independent bl e colour when in the field by itself, and with ' - A 1 0 no lamp light and no bright star. bout north of it is an - s . orange coloured tar, eighth magnitude When this is brought into view the bl u e colour of the n e bula becomes intense u u e e u colo r a beautiful rich bl , b tween Pr ssian blue and ver u ditter green . Total light of nebula eq al to a star of sixth ’ or sixth and a half magnitude . ° : 6 0 m 1 . . 2 B Struve 5 N h 4 3 , N . 3 etween B Herculis — ’ 1 D A r r and 5 Herculis nearer the latter star. e st estimated it ‘ n at eighth mag itude . Webb calls it very bright , not sharply ’ L . o defined , like a star out of focus rd Rosse saw it of an — 7 2 1 00 TH E STELLAR H EAVEN S

o . intense blue c lour Secchi thought it resolvable into stars,

but Huggins ﬁnds a gaseous spectrum . ° . : 1 8 6 m . . 66 H I V 3 7 7 h 5 , N . Near the pole of the to 6 ‘ Ecliptic and between and 3 Draconis . Webb saw it as a ’ very luminous disc, much like a considerable star out of focus . ‘ Smyth describes it as a remarkably br ight and pale blue ’ object . It may be well seen with a telescope of four inches

. aperture Examined with the great Lick telescope , Holden ‘ u u fo nd it an object of extraordinary struct re . H e says it is apparently composed of rings overlying each other, and it is ‘ d iﬁ icu lt to resist the conviction that these are arranged in ’ S u pace in the form of a true helix . H ggins found the spectrum gaseous . N G 6 2 1 8 ° ° . . : 6 C . . m . 2 57 h , N . About south of the 1 O hiu chi star 7 p . A small but very bright planetary nebula , which Struve thought ‘ one of the most curious objects in the ’ heavens . I t has a gaseous spectrum . ° ’ ‘ - 2 : 1 . m . 2 2 Messier 7 9 h , N . The Dumb bell 1 Nebula . A little south of the star 4 Vulpecula . It may be perhaps included in this Class , although its form is not exactly that of a planetary disc . It has been drawn by Sir John ’ D A r r e st L Herschel, , ord Rosse, and Lassell . At one time

Lord Rosse thought it might be resolvable into stars , but i u Hugg ns fo nd a gaseous spectrum . Photographs by Dr .

Roberts and D r. Wilson show that it is really a globular mass o ff surrounded by a broad and darker ring, which cuts some of i t - the light and gives the dumb bell appearance . ° IV 20 8 m 1 1 1 . . . H . h 5 7 , S Discovered by Sir Wil °

1 82 . 1 v liam Herschel in 7 About 5 west of the star Aquarii .

One of the ﬁnest specimens of the Class . Viewed in a large telescope , a projection on each side gives it an appearance somewhat like Saturn , with the rings seen edgeways . The great ‘ Li ck telescope shows it to be a wonderful object : a central ’ u ring lies upon an oval of much fainter neb losity . Holden says u the colour is a pale bl e , and he compared the appearance of ‘ the central ring to that of a footprint left in the wet sand of a ’ - sea beach . Huggins ﬁnds a gaseous spectrum .

T a Annu lar N ebu la . here are nebul which are , T f apparently at least , shaped like a ring . hey orm a

1 0 2 TH E STELLAR H EAVEN S star exactly in the centre of an exactly round bright atmosphere ’ 2 ” 5 in diameter. Lord Rosse saw it as a star surrounded by a B dark and then by a luminous ring . urnham , who Classes it as ‘ t u a plane ary nebula, describes It as one of the most beautif l ’ objects of the kind in the heavens . The spectroscope shows it to be gaseous . ° 1 2 1 8 m 0 8 . 1 . o h 3 h 3 , S . 4 Sir J hn Herschel described it as an eighth or ninth magnitude star ‘ involved in a pretty bright, round nebula a decided and perfectly unequivocal nebula . Diameter ° °

8 1 . 1 m . . 2 5 h 3 54 3 h 5 7 , S 3 9 About north of 9 Cen ‘ . r u tauri Sir John Herschel desc ibes it as a Close do ble star, ' u u 2 involved in a very large , bright, l mino s atmosphere, dia meter . It is no illusion other stars are sharp and brilliant, ’ and have not the least nebulous appearance . Some of the long-period variable stars seem to be surrounded u by neb lous envelopes . This has been seen by Grover in the a a case of R , S , and T Cassiopei , R Cygni , S Herculis , S Coron , t he S Cephei , and T Draconis , when variable is at or near its minimum light . At maximum the light of the star is generally u s u fﬁ cient to obliterate the neb losity .

Star Clusters are chieﬂy found in the Milky Way . The gaseous nebula crowd towards the poles of the Galaxy . There are, however, some exceptions to this rule . C H APTE R V

TH E STELLAR UN IVERSE — — The Milky Way The St ellar Univer se The N ebu lar H ypothesis

The i k — The - or M l y Way , nebulous looking ban d zone of fa a M Wa a int light known s the ilky y, or G laxy , is a f on prob bly amiliar to the most casual observer , and a a f cle r , moonless night orms a conspicuous obj ect in the

a has a of nocturn l heavens . It attr cted the attention astronom ers and philosophers from the e arliest ages of a and a a ntiquity , v riou s hypotheses have been dvanced to a for its a a or ccount ppearance . Plut rch saw in it , pre ’

of a . a tended to see , the marks Phaeton s ccident An x

a a sa t he S a of agor s , str nge to y, thought it was h dow the earth ! but wh y a sh adow Should be l uminous he does a not explain . Aristotle thought it was due to tmospheric — vapours another wild h ypothesis . Other equally absurd ideas were entertained by the ancients , but the a of true theory , namely , that its light is due to myri ds — small st ars too faint to be in dividually visible to the — was naked eye , however , advanced by Democritus , M a and of anilius , and Pyth goras , the invention the tele f f scope ully conﬁrmed the truth o this hypothesis . A little attention will show that the Milky Way very 1 03 l 1 9 4 T H E STELLAR H EAVEN S

’ nearly follows the course of a great circle of the star S a f phere , act which implies that the su n and solar or f system lie in close to the general plane o the Gal axy . The mean centre lin e of the luminou s band is inclined to t he E quator at an angle of about an d intersects that 1 of circle at about 7 hours and 9 hours right ascension . The position of the North Pole of the Milky Way has been given as follows :

