Andromeda (aka M31 and NGC 224) is an enormous spiral galaxy located a mere 2 million light years from us. Although it is hard to see from a light-polluted city, Andromeda is the brightest galaxy in the Northern Hemisphere (you can easily spot the Large and Small Magellanic Clouds in the sky, but you have to be in Australia). About 157,000 light years in length, Andromeda may be twice the size of our own Milky Way. Because Andromeda is so near, astronomers can study it to understand how spiral galaxies rotate or to compare stars in our own galaxy with those in others. Andromeda has also helped astronomers calculate the size of the universe.
This image of Andromeda shows its two major parts: the disk and
