M39
Pyramid Cluster
物性
位置と識別子
可視性
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M39について
説明
M39 is a large, bright, very loose open cluster in Cygnus, about 825 light-years from Earth — one of the nearest Messier objects. It contains only about 30 members spread across 7 light-years, with an age of 230-300 million years. The cluster's sparse, scattered nature and large angular size make it best suited for binocular observation.
観測のコツ
Located about 9 degrees east-northeast of Deneb (Alpha Cygni). Visible to the naked eye as a hazy patch in the Cygnus Milky Way. The cluster spans nearly a full degree, so binoculars or a very wide-field telescope at low power (20-30x) are ideal. A telescope at higher power loses the cluster in the field. About 25 stars form a large triangular pattern. Best observed from August through November.
歴史
Possibly observed by Aristotle around 325 BC as a 'cometary object,' which would make it one of the earliest deep-sky records. Charles Messier cataloged it on October 24, 1764. Guillaume Le Gentil independently noted it in 1750.
豆知識
If Aristotle's 325 BC observation truly refers to M39, it would be the oldest recorded observation of an open cluster, predating all other deep-sky records by nearly two millennia. At 825 light-years, it is one of the closest Messier objects and will eventually disperse completely into the galactic background over the next few hundred million years.
コミュニティ写真 (1)
Credit: Chuck Ayoub. License: CC0. (Wikimedia Commons)
Skybred Feb 28, 2026