移过天空的天王星和卫星

2021年11月30日

In Motion: Uranus and Moons
Video Credit: David Campbell (U. Hertfordshire), Bayfordbury Observatory

Explanation: What’s that moving across the sky? A planet just a bit too faint to see with the unaided eye: Uranus. The gas giant out past Saturn was tracked earlier this month near opposition — when it was closest to Earth and at its brightest. The featured video captured by the Bayfordbury Observatory in Hertfordshire, UK is a four-hour time-lapse showing Uranus with its four largest moons in tow: Titania, Oberon, Umbriel and Ariel. Uranus’ apparent motion past background stars is really dominated by Earth’s own orbital motion around our Sun. The cross seen centered on Uranus is called a diffraction spike and is caused by light diffracting around the four arms that hold one of the telescope’s mirrors in place. The rotation of the diffraction spikes is not caused by the rotation of Uranus but, essentially, by the rotation of the Earth. During the next few months Uranus itself will be visible with binoculars, but, as always, to see its moons will require a telescope.

Tomorrow’s picture: the blood moon band

移过天空的天王星和卫星
影片提供: David Campbell (U. Hertfordshire), Bayfordbury Observatory

说明: 移过天空的是什么？是太暗肉眼不得见的天王星。这部影片记录了这颗位在土星外头的气态巨行星，这个月稍早运行到“天王星冲”附近，于最靠近地球也因此最明亮时的身影。这部原始长度为4小时，呈现天王星和4颗大卫星：天卫三、天卫四、天卫二、和天卫一的缩时主题影片，则是摄于英国赫特福德郡的贝佛贝瑞 天文台。天王星移过背景恒星前方的视运动，主要来自地球绕太阳公转的轨道运动。以天王星为中心的星芒，其实是源自它的光，在通过这座望远镜一面镜子的4道支撑臂时，所产生的绕射芒。而绕射芒的转动，并非来自天王星的自转，而是源自地球的自转。在接下来的数个月里，天王星用双筒望远镜即可见，不过要看到它的卫星，则必需借助于望远镜。 （Titania 天卫三； Oberon 天卫四； Umbriel 天卫二； Ariel 天卫一）

明日的图片: the blood moon band