时差N小时:离星星有多远?

Aristotle thought the stars were all exactly the samedistance away, stuck to a dark shell that surroundedthe Earth like the dome of a planetarium. Now weknow that the farthest galaxy is over a billion timesmore distant than the nearest star. How doastronomers tell how far away the stars are?

亚里士多德认为所有星星离我们的距离都是相等的，它们镶嵌在一个环绕在地球四周的，像天文馆的穹顶一样的黑色的硬壳上。现在我们知道最远星系的距离是最近星系的十亿倍。天文学家是如何知道星星离我们有多远呢?

One method works like the way your own eyes determine how far away earthbound objects are.Hold a finger upright at arm's length, then close an eye as if you were winking. Open that eyeand close the other. As you alternate eyes, your finger will seem to change position. Keepwinking back and forth, then move your finger closer to your face.

有一种方法跟你目测地面上物体的距离一样。竖起一根手指，并保持一段距离，然后闭上眼睛，仿佛你在思考一样。睁开一只眼睛并闭上另一只。当你变换眼睛的时候，手指的位置似乎改变了。继续来来回回地眨眼，然后移动手指，靠近你的脸。

The closer your finger is, the more it appears to jump compared to the background. This is thekey to one method of measuring how distant the stars are. Closer stars seem to shift more thandistant ones do when seen from different places. The farther apart your two observation pointsare, the more dramatic this shifting becomes.

你的手指靠脸越近，相对于背景物它似乎越是有大的跳跃。这是测量星星距离的方法的关键。从不同的地方看时，近一点的星星似乎比远一点的星星跳跃幅度要大。两个观测点相距越远，这种跳跃就更明显。

Your eyes are only inches apart, so no matter how much you wink at the stars, you won't beable to shift them with your eyes alone. Astronomers, however, can use telescopes in differentparts of the world, thousands of miles apart. Even better, they can photograph a star once, thenagain six months later. During six months the Earth will have orbited to the other side of thesun, creating a pair of telescopic eyes that are almost two hundred million miles apart. With thisdistance, the shift becomes quite noticeable. This method has been used to math the locationof thousands of nearby stars.

你的双眼只相距一英尺远，因此不论你的眼睛眨多少下，光靠眼睛来看星星你是不会产生这种视觉落差的。但是宇航员能在世界上相隔上千英里的不同角落使用望远镜。甚至更好的，他们能给一颗星星拍照，然后六个月后再拍一次。六个月之后，地球就在太阳另一侧的轨道上转动，这样就创造出一对相隔差不多一亿英里的望眼镜“双眼”。在这么远的距离下，跳跃就非常引人注目了。这种方式已被用来演算上千颗附近恒星的位置。