THE BAA OBSERVERS’ WORKSHOPS

Cambridge Winchester York 2003 February 15 2003 April 26 2003 September 6 Milton Keynes Nottingham 2004 February 28 2004 April 24

Observing variable stars Workshop No. 3: with binoculars York 2003 September 6 by Melvyn D. Taylor

Introduction (GCAS, RCB), Universal Time, that is British Summer Pulsating (M, SR, Time minus one hour. Universal Time RV), Cataclysmic (N, NR, ZAND), abbreviated UT (or Greenwich Mean One of the finest aspects of visual observ- Eclipsing (subtypes EA, EB, EW). The Time, GMT) beginning at midnight is used ing is freely roaming around a dark night General Catalogue of Variable Stars (GCVS) in nearly all astronomical records. Some sky picking out galactic and solar system and Information Bulletin on Variable Stars observers specialising in eclipsing binaries bodies, noting patterns of stellar hues and (IBVS) are the source for descriptions of use the Greenwich Mean Astronomical brightness. The binocular is an ideal tool for the categories. Dependent on an individual’s Time (GMAT) system that can be this pursuit. Use of two eyes, the natural interests the longer period (interval between confusing in relation to the date, as it state, is relaxing, easy and relatively quick, successive maxima) objects may be more commences a new ‘day’ at noon. although for optimum night-time observing appropriate for observers with limited time In the 1850s Norman Pogson (1829– the eyes have to adapt to the conditions to spend. Those with lots of spare time 1891) instigated the modern definition of which does take time. available may choose eclipsing binaries that a stellar magnitude scale and a fixed ratio Whether observing as a beginner or a show an eclipse in one night; these objects of 2.512 corresponding to one magnitude more experienced astronomer, binoculars require an estimation of the magnitude difference. Five magnitudes therefore are useful in many areas; eclipses, lunar every 10 to 15 minutes around the time relate to a ×100 change of brightness. occultations, comets, meteors, asteroids, when an eclipse is predicted. In general the Visual magnitude differences of the deep sky, artificial satellites, novae frequency of clear skies will also prove comparison ‘standard stars’ may be hunting and variable stars. The BAA important in selecting the type and number appreciated by habitual and systematic Variable Star Section, formed in 1890, has of variables to follow. The basic visual observing using a particular specification in its database around 1.6 million observation is an estimate of the star’s of binocular. In general, the naked eye observations available to amateur and magnitude as compared with ‘standard under a very clear sky could detect stars professionals. Programmes of observation stars’ at that time. to a magnitude of 6.2, a typical 50mm include long-standing telescopic and binocular with similar conditions may binocular variables, also a list of recurrent allow magnitude 10.5 objects to be seen variables, a set of eclipsing binary stars Time and magnitudes but these values are unlikely in practice and an important area called the ‘new (Table 1). variables’ based on those stars which Time to the nearest minute, from an Mike Collins has found and which require accurate source, is normally required and it follow-up work. is useful to have a standard clock, for Table 1. Theoretical limiting magnitude, resolution example, the and magnification for different binocular apertures Rugby MSF (60 Types of programme kHz) receivers Aperture Limiting magnitude Resolution Magnification stars may be acquired (mm) (2+5logA) (90% effic.) (arcsec) for exit pupil of as wall clocks or 5mm 8mm wrist watches. 20 8.5 7.6 5.8 4 2.5 Apart from some variables which defy The signal from 25 8.9 8.1 4.6 5 3.1 being ‘boxed’ there are four major classifica- Mainflingen 30 9.4 8.5 3.9 6 3.7 tion groups, described as eruptive, pulsat- DCF77 on 77.5 40 10.0 9.0 2.9 8 5.0 ing, cataclysmic and eclipsing. The kHz is also being 50 10.5 9.4 2.3 10 6.2 subtypes are many and differing forms of used in similar 60 10.8 9.8 1.9 12 7.5 variation may be occurring in a single star or 70 11.2 10.1 1.7 14 8.7 timepieces. For 80 11.5 10.4 1.5 16 10.0 a stellar system. The main classes and most purposes 100 12.0 10.8 1.2 20 12.5 subtypes (abbreviated) of variable sug- time is best 125 12.4 11.2 0.9 25 15.6 gested for binocular use are: Eruptive recorded in J. Br. Astron. Assoc. 