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Visual Astronomy of the Deep Sky
Appendix E
A Catalog of Deep-Sky Objects

Roger N. Clark

Derived from:
Clark, R.N., Visual Astronomy of the Deep Sky, Cambridge University Press and Sky Publishing, 355 pages, Cambridge, 1990.

This appendix lists the 611 deep-sky objects that, in the author's opinion, are the most interesting for amateur astronomers. The list represents a search of the literature for objects that are both interesting to observe and also have photographs widely available.

In compiling this catalog, the first step was to check that an object might be seen through average amateur telescopes. Then I searched for those that might show some features. Many objects within range of small telescopes were left out because they are so near the limits that most would just look like another fuzzy patch. The present list has many of these (depending on your telescope size and sky quality), but many others clearly show significant detail and have much text devoted to them in books like Burnham's Celestial Handbook.

When going out for an observing session, one wants to know which objects will be visible that night. Some books (e.g. Burnham's) are organized alphabetically by constellation, so a search through the entire work is required in order to find out what there is to see. This list, on the other hand, is ordered by right ascension. For any given night, one can start at some point on the list and work downward.

The following data are tabulated:

ID: The NGC number of the object, or other catalog number if the object has no NGC designation. The Messier number is also given if appropriate. Before the ID, several codes may appear. An asterisk (*) means the object is discussed in the book and a drawing and photograph are presented in Chapter 7. An S indicates the object is a star cluster with star magnitudes given in Appendix B Of Visual Astronomy of the Deep Sky. Exclamation points indicate the object is an especially fine-looking one, with four (!!!!) being the most spectacular visually.

Positions: Positions in right ascension (RA) and Declination (DEC) are tabulated for equinox 2000.0. The RA is given in hours and decimal minutes of time, and the DEC is given in degrees and arc-minutes. The objects are sorted by increasing 1950.0 RA. The positions in the catalog have been checked against several other catalogs, and as many discrepancies as possible have been eliminated. One good reference is Sky Catalog 2000.0, Volume 2, by Hirshfeld and Sinnott (1985). The 2000.0 positions in this list have all been checked against Hirshfeld and Sinnott. Many positions disagree in the last digit between the two catalogs, but the differences are not significant and can be attributed to round-off error, or to where the exact center of a large object was chosen (a center may not be obvious in open clusters and nebulae in particular). When the position disagreement was significant, I investigated and chose the best position. In some cases that meant measuring photographs. Several small galaxies in the couple-of-arc-minute size range had positions disagreeing by about an arc minute or two. However, the coordinates are always accurate enough to find an object with setting circles or by plotting on star charts, even at high power.

Con: The constellation in which the object is located. The following standard abbreviations are used:

Constellation	abbr.	Constellation	abbr.
Andromeda	And	Leo	Leo
Antlia	Ant	Leo Minor	LMi
Apus	Aps	Lepus	Lep
Aquarius	Aqr	Libra	Lib
Aquila	Aql	Lupus	Lup
Ara	Ara	Lynx	Lyn
Aries	Ari	Lyra	Lyr
Auriga	Aur	Mensa	Men
Bootes	Boo	Microscopium	Mic
Caelum	Cae	Monoceros	Mon
Camelopardalis	Cam	Musca	Mus
Cancer	Cnc	Norma	Nor
Canes Venatici	CVn	Octans	Oct
Canis Major	CMa	Ophiuchus	Oph
Canis Minor	CMi	Orion	Ori
Capricornus	Cap	Pavo	Pav
Carina	Car	Pegasus	Peg
Cassiopeia	Cas	Perseus	Per
Centarus	Cen	Phoenix	Phe
Cepheus	Cep	Pictor	Pic
Cetus	Cet	Pisces	Psc
Chamaelon	Cha	Pisces Austrinus	PsA
Circinus	Cir	Puppis	Pup
Columba	Col	Pyxis	Pyx
Coma Berenices	Com	Reticulum	Ret
Corona Australis	CrA	Sagitta	Sge
Corona Borealis	CrB	Sagittarius	Sgr
Corvus	Crv	Scorpius	Sco
Crater	Crt	Sculptor	Scl
Crux	Cru	Scutum	Sct
Cygnus	Cyg	Serpens	Ser
Delphinus	Del	Sextans	Sex
Dorado	Dor	Taurus	Tau
Draco	Dra	Telescopium	Tel
Equuleus	Equ	Triangulum	Tri
Eridanus	Eri	Triangulum Australe	TrA
Fornax	For	Tucana	Tuc
Gemini	Gem	Ursa Major	UMa
Grus	Gru	Ursa Minor	UMi
Hercules	Her	Vela	Vel
Horologium	Hor	Virgo	Vir
Hydra	Hya	Volans	Vol
Hydrus	Hyi	Vulpecula	Vul
Indus	Ind
Lacerta	Lac

The number of listed objects in each constellation is as follows:

