OF THE ROGER N. CLARK

VISUAL ASTRONOMY OF THE DEEP SKY
M31, THE ANDROMEDA GALAXY (NGc
224), M32 (NGC 221), MHO (NGC 205),
GALAXIES IN ANDROMEDA
M31: R.A. OOh 42.7m Dec. 4r 16' (2000.0)
M32 : R.A. OOh 42 .7m Dec. 40° 52 '
MllO: R.A. 00h 40.3m Dec. 4r 41 '
Technical. Messier 31, commonly called
Great Galaxy in Andromeda, is a large
tilted 13° from edge-on. It is the brigh
galaxy we can view in the sky apart from
own Milky Way. Arab astronomers re(Orr1Pn
it in the 10th century as a small,
patch, but under the murky skies of Europe
eluded notice with the unaided eye. No
pean recorded it until 1612, when
Marius saw it with the help of a telescope.
The Andromeda Galaxy is part of the
al Group of galaxies, which is about 5
light-years in size; the four main members
M31, M33, Maffei 1, and our own
About 30 galaxies are currently recognized
members of the Local Group, most of
dwarf ellipticals or irregulars associated
our galaxy or M31.
M31 has approximately twice the mass
our galaxy, or about 300 (Amer.)
times the mass of the Sun, and puts out
11 billion times the Sun's light. Its distance
usually given as 2.3 million light-years, and
is approaching us at about 80 kilometers
second.
On deep-sky photographs M31 covers
1.25° by 4.1°, which corresponds to a
meter of about 100,000 light-years. In
book Galaxies, Timothy Ferris gives an
teresting observation on space and
Since M31 is 2.3 million light-years away,
are seeing 2.3 million years into the
However, since one side of the galaxy is
100,000 light-years more distant, a .
L"'''U.,··
centuries are spanned from one slde to
other. Thus we are not only looking back
time, we are seeing many times at once!
--
V· M31 appears somewhat less than
1
.
° I through most mstruments, though
'th fine binoculars, un d er exce . ent
Isua .
bservers have reporte seemg a ex-
4 ong
0
some
t
A VISUAL ATLAS OF DEEP-SKY OBJECTS
d . 50
11
skies. These outer ar h
ts ar b
e . extrem M
e 3
lY 1
fal r
nt.
Unlike many bn t ects, .
leaves
0 ten
a disappointmg . lmpresslOn , at first
. ht The central reglOn lS very ng t ut
b . h b
; Ig d ' quickly and smoothly toward the edges.
. ' h h
The beautiful detạlls seen m p otograp s are
difficult visually m any telescpe. In fact, t 2
e k B f'
Size,
the outer edge correspondmg to about
I th requires a very dark s y. ecause 0
ng lts
very low power is needed to see all of the
galaxy in one view. ut at such magm lca-
With good skies and a moderate aperture,
the dark lane to the northeast is easily seen at
30x and up. An 8-inch telescope will show
this lane under moderate skies, as well as the
bright star cloud to the soutwest (upper
right in the photograph) at hlgher powers.
This star cloud is known as NGC 206. There
are many dark patches in the galaxy, especially
near the bright central portion, but
none have been reported by amateur observers.
The brightness of M31 varies tremendous­
tions, almost no . detaIl appears.
ly from the nucleus to the outer edges.
Assuming a size of 150 by 50 arc-minutes and
a total magnitude of 4.0, the mean surface
brightness is 22.3 magnitudes per square arcsecond.
However, the nucleus is many magnitudes
brighter than this, while the edges are
fainter.
Near M31 are two of its companion galaxies:
M32 and M 11 O. These are dwarf elliptical
systems that have a relationship with M31
similar to that of the Magellanic Clouds with
our own galaxy.
M32 is south of M31 's nucleus. It appears
on the edge of a spiral arm whose boundary is
evident in good skies with a 6- or 8-inch
telescope. M32 was first seen by Le Gentil in
1749; it can be found by careful observers
with a 2-inch telescope. Its angular size is 3.6
by 3.1 arc-minutes, and its total magnitude of
9.5 yields an average surface brightness of
20.7 magnitudes per square arc-second.
MIIO (NGC 205), northwest of the nucleus
of M31, is considerably more difficult
than M32 because it is spread over a larger
are . a and has a fainter total magnitude, 10.8.
It IS 8 by 3 arc-minutes in size, and has an
'fi
average surface brightness of 22.9 magnitudes
per square arc-second. This galaxy has
been seen with telescopes as small as 2.4 inches.
In fact, a good friend of mine, Jon Seamans,
has observed all the Messier objects
with a 2.4-inch refractor.
M31 has two more companion galaxies about
7° to the north: NGC 147 and NGC 185 .
Both are about the same difficulty visually as
NGC 205. They are described in Appendix E
and in Burnham's Celestial Handbook.
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