N or th Declination. ° 1 2 2 Sir John h . 47 Hi . 7 ° 1 2 2 1 880 h . Hi . 7 ( ) 1 2 2 ° Houzeau h . 49 m . 75 ° ' 1 0 . 2 2 1 1 8 Gould 2 h . 4 1 In . 2 s 7 ( 75)

T a hese results are in close greement , and place th e a B pole in the constell tion Coma erenices , a little south

of 1 The R. A . the star Flamsteed 3 . south pole is in m 0 . h . 47 , S . Various representations of the Milky Way ar e given ’ a i n star tlases , such as Proctor s and others , but these

ff of a S merely a ord a general idea its ppearance , and how no details of the brightness o r faintness of its various — p arts fe at ures which are very obvious when carefully observed . A mere casual glance might lead an observer t osu ppose that the G alaxy stretched as a band of nearly f B u t uni orm brightness across the heavens . good eye

a f a C a Sk sight , c re ul attention , and le r y will soon disclose — n umerou s details previously u nsuspected streams an d of ff f of rays di erent brightness , intersected by ri ts dark n ess and interspersed with spots an d channels of com

ar at iv el a p y starless sp ces . A n attempt w as m ade by H eis and H ouzeau in their a maps to delineate this varying brightness , but their dr w — — ings especially th at of H ouzea u are deﬁcient in detail ’ and a merely Show the principal feat ures . Gould s dr w

1 06 TH E STELLAR HEAVEN S p. Velor um i r Puppis 77 Canis Majoris a Ar a and a Musca or a total of 3 3 stars out of 99. Of those between third and 262 fourth magnitude , I ﬁnd 73 stars on the Milky Way out of , or a grand total of 1 1 8 stars out of 392 stars above the fou rth

0 1 . magnitude , or 3 per cent Considering the stars north and u 1 6 so th of the Equator, there are 4 stars above fourth magni e 2 tude in the Northern Hemispher , of which 5 are on the Milky 1 Way, or a percentage of 3 7 . In the Southern Hemisphere 2 2 8 66 there are stars , of which are on the Milky Way, or a percentage of 2 8 9 . As the area of the heaven scovered by the Milky Way does not probably exceed one -seventh of the whole - u sphere (Proctor assumed one tenth) , the percentage sho ld be only so that the number of bright stars is considerably d u e . more than that to its area As it may be objected, how u ever, that the number of stars brighter than the fo rth magni tude is too small to base any conclusion upon , I made an ’ en u meration of all the stars in Heis s Atlas that lie on the b e Milky Way, and found the number to Now, the total number of objects shown by Heis (excluding variable stars , a u Clusters , and nebul ) is from his catalog e so that for all the stars visible to the naked eye in this cou ntry (down to magnitude) the percentage of stars on the Milky Way is

or about one and a half times that due to its area . ar kw ick A similar count was made by Colonel M , ’ of the stars in Gould s Charts of the Southern Hemisphere 2 28 Uranometria and he ﬁnds that, out of stars e 1 2 1 brighter than the fourth magnitude, th re are on the Milky

Way, or a percentage of 53 ; and for the total number shown down to the seventh magnitude inclusive there are on

8 . the Milky Way, out of or a percentage of 4 5 From a careful calcu lation of the area of the Milky Way as Shown in M ar k wick these Charts , Colonel ﬁnds that it covers an area

- e . equal to one third of the whole h misphere , or per cent From the se ﬁgures it will be seen that there is a marked tendency in the Southern bright stars also to aggregation on the Milky Way. The apparent connection of some of the naked-eye stars with the brighter portions of the Milky Way is in some cases r e

‘ 7 x . a 1 a markable The stars , B , y, , and Cassiopei mark a very TH E STELLAR U N IVERSE 1 0 7

L K A a luminous spot of milky light . The stars , , and Andromed

° ‘ e 6 e mark anoth r. , , and 5 Cephei lie near the edge of a Coal ’ The u . sack, or dark space , in the midst of a lumino s region ' 6 o Pe r se i oﬂ sho ot stars , 5, and mark an from the Galaxy in the direction of the Pleiades . The remarkably bright oblong

7 5 spot in Cygnus includes the stars B , 7 , 7, 9 , the variable x Cygni , and other smaller stars . The stars forming Sagitta Wa are situated in a bright portion of the Milky y, and those ’ forming the Dolphin s Rhomb in a fainter offshoot . The stars 6 68 0 O hiu chi 7, , and 7 p lie at the extremity of a luminous spot A 6 on the broken branch in Ophiuchus . The stars , , 9, and 1 2 Aqu il a are ranged along the northern border of a bright ’ spot in Sobie ski s Shield ; and other interesting cases might u be pointed o t . Many attempts have been made to form a satisfactory theory u ff of the constr ction of the Milky Way, but these e orts have not been hitherto attended with b u t little success . This is

e f . surprising, as the probl m is one of great di ﬁculty The ’ e w Cloven disc theory of Sir William Hersch l , hich ﬁgured for u so many years in popular books on astronomy, altho gh it was practically abandoned by that eminent astronomer in his late r u e writings , has been well shown by Proctor to be tt rly unten

e . able , and it has now been reject d by nearly all astronomers The real shape of the Galaxy is mu ch more probably that of a u e ring (ro ghly speaking) than a disc . Proctor, how ver, inclined

to the opinion that it is probably somewhat of a spiral form , and ‘ a ﬁgu re of this su pposed Spiral is given by him in his Essays ’ y e u on Astronom (p . In an int resting paper on the s bject

. I llu st r ated S cience M onthl by Mr . J R . Sutton in the y, some u e years since , he arg es , and, I think, with consid rable force, ’ that Proctor s spiral doe s not account very satisfactorily for the e u observed f at res of the Milky Way, and he contends that its

real form is what it seems to be, namely, that of a ring , roughly u c u t the - speaking, and act ally across its width at well known ‘ - ’ gap in Argo . The aspect of the Coal sack near the So u thern Cross ce rtainly suggests that it is a r ea l opening through the e Milky Way, and not merely due to a loop in the str am , as ‘ ’ - ’ shown in Proctor s spiral . The Coal sacks and dark spaces

near the neck of the Swan are , as I have shown above, more 1 0 8 THE STEL LAR HEAVEN S

a pparent than real , and are, I think , probably due more to a sparseness of star distribution than to any real bifurcation of

the Galactic stream in that vicinity . The separation of the two ° a streams commences, according to Heis , near the star 5 Aquil , ’ and , according to Sir J . Herschel s drawing, the streams unite ’ again in Scorpio . Heis s delineation shows that the continuity of the wester n branch in Ophiuchus is interrupted for a width 6 ° r. O hiu chi of only north of p p . The portions of this branch 0 hiu hi extending from Aquila to 7 Op c are tolerably bright , and do not agree well with the supposed great increase in distance ’ at this p oint indicated by Proctor s spiral . Even in the middle of the gap in Ophiuchus , Heis shows a somewhat bright spot

