Astronomical Coordinate Systems

Appendix 1

A basic requirement for studying the heavens is being able to determine where in the sky things are located. To specify sky positions, astronomers have developed several coordinate systems. Each system uses a coordinate grid projected on the celestial sphere, which is similar to the geographic coordinate system used on the surface of the Earth. The coordinate systems differ only in their choice of the fundamental plane, which divides the sky into two equal hemispheres along a great circle (the fundamental plane of the geographic system is the Earth’s equator). Each coordinate system is named for its choice of fundamental plane.

The Equatorial Coordinate System

The equatorial coordinate system is probably the most widely used celestial coordinate system. It is also the most closely related to the geographic coordinate system because they use the same fundamental plane and poles. The projection of the Earth’s equator onto the celestial sphere is called the celestial equator. Similarly, projecting the geographic poles onto the celestial sphere defines the north and south celestial poles. However, there is an important difference between the equatorial and geographic coordinate systems: the geographic system is fixed to the Earth and rotates as the Earth does. The Equatorial system is fixed to the stars, so it appears to rotate across the sky with the stars, but it’s really the Earth rotating under the fixed sky. The latitudinal (latitude-like) angle of the equatorial system is called declination (Dec. for short). It measures the angle of an object above or below the celestial equator. The longitudinal angle is called the right ascension (R.A. for short). It measures the angle of an object east of the Vernal Equinox. Unlike longitude, right ascension is usually measured in hours instead of degrees because the apparent rotation of the equatorial coordinate system is closely related to Sidereal Time and Hour Angle. Since a full rotation of the sky takes 24 h to complete, there are (360°/24 h) = 15° in 1 h of right ascension (Fig. A.1).

North Celestial Pole

Ecliptic Autumnal Summer Equinox Solstice Celestial Vernal Equator Equinox

h h 1h 2 3 Winter -10° Solstice -20° Declination Right -30° Ascension

South Celestial Pole

Fig. A.1 The equatorial coordinate system (Image courtesy of the author)

The Galactic Coordinate System

The galactic coordinate system has latitude and longitude lines, similar to what you are familiar with on Earth. In the galactic coordinate system, the Milky Way uses the zero degree latitude line as its fundamental plane. The zero degree longitude line is in the direction of the center of our galaxy. The latitudinal angle is called the galactic latitude, and the longitudinal angle is called the galactic longitude. This coordinate system is useful for studying the galaxy itself. The reference plane of the galactic coordinate system is the disc of our galaxy (i.e. the Milky Way) and the intersection of this plane with the celestial sphere is known as the galactic equator, which is inclined by about 63° to the celestial equator. Galactic latitude, b, is analogous to declination, but measures distance north or south of the galactic equator, attaining +90° at the north galactic pole (NGP) and −90° at the south galactic pole (SGP). Galactic longitude, l, is analogous to right ascension and is measured along the galactic equator in the same direction as right ascension. The zero-point of galactic longitude is in the direction of the Galactic Center (GC), in the constellation of Sagittarius; it is defined precisely by taking the galactic longitude of the north celestial pole to be exactly 123° (Fig. A.2). Appendix 1 315

90° Galactic latitude b :Galactic Latitude (b) l :Galactic Longitude Star Centre of our Galaxy b

Plane of Milkyway Sun Galactic 180° Galaxy l longitude (l)

Sense of rotation 90° of Galaxy

Fig. A.2 The galactic coordinate system (Image courtesy of the author) Appendix 2

Magnitudes

The first thing that strikes even a casual observer is that the stars have different brightness – some are faint, some are bright, and a few are very bright. This brightness is called the magnitude of a star. The origins of this brightness system are historical. All the stars seen with the naked eye were classified into one of six magnitudes, with the brightest being called a “star of the first magnitude” and the faintest a “star of the sixth magnitude”. Since then the magnitude scale has been extended to include negative numbers for the brightest stars, decimal numbers used between magnitudes and a more precise measurement of the visual brightness of the stars. For instance, Sirius has a magnitude of −1.44, while Regulus has a magnitude of +1.36. Magnitude is usually abbreviated to m. Note that the brighter the star, the smaller the numerical value of its magnitude. A difference between two objects of 1 magnitude means that the object is about 2.512 times brighter (or fainter) than the other. Thus, a first-magnitude object (m = 1) is 2.512 times brighter than a second-magnitude object (m = 2). This definition means that a first-magnitude star is brighter than a sixth-magnitude star by the factor 2.512 to the power of 5. That is a hundredfold difference in brightness. The naked-eye limit of what you can see is about magnitude 6 in urban or suburban skies. Good observers report seeing stars as faint as magnitude 8 under exceptional conditions and loca- tions. The magnitude brightness scale does not tell us whether a star is bright because it is close to us or whether a star is faint because of its size or distance away. This classification only tells us the apparent magnitude of the object – that is, the brightness of an object as observed visually with the naked eye or with a telescope. A more precise definition is the absolute magnitude, M, of an object. This is defined as the brightness an object would have at a distance of 10 parsecs from us. It is an arbitrary distance deriving from the technique of distance determination known as parallax; nevertheless, it does quantify the brightness of objects in a more rigorous way. For example, Rigel has as an absolute magnitude of −6.7, and one of the faintest stars known, Van Biesbroeck’s star, has a value of +18.6. Of course, the explanations above assume that we are looking at objects in the visible part of the spectrum. There are several further definitions of magnitude that rely on the brightness of an object when observed at a different wavelength, or waveband, the most common being the U, B and V wavebands, corresponding to the wavelengths 350, 410 and 550 nanometers, respectively. There is

also a magnitude system based on photographic plates: the photographic magnitude, mpg, and the photovisual magnitude, mpv. Finally, there is the bolometric magnitude, mbol, which is the measure of all the radiation emitted from the object.1 Objects such as nebulae and galaxies are extended objects, meaning that they cover an appreciable part of the sky: in some cases a few degrees, in others only a few arcminutes. The light from, say, a galaxy is therefore “spread out” and thus the quoted magnitude will be the magnitude of the galaxy were it the “size” of a star; this magnitude is often termed the combined or integrated magnitude. This can cause confusion because a nebula with, say, a magnitude of 8, will appear fainter than an 8th-magnitude star, and in some cases, where possible, the surface brightness of an object will be given. This will give a better idea of what the overall magnitude of the object will be. Finally, many popular astronomy books will tell you that the faintest, or limiting magnitude, for the naked eye is around the 6th magnitude. This may be true for people who live in an urban location. But magnitudes as faint as 8 can be seen from exceptionally dark sites with a complete absence of light pollution. This will come as a surprise to many amateurs. Furthermore, when eyes are fully dark-adapted, the technique of averted vision will allow you to see with the naked eye up to three magnitudes fainter! Before you rush outside to test these claims, remember that to see really faint objects, either with the naked eye, or telescopically, several other factors such as the transparency and seeing conditions, as well as the psychological condition of the observer will need to be taken into consideration. Light pollution is the greatest evil here.

