時差N小時:流星雨是怎樣形成的?

If you find yourself away from a city, spend anhour looking up on any clear, moonless night,you'rebound to see a few brilliant "shooting stars." Theseactually have nothing to do with stars: They'remeteors, and if your viewing conditions are good, youcan see about seven per hour on any given night.During a "meteor shower" however, this rate mayincrease to over a hundred meteors an hour. Whatare meteors, and what makes them gather intoshowers?

如果在沒有月亮的晴朗夜晚，你遠(yuǎn)離城市，花一個小時觀察天空。你一定會看見許多絢麗的一劃而過的星星。它們其實不是真正的星星。它們只是流星，如果觀察條件允許，你每小時大約可看見七顆流星。然而，如果遇上一場流星雨，你流星出現(xiàn)的頻率會增加，達(dá)到每小時100多顆。什么是流星?它們是怎么聚集從而形成流星雨的?

Meteors are caused by bits of rocky material that enter our atmosphere from space, thenburn up because of friction. They don't have to be big for you to see them. Surprisingly, mostvisible meteors are caused by debris no larger than a single grain of sand. They burn sobrightly because of tremendous friction when they hit our atmosphere at more than forty milesper second.

流星是由很小的外太空隕石進(jìn)入大氣層，與空氣摩擦燃燒引起的。那些隕石很小，人類并不能用肉眼看見。出人意料的是，大多數(shù)可見的流星其實是由比沙粒還小的碎石屑形成的。隕石以每秒40多英里的速度闖入大氣層，產(chǎn)生巨大的摩擦力，從而發(fā)出明亮的光芒。

Why would something as random as flying specks of space debris gather into showers? It'sbecause the Earth passes through the same regions of space each time it orbits the sun. Certainregions have more debris than others, so we have meteor showers on those nights.

為什么從外太空隨機飛入的隕石屑會匯聚成流星雨呢?這是因為地球每次繞太陽軌道公轉(zhuǎn)會經(jīng)過同樣的區(qū)域。某些區(qū)域比其它區(qū)域有更多的隕石屑，所以地球經(jīng)過這些區(qū)域時的夜晚，我們就會看見流星雨。

Of course this raises the question of why certain parts of our orbit would be especially fullof debris. The answer has to do with comets. Comets are big, dirty snowballs that orbit our sun.Long after a comet and it's tail have passed us by, it leaves behind a thin trail of dust anddebris. If a comet crosses the Earth's orbit, we pass through this trail each year. For example,every October twenty-first we pass through the Orionid shower, which is debris left behind fromHalley's comet.

當(dāng)然這又會引出另一個問題，為什么地球公轉(zhuǎn)軌道上的某些區(qū)域會有特別多的隕石屑。答案與彗星有關(guān)。彗星就像是圍繞太陽轉(zhuǎn)的巨大的，臟兮兮的雪球。彗星及其彗尾掃過之后，會留下一道充滿細(xì)小塵埃和碎屑的痕跡，并存在很長一段時間。如果有一顆彗星經(jīng)過地球公轉(zhuǎn)軌道，那么我們每年都會經(jīng)過這道滿是塵埃和碎屑的區(qū)域。例如，每年10月21號我們會經(jīng)過獵戶座流星雨，這就是哈雷彗星殘留的隕石屑引起的。