1. v hi between 1 and Op u chi. Gould considered the phenomenon of the Milky Way as ‘ ’ u u probably the res ltant of two or more s perposed Galaxies, and certainly the complicated structure and gradations of ’ s brightne s shown in Heis s drawing, especially in Cepheus and

Cygnus , seem to favour this hypothesis . I t is possible , how d u e r eal u ever , that the brighter portions may be to a Cl stering o f the smaller stars , which have perhaps been swayed into their present position by the attractive inﬂuence of the larger u ~ stars . This View of its str cture would account for the occur u rence of dark spaces close to l minous portions, which form so u remarkable a feature in Cepheus, Cygnus , Perse s , Scorpio , and near the Southern Cross . Photography will probably throw some light on this point . The observed excess of bright stars on the portion of the heavens covered by the Milky Way might be explained by supposing the Galactic ring to be placed at a much greater d e istanc from the earth than the general star sphere . If we suppose the component stars of the larger or more extended group to be scattered over the heavens with some general approach to uniformity, and that the Milky Way contains its own proportion of bright stars, but wholly separated from the e others by a starless interval , then , wh n the two systems are an e seen in the same direction, incr ase in the number of the brighter stars would necessarily follow . On this hypothesis , it might be expected that some of the brighter stars wou ld show e u a measurabl parallax, while in others the parallax wo ld be

1 1 0 TH E STE LLAR H EAVEN S

Easton thinks that the Milky Way between a and B Cygni is ‘ ’ ‘ much nearer to us than the average . The region between 68 (A) and B Cygni is richer in stars than any other zone in ’ Argelander s Sir W. Herschel found one ‘ ’ — of his m axima of gau ges here 588 stars in the ﬁeld of his e telescop . Easton thinks that the central accumulation of the ’

and . ad vanc e s Milky Way probably lies in this direction , the theory that its general form may be that of a vast spiral nebula, ‘ ’ ‘ the so-called solar Cluster being the expression of the central condensation of the Galactic system itself, composed for the most part of suns comparable with our own (and which must thus embrace most of the bright stars to the ninth or tenth

— T The e M r . of he St e llar Univ er se , lat Proctor was O ‘ all a pinion that all the visible stars , and the nebul or a hitherto discovered , whether gaseous stell r , irregular ,

-f planetary , ring ormed , or elliptic , exist within the limits ’

f h . If o t e sidereal system This is probably true . ’ ‘ ou r external universes exist , they are not visible in T f telescopes . here seems to be no escap e rom th e conclusion that ou r su n and solar system form members F r of a limited u niverse . o were the stars scattere d

e a a f through inﬁnit sp ce with any appro ch to uni ormity , it m ay be shown that the whole heavens wou ld Shine f fa o f with th e brightness o the sun . A s the sur ce a sphere

a a of and v ries s the square the radius , light inversely as the s quare of the distance (or radius of the st ar-sphere at of an y point) , we have the diminished light the stars exactly cou nterbalanced by their increased n umber at any

F r a f a n . o o dista ce a dist nce , say , ten times the dist nce of - of the nearest star (or , rather , star sphere) the light e ach star would be diminished one h u n dred times (ten multiplied by ten) but the total n umber of stars at this a distance would be one h u ndred times greater , so th t the T total starlight would be the same . his would be true TH E STELLAR U N IVERSE 1 1 1

ll i The f for a d stances . total light will there ore (by a and for addition) be proportional to the dist nce , hence an inﬁnite dist ance we Should h ave a contin uou s blaze of f f F r light over the whole sur ace o the visible heavens . a

~ a of from this being the c se , the total amou nt starlight on the clearest nights is very small (only a small fraction and of of moonlight) , portions the sky , even in large a a o f a telescopes , seem absolutely bl ck . I n a photogr ph rich region of the Milky Way in Cygn us (near 71 C ygni) R ar e a on an by Dr . oberts , there bout stars T f area of about four square degrees . his gives or the whole heavens 53 squ are degrees) a tot al of about — a stars a comp ratively small n umber . On a photograph of the Pleiades taken at the Paris Observa an of ar e a tory with exposure three hours , there st rs , where ordinary eyesight can see only six or seven . As a a this pl te includes about three squ re degrees , this gives for the whole he avens a tot al of only B u t of S a other regions the sky how a much sm ller n umber , m a af a a and we y s ely ssume th t , when the whole sky has a of all a been photogr phed , the total the st rs to the seven t e e nth magnitude (about the faintest visible in the great Y erkes telescope) will not much exceed a Possibly larger telescopes , more sensitive pl tes , an d longer exposures m ay hereafter sensibly increase this tot al ; but even if we multiply the number found above

visible a i by ten , we must still consider the st rs as ﬁnite n

The of f number . way in which some the aint stars in the ch art of the Pleiades and elsewhere seem mixed u p and a with the nebulou s matter , the nebul with the a a brightest st rs , suggests the ide that these smaller stars f are probably aint , owing to their small size rather than of a and to immensity dist nce , probably belong to the same family of which the brighter stars are evidently 1 1 2 TH E STELLAR HEAVEN S

. M n of fa components a y the inter stars , however , probably lie far behin d the Pleiades , and do not form members of the n e the grou p visible to ak d eye . It was long since suggested that the light of very distant stars m ay possibly be absorbed by the ether of space ; bu t as this V iew of the matter now seems im pr ob a a ble , we must h ve recourse t o some other hypothesis to

of visible explain the very limited n umber the stars . ‘ ’ In my Planetary an d Stellar St udies (1 888) I have suggested a possible thin ning ou t of the e ther beyond the of ou r V bou nds isible u niverse , which would evidently ‘ have the eﬂe c t of cutting off for ever the light of external

a a . of in f g l xies I n t he absence , however , evidence avour of f this h ypothesis , it will perhaps be sa er t o assume if that , these external u niverses exist , they are probabl y of n invisible to u s owing to immensity dista ce , the spaces sep arating each galaxy from its neighbours being su pposed to be very great compared with the dimensions of each

