美国国家航空航天局NASA每日一图(天文)-2017年7月21日

2017 July 21

Phobos: Moon over Mars
Image Credit: NASA, ESA, Zolt Levay (STScI) - Acknowledgment: J.Bell (ASU) and M.Wolff (SSI)
Explanation: A tiny moon with a scary name, Phobos emerges from behind the Red Planet in this timelapse sequence from the Earth-orbiting Hubble Space Telescope. Over 22 minutes the 13 separate exposures were captured near the 2016 closest approach of Mars to planet Earth. Martians have to look to the west to watch Phobos rise, though. The small moon is closer to its parent planet than any other moon in the Solar System, about 3,700 miles (6,000 kilometers) above the Martian surface. It completes one orbit in just 7 hours and 39 minutes. That's faster than a Mars rotation, which corresponds to about 24 hours and 40 minutes. So on Mars, Phobos can be seen to rise above the western horizon 3 times a day. Still, Phobos is doomed.

 

2017年7月21日

Phobos:月球在火星上
图片来源: NASA, ESA,Zolt Levay(STScI) - 致谢:J.Bell(ASU)和M.Wolff(SSI)
说明: 一个可怕名字的小月亮,Phobos从地球轨道哈勃太空望远镜的这个时间序列中出现在红色星球后面 。超过22分钟,在2016年最接近的火星接近地球的地球捕获了13次独立曝光 。 火星人必须向西看,看着Phobos的兴起。太阳系中的小月亮比火星表面上方大约3,700英里(6000公里)的太阳系中的任何其他月亮都比 其父星更接近 。它只需7个小时39分钟即可完成一个轨道。这比火星旋转速度快,对应于大约24小时40分钟。所以在火星上,Phobos可以看到每天上升到西方地平线3次。尽管如此, Phobos注定了失败。

 

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