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Proper NamesAndromeda Galaxy, Great Nebula in Andromeda
Messier NumberM31
NGC/IC NumberNGC 224
Right Ascension0h 42m 44s
Declination+41° 16' 8"
Distancec.2,500,000 light years
c.800,000 parsecs
MagnitudeApparent: +3.28
Absolute: -21.17
Mean DiameterApparent: 5° 12'
Actual: c.200,000 light years
Hubble TypeSb spiral
Optimum VisibilityOctober
NotesThe 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 the Milky Way. In some ways its spiral structure resembles that of our own Galaxy, but it is about twice as massive.

Largest of the galaxies in our own Local Cluster, the Andromeda Galaxy has a diameter twice that of our own Milky Way spiral. Like our own Galaxy, it has a numer of smaller attendant galaxies: M110 (top right) and M32 (bottom centre) are both visible in this image. Imagery provided by Aladin sky atlas

The Local Group of galaxies is relatively small in comparison to many others: it only contains about thirty galactic systems. Our own Galaxy and the Triangulum Galaxy are among the most prominent members, but easily the largest is the huge spiral of the Andromeda Galaxy, with roughly twice the mass of our own Milky Way.

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 Andromeda Galaxy is not hard to locate in the sky, lying directly to the south of Cassiopeia's famous 'W' shape. A line through the relatively bright stars Mirach and Mu Andromedae points directly to the galaxy.

The Milky Way Galaxy from M31

If there are any astronomers in the Andromeda Galaxy, then this will be a familiar sight to them - their view of our own Galaxy, some 2,500,000 light years from their own.

The distance to the Andromeda Galaxy is immense: some 2,500,000 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.


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