Andromeda	And	Leo	Leo
7 And	1 Ant	1 Aps	5 Aql	5 Aqr	5 Ara	2 Ari
8 Aur	3 Boo	7 CMa	26 CVn	7 Cam	2 Cap	5 Car
12 Cas	8 Cen	11 Cep	21 Cet	1 Cir	3 Cnc	2 Col
34 Com	3 CrA	4 Crt	4 Cru	6 Crv	18 Cyg	3 Del
5 Dor	9 Dra	15 Eri	20 For	5 Gem	5 Gru	5 Her
2 Hor	9 Hya	5 LMi	1 Lac	14 Leo	3 Lep	1 Lib
3 Lup	3 Lyn	3 Lyr	6 Mon	3 Mus	3 Nor	9 Oph
12 Ori	2 Pav	7 Peg	12 Per	4 Psc	7 Pup	3 Pyx
2 Ret	9 Scl	19 Sco	5 Sct	5 Ser	4 Sex	32 Sgr
9 Tau	1 Tel	1 TrA	4 Tri	3 Tuc	37 UMa	10 Vel
74 Vir	6 Vul

Type: The type of object:

• Plan: planetary nebula.
• Glob: globular star cluster.
• Neb: diffuse nebula.
• DNeb: dark nebula.
• OpCl: open cluster.
• S0: a galaxy with no discernible spiral structure, asembling an elliptical galaxy but may have a barely detectable flattened central plane or disk.
• S0p: peculiar S0 galaxy.
• Sa, Sb, Sc, Sd: spiral galaxies type a, b, c, and d. In type a, the central bulge dominates the spiral arms; the central bulge decreases to type d, where it is almost nonexistent. The spiral arms are tightly wound at type a, very loose and open at type d.
• Sb: barred spiral galaxy, followed by type a, b, or c as defined above.
• En: elliptical galaxy, where n is a number from 0 to 8 describing the ellipticity; 0 being circular, 8 most elongated. A "p" indicates peculiar.
• DwEl: dwarf elliptical galaxy.
• Irr: irregular galaxy.
• Pec: peculiar galaxy.
• QSO: quasi-stellar object, also called quasar
• Star: The only star in the catalog is "Messier 40."

This catalog lists 340 galaxies, 108 open clusters, 65 globular clusters, 49 bright nebulae, 38 planetary nebulae, 9 dark nebulae, 1 QSO, and 1 star. The galaxies types are: 237 spiral (S), 76 elliptical (E), 19 irregular, and 8 peculiar.

Charts: The chart number in an atlas where the object can be found:

• 2000: Sky Atlas 2000.0 by Wil Tirion.
• VPSA: Vehrenberg's Photographic Star Atlas.
• Uran: Uranometria 2000.0 by Tirion, B. Rappaport and G. Lovi.

v mag: The visual magnitude of the object. For an extended object this is difficult to determine, and references often disagree. Furthermore, some objects only have a photographic magnitude determined, which may depart significantly from the visual. A magnitude measurement also depends on how much of the object is included; some objects have very large, very dim outlying areas that cannot be seen visually but contribute substantially to the listed total magnitudes. Thus, the values cannot be relied upon to better than about a half magnitude at best.

Size: The visual size of the object in arc-minutes. This is approximately the size that should be detectable in a telescope by eye. The values are consistently smaller than those in Sky Catalogue 2000.0 because, as described in that work, the largest sizes that can be determined were listed -- and those are often larger than can be seen visually in any amateur telescope.

S.B.: The surface brightness in magnitudes per square arc second. This value is only a rough approximation computed from the visual magnitude and the object's size. The S.B. can be found by the equation: S.B. = v mag + 2.5 log(2827 a b) where a and b are the objects' major and minor dimensions in arc-minutes (an elliptical shape is assumed). The constant equals pi(60 arc-sec/arc-minute)² /4.

C1: The logarithm of the contrast between the mean surface brightness (column S.B.) and a sky background of 24.25 magnitudes per square arc-second. This sky background corresponds to a dark country sky, as described in Chapter 6. The greater this value, the higher the contrast and the easier the object is to detect. We use a logarithmic parameter here because the eye's response to contrast follows a log scale. To compute C1, equation 6.1 was used, except that the sky surface brightness (M_o) was added to the object's surface brightness (M) to give the equivalent value seen by the eye. This must be done in linear units: if
B = 10^-0.4M and B_o = 10^-0.4M_o
then B' = B + B_o, and the contrast is
C = (B'-B_o)/B_o, or
C = B / B_o,
which, when converted to magnitudes is:
C = 10^-0.4(M-M_o), or
C1 = log (C)
C1 = -0.4(M-M_o)

MDM: The Minimum Optimum Detection Magnification. This is the magnification that enlarges the object to the optimum visual angle shown in Figure 2.7b assuming the telescope is being used at its lowest usable power. If an object is very difficult to detect then the MDM divided by about 3.5 (representing a telescope's minimum useful magnification per inch of aperture) gives the optimum telescope aperture in inches to view the object! Of course if the contrast is high enough then the object is easily detected at many magnifications and with many telescopes.

The MDM was computed using the smaller of the two size dimensions and the object's mean surface brightness. It also assumes that the object is viewed through optics with a transmission factor of 0.7, reducing the surface brightness by 0.38 magnitudes at the telescope's lowest usable magnification.

Note that the MDM is not the optimum detection magnification (ODM) unless it is also the telescope's lowest usable power. If the magnification listed is greater than the telescope's minimum (3.5 or 4 times the aperture in inches), then the best magnification is greater than the MDM. The MDM is only an approximate lower limit for detection. It is approximate because the object's mean surface brightness is used, not the peak brightness.

Comments: General notes that further describe the object (including the Messier number) or its neighbors.

Notes: Additional comments too long to fit in the table. They are listed at the end of the catalog.