114, 6, 2004 349 Taylor: Observing variable stars with binoculars restored without it being lost completely. A torch’s white light covered with red paint or cellophane is an essential item for visual observers. Those troubled by stray lights often use a black cloth placed over the head and eyepieces to help cut down side reflections. Binocular eye- pieces with rubberised side guards are particularly handy in these circumstances Figure 3. Exit pupils (4mm) of a 20×80 and may help larger apertures to be binocular (courtesy Leeds AS). steadied. Shape of the binocular for hand holding is tion is a bad sign and if used persistently important and before purchasing, different without being properly recognised it could models should be compared and examined affect one’s eyesight. It should be possible visually and mechanically. A one-piece for an optical specialist to amend this fault (American styled) barrel design is inher- but the cost may well be a large proportion Figure 1. Three low power binoculars. Left to ently tough, a genuine Zeiss style (H of its original value. Large and heavier right: 8×40 Swift Trilyte (roof prisms), 3×20 profile) which has a two-piece body is also binoculars that have a long rod extending opera glass, 8×42 Opticron (porro prisms). strong. Bird-watching and photographic from the hinge base to a support bridge suppliers of small telescopes and binoculars nearer the objectives are guarding against vary in their sympathy to an amateur distortion and bad collimation. Binocular basics and astronomer keen to critically inspect their Waterproofing of the binocular is an added the eye wares so it is probably wise to inform them bonus since repeated temperature and of the quality expected. humidity changes cause condensation and mould to affect the internal parts. Over time The basic binocular specification such as with use and possibly the odd accident, 8×30 or 10×50 has the power first, the optical degradation of stellar images will number of times an object is magnified. The Binocular parts and occur probably due to the prisms moving or second number is the diameter in millime- choices coating corrosion. A suggestion for anyone tres of the front lenses, the aperture. Large with ideas about multiple use (daytime and objectives are for fainter stars and more night-time) would be to own two binoculars detailed views. Comparing a 10×40 with a Most binoculars have the angular field of so the astronomical one is kept for that 10×70 the larger collects 70×70/ 40×40 or view or its dimensional cotangent inscribed purpose only. 3.0 times more light, so objects appear 1.2 on the body housing as a number of feet In quality binoculars all air-to-glass magnitudes brighter. A table of fairly seen at a distance of 1000 yards. (1 degree surfaces are fully multicoated, which means common specifications is given as a guide of arc or two lunar diameters approximately that ghost images and internal reflections only. The choice of binoculars will involve corresponds with 52ft at 3000ft). For a true are reduced. The technique of depositing the observer’s interest(s) and age, condi- binocular field of 5° on an 8×30, the optical coats on polished glass began in the tions of use (e.g. if from a dark or polluted apparent field is 40°. A simple check on the 1930s. The best coatings can be judged by site), aperture, magnification, body design true field of view is useful and this may be looking down on the objective with a hand (handling appeal), weight and the cost. simply done by finding two stars that fit over the eyepiece and examining reflections. Size of the binocular exit pupil, that is, across the circle diameter and then check A totally white reflection means an optical aperture in millimetres divided by the the celestial spacing in degrees and minutes surface is not coated. Multi-coatings reveal magnification, is likely to be the critical of arc from the scale of a star atlas. reflections that are noticeably fainter. factor since it is important to try to The hinged bridge that gives the eyes Checking for blemishes on the optics by match this with the observer’s eye pupil access to the eyepiece centres should be turning the binocular around and inspecting under working conditions. The eyes will smooth and capable of staying in the the objectives against various lighting angles give the clearest detail operating in the required position. The two circular fields of is a useful task. Looking at a thin vertical or range 2mm to 5mm, their normal size view should merge into one if both optical horizontal element (a radio mast, or an during daylight. Andrew Langley’s barrels are aligned correctly and for all aerial) through one barrel at a time should comments (BAA Journal, 2004 April) on positions around the hinge. Poor collima- display minimal curvature and little false visual acuity in relation to the exit pupil are well worth noting. Maximum pupil size may be 7mm to 8mm but the aging process will reduce this to about 4mm or 5mm. There is an approximate relation of 0.35mm reduction per 10 years as suggested in Sky & Telescope, 1992 May. Sky Publications market a small device that allows the pupil size to be measured. Ten or more minutes after going outside the eyes will have adapted (but not fully) to darker conditions and faint objects and stars will be apparent. Shine a bright white light on a chart or open the ‘fridge’ door and this will immediately decrease the pupils’ size – faint stars will now be lost to view. A dim red light will have a less dramatic effect since night-time response to this wavelength is not so adverse and dark adaptation can be Figure 2. Cross sections and light paths of different binoculars (Melvyn Taylor). 350 J. Br. Astron. Assoc. 