OUR CLOSEST GALAXY ANDROMEDA.. Andromeda is the largest galaxy in the Local Group, which includes the Milky Way, the Triangulum Galaxy, and dozens of smaller dwarf and irregular galaxies. A recent estimate gave Andromeda 700 billion solar masses. Our Milky Way is only 80% the mass of Andromeda. IMAGE BY : jpl.nasa.gov The Andromeda galaxy was first observed by Persian astronomers, thousands of years ago, and was later cataloged by Charles Messier in 1764. He classified it as M31. In 1912, astronomers calculated its speed to be 300 kilometers per second, moving towards the Sun. Edwin Hubble first calculated the distance to Andromeda, by detecting Cepheid variables in the galaxy. He measured that it was 450 kpc, or 2.5 million light-years away; well outside the Milky Way galaxy. Rec...
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