Andromeda Galaxy, Messier 31

Andromeda Galaxy, Messier 31 is about 2.5 million light-years away from Earth. It is the nearest major galaxy to our own Milky Way Galaxy?  In fact, our Galaxy is thought to look much like Andromeda but is about half its size and contains 200 billion stars compared with the Andromeda which contains a trillion stars. Together these two galaxies dominate the Local Group of galaxies that are gravitationally bound together. The diffuse light from Andromeda is caused by its trillion stars. The several distinct stars that surround Andromeda‘s image are actually stars in our Galaxy. M31 is so distant it takes over two million years for light to reach us from there. The spiral arms of the Andromeda Galaxy are being distorted by gravitational interactions with two companion galaxies, M32 and M110 which are the two bright objects to the left and to the right of the Andromeda in the image. At a magnitude of 3.4, the Andromeda Galaxy is the most distant object you can spot with the naked eye. You need a good spot away from bright lights in order to see it. While most galaxies are moving away from us, the Andromeda is destined to collide with the Milky Way Galaxy in 4.5 billion years.

The Andromeda is also famous because Edmund Hubble in 1924 measured its distance to be millions of light years away and ended the “Great Debate” showing that these “spiral nebulas” were actually distant “island galaxies “ rather than nebulas within the Milky Way.