1 It is interesting to reflect that all magnitudes are in fact not a true representation of the brightness of an object, because every object will be dimmed by the presence of interstellar dust. All magnitude determinations therefore have to be corrected for the presence of dust lying between us and the object. It is dust that stops us from observing the center of our Galaxy. Appendix 3

Stellar Classification

For historical reasons, a star’s classification is designated by a capital letter in order of decreasing temperature:

O B A F G K M L R N S

The sequence goes from hot blue star types O and A to cool red stars K, M and L. In addition, there are rare and hot stars called Wolf–Rayet stars, class WC and WN, exploding stars Q, and peculiar stars P. The star types R, N and S, actually overlap class M, and so R and N have been reclassified as C type stars – the C standing for carbon stars. A new class has recently been introduced: the L class.2 Furthermore, the spectral types themselves are divided into ten spectral classes from 0 to 9. A class A1 star is thus hotter than a class A8 star, which in turn is hotter than a class F0 star. Other prefixes and suffixes represent additional features of stars:

emission lines e (also called f in some O type stars) metallic lines m peculiar spectrum p a variable spectrum v a star with a blue or red shift in the line q (for example P-Cygni stars)

For historical reasons, the spectra of the hotter star types O, A and B are sometimes referred to as early-type stars, while the cooler ones, K, M, L, C and S, are late-type. F and G stars are interme- diate-type stars.

2 These are stars with very low temperatures – 1900–1500 K. Astronomers believe these are brown dwarves.

Light Filters

One of the most useful accessories an amateur can possess is one of the ubiquitous optical filters. They were previously only accessible to professional astronomers. They are useful, but they still have limitations. Some of the advertisements in astronomy magazines show how they will make hitherto faint and indistinct objects sometimes burst into vivid observability. What the manufacturers do not mention is that regardless of the filter used, you will still need dark and transparent skies for the use of the filter to be worthwhile. Don’t make the mistake of thinking that using a filter from an urban location will always make objects become clearer. The first and most immediately apparent item on the downside is that in all cases, the use of a filter reduces the total amount of light that reaches the eye and often quite substantially. However, the filter helps observability by selecting specific wavelengths of light emitted by an object that may be swamped by other wavelengths. It does this by suppressing the unwanted wavelengths. This is particularly effective when observing extended objects, such as emission nebulae and planetary nebulae. For emission nebulae, use a filter that transmits light around the wavelength of 653.2 nm, which is the spectral line of hydrogen alpha (Hα) and the wavelength of light responsible for the spectacular red color seen in photographs of emission nebulae. Some filters may transmit light through perhaps two wavebands: 486 nm for hydrogen beta3 (Hβ) and 500.7 nm for oxygen-3 [OIII], two spectral lines which are very characteristic in planetary nebula. Use of such filters will enhance the faint and deli- cate structure within nebulae, and, from a dark site, they really do bring out previously invisible detail. Don’t forget (as the advertisers sometimes seem to) that “nebula” filters do not usually transmit the light from stars. Thus, the background will be dark with only nebulosity visible which makes them impractical for observing stars, star clusters and galaxies unless they are associated with nebulosity as can often be the case.

3 This filter can be used to view dark nebulae that are overwhelmed by the proximity of emission nebulae. A case in point is the Horsehead Nebula, which is incredibly faint, and swamped by light from the surrounded emission nebulosity.

One kind of filter that helps in heavily light-polluted areas is the LPR (light pollution reduction filter), which effectively blocks out the light emitted from sodium and mercury street lamps, at wavelengths 366, 404.6, 435.8, 546.1, 589.0 and 589.5 nm. The filter will only be effective if the light from the object you want to see is significantly different from the light-polluting source. Light pollution reduction filters can be very effective visually and photographically, but remember that there is always some overall reduction in brightness of the object you are observing. Whatever filters you decide on, it is worthwhile trying to use them before you make a purchase, especially because they can be expensive. Try borrowing them either from a fellow amateur or from a local astronomical society. You can then see whether the filter really makes any difference to your observing. There is no doubt that modern filters can be an excellent purchase, but it may be that your location or other factors will prevent the filter from realizing its full potential or value for money. Most com- mercially available filters are made for use at a telescope and not for binoculars, so unless you are mechanically minded and can make your own filter mounts (and are happy to pay – two LPR filters could easily cost more than the binoculars), it’s likely that only those observers with telescopes can benefit. Appendix 5

Star Clusters

Open or galactic clusters, as they are sometimes called, are collections of young stars, containing anything from a dozen members to hundreds. A few of them, such as Messier 11 in Scutum, contain an impressive number of stars, equaling that of globular clusters (Fig. A.3.). Other, smaller groups appear little more than a faint grouping set against the background star field. Such is the variety of open clusters that they come in all shapes and sizes. Several are over a degree in size and their full impact can only be appreciated by using binoculars, as a telescope has too narrow a field of view. An example of such a large cluster is Messier 44 in Cancer. There are also tiny clusters, seemingly noth- ing more than compact multiple stars, as is the case with IC 4996 in Cygnus. In some cases, all the members of the cluster are equally bright, such as Caldwell 71 in Puppis, but there are others that consist of only a few bright members accompanied by several fainter companions, as is the case of Messier 29 in Cygnus. The stars which make up an open cluster are called Population I stars, which are metal-rich4 and are usually found in or near the spiral arms of the galaxy. The reason for the varied and disparate appearances of open clusters is the circumstances of their births. It is the interstellar material out of which stars form that determines both the number and type of stars that are born within it. Factors such as the size, density, turbulence, temperature, and mag- netic field all play a role as the deciding parameters in star birth. In the case of giant molecular clouds, or GMCs, the conditions can give rise to both O- and B-type giant stars along with solar-type dwarf stars. In small molecular clouds (SMCs) only solar-type stars will be formed, with none of the luminous B-type stars. An example of a SMC is the Taurus Dark Cloud, which lies just beyond the Pleiades. An interesting aspect of open clusters is their distribution in the night sky. Surveys show that although well over a thousand clusters have been discovered, only a few are observed to be at distances greater than 25° above or below the galactic equator. Some parts of the sky are very rich in clusters – Cassiopeia, and Puppis – and this is due to the absence of dust lying along these lines of sight, allowing us to see across the spiral plane of our galaxy. Many of the clusters mentioned here actually lie in different spiral arms and as you observe them, you are actually looking at different parts of the spiral structure of our galaxy.