. S a of u niverse We know that the ol r System , which our f a on all earth orms member , is surrou n ded sides by a S of starless phere , the diameter which is very great compared with the diameter of the planet ary system . — Assuming the distance of the nearest ﬁxed star a Cen

— - tauri at twenty fi v e billions of miles (corresponding t o a parallax of we have the diameter of this void f f If S S sphere fi ty billions o miles . we call the olar ystem of all a system the first order , we may consider the visible a M Wa stars , clusters , an d nebul , including the ilky y, as forming a system of the second order ; and as we may consider the members composing this system as finite in n l umber (as shown above) , we may a so consider the f f a n umber o systems o the secon d order as finite lso . We may further consider all the systems of the secon d f n of order as together ormi g a system the third order ,

1 1 4 TH E STE LLAR HEAVEN S a t n n f h pproaching the otal exti ctio o their lig t . I n this view of the ‘ evol utional order Sir William H uggins

H e t concurs . is disposed o think that the hottest stars

for f The m ust be looked among those o the Solar ty pe . evolutional order now adopted by H uggins seems to so- a f-R B be (omitting the c lled Wol ayet stars) , ellatrix ,

R a C R V S f igel , ygni , egulus , ega , irius , Castor ( ainter C component) , Altair , Procyon , 7 Cygni , apella (hottest A B star) , rcturus , an d etelge use , the youngest being B B ellatrix , an d the oldest etelgeuse . That stars of the Sirian type are less dense than those in the Solar stage has been recently proved by calcula R f f n f tion s by Dr . oberts (o South A rica) a d Pro essor R of of ussell the densities the Algol type variables , which of a The show spectra th e Siri n t ype . investigation shows that t he average density of these stars is less th an that of a f e e w ter , and that they are there ore in an arlier stag of condensation . e f r of s Dr . S e accou nts o the origin binary tars by sup posing a rotating nebulous mass to assume th e dumb E bell form by the force of the rotation . vent ually it would separate into two bodies which would then form a ’ ‘ sp ectroscopic bin ary ; an d afterwards the two bodies ff of fu a would , by th e e ect tidal action , move rther part , still revolving rou nd their Common centre of gravity in f f elliptic orbits o large eccentricity , th us orming the bin ary stars visible in the telescope . N umerous double a or a ar e nebu l , nebul with two n uclei, visible in the T f s heavens . hese probably orm the ﬁrst tage in the f evolution o binary stars . A P P E N D I !

E A NOT .

TH E the c e a in u se the following is a list of onst ll tions now , with English equ ivale nts and the Arabi c and other nam es of the principal stars

A d m ed the Chained Lad B e the H er dsman n ro a, y oot s ,

61 A he . a A c u u . , lp ratz , r t r s

M h M ekkar . c . B , ira , izar B , N

A m ch e a M M c . y, l a . , Iz r , izar, ira - 7 M u A the A ir Pu m . h d . ntlia, p 7, p ri

A u the B ir d o Par adise. Alkalar o s. p s, f a, p ’ W - a um th t or s T l A u u the at er B ear er C e Scu l oo s. q ari s , l , p ‘

a S d me Cam e d i the Gir a e. , a al lik . lopar al s , ﬁ S d u u d C c e the Cr ab B , a als . an r,

G e nu la. Te m e . y , j I g in 6 S a a e Ve natici the H u ntin Do s , k t . C n s , g g

A u the E a le on Co r C . q ila , g , aroli 01 A C M a the Gr eat Do , ltair. anis jor, g 61 M h A h n. u r B, ls ai , Siri s, azza ot .

M m . z ed . y, Tara B, irza

A r a the lt r 6 We . A a . e , , z n A the Shi A r o d ded e Ad rgo, p g , ivi into , ara.

Ca t he K eel. 7 A u d . rina, 7, l ra M a u t M ast Phu he . r u d l s, . P a M he e u the P oo . t L ittl Do ppis, p C nis inor, g e the Sails 61 P c V la, . , ro yon .

a Ca u . G me s . , nop s B, o i a ' ’ c Tu r eIs C c u t he Goat , . apri orn s, A e the Ram a m Gi di e . ri s, , Pri a

a H am . Sec u d Giedi. , al n a h 6 D e a . e e Al iedi. B , S r tan , n b g M m e a . e t he Lad in the y, s rti Cassiop ia, y Au a the Char ioteer Cha ir rig ,

a C el . a Sc ed . , ap la , h ar M e a a . Cha h. B , nk lin n B, p

h now au i . Cen u au r . 7 , Nat ( T r ) ta rus the Cent B — 1 5 ] 8 2 1 1 6 TH E STE LLAR HEAVENS

’ e heu the A in h s Ce eu A he . C p s , g p y , l na a A de m 6 W , l ra in . , asat . Al hir k e W bs e u ta. B , p . ,

E a . Me ud y, rr i f, kb a. e u the Wh ale Te at . C t s, a, j Post a M r e . G u the C ane. , nkar r s,

Di hda. H e cu e H er cu les B , p r l s,

Kaffal idhm a. a l i A eth . y, j , Ras g

B e K aitos. Cor ne for os at n B , . o M x M . c. , ira , arsi

Chama leon the Chameleon . Mas m , y . C c u the Com ass H d a t he Sea-Ser ent ir in s, p y r , p u m t Dov e a A C he h d Cor H d a . ol ba , , lp ar , y r a h e H d t W - . he ater Sn ahe. , P a t y ras, ’

m Be e ce B er enice s H air . du the I ndian . Co a r ni s, In s,

C B e the N or ther n Lace t he Liz ar d . orona or alis, rta,

Cr own Leo, the L ion f m m 61 a A he c Al eta Ge e u u Cor Le . , lp c a, , a , R g l s , onis F e e oca . B , D n bola . a A u the Sou ther n Al eiba Coron stralis, y , g .

Cr own . 6 Z m , os a. R l u the Cr ow assa as. Corv s, a Le M t 61 Alchiba A a . o t he Lit le Lion , , lgor b inor, .

