M31 Andromeda Galaxy

In the Messier Catalog it is listed as M31 and in the New General Catalogue as NGC 224. In the starry sky it is located in the constellation Andromeda, after which it is named. On clear nights the Andromeda galaxy can be seen with the naked eye from a dark location without any technical aids. This makes it the most distant object that can be seen with the naked eye.

The Andromeda galaxy is about 2.5 million light years away from the solar system. It has a halo diameter of about one million light years. This makes it the largest member of the Local Group. The Andromeda galaxy has a total mass of about 800 billion solar masses. It and the Milky Way are the two most massive galaxies of the Local Group.
The diameter of the visible disk is about 140,000 light-years. The Milky Way has a comparable diameter.
New data from the Hubble Space Telescope show that the core consists of a ring of older red stars and a ring of younger blue stars trapped in the gravitational field of a supermassive black hole. With about 100 million solar masses, this black hole is about 24 times as massive as the Galactic Center of the Milky Way.
The Andromeda galaxy has a radial velocity of -114 km/s (approx. -410,000 km/h) compared to the Milky Way system. The minus sign indicates that the two galaxies are moving towards each other.