2019 November 30

Star Trails for a Red Planet
Image Credit & Copyright:
Dengyi Huang

Explanation: Does Mars have a north star? In long exposures of Earth’s night sky, star trails make concentric arcs around the north celestial pole, the direction of our fair planet’s axis of rotation. Bright star Polaris is presently the Earth’s North Star, close on the sky to Earth’s north celestial pole. But long exposures on Mars show star trails too, concentric arcs about a celestial pole determined by Mars’ axis of rotation. Tilted like planet Earth’s, the martian axis of rotation points in a different direction in space though. It points to a place on the sky between stars in Cygnus and Cepheus with no bright star comparable to Earth’s north star Polaris nearby. So even though this ruddy, weathered landscape is remarkably reminiscent of terrain in images from the martian surface, the view must be from planet Earth, with north star Polaris near the center of concentric star trails. The landforms in the foreground are found in Qinghai Province in northwestern China.

Dengyi Huang

说明: 火星有极星吗?在地球夜空的长曝光影像里,恒星以地球自转轴所指的北天极中心,曳出一道道同心的圆弧。在目前,北极星是离地球北天极最近的亮星。在摄于星的长曝光影像里,恒星也会因火星自转而曳出绕天极的迹线。虽然火星自转轴的倾角和地球相近,不过它在空间的指向和地轴不同。它目前指向天鹅座和仙王座之间的恒星,不过该区并没像地球北极星这种亮星。所以虽然这幅影像里的暗红风化地貌,酷似火星表面的原野,但实际上是摄于地球。在影像里,北极星位在同心星像迹线的中心。而前景的地貌,则位在中国西北部的青海省。

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