4 Astronomers call every element other than hydrogen and helium, metals.

An open cluster presents a perfect opportunity for observing star colors (see Appendix 7: Star Colors). Many clusters, such as the ever and rightly popular Pleiades, are all a lovely steely blue color. On the other hand, Caldwell 10 in Cassiopeia has contrasting bluish stars along with a nice orange star. Other clusters have a solitary yellowish or ruddy orange star along with fainter white ones, such as Messier 6 in Scorpius. An often striking characteristic of open clusters is the apparent chains of stars that are seen. Many clusters have stars that arc across apparently empty voids, as in Messier 41 in Canis Major. Another word for a very small, loose group of stars is an asterism. In some cases, there may only be 5–6 stars within the group. The previous section on open clusters dealt with groups of stars that were usually young, have an appreciable angular size and may have a few hundred components. Globular clusters are clusters that are very old, compact and may contain up to a million stars, and in some cases even more. The stars that make up a globular cluster are called Population II stars. These are metal-poor stars and are usually found in a spherical distribution around the galactic center at a radius of about 200 light years. Furthermore, the number of globular clusters increases significantly the closer one gets to the galactic center. This means that particular constellations that are located in a direction towards the Galactic bulge have a high concentration of globular clusters within them, such as Sagittarius, and Scorpius. The origin and evolution of a globular cluster is very different from that of an open or galactic cluster. All the stars in a globular cluster are very old, so any star earlier than a G or F type star has already left the main sequence and is moving toward the red giant stage of its life. In fact, new star formation no longer takes place within any globular clusters in our galaxy, and they are believed to be the oldest structures in our galaxy. The youngest of the globular clusters is still far older than the oldest open cluster. The origin of the globular clusters is a scene of fierce debate and research with the current models predicting that the globular clusters may have been formed within the proto-galaxy clouds that eventually made up our galaxy. There are about 150 globular clusters ranging in size from 60 to 150 light years in diameter. They all lie at vast distances from the Sun and are about 60,000 light years from the galactic plane. The nearest globular clusters, for example, Caldwell 86 in Ara, lie at a distance of over 6000 light years, and thus the clusters are difficult objects for small telescopes. Appendix 6

Double Stars

Double stars are stars that look like a single star, but will resolve into two stars using either binoculars or a telescope. Many stars may appear as double due to them lying in the same line of sight as seen from the Earth, and this can only be determined by measuring the spectra of the stars and calculating their red (or blue) shifts. Such stars are called optical doubles. It may well be that the two stars are separated in space by a vast distance. Some, however, are actually gravitationally bound and may orbit around each other over a period of days or even years. Many double stars cannot be resolved by even the largest telescopes, and these are called spectro- scopic binaries, the double component only being fully understood when the spectra are analyzed. Eclipsing binaries, such as Algol (β Persei), are where one star moves in front of its companion during orbit, thus brightening and dimming the light observed. A third type is astrometric binaries, such as Sirius (α Canis Majoris), where the companion star may only be detected by its influence on the motion of the primary star. The brighter of the two stars is usually called the primary star, whilst the fainter is called the secondary or companion. This terminology is employed regardless of how massive either star is, or whether the brighter is in fact the less luminous of the two in reality, but just appears brighter as it may be closer. Perhaps the most important terms used in double star work are the separation and position angle (PA). The separation is the angular distance between the two stars, usually in seconds of arc, and measured from the brightest star to the faintest. The position angle is the relative position of one star, usually the secondary, with respect to the primary, and is measured in degrees, with 0° at due north, 90° at due east, 180° due south, 270° at due west, and back to 0°. This is shown in Fig. A.3. with the double star γ Virginis, which has components of magnitude 3.5 and 3.5, a separation of 1.8″ (arcsec- onds) and a PA of 267° (epoch 2000.0). Note that the secondary star is the one always placed some- where on the orbit, while the primary star is at the center of the perpendicular lines. The separation and PA of any double star are constantly changing, and should be quoted for the year observed. When the period is very long, some stars will have no appreciable change in PA for several years; others, however, will change from year-to-year.

2070

2100

2040 2120 2030 0º

2140 2020

2015 2160 2010 90º

270º 2000 180º 2005

Fig. A.3 The motion of γ Virginis (Image courtesy of the author) Appendix 7

Star Colors

The most important factor that determines the color of a star is you: the observer! It is purely a matter of both physiological and psychological influences. What one observer describes as a blue star, another may describe as a white star or one may see an orange star, whilst another observes the same star as being yellow. It may even be that you will observe a star to have different color when using different telescopes or magnifications, and atmospheric conditions will also have a role to play. The important thing to remember is that you should record the color you observe.5 It may seem to a casual observer that the stars do not possess many bright colors, and only the brightest stars show any perceptible color. Betelgeuse can be seen to be red, and Capella, yellow, whilst Vega is blue, and Aldebaran has an orange tint, but beyond that, most stars seem to be an overall white. To the naked eye, this is certainly the case, and it is only with some kind of optical equipment that the full range of star color becomes apparent. However, what is meant by the color of a star? A scientific description of a star’s color is one that is based on the stellar classification, which depends upon the chemical composition and temperature of a star. In addition, a term commonly used by astronomers is the color index. This is determined by observing a star through two filters, the B and the V filters, which correspond to wavelengths of 440 nm and 550 nm respectively, and measure a star’s brightness. Subtracting the two values obtained gives B – V, the color index. Usually, a blue star will have a color index that is negative, i.e., −0.3. Orange-red stars could have a value greater than 0.0, and upwards to about 3.00 and greater for very red stars (M6 and greater). But as this is an observationally based book, the scientific description will not generally apply. As mentioned above, red, yellow, orange and blue stars are fairly common, but are there stars which have, say, a purple tint, or blue, or violet, crimson, lemon, and the ever-elusive green color? The answer is yes, but it depends on how you describe the color. A glance at the astronomy books from the last century and beginning of the twentieth century will show you that star color was a hot topic, and descriptions such as Amethyst (purple), Cinereous(wood-ash tint), Jacinth (pellucid orange), and Smalt (deep blue), to name but a few, were used frequently. Indeed, the British

5 An interesting experiment is to observe a colored star first through one eye, and then the other. You may be surprised by the result!

