What is the Messier catalog number of the Andromeda Galaxy?

The Messier catalog number of the Andromeda Galaxy is M31. The Andromeda Galaxy, known as the nearest spiral galaxy to the Milky Way and one of the most studied objects in the night sky, was included in the Messier catalog by the astronomer Charles Messier in the 18th century to help distinguish it from comets. The M31 designation indicates its position as the 31st entry in this catalog, which is primarily focused on nebulae and star clusters visible from Earth.

This designation helps astronomers and hobbyists alike communicate effectively about this significant astronomical object. The other options listed correspond to different celestial objects: M32 is a satellite galaxy of M31, M51 is the Whirlpool Galaxy, and M87 is known for containing the first black hole ever imaged. Each of these possesses its own unique features and importance in the study of astronomy, but M31 specifically refers to the Andromeda Galaxy itself.