114, 6, 2004 Taylor: Observing variable stars with binoculars and optically. A wheel instruments should show these tiny circlets centre focus that of light to near the field edge. The technique turns both eyepieces of bringing variable star and comparisons to at once is fast, the optical centre is a standard method that individual ones a bit tends to offset the mercenary comment that slower. Long follows. Image stabilised binoculars have a dewshields extending reputation for producing virtual pinpoint from the objectives images from edge to edge, however their Figure 5. 8×40 Hoya fixed and large enough not higher cost has to be considered in relation to with a screw V-clamp around to lessen the field of a conventional instrument of larger aperture focusing spindle. view will reduce mounted firmly. Resolving close stellar pairs reflections into the is an interesting pastime and another check Figure 4. 16×70 Swift fixed to tripod objective lenses, assist seeing faint objects on the binocular performance. head with angle bracket screwed to end and delay dew forming on the glass. of prism housing. colour to its edges. The eyepiece coatings Variable star names are also worth checking. Quality lenses Free or fixed including the eyepiece design and fully binoculars The system started by F. W. Argelander multi-coated optics with BAK-4 prisms (1799–1875) has, for example, the first- (light crown) are superior to BK7 named variable star in Scutum as R Scuti, (borosilicate) prisms bearing in mind A magnification of up to about ×10 if hand then proceeding with additional ones to Z relative cost of the type and body style. If held and steadied may give suitable views, Scuti. There were hundreds or thousands the binocular is aimed at a bright back- but over ×12 a stellar image will be ‘jittery’ more found in particular constellations so ground and is held about a foot away the and it is advisable to have the binocular after Z, RR, RS to RZ came about. bright exit pupils should have a dark or secured to a mounting black surround and no internal parts should for critical observations. be visible. There are two commer- Eye relief relates to how far the eye may cially made clamps that be from the eyepiece and still see the full connect a binocular to a field of view. Observers who have astigma- photographic tripod, tism and use spectacles will need a long eye the view will then be relief; those who have near or far sight superior to a hand held normally take spectacles off and focus one, fainter objects will without any thought. The modern focusing be seen better and you mechanism is to have the left eye adjusted are hands free. A screw first by the wheel, with this one then shut connection in the base (or objective capped) the right eyepiece is of the hinged bridge is a turned on its housing and the focus refined. better position than one This technique also corrects for different to either of the barrels. eye strengths. However, a binocular that Several large binoculars has individual eyepiece focus could be use a centre bar with considered slighter superior mechanically sliding clamp that is Figure 7. Orion Telescopes parallelogram binocular mount. screwed into the tripod mount. There have been a number of mountings Thereafter SS to SZ, and so on. From ZZ devised on an individual basis by binocular the formation went to double form AA to specialists with balanced/stabilised ones AZ and so on but J was not used because available from instrument suppliers. A of its similar character shape to I. The sturdy tripod with fittings to mount the double lettering to QZ provided for 334 instrument in alt-azimuth mode is one designated variables. Identifying and naming method, but for real comfort a chair or additional objects then started at V335, in recliner with a binocular attachment is every case followed by the genitive form of potentially ideal. Urban observers hounded the constellation or its accepted abbrevia- by permanently bright night skies may find tion. The 88 constellations have standard that a higher magnification will show fainter short forms using three letters, for example, stars, and in this respect large, custom- V465 Cas (or in full Cassiopeiae). mounted instruments with interchangeable eyepieces would be an option. Charts, atlas and a torch or logbook can be used more Charts and sky scale easily if the binoculars are mounted. Some observers dispense with a record book and use a voice record, thereafter writing the The Variable Star Section observing charts observations directly into a log book or on a use an analogy of stellar magnitude computer file for personal use and/or sending differences by the commonly used proce- to a variable star organisation. dure of showing brighter stars with a larger The ultimate test for the casual observer is diameter in comparison to fainter ones. on focused stars. The changing aspect of a Night-time stellar observers are looking at Figure 6. Modified car seat with steel bracket focused star image as the observer takes it the smallest of tiny circles of light as for binocular housing (courtesy The Astrono- across the field of view will make for defined by the diffraction of light across the mer, John Hosty, Peter Madej). interesting comparisons – higher quality objective’s clear diameter. By placing the J. Br. Astron. Assoc. 