北斗七星 @ 小雅 :: 痞客邦 ::

The Big Dipper Cluster

影像版權與提供: Noel Carboni

Explanation:
   A well-known asterism in northern skies, The Big Dipper is easy to recognize even when viewed upside down. Part of the larger constellation of Ursa Major, the bright dipper stars above are named (left to right along the dipper) Dubhe, Merak, Phecda, Megrez, Alioth, Mizar/Alcor, and Alkaid. Of course, stars in any given constellation are unlikely to be physically related. But surprisingly, most of the big dipper stars do seem to be headed in the same direction as they plough through space, a property they share with other stars spread out over an even larger area across the sky. Their measured common motion suggests that they all belong to a loose, nearby star cluster, thought to be on average only about 75 light-years away and up to 30 light-years across. The cluster is more properly known as the Ursa Major Moving Group.

說明:
   北天最有名的星座就是北斗七星(The Big Dipper)，它很好認，像是大勺子，甚至顛倒看也認得出。它是大熊星座(Ursa Major)的一部份，北斗七星最亮的星，由左到右分別命名為天樞(Dubhe)、天璇(Merak)、天璣(Phecda)與天權(Megrez)為魁，玉衡(Alioth)、開陽 (Mizar/Alcor) 與搖光(Alkaid)為杓，合成為斗。當然這並不表示任何星座的星星有任何的關連，但是令人驚訝的是，它們卻朝著同一個方向運行，雖然它們散佈在天空中很大的區域。測量它們的共同運行暗示著屬於同一個疏散星團，平均離我們的距離約有75光年遠，橫跨約30光年。這個星團是屬於大熊移動群。

資料來源: Scientific American
            Department of Physics, NCKU