M31, The Brilliant Andromeda Galaxy
September 04, 2010
The stunning Andromeda Galaxy (Messier Number 31) is the most well known galaxy next to our own Milky Way. Because it's "only" about 2.5 million light-years distant, it appears as the largest and brightest spiral galaxy in the sky. Like our own galaxy, M31 also has several satellite galaxies; the brightest ones are M32 and M110. On a clear, moonless night, the Andromeda Galaxy, named for its location in the constellation of Andromeda, is perhaps the farthest object visible to the naked eye. About one trillion stars allow this resplendent jewel to appear as a faint smudge, in spite of its enormous distance -- it's apparent magnitude is 3.4. Long exposure images reveal a perceived diameter more than six times that of the full Moon. A recent study concludes that the Andromeda Galaxy and the Milky Way Galaxy are nearly equal in mass but the diameter of M31 is about 50 percent larger. Andromeda will soon be in optimal viewing position for observers in the Northern Hemisphere. If you live in an area removed from city light, see if you can spy M31. Using averted vision helps. Photo taken in Gossau, Switzerland in April 2010.
Photo details: This image combines a total of 28 hours and 10 min exposure time. Separate narrow band data was taken to bring out the bright HII-regions, representing active areas of star formation. More details can be found here.