Astronomical Association even had a section devoted to star colors. But today, observing and cataloguing star color is just a pleasant past-time. Nevertheless, under good seeing conditions, with a dark sky, the keen-eyed observer will be able to see the faint, tinted colors from deepest red to steely blue and all the colors in between. It is worth noting that several distinctly colored stars occur as part of a double star system. The reason for this may be that although the color is difficult to see in an individual star, it may appear more intense when seen together with a contrasting color. Thus, when I discuss double and triple stars, there are descriptions of many beautifully colored systems. For instance, in the following double star systems, the fainter of the two stars in η Cassiopeia has a distinct purple tint; whilst in γ Andromadae and α Herculis, the fainter stars are most definitely green. Appendix 8

Books, Magazines and Astronomical Organizations

I have selected a few of the many fine astronomy and astrophysics books in print. You do not have to buy, or even read them all, but I recommend checking at your local library to see if they have some of them.

Star Atlases and Observing Guides

Norton’s Star Atlas & Reference Handbook, I. Ridpath (Ed.), Longmans, 1999, Harlow, UK. Sky Atlas 2000.0, W. Tirion, R. Sinnott, Sky Publishing & Cambridge, University Press, 1999 Massachusetts, USA. Millennium Star Atlas, R. Sinnott, M. Perryman, Sky Publishing, 1999, Massachusetts, USA. Uranometria 2000.0 Volumes 1 & 2, Wil Tirion (Ed), Willmann-Bell; Virginia, 2001, USA. Observing Handbook and Catalogue of Deep-Sky Objects, C. Luginbuhl, B. Skiff, Cambridge University press, 1990, Cambridge, USA. Observer’s Guide To Star Clusters, M. D. Inglis, Springer, 2013. Deep-Sky Companions: The Messier Objects, S. O’Meara, Cambridge University Press, 1999 Cambbridge UK. Observing the Caldwell Objects, D. Ratledge, Springer-Verlag, 2000, London, UK. Burnham’s Celestial Handbook, R. Burnham, Dover Books, 1978, New York, USA. Amateur Astronomer’s Handbook, J. Sidgwick, Pelham Books, 1979, LONDON, UK.

Astronomy and Astrophysics Books

Field Guide to the Deep Sky Objects, M. D. Inglis, Springer, London, 2012. Astrophysics Is Easy, M. D. Inglis, Springer, 2015 The Milky Way, Bart & Priscilla Bok, Harvard Science Books, Massachusetts, 1981 Voyages Through The Universe, A. Fraknoi, D. Morrison, S. Wolff, Saunders College Publishing, 2000, Philadelphia, USA

Introductory Astronomy & Astrophysics, M. Zeilik, S. Gregory, E. Smith, Saunders College Publishing, 1999, Philadelphia, USA Galaxies and Galactic Structure, D. Elmegreen, Prentice Hall, 1998, NEW JERSY Stars, J. B. Kaler, Scientific American Library, 1998, New York, USA Stars, Nebulae and the Interstellar Medium, C. Kitchin, Adam Hilger, 1987, Bristol, UK

Magazines

Astronomy Now UK Sky & Telescope USA New Scientist UK Scientific American USA Science USA Nature UK

The first three magazines listed are aimed at a general audience and the last three are intended for the well-informed lay person. In addition, there are many research level journals that can be found in university libraries and observatories.

Organizations

The Federation of Astronomical Societies. http://fedastro.org.uk/fas/ Society for Popular Astronomy http://popastro.com The American Association of Amateur Astronomers http://astromax.com The Astronomical League http://www.astroleague.org/ The British Astronomical Association https://britastro.org The Royal Astronomical Society https://www.ras.org.uk The Webb Society http://webbdeepsky.com International Dark-Sky Association http://www.darksky.org/ Campaign for Dark Skies http://www.britastro.org/dark-skies/ Appendix 9

The Greek Alphabet

The following is a quick reference guide to the Greek letters, used in the Bayer classification system. Each entry shows the uppercase letter, the lowercase letter, and the pronunciation.

Α α Alpha Η η Eta Ν ν Nu Τ τ Tau Β β Beta Θ θ Theta Ξ ξ Xi Υ υ Upsilon Γ γ Gamma Ι ι Iota Ο ο Omicron Φ ϕ Phi Δ δ Delta Κ κ Kappa Π π Pi Χ χ Chi Ε ε Epsilon Λ λ Lambda Ρ ρ Rho Ψ ψ Psi Ζ ζ Zeta Μ μ Mu Σ σ Sigma Ω ω Omega

Astrophotography Web Sites

Matt BenDaniel – http://starmatt.com/ Mario Cogo – www.intersoft.it/galaxlux Bernhard Hubl – http://astrophoton.com Dr. Jens Lüdeman – http://www.ias-observatory.org/IAS/index-english.htm Axel Mellinger – http://home.arcor-online.de/axel.mellinger/ Thor Olson – http://home.att.net/~nightscapes/photos/MilkyWayPanoramas/ Harald Straus (Astronomischer Arbeitskreis Salzkammergut) – http://www.astronomie.at/ Chuck Vaughn – http://www.aa6g.org/Astronomy/astrophotos.html http://www.seds.org/~spider/ngc/ngc.html

0-9, and Symbols 56 Persei, 227, 247 1 Camelopardalis, 183, 189 59 Serpentis, 52, 60 3 C84, 233 61 Cygni, 114, 136 4 Vulpeculae, 100 95 Herculis, 81, 83 5 Serpentis, 52 118 Tauri, 270, 281 5 Vulpeculae, 100 ΟΣ 147, 250, 269 7 Vulpeculae, 100, 102 ΟΣ 390, 111, 136 8 Lacertae, 145 ΟΣ 437, 111, 136 9 Sagittarii, 29 ΟΣ 440, 156, 175 11 Aquilae, 68, 81 Σ (Struve) 268, 225, 247 14 Aurigae, 250, 269 Σ (Struve) 270, 225, 247 15 Geminorum, 281, 292 Σ (Struve) 304, 225 16 Aurigae, 258 Σ (Struve) 336, 225, 247 16 Cygni A, 114, 136 Σ (Struve) 369, 225, 247 16 Cygni B, 114, 136 Σ (Struve) 390, 89, 183, 189 17 Aurigae, 258 Σ (Struve) 392, 225, 247 17 Cygni, 111, 136 Σ (Struve) 485, 183 18 Aurigae, 258 Σ (Struve) 550, 183 20 Geminorum, 281, 292 Σ (Struve) 559, 270, 281 20 Vulpeculae, 104 Σ (Struve) 572, 270, 281 21 Sagittarii, 12, 51 Σ (Struve) 698, 250, 269 23 Aquilae, 81 Σ (Struve) 928, 250 27 Cygni, 114 Σ (Struve) 929, 250, 269 29 Persei, 219 Σ (Struve) 1108, 283, 292 34 Persei, 219 Σ (Struve) 2303, 52, 60 38 Geminorum, 283, 292 Σ (Struve) 2306, 61, 67 39 Cygni, 116 Σ (Struve) 2325, 63 41 Tauri, 270 Σ (Struve) 2373, 61, 67 46 Persei, 229 Σ (Struve) 2404, 68, 81 49 Cygni, 111, 136 Σ (Struve) 2445, 100, 110 52 Cassiopeiae, 197 Σ (Struve) 2470, 137, 144 52 Cygni, 127 Σ (Struve) 2474, 137, 144 53 Arietis, 250, 306 Σ (Struve) 2576, 111 54 Sagittarii, 13, 51 Σ (Struve) 2587, 70, 81