6 A e . Le u the H ar e , lgor s p s ,

C e the Cu a A e . rat r, p , rn b

a A e . h . , lk s B , Ni al

C u t he Sou ther n Cr oss. L b the B alance r x, i ra, C u the Sw an 61 ff Au Z u e el ygn s, , Ki a stralis , b n

(1 De e A ded . Ge . , n b , ri nabi

A e . ff B e Z u e el , lbir o B , Ki a or alis, b n B1 7r A e f a e . Cham eli. , z l af g

e h u t he Dol hin . Z u be H akr abi . D lp in s, p y, n - d the Swor d F ish . L the L r e Dora o, yra, y

Dr a n a e . c the o . Dra o, g , V ga

a hu . he . , T ban B, S liak

Alwaid . Su la hat . B , y, p M e abl Etanin. the T e. y , nsa, M h c A Giau z ar . c c u m t e M i r osco e. , i ros opi , p M G r um m iu m . e the Unicor n . E, onoc ros, M E u eu t he Little H or se. u c t he Fl . q u l s s a, y Ru le E d u the River E r idan u s m the . ri an s, Nor a,

a A che Oc the Oct ant . , rnar. tans, h nt - eare r Cu a . O h u chu t e Ser e B B , rs p i s, p

a Ra l thi. Z a t . Alha u e s A e y , n ac , Ras g , g

7 A h Ce a . 7, z a. B , balr i ' ’

B i d A Mar ﬁk . o, e . , 0 e d Al- a d O t he Giant H u nt er 2, K i , K i . rion ,

the F u r nace (1 B e e eu e . Fornax, , t lg s

Gem the Twins e . ini , B , Rig l

61 Ca . Be . , stor y , llatrix

M a. u . 6 n B, Poll x , i tak

I 1 8 TH E STE LLAR HEAVEN S

Area 41:

— 720 x

720 x 57 29578 _ 4 1 253 nearly.

“ ’ ee the n u u I have found the following relation betw n a g lar nit , or d h the e the c e e c c e u e ded ar e ra ian (t at is, angl at ntr of a ir l s bt n by an d in c d and the e equ al in length to the radi us) expresse se on s of arc, ar a of a sphere in square degre e s

Radian

° Ar ea of a Sphere s-1 720 x A (as above)

” 720 x a 3600

” = — a and 1 2 e . [ 4 53 , as abov ]

N TE O C .

The ar e the e e in the e en cc d following tw nty bright st stars h av s, a or i ng to the H arvard photom etric m easu res

Phot om.

a Those marked with an aster isk lie on or near the Milky W y. APPEN D I X 1 1 9

L s o Q E o o m ? “ i t P c m o 8 o m E ” 0 A m 5 3 m : 8 A $ 8 8 E E 9 2 a 5 2 é 3 8 0 f E 5 x w w $ A e n w 8 a a 1 5 c 0 c 8 “ 5 o . c s m s E 5 8 fi bn o m 2 . d m a 8 2 8 n E o n e c u m 8 m A e 6 A 8 a w a 3 k m 2 e e e x v 3 c “ w 3 u L f m s E o e o v 3 0 8 o o 8 s n e 0 o E a k 3 o b 3 5 n a 0 n 9 m 8 e m 8 v 3 h é o g o o u 5 ? 2 o 8 a e 8 m b fl w a o c 5 é v x e : a n 2 fi s 6 c 0 : m .3 5 > . m . w a e . m m E c 0 z . o B . é L L . $ o n 2 w e o m a m o m 8 w 6 a e o 9 s a w 0 b o m 8 k 5 8 8 d 8 S 3 a x é a a s ? o s n m n 5 4 m . . m m m . m E 5 m . 5E

m fi ' fi ' fi ‘ fi ' Q N O Q N

m o e E n m o m 0 w 0 o c c 5 v m 8 C 3 o 9 aﬁ e o a o m 8 : u m B m m a 6 a ﬁ a . o m o d 5 5 S 5 d m q é U m 8 o 5 m 2 : 5 e i 5 m m 0 m m Mmm mm M »2 mmm 1 20 THE STELLAR H EAVEN S

a 0 0 m 5 4 . 0 x 5 0 0 5 0 9 8 8 > 8 0 0 2 m 8 5 0 0 0 5 0 0 0 0 8 0 0 0 L 0 0 @ m 8 0 8 8 u 0 m 5 0 9 . 0 0 0 0 5 0 0 0 0 8 > . . 8 “ 0 0 0 8 > 6 Q~ _ 0 8 : 0 0 3 0 0 A 8 8 0 0 8 0 0 8 5 5 3 a A 0 u : 0 0 c 8 0 0 m 8 0 0 £ 9 0 0 0 0 a w : m fi 5 0 0 g 5 0 0 m 3 0 0 0 0 0 0 A 3 0 2 a 6 8 3 m m 0 > é 8 c 0 0 1 0 8 m v 6 8 w 0 A 0 w 8 8 0 m 8 0 c a A 0 W 0 8 m 0 = y 5 8 0 8 m 8 m s 5 m 0 0 0 0 0 5 0 0 8 0 w ~ 0 fl v 0 > 0 : a v 8 c 0 8 8 8 0 0 9 m s 0 0 0 2 a 0 w . 5fi v 0 0 8 v 8 5 m . é 0 2 0 m F . 2 8 > 0 b m w 0 0 . 0 0 0 > m 0 0 0 a 0 0 u 0 m a 8 E 5 8 3 9 3 m 0 z v 8 2 0 5 0 8 0 5 8 8 0 0 0 0 8 fl 0 c 0 2 3 2 v 0 8 é 0 0 3 5 0 fl 3 0 3 5 0 0 0 0 w 0 8 8 0 9 a 0 5 8 8 A 0 0 0 0 0 c 2 9 8 . c 3 6 w s 0 1 0 0 0 . 3 8 0 8 8 0 £ fi “ fl 2 0 v 3 m . . 0 0 0 8 m 0 5 . “ 0 8 0 o m 0 m : A 5 . 3 . 0 w 0 8 0 a m 0 c 0 0 3 8 w 8 0 m . 1 8 k 8 8 ~ 0 m 2 5 0 0 a 8 w 0 0 0 0 1 0 1 0 5 0 8 8 0 0 =8 8 8 8 0 0 8 0 8 8 8 0 8 m 8 2 3 > 0 0 0 m 0 8 0 3 v “ $ 0 8 : 0 m a w m 2 . 5 fi r 4 b “ . b n m

ﬁ ' M N

w m 3 e 2 v 6 ; 0 0 m m c 8 0 E E 5 8 s 8 w . w . t w a 0 8 0 > 0 8 > 8 A 8 ? O 0 3 : 0 m : 0 > h m D m 5 . m N m 0

1 22 TH E STE LLAR H EAVENS

c ed the d ce th a e au th u pla at istan of e star. For C nt ri e calc lation is as follows 206 265 206 265 _ 2 020 75 , P 2 og 2 75020 and l 0 4 ’ D educt su n s ste llar m agnitud e 2 6 5

and we have 0 6 9

ha the su n u d be edu ced a u m T t is, wo l r to a st r of abo t if re oved to a A s t he m a u the d istan ce of a Ce nt u ri . gnit de of a Centau ri is it a e h the a e h e h ou r su n h u d be pp ars t at st r is a littl brig t r t an , as it s o l , owing to its larger mass . From the above considerations I have d e du ce d the following sim ple

