When you look up at the night sky, what do you see? There are other heavenly bodies out there besides the moon and stars. One of the most fascinating of these is a comet (彗星).
当你抬头看向夜空时，你会看见什么？除了月亮和星星以外，天空中还有其他星体 。其中最迷人的就是彗星 。
Comets were formed around the same time the Earth was formed. They are made up of ice and other frozen liquids and gases. Now and then these "dirty snowballs" begin to orbit the sun, just as the planets do.
彗星的形成时间大致与地球相同 。彗星由冰和其他冷液以及气体构成 。这些“脏雪球”和行星一样，会时不时地绕太阳运转 。
As a comet gets closer to the sun, some gases in it begin to unfreeze. They combine with dust particles from the comet to form a huge cloud. As the comet gets even nearer to the sun, a solar wind blows the cloud behind the comet, thus forming its tail. The tail and the generally fuzzy (模糊的) atmosphere around a comet are characteristics that can help identify this phenomenon in the night sky.
当彗星接近太阳时，就会解冻一些气体 。这些气体同彗星释放出来的尘粒相结合，形成巨大的云团 。当彗星离太阳更近一些时，太阳风会将云团吹至彗星身后，这样就形成了慧尾 。慧尾和彗星周围模糊的大气是在夜空中看到彗星的两大要素 。
In any given year, about a dozen known comets come close to the sun in their orbits. The average person can't see them all, of course. Usually there is only one or two a year bright enough to be seen with the naked eye. Comet Hale-Bopp, discovered in 1995, was an unusually bright comet. Its orbit brought it relatively close to the Earth, within 122 million miles of it. But Hale-Bopp came a long way on its earthly visit. It won't be back for another four thousand years or so.
在任意年份，都有约12颗彗星在自己的轨道上接近太阳 。当然，一般人完全看不到彗星 。通常一年中人们只能有一两次机会可以用肉眼观赏到足够明亮的彗星 。海尔-波普彗星是一颗异常明亮的彗星，在1995年被发现 。这颗彗星的轨道离地球相对较近，距离不超过1.22亿公里 。但是海尔-波普彗星运转了很长一段路才得以访问地球 。该彗星要在约4千年以后才会再经过地球 。