仙女座的宇宙岛
翻译：李颋（福建ltycho)
资料来源：Robert Gendler
说明：你能看得多远呢？用肉眼容易见到的最远天体是大约200万光年外的仙女座大星系（M31)。不使用望远镜，这个在仙女座的大旋涡星系只是一个不明显的、模糊的的云状物。但是这张令人兴奋的用望远镜拍摄的最近宇宙岛的数字拼接图像却记录下了一个黄色的亮核、暗淡的旋涡尘埃带、美丽的蓝色旋臂和星团。现在当观星者不经意地想到有很多像M31这样遥远的星系时，殊不知天文学家在80年前就认真地讨论过这个基本的概念了。这些“旋涡状星云”是简单地位于我们的银河系之外，还是替代了“宇宙岛”——与银河系相比遥远的恒星系统呢？这个论题是1920年著名的沙普利－柯蒂斯争论的中心，它在稍后的对M31的观测中被断定是仙女座的宇宙岛。
原文:
Andromeda Island Universe
Credit & Copyright: Robert Gendler
Explanation: How far can you see? The most distant object easily visible to the unaided eye is M31, the great Andromeda Galaxy some two million light-years away. Without a telescope, even this immense spiral galaxy appears as an unremarkable, faint, nebulous cloud in the constellation Andromeda. But a bright yellow nucleus, dark winding dust lanes, gorgeous blue spiral arms and star clusters are recorded in this stunning telescopic digital mosaic of the nearby island universe. While even casual skygazers are now inspired by the knowledge that there are many distant galaxies like M31, astronomers seriously debated this fundamental concept only 80 years ago. Were these "spiral nebulae" simply outlying components of our own Milky Way Galaxy or were they instead "island universes" -- distant systems of stars comparable to the Milky Way itself? This question was central to the famous Shapley-Curtis debate of 1920, which was later resolved by observations of M31 in favor of Andromeda, island universe.
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