114, 6, 2004 351 Taylor: Observing variable stars with binoculars one comparison to the variable centring each in turn until a brighter and fainter one are definitely found. The process of light estimation may go as follows using what is known as the fractional method. The brightness of the variable is placed mentally between that of the two comparisons, labeled, say A and C. Figure 9. BAAVSS lightcurve for R CrB, 1998 to 1999. This difference is divided into small number fractions such as recorded as A–2, C+3 with the conven- Figure 8. 5° square field (long exposure) of 1/2, 1/3 and 1/4. If the variable’s brightness tion that minus means 0.2 is added Corona Borealis with R CrB and three com- looks 1/3rd of the way from A to C then the (fainter than) to A’s value. The plus 3 parison stars. light estimate is placed in the observer’s log means 0.3 is subtracted (brighter than) as A(1)V(2)C. The brighter comparison is from C’s value. The variable’s magnitude comparisons and variable into a brightness always written first as a matter of conven- is deduced as [(7.0+0.2)+(7.6–0.3)]/2 = order sets of observations made at differing tion, with V being the variable. It may be 7.25, and this is rounded to 7.3. times allow a light curve to be drawn. By that the variable looks equal in brightness to Observers have used many in-situ plotting a series of magnitude estimates comparison B and so it is written, simply experiments to train their appreciation of with smaller values (bright) at the top of =B. Leaving nothing to memory light brightness differences, even assessing the y-axis and time on the x-axis the basic estimates are recorded in an observing log differing street lamps at large distances as properties of the star’s period, maximum dedicated to variables, or an audio recorder an exercise(!). A meteor observer may use a and minimum brightness are displayed. could be used. For the visual observer it has set of stars of magnitude 0.0, 1.0 to 5.0 in With many light estimates from a team of become standard practice to record the full order to gauge the brightest part of an event observers the analyst is able with suitable estimate as a means of insurance and seen for a fraction of a second. Variable star data to confirm or refine these values possible maintenance of the observational observers at least have the object in view making the results available to other data. A comparison star may be found to for as long as may be required and are scientific users. Period analyses on VSS vary, even on a small scale, so the observa- required to round the estimated magnitude programme stars UU Aur, U Boo, RX Boo, tion will require amendment if that is to a tenth of a magnitude. ST Cam, W Cyg, VY UMa have appeared possible. Otherwise the work of the in the BAA Journal. observer will be inappropriate to use in It is very useful to have access to a star further analysis or research. chart or software to print large areas of sky Pogson devised an alternative method Records, errors and with bright stars that are then used in of light estimation that in principle reporting conjunction with a variable star chart. The requires only one comparison, yet it is charts include the right ascension and always good practice to use another or a declination of the variable, and a guide to third. The variable is compared with A typical observational record with the scale of the chart, usually either 18°, 9°, brighter and fainter comparisons but with deduced magnitudes using differing 3° or 1° size plots. In order to assist in one at a time. By checking the magnitude methods is shown below (Figure 11). finding objects the chart has an arrowed difference of the comparisons shown on Often there is no point in reducing the marker to the north-south axis. the chart the observer has to judge a observation to a final magnitude whilst out One of the first steps is to hold the chart so difference of tenths of a magnitude. The observing, since this may be done indoors. that its north-south marker is approximately number of tenths fainter than A and If there are any other items that may have aligned with the north pole star, to appreciate brighter than C are estimated. Say the affected the observation like a nearby the chart’s orientation. How large or small variable looks 0.2 fainter than A and 0.3 Moon, haze/thin cloud or bad sky things appear on the sky, the scale, is not easy brighter than C, then the observation is pollution then a note should be added after to grasp at first. A degree of arc, about twice the lunar size, is shown as a bar on the chart so it may be compared with the observed field size. A typical 10×50 binocular field of view is 5° across the diameter, so ten Moons will fit in the circle. Finding an object for the first time may take some effort but it is essential to identify it with certainty so it is worthwhile cross-checking, going back and forth between the chart and sky.

