The Milky Way Galaxy is a spiral galaxy, of which our Sun is a member. Because we are inside the galaxy, we see the Milky Way as a dense band of stars in the night sky. The Milky Way might appear to an outside observer to look like the Andromeda Galaxy, shown below.

From the ancient Greeks through the Renaissance, the cosmos was thought to consist of the solar system and stars on a spherical surface with finite radius. Understanding of the Milky Way, a patchy diffuse band of light crossing the sky, did not emerge until the 18th century when it was understood that the solar system is embedded in a flattened distribution of stars lying at a wide range of distances. In the early 20th century, Harlow Shapley, Jan Oort and others correctly inferred that the Milky Way Galaxy is tens of thousands of parsecs in extent, consists of a flat circular disk and a spheroidal halo, and that the Sun lies off-center in the disk. Simultaneously in the 1920s, Edwin Hubble conclusively determined that certain nebulous objects in the sky, such as the Andromeda Nebula, were independent galaxies, each containing billions of stars.

During the years from 1758 to 1782 Charles Messier, a French astronomer (b. 1730 d. 1817), compiled a list of approximately 100 diffuse objects that were difficult to distinguish from comets through the telescopes of the day. Although Messier may not have been the first to discover that we are in the Milky Way Galaxy, he was a very important figure in the classification and discovery of Galaxies, as well as a number of other deep space objects.