Sagittarius (The Archer).
The southernmost constellation of the zodiac, and one of those listed by Ptolemy (c. AD 140). The centre of the Galaxy (the Milky Way) lies behind the star clouds in Sagittarius. It is a large constellation, with many bright stars; there are 14 brighter than fourth magnitude. It also contains a large number of star clusters and diffuse nebulae. The Messier Catalogue lists 15 objects in Sagittarius, more than in any other individual constellation. They include the Lagoon Nebula, the Trifid Nebula, theOmega Nebula and the third brightest globular cluster in the sky, M22.