Estimating brightness – the basic methods

The variable is compared in brightness with usually at least two of the (fixed brightness) comparison stars, one brighter and the other a little fainter than the variable. Glance from Figure 10. BAAVSS light curve for CH Cygni, 1968 to 2000. 352 J. Br. Astron. Assoc. 114, 6, 2004 Taylor: Observing variable stars with binoculars about worth recording, possibly due to being pressured by cloud, light pollution, a nearby Moon or bright planet. Class 2 is obviously in between. Errors are many but a biased estimate is a common one: this is the effect of recalling the last observation of the same star and possibly making a similar light estimate. A very useful guide to observational errors in variable star observing is seen in Variable Stars, Webb Society Handbook vol. 8 by J. E. Isles. Overall advice to guard against errors is to be systematic and consistent in the making of light estimates. Reporting to the VSS is done either on paper reports on a 6-monthly basis or by electronic means to the Computer Secretary on a more regular timescale. The VSS web Figure 11. A record/log of binocular variable observations with deduced magnitudes pages at http://www.britastro. org/vss give (Melvyn Taylor). observers assistance and advice in many areas of variable star observing. the instrument code. Class of an observa- made under the best observing conditions tion refers to the quality an observer gives for your site and that it seemed a reliable Address: 17 Cross Lane, Wakefield, West Yorkshire to it at the time. A Class 1 suggests it was estimate. A Class 3 means it was just WF2 8DA. [melvyn.taylor @breathemail.net]

Centenaries for 2005 by Barry Hetherington

705 An appulse of Mars and 1 Librae seen from 1805 Alexander Aubert died; China. built a private observatory at 805 Albumazar born, an Arabian astronomer, Loampit Hill, near Deptford. author of a book on the stars. Joseph Bernard, Marquis de 1005 Abe Seimei died, a Japanese astronomer Chabert died; a French admi- and philosopher. ral, astronomer and geographer. 1205 Two full moons were seen in the daytime, Francesco di Vico born; an Ital- recorded at Worcester. ian Jesuit astronomer; director of the Observatory of the η 1305 An occultation of Virginis by Jupiter on Collegio Romano; discovered 6 10 June, seen from China. comets 1605 Ismael Bouillaud born, wrote on astronomy. Felice Fontana died; an Italian Martin van den Hove Hortensius born, a naturalist who introduced the Dutch astronomer, measured the diameter employment of spiders’ webs of the planets and stars. Founded in 1705: Berlin Observatory for telescope positioning. Pontus de Tyard died, a French poet who wrote on as- Friedrich, Graf von Hahn died; a German amateur astrono- tronomy. mer who built the Remplin Observatory. 1705 Jacob Bernoulli died; a Swiss mathematician and astrono- William Rowan Hamilton born; an Irish astronomer; As- mer; stated that comets were not meteors but stars having tronomer Royal for Ireland; wrote on optics. regular orbits. Manuel John Johnson born; a British astronomer who was Georg Christoph Eimmart died; a German astronomer; in charge of the East India Company Observatory at St. founded an observatory within the walls of Nuremberg Helena. castle and made a map of the moon. Johann Lamont born; a Scottish-born German astronomer; Valentin Stansel died; a Moravian astronomer; observed compiled a star catalogue containing upwards of 35,000 comets and wrote on astronomy. stars. The Royal Observatory, Berlin, founded. Edward Sang born; a Scottish mathematician; compiled loga- A new observatory for Oxford University erected at Stable rithmic astronomical tables. Hall, in New College Lane. Sears Cook Walker born; an American astronomer; made a Treatise of Cometary Astronomy by Edmund Halley in large collection of observations of moon-culminations and which he calculated 24 cometary orbits and predicted the occultations. return of a comet. The Dorpat observatory founded by Johann Pfaff.