Σ (Struve) 2634, 83 Beta (β) 246, 32 Σ (Struve) 2922, 145, 152 Beta (β) Aquilae, 68 Σ (Struve) 2942, 145 Beta (β) Aurigae, 250, 269 Beta (β) Cassiopeiae, 61 Beta (β) Cephei, 156, 175 A Beta (β) Cygni, 102 Abell 84, 203, 218 Beta (β) Delphini, 93, 100 Abell 426, 232 Beta (β) Lyrae, 137, 144 AC (Alvin Clark) 11, 52, 60 Beta (β) Persei, 227, 247 AE Aurigae, 250, 261, 269, 306 Beta (β) Scuti, 61, 63 Albireo, 102, 111, 114, 136, 225, 281 Betelgeuse, 295, 312 Aldebaran, 270, 273, 281 BL Lacertae, 149, 152 Algol, 83, 183, 227, 228, 231, 247, 250 Black Pillar, 55 Alpha (α) Aquilae, 68, 81 Blinking Planetary, 118, 136 Alpha (α) Aurigae, 251, 269 Blue Flash Nebula, 95, 100 Alpha (α) Cassiopeiae, 206, 217 Blue Snowball, 177, 182 Alpha (α) Cygni, 114, 136 Brocchi’s Cluster, 100, 110 Alpha (α) Orionis, 295, 312 BU Geminorum, 281, 292 Alpha (α) Persei, 183, 219 Bubble Nebula, 199 Alpha (α) Persei Stream, 247 Burnham (β) 441, 100, 110 Alpha (α) Scuti, 63 Burnham 677, 111, 136 Alpha (α) Tauri, 270, 281 Andromeda, 125, 150, 175–184, 207, 233 Andromeda galaxy, 4, 201 C AQ Sagittarii, 12, 51 Caldwell 2, 159, 175 Aquila, 68–82, 207, 308 Caldwell 10, 196, 218 Auriga, 247–270, 278, 308 Caldwell 11, 199, 218 Aurigae 19, 258 Caldwell 13, 195, 218 Caldwell 14, 223 Caldwell 15, 118 B Caldwell 16, 145, 152 Barnard 1, 232 Caldwell 17, 201, 218 Barnard 2, 232 Caldwell 18, 201, 218 Barnard 33, 301, 305, 312 Caldwell 19, 121 Barnard 86, 13, 38, 51 Caldwell 20, 119 Barnard 87, 36, 51 Caldwell 22, 177, 182 Barnard 90, 40 Caldwell 27, 120 Barnard 92, 15, 38, 51 Caldwell 31, 261 Barnard 103, 64, 67 Caldwell 33, 127 Barnard 110, 64, 67 Caldwell 34, 127 Barnard 111, 64, 67 Caldwell 37, 104, 110 Barnard 112, 64, 67 Caldwell 39, 284, 292 Barnard 119a, 64 Caldwell 57, 44, 51 Barnard 133, 74, 81 California nebula, 227, 229, 247 Barnard 142, 70 Camelopardalis, 1, 150, 183–189, 207, 308 Barnard 143, 70, 81 Campbell’s Hydrogen Star, 119, 136 Barnard 145, 125, 136 Capella, 156, 251 Barnard 168, 121, 133 Cassiopeia, 4, 150, 183, 189–218, 223, 308 Barnard 169, 159, 175 Cepheus, 1, 150, 153–176, 207, 308 Barnard 170, 159 Cepheus OB2, 157 Barnard 171, 159, 175 Chi (χ) Aquilae, 70, 81 Barnard 173, 159, 175 Chi (χ) Cygni, 114, 136 Barnard 174, 159, 175 Chi (χ) Persei, 223 Barnard 289, 36, 51 Clown Face nebula, 284 Barnard 318, 64, 67 Coathanger cluster, 100 Barnard 343, 125, 136 Cocoon Nebula, 121, 133, 136 Barnard 352, 125, 136 Collinder3, 189, 217 Barnard’s Galaxy, 44 Collinder 15, 196, 218 Barnard’s Loop, 301, 306, 311, 312 Collinder 33, 198, 218 Becklin–Neugebauer Object, 297 Collinder 34, 218 Index 337

Collinder 38, 295, 312 Eta (η) Orionis, 293, 312 Collinder 50, 270, 281 Eta (η) Persei, 223, 225, 247 Collinder 62, 252, 258, 269 Eta (η) Sagittarii, 13, 51 Collinder 65, 274, 276, 295 Collinder 69, 295, 309, 312 Collinder 70, 295, 312 F Collinder 73, 295, 312 FG Sagittae, 83, 86, 93 Collinder 77, 283, 292 FG Vulpeculae, 106 Collinder 80, 283, 292 Filamentary Nebula, 127 Collinder 81, 283, 292 Flaming Star Nebula, 250, 261, 269 Collinder 89, 283, 287, 292 Collinder 126, 283, 292 Collinder 144, 284, 292 G Collinder 399, 100, 102, 110 Gamma (γ) Andromedae, 177 Collinder 403, 114, 136 Gamma (γ) Aquilae, 68 Collinder 413, 114, 136 Gamma (γ) Cassiopeiae, 199, 206, 217 Collinder 445, 145, 152 Gamma (γ) Cygni, 111, 116, 121, 130 Crab Nebula, 277, 278 Gamma (γ) Delphini, 93, 100 Crab Pulsar, 278 Gamma (γ) Sagittarii, 8, 12, 16 Crescent Nebula, 120, 136 Garnet Star, 156, 157, 160, 175 CRL 2688, 125, 136 Gemini, 150, 207, 278, 281–293, 308 Cygnus, 2, 4, 12, 52, 63, 111–137, 150, 207, 223, 295, 308 Great Cygnus Loop, 127 Cygnus Star Cloud, 111 Great Rift, 52, 63, 64, 68, 100, 111, 125 Czernik 43, 189 Great Sagittarius Star Cloud, 12, 13, 38 Groombridge 34, 175, 182

