Astronomy Picture of the Day

Explanation:

木星的某些部分消失了。 實際上，缺了3塊。 然而，上面照片裡的三個暗色斑點只是影子。 這幅攝於去年11月10日的影像，記錄了3顆木星的衛星，罕見的同時出現在太陽與這顆巨行星之間。 而隨著這些衛星在個別的軌道上的運行，木衛一、木衛三及木衛四的影子也在木星上移動。 正是通過觀察木星的衛星食之時間，奧勒·羅默成為第一個成功測量光速的人。 當月球的影子掃過地球表面時，位於影子裡的人們會看到日食。

Part of Jupiter is missing. Actually, three parts appear to be missing. In reality though, the three dark spots seen in the above photograph are only shadows. The unusual alignment of three of Jupiter's moons between the Jovian giant and the Sun was imaged last November 10th. The shadows of Io, Callisto, and Ganymede move across Jupiter as these moons progress in their orbits. It was by noting the times of eclipse of Jupiter's moons in 1675 that Ole Roemer became the first person to measure the speed of light. When a shadow from Earth's Moon crosses the Earth's surface, the people inside the shadow see an eclipse of the Sun.