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NGC 2682 (Open Cluster, M67)


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NGC 2682, M67
Open Cluster (散開星団)
OC II2m


別名 (Other names)
OCL 549, Messier 67

明るさ (Brightness)
6.9等級

星座 (Constellation)
かに座 (Cnc) (Cancer)

距離 (Distance)
2,800光年 (2,800 light-years)

M67(NGC2682)は、かに座にある散開星団。
1772年~1779年の間にヨハン・ゴットフリード・ケーラーが発見した。「かに座αに近い楕円形の星雲」と記している。1780年メシエは「かに座の南の爪で星雲状のものを交えた星の群れ」と記している。
1783年ウィリアム・ハーシェルは「星に分解。非常に密集したまことにきれいな星団で、どんな望遠鏡でもたやすく見える」とした。ジョン・ハーシェルは「顕著な目標。非常に明るくて大きく星数が多く、10~15等級」とした。フランマリオンは「とうもろこしの一束」と表現している。

光度は肉眼で見えるぎりぎりにある。ジョーンズは条件がよければ肉眼でも見えるとしたが、マラスは誰も肉眼で見ていないと記している。

双眼鏡ではまるい星雲状の光の上に星が見えてくる。星の配置が見えてくるのは口径8cmの望遠鏡からである。口径10cmの望遠鏡で、冠のように宝石をちりばめたような眺めになる。口径20cmになると背後にある微星が見えてくる。口径30cmになるとさらに微星がみえすばらしい眺めになる。どの口径でも楽しめる散開星団です。

散開星団の中でも年齢がふるく、星団の年齢は太陽と同程度である。また、構成する化学組成も太陽と似ているとされるため、太陽と同じタイプの星の研究に使われている。

M67に属する恒星は性質が太陽に似ているため、M67は太陽の生まれ故郷で、太陽は誕生後に星団から離れて現在の位置に落ち着いたという説がある(一般的に恒星は集団で誕生し次第に離散していくことが知られている)。一方で、星団と太陽の運動から考えて、太陽がM67で誕生した可能性は低いという研究もある。
NGC 2682 (M67) is an open cluster located 2,800 light years from the Earth in the constellation Cancer.

NGC 2682 (Open Cluster, M67) : Picture

Star Cluster Messier 67
Star Cluster Messier 67
(C) Processing - Noel Carboni, Imaging - Greg Parker
Gathered at the center of this sharp skyview are the stars of Messier 67, one of the oldest known open star clusters. In fact, though open star clusters are usually much younger, the stars of M67 are likely around 4 billion years old, about the same age and with about the same elemental abundances as the Sun. Open clusters are almost always younger because they are dispersed over time as they encounter other stars, interstellar clouds, and experience gravitational tides while orbiting the center of our galaxy. Still, M67 contains over 500 stars or so and lies some 2,800 light-years away in the constellation Cancer. At that estimated distance, M67 would be about 12 light-years across.

Messier 67
Wide-field view of the open star cluster Messier 67
(C) ESO
This wide-field image of the sky around the old open star cluster Messier 67 was created from images forming part of the Digitized Sky Survey 2. The cluster appears as a rich grouping of stars at the centre of the picture. Messier 67 contains stars that are all about the same age, and have the same chemical composition, as the Sun.

Artist's impression of an exoplanet orbiting a star in the cluster Messier 67
Artist's impression of an exoplanet orbiting a star in the cluster Messier 67
(C) ESO
This artist's impression shows one of the three newly discovered planets in the star cluster Messier 67. In this cluster the stars are all about the same age and composition as the Sun. This makes it a perfect laboratory to study how many planets form in such a crowded environment. Very few planets in clusters are known and this one has the additional distinction of orbiting a solar twin — a star that is almost identical to the Sun in all respects.

The star cluster Messier 67 in the constellation of Cancer
The star cluster Messier 67 in the constellation of Cancer
(C) ESO
This chart shows the location of the star cluster Messier 67 in the constellation of Cancer. This map shows most of the stars that are visible to the unaided eye under good conditions, and the location of the cluster is highlighted with a red circle on the image. This object can be spotted with binoculars and many of its component stars seen with a moderate-sized telescope.
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NGC 2682 (Open Cluster, M67) : Movie

ESOcast 62: Three planets found in star cluster
In this ESOcast we look at how astronomers have used ESO's HARPS planet hunter in Chile, along with other telescopes around the world, to discover three planets orbiting stars in the cluster Messier 67. Although more than one thousand planets outside the Solar System are now confirmed, only a handful have been found in star clusters. Remarkably one of these new exoplanets is orbiting a star that is a rare solar twin — a star that is almost identical to the Sun in all respects.

Zooming in on the star cluster Messier 67
This zoom sequence takes the viewer from a broad view of the entire night sky into a close up view of the old star cluster Messier 67 in the constellation of Cancer. Observations using ESO's HARPS instrument on the 3.6-metre telescope at La Silla in Chile, along with other telescopes, have found three planets orbiting stars in this cluster.

Panning across the star cluster Messier 67
This artist's impression shows the old star cluster Messier 67 in the constellation of Cancer. Observations using ESO's HARPS instrument on the 3.6-metre telescope at La Silla in Chile, along with other telescopes, have found three planets orbiting stars in this cluster. The three stars with planets are marked with their names.
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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。
M67 (天体). (2013, April 9). In Wikipedia.
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