From the January 2022 issue

101 Must-See Cosmic Objects: The Small Sagittarius Star Cloud

By | Published: July 7, 2022 | Last updated on September 7, 2023
Chris Schur
Charles Messier first noted the Small Sagittarius Star Cloud (M24) on June 20, 1764. He subsequently recalled it as a “large nebulosity in which there are several stars of different magnitudes: the light which is diffused over this cluster is divided into several parts.” Although it could not be mistaken for a comet, which was the basis for his catalog, he still added it in as M24.

Later observers went on to misidentify M24 as NGC 6603, which is a separate, small, tightly packed open cluster. The confusion wasn’t laid to rest until the 1960s, when British astronomer Kenneth Glyn Jones suggested that M24 was actually the larger region known as the Small Sagittarius Star Cloud, which encompassed NGC 6603.

The name “star cloud” is misleading, though. We are not looking at a distinct deep-sky object, such as a star cluster or a nebula. Instead, we are peering through an open window into the inner depths of the Milky Way. The plane of our galaxy is littered with cosmic dust, which is so opaque in some spots that we have no idea what’s going on behind it. But in this 1.5° by 0.5° rectangular frame, the dust curtains have been pulled aside, revealing stars more than halfway to the galactic core.

Only appearing as a bright patch of the Milky Way to the naked eye, the Small Sagittarius Star Cloud blossoms through binoculars into countless stars. But what about NGC 6603? This packed but faint open cluster resides in the richest part of the cloud, northeast of its center. Don’t expect to see many of this cluster’s individual stars, though, unless you observe it through at least a 10-inch scope.

A view of the star cloud does not come without a few intervening dust clouds, either. A pair of dark nebulae, Barnard 92 and Barnard 93, create a silhouette along its northern edge. Barnard 92 is a rectangular ink blot oriented north-south and measuring about 14′ by 8′. To its east, Barnard 93 is a smaller 8′ by 3′, as well as less defined.

Make sure to explore Astronomy’s full list of 101 cosmic objects you must see. New entries will be added each week throughout 2022.

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