帕拉纳尔上空的旋转天幕

探索宇宙（Universe）！每天都会精选一张关于我们迷人宇宙的不同图像或照片，并附上一段由专业天文学家（Astronomer）撰写的简短说明。

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

说明：在位于智利的欧洲南方天文台（ESO）帕拉纳尔天文台（Paranal Observatory），纬度约为南纬25度，地球（Earth）的自转使行星（Planet）表面以每小时超过1,500公里的速度向东移动。虽然这比海平面（Sea level）的声速（Speed of sound）还要快，但这种运动是无法察觉的。不过，通过拍摄星像迹线（Star trail），这种运动可以在夜天（Night sky）的视自转（Apparent rotation）中显现出来。这张星像迹线图像是由300张连续的25秒曝光照片数字叠加而成，相机固定在三脚架上，以追踪星像迹线弧。这些优美的弧线呈同心圆状，中心位于南天极（South celestial pole），即地球自转轴（Axis of rotation）在空间中向南半球（Southern hemisphere）的延伸。在该天文台运行的1.8米辅助望远镜（Telescope）之一，即AT 3，出现在南天极下方，在这幅来自旋转行星的精心构图场景中，于前景处被微弱地照亮。

Explanation: At the latitude of ESO's Paranal Observatory in Chile, about 25 degrees south, Earth's rotation moves the planet's surface eastward at over 1,500 kilometers per hour. And while that's faster than the speed of sound at sea level, the motion is imperceptible. Still, that motion can be revealed in the apparent rotation of the night sky by photographing star trails. This star trail image was composed from a digital stack of 300 consecutive 25-second exposures made with a camera fixed to a tripod to trace the star trail arcs. The graceful arcs are concentric and centered at the south celestial pole, the southern hemisphere extension of Earth's axis of rotation into space. One of the observatory's operating 1.8 meter auxiliary telescopes, AT 3, appears beneath the south celestial pole, faintly illuminated in the foreground of this well-planned scene from a rotating planet.