英語聽力文摘 小小灶神星

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Vesta 灶神星

You can see the planet Jupiter on a clear night, but Jupiter is humongous. Mars and Mercury are smaller than that, and you can see them, too. Wait a minute, our moon is even smaller, and you can see that. Could anything smaller than the moon be visible without a telescope?

Actually, yes. Though it takes a lot of patience and excellent sky conditions, it is possible to see a tiny object called Vesta. Although it had a molten interior and volcanoes, Vesta isn’t a planet or a moon: it’s an asteroid. Asteroids are straychunks of rocky or metallic materials that orbit the sun but were never drawn into any of the planets.

Vesta is quite far away. Like many asteroids, it has an orbit out between the orbits of Mars and Jupiter. Astronomers first spotted it when looking for a new planet they thought should exist between these two.

As I said, Vesta is quite small–about three hundred and twenty-five miles across. So if it’s small and far away, how come we can see it from here? Vesta’s surface has a coating of pyroxine and olivine, two minerals that are actually also spewed up by volcanoes here on earth. They give it a whitish exterior that reflects well, making it just possible to see Vesta with your eyes, even when the only two larger asteroids, Ceres and Pallas, are completely invisible.

在晴朗的夜空下我們能夠看到木星，那是因?yàn)槟拘菈虼?盡管火星和水星比木星要小，但我們依然能看到。等等，月球更要小一些，我們還是能看到。那么，在不使用望遠(yuǎn)鏡的情況下，我們還能看到比月亮更小的天體嗎?

事實(shí)上，答案是肯定的。只要我們足夠有耐心，天公也作美，我們還有機(jī)會(huì)看到一個(gè)小天體——它就是被命名為灶神星的小天體。盡管它以溶化的金屬為核心且地表遍布火山，灶神星卻既不是行星也不是月球：它僅僅是一顆小行星。小行星是由巖石或是金屬塊構(gòu)成的小天體，他們繞太陽運(yùn)動(dòng)但絕不會(huì)卷入其他行星的運(yùn)行軌道中。

灶神星距地球的距離很遠(yuǎn)。像其它許多小行星一樣，它在火星與木星之間有自己的運(yùn)行軌道。天文學(xué)家們首次發(fā)現(xiàn)它時(shí)是在尋找介于這兩大行星間的另一個(gè)行星。

正如我所說，灶神星是很小的——它的直徑也就只有325英里而已。那問題就是，它又小，距離我們又遠(yuǎn)，我們?cè)趺茨軓牡厍蛏峡咳庋劬涂吹剿?在灶神星的表面覆蓋了厚厚的一層玄武巖和橄欖石，這兩種礦物質(zhì)都是由此處的火上噴發(fā)而出的。這兩種礦物質(zhì)使得灶神星的表面呈白色，且發(fā)光的效果相當(dāng)好。如此一來，我們便僅憑肉眼就可以看到灶神星了。甚至在比它還大的另外兩個(gè)小行星——谷神星和智神星都無法看到的情況下，我們還是能看到它。

Note: spew up 噴出