D Dawes 5, 293 H Delphinus, 93–100, 150, 207, 308 H1123, 223 Delta (δ) Cephei, 156, 175 Harrington 4, 258, 269 Delta (δ) Cygni, 111, 136 Harrington 9, 95, 99, 100 Delta (δ) Geminorum, 283, 292 Harrington 10, 127, 136 Delta (δ) Orionis, 293, 312 Harrington 11, 157, 175 Delta (δ) Persei, 219 Harvard 20, 89 Delta (δ) Sagittarii, 12 Harvard 21, 189, 217 Delta (δ) Scuti, 61, 67, 250 HD 7902, 195 Delta (δ) Serpentis, 52, 60 Hercules, 81–83, 150, 207 Delta1 (δ1) Lyrae, 137 Herschel 2, 283, 292 Delta2 (δ2) Lyrae, 137 Herschel 6, 284, 292 Demon Star, 227 Herschel 7, 13, 51 Deneb, 68, 111, 114, 119, 125, 127, 136 Herschel 12, 19, 51 Dolidze-Dzimselejsvili 3, 275, 281 Herschel 21, 283, 292 Dolidze-Dzimselejsvili 4, 275, 281 Herschel 25, 223, 247 Double Cluster, 223 Herschel 30, 191, 217 Dumbbell Nebula, 106, 110 Herschel 33, 253, 269 Herschel 35, 193, 217 Herschel 42, 195 E Herschel 45, 195, 218 Eagle Nebula, 55, 60 Herschel 48, 195 Egg Nebula, 125, 136 Herschel 49, 16, 51 Epsilon (ε) Cassiopeiae, 203 Herschel 53, 187 Epsilon (ε) Cygni, 116 Herschel 56, 191, 217 Epsilon (ε) Lyrae, 137 Herschel 60, 223, 247 Epsilon (ε) Persei, 156, 219 Herschel 61, 223, 247, 251, 269 Eskimo Nebula, 187, 284, 292 Herschel 64, 195, 218 Eta (η) Aquilae, 68, 81 Herschel 66, 175, 198, 218 Eta (η) Cassiopeiae, 206, 217 Herschel 68, 258, 269 Eta (η) Cephei, 156 Herschel 69, 177, 182 Eta (η) Cygni, 114, 116 Herschel 78, 191, 217 Eta (η) Lyrae, 137, 144 Herschel 88, 223, 247 338 Index

Herschel 156, 232, 247 Krueger 60, 156, 175 Herschel 200, 16, 51 KW Aurigae, 250 Herschel 258, 232, 247 Herschel 261, 259, 269 Herschel 743, 76, 81 L h (Herschel) 2827, 32 Lacerta, 145–152, 207, 308 h (Herschel) 5003, 12, 51 Lagoon Nebula, 29, 39, 51 HN 119, 12, 51 Lambda (λ) Orionis, 293, 295, 312 Horsehead Nebula, 293, 305, 308, 312 LDN (Lynds) 619, 76 Hourglass Nebula, 29 Little Dumbbell Nebula, 228 h Persei, 223 Little Gem, 42, 51 HR Delphini, 93 Little Star Cloud, 14 Hyades, 156, 270, 281 Local Group, 44, 201 Lynds 906, 136 Lynds 935, 120 I Lynds 1151, 159, 175 IC 59, 199, 218 Lynds 1164, 159, 175 IC 63, 199, 211, 218 Lyra, 76, 137–145, 150, 207, 308 IC 289, 203, 216–218 IC 351, 229, 234, 247 IC 405, 250, 261, 265, 267, 269 M IC 410, 253, 259, 261, 265, 269 Markarian 50, 157, 175 IC 417, 259, 261, 265, 269 Melotte 15, 197, 199, 218 IC 430, 302, 312 Melotte 20, 219, 230, 244, 247 IC 431, 302, 312 Melotte 25, 270, 281 IC 432, 301, 302, 312 Melotte 28, 273, 281 IC 434, 301, 305, 308 Messier 1, 277, 279–281 IC 1283-84, 32 Messier 8, 29, 40, 51 IC 1287, 63, 67 Messier 11, 61, 64, 66, 67 IC 1295, 63, 66, 67 Messier 16, 55–57, 60 IC 1396, 156, 157, 160, 161, 175 Messier 17, 29, 42, 51, 55 IC 1434, 145, 147, 150, 152 Messier 18, 15, 17, 51 IC 1590, 193, 217, 218 Messier 20, 27, 38, 51 IC 1795, 199, 208, 218 Messier 21, 13, 15, 51 IC 1805, 197, 208, 218 Messier 22, 22, 28, 29, 51 IC 1848 Messier 23, 12–14, 20, 51 IC 2003, 229, 234, 247 Messier 24, 14, 16, 51 IC 2149, 262, 263, 268, 269 Messier 25, 12, 15, 18, 51 IC 2157, 283, 292 Messier 26, 61, 63, 66, 67 IC 4703, 55, 56, 60 Messier 27, 105–107, 110 IC 4725, 15, 51 Messier 28, 19, 25, 51 IC 4756, 52, 54, 60 Messier 29, 116, 119, 136 IC 4997, 89, 92, 93 Messier 31, 175, 201 IC 5067/70, 120, 136 Messier 34, 223, 226, 227, 244, 247 IC 5146, 121, 132, 136 Messier 35, 283, 285, 292 IC 5217, 148, 151, 152 Messier 36, 255, 257, 259, 269 Ink Spot, 38, 51 Messier 37, 258, 260, 261, 269 Iota (ι) Orionis, 293, 299, 312 Messier 38, 253, 255, 257, 258, 269 IQ Aurigae, 258 Messier 39, 116, 120, 136 Messier 42, 31, 295, 297, 299, 301, 302, 312 Messier 43, 299, 301, 304, 312 K Messier 52, 189, 192, 193, 217 Kappa (κ) Geminorum, 281 Messier 54, 24, 32, 51 Kemble’s Cascade, 187, 189 Messier 55, 25, 35, 36, 51 King 5, 223, 247 Messier 56, 137, 143, 144 King 10, 157, 175 Messier 57, 142, 144 King 12, 189, 217 Messier 69, 22, 26, 27, 51 King 14, 193, 217 Messier 70, 24, 30, 31, 51 Kleinmann–Low Sources, 297 Messier 71, 89–91, 93 Index 339

