金字塔山上空的北斗七星

2023年12月10日

Big Dipper over Pyramid Mountain
Image Credit & Copyright: Steve Cullen

Explanation: When did you first learn to identify this group of stars? Although they are familiar to many people around the world, different cultures have associated this asterism with different icons and folklore. Known in the USA as the Big Dipper, the stars are part of a constellation designated by the International Astronomical Union in 1922 as the Great Bear (Ursa Major). The recognized star names of these stars are (left to right) Alkaid, Mizar/Alcor, Alioth, Megrez, Phecda, Merak, and Dubhe. 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. The featured image captured the iconic stars in 2017 above Pyramid Mountain in Alberta, Canada.

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金字塔山上空的北斗七星
影像提供与版权: Steve Cullen

说明: 你是何时学会如何辨识这个星官的？虽然它们是世界各地都很熟悉的一群恒星，不过，不同文化的人赋予它们不同的意象和传说。在美国，它们称为大勺子，是国际天文联盟在1922年划定的大熊座之一部分。其成员的星名，由左到右分别是摇光、开阳、玉衡、天权、天玑、天璇和天枢。当然，对某个星座而言，其成员未必有物理上的关联性。不过很意外的是，北斗七星大部分的成员在空间的运动，看似都朝同一个方向移动，而附近更大区域里的其他恒星，移动的方向也很相近。这个测定共同运动的特征，指出它们可能都是平均约75光年远、宽30光年，名为大熊座移动星群这个邻近星团的成员。这张主题影像，呈现了悬在加拿大亚伯达省金字塔山上空的这群标志性恒星。（Alkaid 摇光、 Mizar/Alcor 开阳、 Alioth 玉衡、 Megrez 天权、Phecda 天玑、Merak 天璇、Dubhe 天枢）