The Small Sagittarius Star Cloud (also known as Messier 24 and IC 4715) is a star cloud in the constellation of Sagittarius approximately 600 light years wide, which was catalogued by Charles Messier in 1764. It should not be confused with the nearby Large Sagittarius Star Cloud which lies about 10° to the south.
Messier described the cloud as "a large nebulosity in which there are many stars of different magnitudes" and gave its dimensions as being some 1.5° across. Some sources, improperly, identify M24 as the small open cluster NGC 6603. The location of the Small Sagittarius Star Cloud is near the Omega Nebula (also known as M17) and open cluster Messier 18, both north of M24.
Messier 24 is not a distinct deep-sky object, rather an open window through the Great Rift into deeper regions of the Milky Way galaxy. It fills a space of significant volume to a depth of 10,000 to 15,000 light years away, including stars from the Scutum-Centaurus Arm, the major spiral arm between Earth and the Galactic Center.
The star cloud incorporates two prominent dark nebulae which are vast clouds of dense, obscuring interstellar dust. This dust blocks light from the more distant stars, which keeps them from being seen from Earth. Lying on the northwestern side is Barnard 92, which is the darker of the two. Within the star field, the nebula appears as an immense round hole devoid of stars. American astronomer Edward Emerson Barnard discovered this dark nebula in 1913.