彗星 220P 爆发

探索宇宙（universe）！每天都会展示一张我们迷人宇宙的不同图像或照片，并附上一段由专业天文学家（astronomer）撰写的简短说明。

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

说明：彗星（comet）220P 意外地变得明亮。通常情况下，周期彗星（periodic comet）220P/McNaught 非常暗淡，需要使用望远镜（telescope）才能观测到。然而，今年两次令人惊讶的爆发使其亮度比平时增加了约 20,000 倍，因此现在通过双筒望远镜和相机的长曝光拍摄即可观测到它。正如预期，彗星 220P 继续在火星（Mars）和木星（Jupiter）之间绕太阳运行，公转周期超过 5 年。这张精选的长曝光照片于 10 天前在南非拍摄，展示了该彗星明亮的绿色彗头和短小的尘埃彗尾（dust tail）。彗星 220P 发生惊人爆发的原因尚不清楚，但可能是由地下积聚气体的释放或彗震引起的。彗星 220P 将于 10 月经过距离地球（Earth）约一个日地距离的位置，此后随着它开始返回轨道远端，预计其亮度将迅速减弱。

Explanation: Comet 220P is unexpectedly bright. Normally, periodic Comet 220P/McNaught is so dim that to see it requires a telescope. Two surprising outbursts this year, however, have made it about 20,000 times brighter than usual, so that it is now visible with binoculars and long-duration camera exposures. As expected, Comet 220P continues to orbit the Sun between Mars and Jupiter with a period of over 5 years. The featured long duration exposure, taken 10 days ago from South Africa, shows the comet's bright green head and short dust tail. Reasons for Comet 220P's impressive outbursts are unknown but could be caused by the release of built-up subsurface gas or comet quakes. Comet 220P will pass about one Earth-Sun distance from the Earth in October, after which it is expected to fade quickly as it begins its return to the far part of its orbit.