火星卫星之间的交食
Martian Moon Eclipses Martian Moon
Video Credit: ESA, DLR, FU Berlin, Mars Express; Processing & CC BY 2.0 License: Andrea Luck
Explanation: What if there were two moons in the sky — and they eclipsed each other? This happens on Mars. The featured video shows a version of this unusual eclipse from space. Pictured are the two moons of Mars: the larger Phobos, which orbits closer to the red planet, and the smaller Deimos, which orbits further out. The sequence was captured last year by the ESA’s Mars Express, a robotic spacecraft that itself orbits Mars. A similar eclipse is visible from the Martian surface, although very rarely. From the surface, though, the closer moon Phobos would appear to pass in front of farther moon Deimos. Most oddly, both moons orbit Mars so close that they appear to move backwards when compared to Earth’s Moon from Earth, both rising in west and setting in the east. Phobos, the closer moon, orbits so close and so fast that it passes nearly overhead about three times a day.
Tomorrow’s picture: spaghetti star
火星卫星之间的交食
影片提供: ESA, DLR, FU Berlin, Mars Express; 影片处理与CC BY 2.0 License: Andrea Luck
说明: 如果天空中的2颗卫星发生了交食，那么它们所形成的景观何似？火星还真的出现了这种景观。这部主题影片，呈现了记录这例特殊交食事件的版本之一。而影像的主角分别是火星的2颗卫星：位于较密近轨道、个头也较大的火卫一，以及位于较外围轨道、较娇小的火卫二。这个影像序列，是由欧洲航天局绕行火星的火星快车空间探测器摄于去年。在火星表面也可以见到类似的交食景观，只是很罕见。从火星表面看出去，较密近的火卫一看似掠过较远的火卫二前方。由于这两颗卫星的轨道非常接近火星，因此很奇特的是，它们会西升东落，它们运动的方向与月亮完全相反。较接近火星的火卫一，轨道非常密近且速度非常快，每天大约会掠过头顶3次。
明日的图片: spaghetti star
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两颗卫星的交食真有趣，但这样罕见的现象有多少人能亲眼见到呢？感觉就像在期待不太可能出现的流星雨。