M31, the great Andromeda Galaxy, is one of the most famous objects in the entire sky, and the nearest of all spiral galaxies. This object is first mentioned by the Persian astronomer Al Sufi in the 10th Century, but the world becomes aware of its existence only in 1764, when Charles Messier includes it in his catalogue. Messier has also made a drawing showing M31 and its companions M32 and M110.
On clear nights M31 can be seen with the naked eye as a hazy smudge, and binoculars show its elliptical shape that can be traced to its full extent of over two degrees. That is four times the width of the full Moon!
M31 is not very spectacular when observed with a
M31, the great Andromeda
Galaxy. T.A.Rector and
NSF [larger image]
telescope. Even the largest instruments reveal only the brightest central part of the galaxy, an elongated patch which gradually brightens in the center to a nearly star-like nucleus. 8-inch or larger telescopes reveal the prominent dark lane on the northwest edge of the galaxy's core, and the bright star clouds near the south-tip.
These faint details are pretty hard to spot, but averted vision will help a lot. When observing M31 use a wide-field eyepiece, otherwise you won't be able to fit the galaxy in the visual field.
Two more satellite galaxies lie near M31. The brightest of these is 9th-magnitude M32
, located half a degree south of M31. The other satellite is M110
, one degree northwest of M31. These two satellite galaxies are pretty faint, and the key to viewing them is to set up your scope away from local lights on a dark, transparent, moonless night.
- field width 30 degrees, stars to magnitude 6.