= o for m u l a : If m m agnitude of su n see n at the distan c e of a star whose he parallax is p, t n

’ ° (for sun s stellar magnitu de 26 ’ If this assum ed valu e for the su n s ste llar m agnitud e is not qu ite c ec the m u be h e ed . If we s u m e th u e orr t , for la will slig tly alt r a s e val the n 1 m =5 log P

° on the e h d we u m e the u e 2 C If, oth r an , ass val 7 , E 772 5 log (1) ) But probably the simple formu la m =5 log

h is near enou g . For = m : 1 0 ze o m u de . 5 log , or r agnit For we have

= ” and for P r h

TE NO G.

the a and e m ar e ac u a When parall x prop r otion of a star known , its t l veloc ity at right angles to the line of sight m ay be compu ted by the following form u la

Le t z ar allax ec d ar c p p in s on s of , m = r o r m e c d ar p pe otion s on s of c.

Then ve loc ity in miles per second P APPEN D IX 1 23

T H NO E .

When the period and the semi -axis major of the orbit of a binary ar e and a its a the m a the em can e star known , lso par llax, ss of syst asily ’ be c m u ed e m he u m F or P be the e d of o p t in t r s of t s n s ass . if p rio ’ e u ea a the e m - the m e d ce 772 r vol tion in y rs, s i axis of orbit (or an istan ) , ’ and n the m e the c m e and M the u m a m e ass s of o pon nts, s n s ss (or, or c ec the c mb ed m the su n and e h we h e the orr tly, o in ass of art ) , av by laws of orbital m otion ’3 a l on + n M 3 ( h c m n w e n e + 34g.

a be the em - m the a Now, if s i axis ajor of orbit , parall x

the we h e and of star, av hence

m + n _

we ut M : 1 or, if p ,

m n _ ’ PT’F2 ’ In the c a e a e u we e m Dr ee P s of C nta ri , hav fro . S s orbit ea a : and he ce y rs , n

’ the m ed m the em m M e or co bin ass of syst is twic e the su n s ass . an ’—ff ’ d ce e een c m e o . 2 6 m e the e istan b tw o pon nts, 3 ti s arth s P m e d a c m th n an ist n e fro e su .

NOTE I .

u e The following m ethod of calc u lation is given by Dr . B n r

Let A = u f c e the i h e s r a of br g t r star, xA = u ace the a e s rf of f int r star, 1 =b i h e u u ce the ﬁ a r g tn ss of nit s rfa of rst st r, =b r i h u a of the ec d y g t ne ss of u nit s rf c e s on star .

The Z H e cu we h e the e u a n for r lis, av q tions A + A xy =3 A = 2 — A A x + A xy = 1 Su btracting 3) from w e have A x =2 ; 1 24 TH E STEL LAR HEAVEN S

and c ombining this with (2) w e have = x 1 , and from (1 ) and (2) z A x : 1 and . y , y é

H e ce the a ar e e u e but one e the n st rs of q al siz , is twic as bright as h ot er . To obtain a ge neral expression for any Algol variable with u nequ al m inima Le t h m aximu m =ll[ lig t at , D e c d m m u s itto at s on ini , Ditto at prin c ipal m inimu m z m The n A -t- A xy z ll/l A =S A

r e ed e e we h e P oc ing as b for , av

Ax M m , —M m s M m and x or , ; from ( 1 ) S + (M — =M S and . y 111 —772

he e is e da m mum A and he m If t r no s con ry ini , as in lgol ot r si ilar e h c a he e u 1 and 2 ar e e u and variabl s of t is l ss, t n q ations ( ) ( ) q al , = A x o and the c m d b d . y , o panion is a ark o y the ca e A he e the h m mu m u ee In s of lgol , w r lig t at axi is abo t thr m e the m m um w e h e ti s light at ini , av _ 3 I —2 3 3 and the diam eters of the two com ponents ar e in the ratio of

° 1 4/O 6666 1 , or

the a A e one and ha m u de If v riation of an lgol variabl is a lf agnit s, he h m mum e u u m e h m mu m and t n lig t at axi is q al to fo r ti s lig t at ini , we have

x _ —Ti 3. 4 4 and the diam eters ar e in the ratio of

1 : ' 66 1 or O 8 .

I N D E !

A BB TT 6 2 Cer aski M d m e O , , a a , 74 , 75 Ab u e e o f 1 2 Ce r aski 6 sol t siz stars , , 59 , 9 , 73 Acher nahr 8 Ch c c 1 0 1 , 7 a orna , Ad m 8 Cha d e 6 6 68 a s , 4 n r, 4 , 3 , , 74 A e 1 Ch e itk n , 3 as , 49 ' ’ A c 1 8 Chu W 6 l or, rl s ain , 7 Ald eb 6 A e d e C C as e o f ar b e 8 aran , , 7 , pp n ix, Not l s s v ia l stars , 3 Al 0 C u e bu la 86 gol , 7 . 79 l st rs , glo r, A ol ab e 6 A e d e I C u e i e u a 8 lg vari l s , 9, pp n ix , Not l st rs , rr g l r, 9 AI-Su ﬁ 8 6 8 6 C u e a b e . 3 . . 7 . 77 . 7 . 79 . 9 l st r v ria l s , 75 A 6 1 1 1 1 1 1 1 1 8 C u o f a ltair, , , 4, 5, olo rs st rs , 7 D A d e r . C m c 2 2 n rson , , 44 , 47 o sto k , 4 , 9 A d m e d e bu 6 C e 1 A e d e A n ro a n la, 9 onst llations , , pp n ix, Not A a e 1 1 1 1 8 C el d P fes nt r s , 7 , op an , ro sor, 44 Anthe lm 2 , 4 ’ A e o f he e A e d e B D A r r e st 1 00 r a star sp r , pp n ix , Not , 97, 99 , A c h m ed e 2 De m c u 1 0 r i s, o rit s , 3 Ar u land er 2 6 8 1 8 De Z ach g , , 4 , , 3 , 77 A eb u a D c e of 1 0 rgo n l , 94 , 95 istan stars, A e 1 6 Dobe r ck 2 1 p x, solar, , 3 , 3 Au e 2 2 D e 0 w rs , 5, 4 oolittl , 3 D u b e 1 o l stars , 7 B e P fes 6 8 D e e A e d e D ail y, ro sor , 75, 7 , 7 r y r, pp n ix , Not B d 8 Du et 2 A e d e arnar , 4 n , 3 , 73 , 74 , pp n ix, Not s B e 1 D and I ay r . . 77 B eh m 2 Diir er A be r ann , , 3 , 77 , l rt , 3 l lsk 6 Be opo y, 7 Be e eu se 6 1 E 1 0 1 0 1 1 0 t lg , aston , 5, 9 , Be Ebe h d 1 6 vis , 93 r ar , , 35 B na 2 2 A e d e H E e 62 i ry stars , , pp n ix , Not ll ry, B m h m 8 2 A e d E c e 2 ir ing a , , 4 , 77 pp n ix n k . 3 e D E 1 8 1 2 6 1 A Not sp n , , 5 . 5 ' 55' 5 ! 59 ! 9 0 p B 6 1 e nd i x e D irt , p , Not B eu E ta A us 6 1 6 2 la , 3 rg , , Bla ko 0 Eu d u 2 j , 5 ox s,