Messier 76, 228, 239, 240, 247 NGC 1952, 277, 280, 281 Messier 78, 301, 302, 306, 312 NGC 1960, 255, 257, 269 Messier 103, 196, 202, 205, 218 NGC 1973, 299, 301, 303, 312 Mu (μ) Cephei, 175 NGC 1975, 299 NGC 1976, 297, 301, 312 NGC 1977, 299, 303 N NGC 1980, 299, 312 NGC 40, 159, 169, 170, 175 NGC 1981, 295, 297, 299, 301, 312 NGC 103, 191, 192, 195, 217 NGC 1982, 299, 301, 312 NGC 129, 191, 192, 196, 217 NGC 1999, 299, 304, 312 NGC 133, 189, 217 NGC 2022, 306, 310, 312 NGC 136, 193, 197, 217 NGC 2023, 301, 302, 307, 309, 312 NGC 146, 193, 198, 217 NGC 2024, 301, 302, 305, 312 NGC 147, 201, 212, 214, 218 NGC 2068, 301, 302, 312 NGC 185, 201, 203, 212, 214, 218 NGC 2099, 258, 260, 269 NGC 189, 193, 199, 217 NGC 2126, 258, 262, 263, 269 NGC 433, 195, 218 NGC 2129, 283, 286, 292 NGC 436, 195, 200, 202, 204, 218 NGC 2158, 283, 285, 292 NGC 457, 195, 200, 204, 218 NGC 2168, 283, 292 NGC 581, 196, 202, 218 NGC 2169, 295, 298, 299, 312 NGC 650-51, 228, 247 NGC 2266, 283, 287, 288, 292 NGC 654, 196, 202, 218 NGC 2281, 259, 264, 269 NGC 659, 196, 202, 206, 218 NGC 2304, 283, 292 NGC 663, 196, 202, 218 NGC 2331, 283, 287, 292 NGC 663, 207 NGC 2355, 284, 290, 292 NGC 744, 223, 224, 228, 247 NGC 2392, 284, 291, 292 NGC 869, 223–225, 247 NGC 2395, 284, 289, 290, 292 NGC 884, 223–225, 247 NGC 6440, 16, 19, 20, 38, 43, 51 NGC 891, 125, 233 NGC 6445, 38, 43, 44, 51 NGC 896, 199, 208, 213, 218 NGC 6476, 27, 51 NGC 1023, 232, 233, 243, 244, 247 NGC 6494, 13, 37, 51 NGC 1027, 198, 209, 218 NGC 6514, 27, 51 NGC 1039, 223, 247 NGC 6520, 13, 21, 23, 45, 51 NGC 1220, 223, 229, 230, 247 NGC 6522, 16, 21, 22, 51 NGC 1245, 223, 230, 232, 247 NGC 6523, 29, 39, 51 NGC 1275, 233, 245–247 NGC 6528, 16, 21, 22, 51 NGC 1333, 232, 241, 242, 247 NGC 6530, 29, 39, 51 NGC 1342, 223, 233, 234, 245, 247 NGC 6531, 13, 51 NGC 1491, 232, 242, 247 NGC 6535, 55, 58–60 NGC 1499, 227, 229, 234, 240, 247 NGC 6539, 55, 58, 60 NGC 1501, 186–189 NGC 6544, 19, 23, 51 NGC 1502, 183, 186, 187, 189 NGC 6553, 19, 23, 24, 51 NGC 1513, 223, 235, 237, 247 NGC 6563, 40, 46, 51 NGC 1514, 270, 272, 273, 281 NGC 6565, 40, 45, 51 NGC 1528, 223, 236, 237, 247 NGC 6567, 40, 47, 51 NGC 1545, 223, 237, 238, 247 NGC 6589, 32, 51 NGC 1664, 251, 252, 269 NGC 6590, 17, 32, 47, 51 NGC 1746, 273–275, 281 NGC 6603, 15, 51 NGC 1750, 273, 274 NGC 6611, 55, 60 NGC 1758, 273, 274 NGC 6613, 15, 41, 51 NGC 1778, 251, 253, 254, 269 NGC 6618, 29, 42, 51 NGC 1807, 275–277, 281 NGC 6626, 19, 51 NGC 1817, 275, 276, 278, 281 NGC 6629, 42, 51 NGC 1857, 253–255, 269 NGC 6637, 22, 30, 51 NGC 1883, 252, 253, 256, 269 NGC 6645, 15, 17, 41, 51 NGC 1893, 253, 256, 259, 265, 269 NGC 6656, 22, 51 NGC 1907, 255, 257, 269 NGC 6681, 24, 51 NGC 1912, 253, 257, 269 NGC 6694, 61, 67 NGC 1931, 257, 259, 266, 269 NGC 6705, 61, 67 340 Index

