佳节来临 NASA分享宇宙中“圣诞花环”

This Hubble image shows RS Puppis, a type of variable star known as a Cepheid variable. As variable stars go, Cepheids have comparatively long periods — RS Puppis, for example, varies in brightness by almost a factor of five every 40 or so days. RS Puppis is unusual; this variable star is shrouded by thick, dark clouds of dust enabling a phenomenon known as a light echo to be shown with stunning clarity. These Hubble observations show the ethereal object embedded in its dusty environment, set against a dark sky filled with background galaxies.
This Hubble image shows RS Puppis, a type of variable star known as a Cepheid variable. As variable stars go, Cepheids have comparatively long periods — RS Puppis, for example, varies in brightness by almost a factor of five every 40 or so days. RS Puppis is unusual; this variable star is shrouded by thick, dark clouds of dust enabling a phenomenon known as a light echo to be shown with stunning clarity. These Hubble observations show the ethereal object embedded in its dusty environment, set against a dark sky filled with background galaxies.

在圣诞节来临之际，美国国家航空航天局（NASA）分享了一张“圣诞花环”的图片，为这个一年一度的佳节增添几分欢乐气氛。这个花环由反射星光的气体尘埃构成，在浩瀚无垠的太空中闪闪发光。

在这张由NASA哈伯太空望远镜（Hubble Space Telescope）所拍摄的图片中，一颗位于南天的闪亮恒星“船尾座RS”（RS Puppis）刚好出现在正中央，被四周气体尘埃包裹着，而这些气体尘埃也反射出它的星光，如同一个耀眼的花环。

船尾座RS是一颗位于船尾座的超级巨星，其质量是太阳的10倍，而大小则是太阳的200倍。

船尾座RS也是一颗变星，它会规律地变亮和变暗，其周期为6个星期。它是所谓的造父变星（Cepheid variable）等级中最亮的恒星之一，平均亮度大于太阳的15,000倍。

这颗造父变星的特别之处在于，它周围有由气体尘埃组成的浓厚暗星云环绕。随着它向外发出忽强忽弱的星光，这些星云的亮度会闪烁不定。

从哈伯太空望远镜拍到的图片可以看到，船尾座RS四周的气体尘埃因反射恒星光而形成所谓的回光（light echo）现象，似烟雾袅绕。

尽管光在太空中行进的速度很快，可以在1秒多的时间内从地球走到月球，但船尾座RS周围的星云却大到足以让反射光在其中行进的轨迹被拍摄下来。

藉由观察船尾座RS本身发出的星光的波动及其反射光横越星云的脉动，天文学家得以测量其回光情况，并得知其与地球的距离约为6,500光年（误差幅度仅有1%）。

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