The Andromeda Galaxy is 2.9 million light years away. When you look at this galaxy, you are in effect looking back in time 2.9 million years, because that is how long it has taken the light hitting your eyes to travel through space and reach us here on Earth. The Sun at this great distance would appear as a visual magnitude 29.1 star, and would be too faint to be detected in the largest telescopes on Earth. Our Milky Way and the Andromeda Galaxy are the two dominate members of a galaxy cluster of about 30 galaxies, known as the Local Group. This gravitationally bound Local Group also includes M33, M32, M110, the Large Magellanic Cloud, the Small Magellanic Cloud, NGC 185 in Cassiopeia, NGC 147 in Cassiopeia, NGC 6822 in Sagittarius, IC 1613 in Cetus, the Fornax Dwarf Galaxy, the Sculptor Dwarf Galaxy, and the Aquarius Dwarf Galaxy, among others.
The Andromeda Galaxy contains over 300 billion individual stars and has a diameter of about 160,000 light-years. The galaxy has a mass of more than 700 billion times that of the Sun. The outer arms of the galaxy were first resolved into stars on long-exposure photographs taken using the 100-inch telescope on Mount Wilson. This galaxy is approaching our galaxy at a velocity of about 35 kilometers per second. Many many years from now, the Andromeda Galaxy will "collide" with the Milky Way galaxy, although the stars in a galaxy have so much space between them the chances of two stars hitting each other are small. When that happens in the distant future, the Andromeda Galaxy will cover a large area of the sky and appear as a second "milky way" band across the sky.
This galaxy was included in the first list published by Charles Messier in 1769.
This image is an RGB color composite CCD image taken with an STL-11000M using a Takahashi Epsilon 180ED telescope at f2.8. The image data was taken at the University of Arizona SkyCenter located on Mount Lemmon.
M31 (NGC 224)
Constellation: Andromeda
RA: 00h 42m 44s Dec: +41d 16' 08" (J2000)
November 22, 2009
Image by Sid Leach
Mount Lemmon, Arizona
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