時差N小時:離星星有多遠?

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?

亞里士多德認為所有星星離我們的距離都是相等的，它們鑲嵌在一個環(huán)繞在地球四周的，像天文館的穹頂一樣的黑色的硬殼上。現(xiàn)在我們知道最遠星系的距離是最近星系的十億倍。天文學(xué)家是如何知道星星離我們有多遠呢?

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.

有一種方法跟你目測地面上物體的距離一樣。豎起一根手指，并保持一段距離，然后閉上眼睛，仿佛你在思考一樣。睜開一只眼睛并閉上另一只。當(dāng)你變換眼睛的時候，手指的位置似乎改變了。繼續(xù)來來回回地眨眼，然后移動手指，靠近你的臉。

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.

你的手指靠臉越近，相對于背景物它似乎越是有大的跳躍。這是測量星星距離的方法的關(guān)鍵。從不同的地方看時，近一點的星星似乎比遠一點的星星跳躍幅度要大。兩個觀測點相距越遠，這種跳躍就更明顯。

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.

你的雙眼只相距一英尺遠，因此不論你的眼睛眨多少下，光靠眼睛來看星星你是不會產(chǎn)生這種視覺落差的。但是宇航員能在世界上相隔上千英里的不同角落使用望遠鏡。甚至更好的，他們能給一顆星星拍照，然后六個月后再拍一次。六個月之后，地球就在太陽另一側(cè)的軌道上轉(zhuǎn)動，這樣就創(chuàng)造出一對相隔差不多一億英里的望眼鏡“雙眼”。在這么遠的距離下，跳躍就非常引人注目了。這種方式已被用來演算上千顆附近恒星的位置。