Messier 31 (M31), better known as the Andromeda Galaxy, is a large spiral galaxy located in the constellation Andromeda. It is a distance of 2.54 million light years from Earth.
The Andromeda Galaxy is the nearest major galaxy to our own and is on a collision course with our home galaxy, the Milky Way. Messier 31 has an apparent magnitude of 3.44.

Messier 31 is the largest and most massive member of the Local Group of galaxies, which also includes the Milky Way, the Triangulum Galaxy (M33) and more than 40 smaller galaxies.
The Andromeda Galaxy contains a trillion stars, more than twice as many as the Milky Way, which is home to 200 to 400 billion stars.
The two galaxies are roughly equal in mass and will collide in about 3.75 billion years. The collision will likely result in a new giant elliptical galaxy or disk galaxy being formed.

The small galaxy above M31 is Messier 110 (M110, NGC 205).

Nikon D7200 (unmodified); Sky-Watcher ED80 Pro Refractor and a Tele Vue 0.8x Reducer/Flattener @ 480mm / f/6; ISO 1600; IDAS LPS-P2 Filter; Celestron AVX mount; guided with SSAG; and PHD2; 36 x 5 minute subs (total integration is 3 hours).

Shot in RAW; converted to 16 bit TIFFs; stacked using DSS; processed in Pixinsight and Photoshop CC.

Imaged from Beckwith Township, Ontario, Canada.