The Andromeda Galaxy is
the brightest galaxy visible from the northern hemisphere. Most of
you have probably observed it many times. Some may even ignore it
now because it's often considered a beginner's object. In any case,
whether you have never looked upon it or haven't for a long while, I
urge you to take a good long look at this magnificent galaxy. Like
the Great nebula in Orion, Andromeda at the very least deserves a
yearly visit.
You should be able to
see M31 with your unaided eyes--quite a feat for something that lies
over 2 million light years away. From a relatively light-polluted
location all you will see is the feeble glow of the nucleus. It may
look like nothing more than a slightly fuzzy star. From a dark site
you can see much of the full extent of the galaxy -- up to 6 times
the diameter of the full moon! You may need to use averted vision
and take into account that the galaxy generally becomes fainter as
you move away from the nucleus. 
M31 as seen at about 8PM
local time.
In the telescope, use
your lowest-power, widest-field eyepiece.
The first thing to look
for is the very bright, nearly stellar nuclear core. The Hubble
Space Telescope has observed the spectral signature of fast moving
hot gas in this core. The gas is moving rapidly around a massive,
unseen object -- probably a "supermassive" black hole.
The bright, elongated
glow surrounding the core is the nucleus. Those observing from
light-polluted locations may mistake this nuclear region for the
entire galaxy. Look carefully at the western edge of the nucleus.
Compare what you see to the eastern edge. The western edge is much
more abrupt. In fact, what we are seeing is actually a lane of dark
matter. Look for another line of haze that parallels the abrupt
edge; this is the other edge of the dark lane. Follow the abrupt
edge along the long axis of the galaxy. Can you see it become a thin
dark line that arcs about the nucleus?
Now look for the
fainter haze that surrounds the nucleus. Try to follow it as far as
you can, particularly along the long axis. At the ends it can be
helpful to move the scope away and then bring it back again. As you
move it back look for the sky background to become brighter. This is
the galaxy.
Look for a
bright, hazy spot less than 1/2o
to the south of the nucleus. This is the galaxy M32, a small galaxy
that is orbiting the much larger M31. Look for the bright, star-like
core.
A bit more than
1/2o to the
northwest lies another small galaxy, M110. This galaxy is larger and
more diffuse than M32. These two galaxies are analogous to the Large
and Small Magellanic clouds which orbit our own Milky Way. In fact,
our Milky Way is similar in many ways to the Andromeda galaxy. An
observer looking back at us from Andromeda would see a similar view
to yours.
Above is a 3o
x 3o region
of sky centered on the nucleus of M31. The circle represents
approximately a 1o field
of view, which is similar to that of most wide field eyepieces.
North is up and East is left. An image of the galaxies derived from
the Digital Sky Survey has been overlaid to provide a realistic
representation of what you may see in the eyepiece. You may need to
adjust your monitor for best results.
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