J. Br. Astron. Assoc. 114, 6, 2004 353 Hetherington: Centenaries for 2005 1905 Ernst Karl Abbe died; a German physicist and optical Albert Edward Whitford born; an American astrophysicist; worker; director of the Astronomical and Meteorological director of Washburn Observatory. Observatory at Jena. Rupert Wildt born; a German astronomer who studied the Carl David Anderson born; an American physicist who spectra of the sun and planets. studied cosmic and gamma rays. Walter F. Wislicenus died; worked at Strassburg Univer- Juan A. Bussolini born; director of the Observatorio de sity Observatory; founded the Astronomische Fisica Cosmica de San Miguel. Jahresbericht. Edward Crossley died; an English astronomer; made ob- Charles Tyson Yerkes died; an American millionaire; fi- servations of occultations and double stars; presented a 3- nanced the Yerkes Observatory with the largest refractor foot telescope to the Lick Observatory. in the world. Ralph Copeland died; an English astronomer; appointed Jupiter VII (Elara) discovered by Charles Dillon Perrine. Astronomer Royal for Scotland; observed and computed Themis, a satellite of Saturn, discovered by William Henry the orbits of comets and made spectroscopic observations. Pickering. but not seen since. William Stephen Finsen born; a South African astronomer; The Dominion Observatory, Ottawa, Canada, founded. director of the Republic Observatory, Johannesburg; ob- served double stars. Edwin Brant Frost appointed Director of Yerkes Observatory. Francois Jacques Philippe Folie died; director of the Royal Observatory of Brussels; worked on the rotation of the Frank Schlesinger appointed Director of Allegheny observa- Earth. tory. Vladimír Guth born; a Czech astronomer; worked at the W. J. Hussey appointed Director of the Detroit Observatory. Ondrejov Observatory, and later at Skalnaté Pleso; studied Herbert R. Morgan appointed Director of the Morrison meteorites. Observatory of Pritchett College, Glasgow, Missouri. Paul Pierre Henry died; a The observatory built by Henry Draper in 1860 was de- French astronomer and stroyed by fire. builder of telescopes; The 6-inch reversible transit circle completed for the Cape worked in the field of Observatory. astrophotography. Albert Einstein formulated his special theory of relativity. Helen Battles Hogg− Priestley born; an Ameri- can astronomer who re- Barry Hetherington, 22 George Street, Darlington. DL1 5DW searched on globular clus- ters. Gerald Kuiper: Born in 1905 Karl Guthe Jansky born; an American radio-physicist; made the first detection of extra- terrestrial radio emission. Otto Kippes born; a German pastor and amateur astrono- mer; studied the asteroids. Gerard Peter Kuiper born; director of the Yerkes and McDonald Observatories; discovered the fifth satellite of Uranus, Miranda, in 1948. György Kulin born; worked at the Konkoly Observatory; director of the Urania Observatory in Budapest; discov- ered and observed asteroids. Roderick Oliver Redman born; an English astronomer who worked on stellar spectroscopy and solar physics. John Hedley Robinson born in Bristol; an English ama- teur astronomer who studied variable stars, the Moon and planets. Vladimir Grigorevich Shaposhnikov born; worked at the Simeis Observatory; an expert in astrometry. Otto Wilhelm Struve died; director of Pulkovo Observatory. Keishin Suzuki born; professor of astronomy at Tokyo Gakugei University; an expert on practical astronomy. Pietro Tacchini died; director of the Modena Observatory; made drawings of sunspots; founded the Memorie della Società degli Spettroscopisti. Albrecht Unsöld born; Director of the Institute for Theo- retical Physics at the Christian Albrecht University at Kiel; studied the spectra of stellar atmospheres. Jules Verne died; a French writer of science fiction; wrote From the Earth to the Moon. Sergei Konstantinovich Vsekhsvyatskij born; a researcher on comets, the sun and solar activity.

354 J. Br. Astron. Assoc. 114, 6, 2004