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Because from trillions of miles away, these small planets get lost in the blinding glare of their stars'brightness.
因为从几万亿光年外看，这些小行星会被周围恒星的耀眼光芒所埋没。
The sad truth of the matter is that earth-like planets are near cosmic specks of dust.
据说类地球的形体好像宇宙中微尘。
And therefore detecting them is really quite hard.
所以说侦测到它们时间十分困难的事情。
Hard, but not impossible. Every now and again, the planet passes directly between us and the star.
困难，但并不是没有可能，行星有时会从我们地球和恒星之间穿过。
And if it does that, it's like a little eclipse. And the star-light drops.
当它穿过时就形成了类似蚀的情况，那么恒星的光亮就会减弱变得灰暗。
It gets darker because the planet is blocking the light from that star. And it turns out we can see that.
因为行星挡住了恒星所发出的光，而结果是我们可以看到那颗行星。
With this in mind, scientists built one of the world's most sensitive telescopes and launched it into space.
具备了这种理论，科学家们制造了世界上最敏锐的望远镜之一并发射入太空。
The mission called Kepler may not help us find E.T, but it could help us find its home.
这项任务叫做开普勒计划，虽然不太可能帮助我们找到外星人，但是可能帮助我们找到他们的家。
Kepler will simply do one thing unbelievably well--measure the brightness of 100,000 stars over and over and over,looking for a few of those 100,000 stars that dim.
开普勒能将它唯一的一件工作做到极致就是一次又一次地测量几十万星星的光亮度，试图找到其中少数发暗的星体。
Seeing the tiniest dim from a small planet travelling in front of a star thousands of light-years away isn't easy to imagine.
从几千光年外观测穿过其恒星的小行星发出的暗光是难以想象的。
But the Kepler telescope is one of the most sensitive cameras ever built.
但开普勒望远镜是世界上最敏锐的照相机。
To give you an idea of just how sensitive Kepler is, I'm gonna demonstrate using this massive World War II search light.
为了让你们知道开普勒到底敏锐到什么程度，我要用这个二战时期的巨大探照灯为你们做演示。
The brightness of that search light represents the extreme luminosity of stars.
探照灯的光亮代表着恒星极高的亮度。
And I'm gonna use this tiny marble to represent the planet.
而我将用这个小弹珠来代表行星。
When this planet passes in front of the star, it blocks out a tiny fraction of the light, dimming the star by a very small amount, and that's exactly what the Kepler space craft can detect.
当这个小行星从恒星面前通过时，它会挡住微小的一部分光，使恒星变暗一小小点，而开普勒就能够侦测到这种十分微小的变化。
Kepler can detect a 0.01% change in the star's luminosity, but even if it spots a dimming star, there's still another problem.
开普勒能够识别恒星万分之一的亮度变化，但即便它检测到一个变暗的恒星，我们还有一个问题需要解决。
When Kepler sees a star that dims, it could be due to a speck of dust that crossed in front of the telescope.
当开普勒检测到恒星变暗有可能是因为望远镜前的一些尘土。
There's a possibility of binary stars, two stars that orbit each other thereby dimming the stars as one blocks the other.
还有可能是双星两个形体相互环绕，就好像是一个挡住了另一个从而使得恒星变暗。
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