Copyright © 1981 by the University of Washington Press

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The Andromeda Galaxy (also known as M31 and NGC 224) is the nearest spiral galaxy to our own Milky Way galaxy. Its relatively early Hubble type (Sb) and bright absolute magnitude (-20) make it an important and unique source of information on galaxies of this nature. M31 forms an important testing ground for ideas about massive galaxies and about galaxy evolution, and is ripe for detailed astrophysical exploration. The purpose of this atlas is to make future exploration and exploitation of this galaxy easier by mapping out some of the thousands of objects of various kinds that have been identified in it and by giving photographic and photometric data that will aid in planning and understanding new research.

Table 1 is a compilation of some measured and inferred properties of M31, along with the quoted sources. Many of these numbers will be adjusted in the future as research continues, but most will not change significantly. A more complete discussion of these and other data is given in the author's monograph on the subject (Hodge 1981).

TABLE 1. Properties of M31

Position (1950)
Right Ascension 00h40m00s.3 (Dressel and Condon 1976)
Declination +41°00'03"
Angular diameter (optical) 240' (de Vaucouleurs 1958)
Apparent magnitude (V) 3.58 (de Vaucouleurs 1958)
Color (B-V) and (U-B) +0.91, +0.50 (de Vaucouleurs 1958)
Distance modulus, apparent 24.88 (Sandage and Tammann 1968)*
Reddening, E(B-V) 0.16 (Sandage and Tammann 1968)
Galactic absorption 0.48
Distance modulus, true 24.40
Distance, kpc 765
Absolute magnitude, MV -20.62
Diameter, kpc 54
Angle of inclination to line of sight 12°.5 (Simien et al. 1978)
Position angle of major axis 37°.7 (de Vaucouleurs 1958)
Radial velocity (wrt sun), km/sec -310 (Rubin and D'Odorico 1969)
Mass (total, solar masses) >4.1x1011 (Roberts and Whitehurst 1975)*
Mass (neutral hydrogen, solar masses) 3.9x109 (Cram, Roberts and Whitehurst 1979)

* Corrected for the revised Hyades distance (+ 0.2 mag.)

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