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NGC 6475 (Ptolemy's Cluster, M7)


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NGC 6475, M7
Open Cluster (散開星団)
Ptolemy's Cluster (トレミー星団)
OC II2r

別名 (Other names)
OCL 1028, ESO 394-SC9, Messier 7

明るさ (Brightness)
3.3等級

星座 (Constellation)
さそり座 (Sco) (Scorpius)

距離 (Distance)
800光年 (800 light-years)

M7 (NGC6475) はさそり座にある散開星団 。距離800光年。プトレマイオス(トレミー)の記述が残っているほど古くから知られている。「トレミーの星団」と呼ばれる場合もある。直径は約22光年。
M7は明るく、肉眼でも見える散開星団の一つ。

10等級より明るい星が約80個ある。真南には暗黒星雲のバーナード287があり、双眼鏡で見ることができる。
天の川の中で最も星が密集したスタークラウドの中のさらに星が密集した部分とも見ることができる。

17世紀ジョバンニ・オディエルナは単に「30個の星を数えた」と書いた。
ラセーユは喜望峰からM7を見て「正方形の中に集まった15ないし20の星の群れ」と書いた。
ジョン・ハーシェルは1864年の彼のカタログに「とても明るく、非常に星数が多く、集まりのゆるい星団」と書いた。

肉眼では星雲状に見えるが、目の良い人は幾つかの星を分離できる。
むしろ半月程度の明るさがある条件の方が肉眼で分離できるという人もいる。
双眼鏡ではM6と同視野で見ることができる。望遠鏡では倍率を上げすぎると星団がはみだしてしまう。
M6との対比では、M6の周囲は暗く、青白い星が多いが、M7の周囲は明るく黄色に見える。
また、M6よりも密集しているように見える。

M7は最も南に位置するメシエ天体。

NGC 6475 (Messier 7) is a ptolemy's cluster located 800 light years from the Earth in the constellation Scorpius.

NGC 6475 (Ptolemy's Cluster, M7) : Picture

M7: Open Star Cluster in Scorpius
M7: Open Star Cluster in Scorpius
(C) Dieter Willasch (Astro-Cabinet)
M7 is one of the most prominent open clusters of stars on the sky. The cluster, dominated by bright blue stars, can be seen with the naked eye in a dark sky in the tail of the constellation of Scorpius. M7 contains about 100 stars in total, is about 200 million years old, spans 25 light-years across, and lies about 1,000 light-years away. The above deep exposure was taken from Hakos Farm in Namibia. The M7 star cluster has been known since ancient times, being noted by Ptolemy in the year 130 AD. Also visible are a dark dust cloud and literally millions of unrelated stars towards the Galactic center.

M7: Open Star Cluster in Scorpius
M7: Open Star Cluster in Scorpius
(C) Louie Atalasidis

M7: Open Star Cluster in Scorpius
M7: Open Star Cluster in Scorpius
(C) Lorand Fenyes
M7 is one of the most prominent open clusters of stars on the sky. The cluster, dominated by bright blue stars, can be seen with the naked eye in a dark sky in the tail of the constellation of Scorpius. M7 contains about 100 stars in total, is about 200 million years old, spans 25 light-years across, and lies about 1,000 light-years away. The above deep image, taken last June from Hungary through a small telescope, combines over 60 two-minute exposures. The M7 star cluster has been known since ancient times, being noted by Ptolemy in the year 130 AD. Also visible are a dark dust cloud and literally millions of unrelated stars towards the Galactic center.

M7: Open Star Cluster M7: Open Star Cluster
M7: Open Star Cluster in Scorpius
(C) Dieter Willasch (Astro-Cabinet)
M7: Open Star Cluster in Scorpius
(C) Louie Atalasidis
M7: Open Star Cluster in Scorpius
M7: Open Star Cluster in Scorpius
(C) Lorand Fenyes
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NGC 6475 (Ptolemy's Cluster, M7) : Movie

Zooming in on the bright star cluster Messier 7
This zoom video starts with a view of the central parts of the Milky Way. We zoom in towards the bright constellation of Scorpius and we see a fuzzy spot close to the tail. This is the bright star cluster Messier 7 and is visible with the naked eye. The final very detailed close up image comes from the MPG/ESO 2.2-metre telescope at ESO's La Silla Observatory in Chile.

Panning across the bright star cluster Messier 7
This video pan sequence gives a close-up view of one of the brightest star clusters in the sky. This image from the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO's La Silla Observatory in Chile, shows Messier 7, also known as NGC 6475. Easily spotted by the naked eye in the direction of the tail of the constellation Scorpius, this cluster is one of the most prominent open clusters of stars in the sky and is an important research target.
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「ウィキペディア(wikipedia):フリー百科事典」より文章引用。
M7. (2012, November 8). In Wikipedia.
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