The diameter value above refers to the maximum extent of the galaxy's halo. The brighter central parts are approximately 3° in diameter, corresponding to an actual value of about 120,000 light years.
The most famous of all galaxies is also the most distant object visible to the naked eye, and
the nearest major galaxy to our Milky Way. In some ways its spiral structure resembles
that of our own galaxy, but it is about twice as massive.
Though the Andromeda Galaxy is considerably larger than our own, the two share many common features. Both have a clearly recognisable spiral structure, and both have various attendant dwarf galaxies associated with them. For the Milky Way, the most prominent of these are the Magellanic Clouds or Nubeculae, while for the Andromeda Galaxy this role is fulfilled by several small galaxies, especially the two catalogued as M32 and M110.
The distance to the Andromeda Galaxy is immense: some 2,300,000 light years, but nonetheless its vast size and luminosity mean that it is still visible to the naked eye (in fact, it is the most distant object that can been seen without a telescope). Even so, much of the structure in its spiral arms is too faint to be seen, so that it appears smaller than it actually is: if we could see the entire galaxy, it would occupy an area of the sky nearly six times the size of the Moon's disc.
The galaxy is most visible in the northern sky towards the end of autumn and beginning of winter. The constellation of Andromeda is simple to locate: a imaginary line from the Pole Star through the 'W' of Cassiopeia leads directly to it, and the pale form of the Andromeda Galaxy is not hard to find in its central regions.