B oed dicker , 1 05 B d e 1 8 2 6 F mm 2 ra l y, . 7 , 7 la arion , 3

B h e ar 6 A e d e C F m eed 2 0 A . e A rig t st st s , , pp n ix , Not la st , , 4 , 77, pp , Not B r u nowski 1 F e 2 6 , 4 lan ry, 5 , 55, 5 m M B u che 6 1 6 2 F e rs . 6 8 r ll , , l ing , , 44 , 45, 4 , 7 B u ham 2 0 2 2 2 2 2 2 6 2 8 F m h u 1 1 1 1 8 rn , , , 3 , 4 , 5, , , o al a t , 7 , F A d e D Bu . 0 1 e rns , Gavin J , 4 [3 , 3 ranks , 79 , pp n ix, Not F ch 6 1 rits , C i a sar , 3 C m b el P fe 1 6 8 G M Wa Ch e V a p l , ro ssor , , 34, 37, 45, 4 alaxy, or ilky y, apt r Ca o u 6 1 1 1 1 8 e 1 1 n p s , , 5, Galil o, 4 , 9 C e a 6 1 0 1 1 1 1 1 1 8 Geelmu de n 8 ap ll , , 34 , 5, 4 , 5, y , 5 C a 1 1 8 e mm C e i u 1 ssini , 3 , G a, orn l s , 4 C 1 1 1 1 6 1 1 8 emm 6 astor, 3 5, 4 , , G ill, 7 Celor ia 2 1 0 Sir D id 1 2 28 8 , 3 , 9 Gill , av , , , 7 [ 1 26 ] I N DEX 1 27

l e 2 0 2 Lu he 2 G as napp , 3 , 3 , 3 t r, 4 G ob u a c u e 86 L me 6 l l r l st rs , y . 5. 3 5, 3 Goodr c e 66 68 0 i k , , , 7 M ad e Gou d 2 6 1 0 1 08 A e d l r, 79 l , , 4 , 5, 5, , pp n ix , M a u d es a A e d N ote L Note D gnit , st r, 5, : pp n ix, M u 1 0 ee e e A e d e anili s , 3 Gr k l tt rs , pp n ix, Not K M 2 G r im mle r 1 02 ann , 3 , 47 [ M u d e e 1 6 8 60 a n r , 44 Grov r, 5 . 53 . 55. 5 . 57 . 5 , 59 , . M r l us 1 au o yc , 4 H ainz e l 1 M ar ald i 6 8 , 4 , 5 , 9 H P o fe so A a h M ar kwic k C e 6 1 06 all , r s r s p , 44 , olon l , 3 , H l e 6 1 6 1 88 M ech a l y, , 3 , , ain , 97 H a d 6 60 M e e Ch e IV r ing , 5 , 57 , ssi r, apt r H a w M e hod o f b e v o f b e rt ig , 49 t o s r ation varia l H e 2 1 0 1 0 8 1 is, , 3 , 4 , 5 stars , H e c e M eu c c n k , 57 i . 3 Rev ohn 2 2 H e sc he Sir W m 1 6 0 8 M c he . r l , illia , , 3 , 79, 7, i ll , I , M Wa 1 0 ilky y, 3 H e che Sir oh 2 6 2 1 02 1 0 M Ce 1 80 rs l , J n , 3 , , , 5, ira ti , 5 . A e d e D M z 1 8 pp n ix, Not i ar, , 3 5 H d 2 2 6 6 1 A e d M c 2 1 2 1 in , 3 , 4 , 5 , 4 . 7 , pp n ix, on k , 3 , H e D M o 0 inks , 49 [Not ntanari , 7 H chu M e 1 ippar s , 3 , 39 oy , 4 H oo e 1 o tions e 1 k , 7 , prop r, 3 M H uz e u 2 6 8 1 0 i e 66 A . e o a , , 3 , 5, 7 , 77 , 7 , 79 , 4 t ll r, , 73 , pp , Not H u r W M 2 1 Si . 1 00 u e ggins , , 44 , 94 , 99 , ltipl stars , H u e 2 2 1 6 M e 6 ss y, 3 , 4 , 3 , 4 y rs , 3 H u e 1 yg ns , 7 ed -e e d u b e 1 8 H o he eb u r 1 1 Nak y o l stars , yp t sis , n la , 3 m e of r A e d e A Na s sta s , pp n ix , Not I e 1 e e a 1 0 1 1 2 nn s , 3 N ar st st r, , I e u lar c u er 8 e bu ae e u a e 8 rr g l st s , 9 N l , irr g lar, 93 pl n tary, 9 I e u a ebu ae s 6 rr g l r n l , 93 piral , 9 I e u a b e 6 1 ebu h he s 1 1 rr g l r varia l stars , N lar ypot is , 3 e bu u a 1 0 1 N lo s st rs , c b 2 Ja o , 3 e wc mb P fes 1 6 N o , ro sor, N e w s K a t e n 1 1 6 star , 39 p y , 3 , , 49 d 1 K ar linski Nijlan , 5 , 55 v Pe r se i ee er 1 6 6 No a , 47 K l , , 9 u m be of 1 1 1 e m f A M a , 3 , 66 . e N r st rs K p , , 73 , pp , Not e Dr 1 60 K lly , . , 5 , 59, Ob e a m e hod of 80 s rv tion , t , e e 1 K pl r, 4 b o f b a 2 Or its in ry stars , 3 c h 2 Kir , 59 , 9 O eb ul io a, 93 e 1 r n n Kl in , 4 O v d 2 i , K linker fu e s 2 , 3 Owl eb u a , 99 c h n l Ko , 55 K r ate s 2 m H 88 Pa e . , l r , K u e e 1 Pau 2 Kr g r, 5 , 53 l , 7 P a o f a 1 0 1 1 A e d ar llax st rs, , , pp n ix, L c i e 1 1 e E a a ll . 77 . 79. 7 Not

