The Andromeda Galaxy (M31) is a large spiral galaxy located about 2.5 million light-years from Earth in the constellation Andromeda. It is the nearest major galaxy to the Milky Way and the largest in the Local Group, which includes the Milky Way and the Triangulum Galaxy. With a diameter of roughly 220,000 light-years, Andromeda contains about a trillion stars. It is moving toward the Milky Way and is expected to merge with our galaxy in about 4.5 billion years. Andromeda is visible to the naked eye from dark-sky locations and is a popular target for astronomers.