Located in the constellation Andromeda, M31 (the Andromeda Galaxy) is the nearest major spiral galaxy to our own Milky Way, situated approximately 2.5 million light-years away^[1].  Its mass, including dark matter, is now understood to be roughly comparable to that of the Milky Way, overturning earlier notions that it was substantially larger^[2].  M31 is currently approaching the Milky Way at a radial velocity of about 125 km/s^[4], and while historical projections predicted a merger in approximately 4 to 5 billion years, recent studies incorporating Gaia and Hubble data suggest there is only a 50% chance of collision occurring within the next 10 billion years^[3].

In a dark sky, M31 can be glimpsed with the unaided eye as a diffuse "fuzzy patch".  M31 becomes distinctly oval when viewed through binoculars.  Long-exposure astro-imaging reveals its spiral structure, dust clouds, and impressive stellar details.

In this image, two of M31's prominent satellite galaxies are visible: M32, the compact elliptical companion just above M31's nucleus, and M110, a more diffuse and elongated galaxy near the bottom of the image.

This image is a 4-panel mosaic captured with a f/3 Officina Stellare RH200-AT astrograph and a KAF-8300 sensor (bin 1x1).  The resulting field of view spans roughly 3.4 by 2.6 degrees, or more than 6 times the width and 5 times the height of the full Moon, wide enough to encompass Andromeda's sweeping spiral structure and its companion galaxies in a single frame.