NGC 6709, 70, 72, 81 NGC 7243, 145, 147, 149, 152 NGC 6712, 61, 65–67 NGC 7261, 157, 165, 166, 175 NGC 6715, 24, 30, 51 NGC 7281, 157, 167, 175 NGC 6717, 24, 51 NGC 7354, 159, 171, 172, 175 NGC 6720, 142, 144 NGC 7510, 157, 168, 171, 175 NGC 6723, 25, 34, 51 NGC 7635, 192, 199, 210, 218 NGC 6738, 70, 72, 81 NGC 7640, 177, 180, 182 NGC 6749, 70, 73, 81 NGC 7654, 189, 192, 217 NGC 6751, 74, 77, 81 NGC 7662, 177, 180–182 NGC 6755, 70, 71, 73, 81 NGC 7686, 177–179, 182 NGC 6760, 70, 73, 74, 81 NGC 7789, 191, 192, 194, 217 NGC 6772, 74, 81 NGC 7790, 191, 192, 194, 217 NGC 6773, 70 Norma Spiral Arm, 12, 14 NGC 6778, 76, 81 North America Nebula, 119, 128, 129, 136, 193 NGC 6779, 137, 144 Northern Coalsack, 125, 136 NGC 6781, 76 Nova Delphini 1967, 93 NGC 6790, 76 Nu (ν) Sagittarii, 24 NGC 6791, 137, 141, 142, 144 Nu (ν) Serpentis, 52, 60 NGC 6795, 70, 81 NGC 6802, 102–104, 110 NGC 6803, 76, 81 O NGC 6809, 25, 51 Omega (ω) Aurigae, 250, 269 NGC 6818, 42, 48, 50, 51 Omega Nebula, 29, 41 NGC 6819, 114, 136 Orion, 4, 12, 31, 150, 207, 223, 250, 275, 284, NGC 6820, 102, 105, 110 293–312 NGC 6822, 42, 49–51 Orion Nebula, 31, 295, 297, 312 NGC 6823, 102, 105, 106, 110 Owl Cluster, 195, 218 NGC 6826, 118, 136 Oyster Nebula, 187, 189 NGC 6838, 89, 93 NGC 6842, 106, 109, 110 NGC 6853, 106, 110 P NGC 6871, 114, 136 Palomar 8, 22, 51 NGC 6873, 83, 93 Palomar 9, 24, 33, 51, 74 NGC 6879, 89, 92, 93 Palomar 11, 81 NGC 6882, 104 Parrot Nebula, 36, 51 NGC 6885, 104 Pelican Nebula, 120, 128, 129, 136 NGC 6886, 89, 92, 93 Per OB2, 227 NGC 6888, 120, 130, 131, 136 Perseus, 83, 150, 188, 207, 219–248, 308 NGC 6891, 95–97, 100 Perseus A, 233, 247 NGC 6894, 118, 121, 122, 136 Perseus I Galaxy Cluster, 232 NGC 6905, 95–97, 100 Perseus OB-3, 219 NGC 6913, 116, 136 Perseus Spiral Arm, 195, 223 NGC 6939, 157–159, 175 Phi (φ) Cassiopeiae, 195 NGC 6940, 104, 108, 110 Phi (ϕ) Tauri, 270, 281 NGC 6946, 157, 158, 175 Pi (π) Aquilae, 70, 81 NGC 6960, 127, 136 PK 036-1.1, 74, 81 NGC 6974, 127, 136 PK 64 + 05.1 NGC 6979, 127, 136 PK 80–6.1, 125 NGC 6992, 127, 136 PK 104.7, 161, 175 NGC 7000, 119 PK 112-10.1, 203, 218 NGC 7026, 118, 123, 124, 136 PK 119-6.1, 203, 218 NGC 7027, 118, 123, 124, 136 PK 130 +1.1, 203, 218 NGC 7048, 118, 123, 125, 136 PK 159-15.1, 229, 247 NGC 7092, 116, 136 PK 161-14.1, 229, 247 NGC 7139, 161, 162, 173–175 PK 165-15.1, 270, 281 NGC 7142, 157, 162, 163, 175 PK 166+10.1, 263, 269 NGC 7160, 157, 162, 164, 175 PK 196-10.1, 306, 312 NGC 7209, 145, 152 Psi (ψ) Persei, 219 NGC 7235, 157, 165, 166, 175 Psi5 (φ5) Aurigae, 250, 269 Index 341

R Theta (θ) Serpentis, 52, 60 R Aquilae, 68, 81 Theta1 (θ1) Orionis, 293, 312 R Scuti, 61, 67 Theta1 (θ1) Tauri, 273 Rho (ρ) Orionis, 293, 312 Tombaugh 5, 183, 189 Rho (ρ) Puppis, 61 Trapezium, 293, 296, 297, 312 Ring Nebula, 76, 121, 142, 144 Trifid Nebula, 14, 27, 29, 37 Roslund 5, 116, 136 Trumpler 1, 196, 218 RR Lyrae, 89, 137, 139, 144 Trumpler 2, 223, 247 RS Cygni, 114, 136 RT Aurigae, 250, 269 Runaway Stars, 183, 250, 306 U Ruprecht 173, 116, 136 U Cephei, 156, 175 RW Tauri, 270, 281 U Delphini, 93, 100 U Geminorum, 281, 292 Upsilon (υ) Geminorum, 281 S U Sagittae, 83, 88, 93 Sagitta, 83–93, 150, 207, 308 U Sagittarii, 15 Sagittarius, 2, 7–44, 46, 47, 50–53, 55, 63, 150, 207 UV Aurigae, 250, 269 Sagittarius A*, 12, 51 UV Camelopardalis, 187, 189 Sagittarius-Carina Spiral Arm, 12, 29, 55 Sagittarius Dwarf Elliptical Galaxy (SagDEG), 24 Scutum, 61–68, 150, 207 V Scutum Star Cloud, 63, 64, 67 van den Bergh 14, 188, 189 Serpens Cauda, 52–62, 150, 207 van den Bergh 15, 188, 189 Sh (Sharpless) 2-71, 74, 81 V1343 Aql, 77, 81 SH2-224, 269 V Aquilae, 68, 81 Sharpless 2–264, 295 V Sagittae, 83, 87, 93 Sharpless 2-276, 306, 312 Vega, 68, 114, 137 Sigma (σ) Cassiopeiae, 206, 217 Veil Nebula (Central Section), 127, 136 Sigma (σ) Orionis, 293, 312 Veil Nebula (Eastern Section), 127, 136 Small Sagittarius Star Cloud, 12, 14, 32, 38, Veil Nebula (Western Section), 127, 136 40, 51 Vulpecula, 2, 100–111, 150, 207 SS 433, 77, 80, 81 Star Queen, 55 Stephenson 1, 137, 140, 144 W Stock 1, 102, 103, 110 W 50, 77 Stock 2, 197, 218 Webb’s Cross, 14 Stock 5, 197, 218 Wild Duck Cluster, 61, 67 Stock 10, 259, 269 WZ Sagittae, 83, 85, 93 Stock 22, 195, 218 Stock 23, 183, 185, 189 Struve 131, 196 X Summer Triangle, 68, 114 X Cygni, 118 Swan Nebula, 29, 55 Xi (ξ) Cephei, 156, 175 SZ Camelopardalis, 187, 189

Z T Zeta (ζ) Aquilae, 68, 81 Taurus, 150, 207, 261, 270–282, 295 Zeta (ζ) Cephei, 156, 157 Taurus Stream, 156 Zeta (ζ) Geminorum, 281, 292 Theta (θ) Aurigae, 250, 259, 269 Zeta (ζ) Orionis, 293, 302, 312 Theta (θ) Cygni, 114 Zeta (ζ) Persei, 227, 247 Theta (θ) Delphini, 95 Zeta1 (ζ) Persei, 156 Theta (θ) Persei, 225, 247 Zeta Persei Association, 227 Theta (θ) Sagittae, 83, 93 Zeta (ζ) Sagittae, 83, 93 342 Index © Axel Mellinger.