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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).
當(dāng)你抬頭看向夜空時，你會看見什么？除了月亮和星星以外，天空中還有其他星體。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.
彗星的形成時間大致與地球相同。彗星由冰和其他冷液以及氣體構(gòu)成。這些“臟雪球”和行星一樣，會時不時地繞太陽運轉(zhuǎn)。
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.
當(dāng)彗星接近太陽時，就會解凍一些氣體。這些氣體同彗星釋放出來的塵粒相結(jié)合，形成巨大的云團(tuán)。當(dāng)彗星離太陽更近一些時，太陽風(fēng)會將云團(tuán)吹至彗星身后，這樣就形成了慧尾。慧尾和彗星周圍模糊的大氣是在夜空中看到彗星的兩大要素。
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，都有約12顆彗星在自己的軌道上接近太陽。當(dāng)然，一般人完全看不到彗星。通常一年中人們只能有一兩次機會可以用肉眼觀賞到足夠明亮的彗星。海爾-波普彗星是一顆異常明亮的彗星，在1995年被發(fā)現(xiàn)。這顆彗星的軌道離地球相對較近，距離不超過1.22億公里。但是海爾-波普彗星運轉(zhuǎn)了很長一段路才得以訪問地球。該彗星要在約4千年以后才會再經(jīng)過地球。
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