M18
Black Swan Cluster
物性
位置と識別子
可視性
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M18について
説明
M18 is a small, sparse open cluster in Sagittarius, about 4,900 light-years from Earth. It contains only about 20 stars spread across roughly 17 light-years. Despite being one of the least impressive Messier objects, it sits in a stunning Milky Way star field between the much grander M17 and M24.
観測のコツ
Located about 1 degree south of M17 and 2 degrees north of M24, making it easy to find when sweeping between these showpieces. Binoculars show a small grouping of stars against the rich Milky Way background. A telescope at low power (30-50x) frames the cluster nicely. The sparse nature makes it hard to distinguish from the background, but a loose triangle of brighter stars marks the core. Best observed from June through September.
歴史
Discovered by Charles Messier on June 3, 1764, the same night he cataloged several other objects in the Sagittarius Milky Way. It is one of the least studied Messier objects due to its sparse nature.
豆知識
M18 is sometimes called the forgotten Messier object — sandwiched between the spectacular M17 and the stunning M24 star cloud, it is often overlooked. Its youth (about 32 million years) means it still contains hot blue stars, and it has not yet had time to gravitationally disperse.
コミュニティ写真 (1)
Credit: Fabian Rodriguez Frustaglia. License: CC BY-SA 4.0. (Wikimedia Commons)
Skybred Feb 28, 2026