La o . M 2 8 C dam e 1 8 Pa hu H . n in , rk rst, 5 , 57, 5 L d e 1 1 Pee 60 alan , 79 , 7 k , 57, 59, La ce 1 1 Pe i e pla , 3 rr n , 49 Le wi 2 2 0 Pe r sei s, 3 , 7 , 3 , Nova, 47 L dau e 1 Pe e in r, 4 t rs , 77 L c e Dr . 6 P c e P fe 1 0 8 8 o ky r. , 7 i k ring , ro ssor, , 3 , 3 Lo . e od a b es 0 P 6 6 ng p ri v ria l , 5 igott , 3 , 7, 77 1 28 I N D EX

Pl e a ebu 8 a , 9 S c 1 1 1 1 8 an t ry n l pi a , 3 5, 7 , P a m , 7 S ebu ae 6 l ss ann 4 piral n l , 9 P e d e , 89 , 90 S b u e ze of 1 2 b l ia s tars , a sol t si , ; inary, P u ch 1 0 a , 3 2 2 c u d ub e 1 m a l t r ; olo rs, 7 ; o l , 7 ; g ni P 2 8 60 og o , 4 , 54 , 5 , u de of m u e 2 1 u mbe s n t s , 5 ; ltipl , ; n r P e S o a , 3 4 o f, , 1 1 1 ax o f 1 0 e l t r 3 ; parall , ; prop r P u 1 1 6 1 1 8 o x , , m of 1 ec of 8 i le ll otions , 3 ; sp tra , ; tr p , P u d 1 8 2 o n , , 7 2 1 P e , 2 S ebb 8 ow ll 3 t ins, 4 P c 2 6 1 0 1 1 1 0 , , , 4 , 07 , S e l u e e 1 1 0 ro tor t l ar niv rs , P c , 6 , 1 1 , 2 , 1 0 , 1 1 1 1 , 1 1 8 S b 2 ro yon 5 5 4 , 5 tra o , P e m 1 S , u e L . 1 6 rop r otions 3 tr v , , P e m 1 I 8 , , 5, 7 . 77. 7 . 79 S u e O 2 28 tol y tr v , tto , 4 , P h 1 0 g , S u m e 1 6 yt a oras 3 t p , ’ Su m in s ce 1 n s otion pa , 5 u che 1 6 Ra n , Su ec ed b e sp t varia l stars , 77 Ra anootha Cha 2 g ry, 5 Su R . 1 0 ’ tton , J . , 7 Red B d 6 ir , 7 , 7 Re d a A e d e D Ta m e st rs , 7 , pp n ix, Not l ag , 79 e u u 1 1 6 1 1 8 Tebbu t t 6 2 R g l s, , , c ha d 1 8 Te m Ri n , porary stars , 39

e 6 1 1 1 1 6 1 1 8 Te 1e500 ic d u b e s a , 1 8 Rig l , , 4 , , p o l t rs che Th me 6 A e d e D Rit y, 49 o , 7 , pp n ix, Not be Dr A W Tr iﬁd eb u ae . . 6 66 1 2 Ro rts , . , 5, , 7 , 7 , n l , 95 8 8 8 1 1 T e 2 1 75, , 9 , 4 ripl stars , b e Dr T ou e . I ac 8 8 , , 95 Ro rts sa , 4 , 7, 9, 95. 97, r v lot

1 0 1 1 1 1 T ch B r ahé 1 6 . 99 , , y o . 4 . 7 . 77 79 b Dr . Ro inson , , 99 U u h Be i h 8 l g g , 77 , 7 e , 6 ’ Ros n U m e A e a 2 1 06 rano tria rg ntin , , e E of 0 1 6 Ross , arl , 9 , 9 , 93 . 94 , 9 . 99 . b e 8 A 6 0 Varia l stars , 3 , 39 ; lgol , 9 , 7 , ’ u S 1 e u a 6 1 - e d 0 R naway tar, 3 79 ; irr g l r , ; long p rio , 5 ; u e P fe 1 1 h - e d 6 ho e w R ss ll , ro ssor, 75, 4 s ort p rio , 4 ; s rt st kno n e d A e d e M su s p rio , pp n ix, Not ; Safar ik 6 e d , 3 p c te , 76 S ffo d 2 e 6 1 1 1 0 1 1 1 1 6 1 1 8 a r , 5 V ga, , , 5, 4 , , S w e 2 6 6 8 0 e oc of in e of h 1 1 a y r, 5 , 7, , 7 , 73 V l ity stars lin sig t , 4 , 5 Schaebe r le 2 V illar c eau 2 , 5 , 3 Sc hm d 6 66 6 el 8 i t , 43 , 4 , , 7 Vog . . 34 Sc ho fe d 6 n l , 43 , 53 , 55, 7 Wa e 1 Schr oter rg ntin , 5 , 79 Webb A e d e D Schu e 1 , pp n ix, Not l r, 4 We M s Sch b lls , is , 74 wa . 47 . 74 . 77 We d e 6 See 2 2 2 2 2 8 2 0 1 2 n ll , 4 , 3 , 4 , 5, 7, , 9, 3 , 3 , 3 , W m S a e 0 1 illia s , t nl y, 47 , 7 , 7 , 74 8 1 00 W Dr W E . Se e e 2 6 ilson , . . , 49, 9 , lig r, , 49 Winne cke 2 Sec ch 1 0 1 , 7 i , W f M ax 8 Se d e ol , , 4 i l , 77 W d 2 Sh - e od b e 6 oo s , 7 ort p ri varia l s , 4 W h 8 S u s 6 1 1 1 2 2 2 1 0 1 0 1 1 rig t , 4 iri , , , , 4 , 5, 5, 9, 4 ,

Y e de 68 n ll , Sm h Ad m a 1 0 yt , ir l , 4 , 9 , 99 S ec of a s 8 1 1 Z w c p tra st r , , 4 a k , 49 S ec sc c b es 2 Z ol e 6 p tro opi inari , 3 ln r,

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