英語(yǔ)聽力文摘 視差

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https://online2.tingclass.net/lesson/shi0529/0007/7643/249.mp3

https://image.tingclass.net/statics/js/2012

Parallax

視差就是從有一定距離的兩個(gè)點(diǎn)上觀察同一個(gè)目標(biāo)所產(chǎn)生的方向差異。從目標(biāo)看兩個(gè)點(diǎn)之間的夾角，叫做這兩個(gè)點(diǎn)的視差，兩點(diǎn)之間的距離稱作基線。只要知道視差角度和基線長(zhǎng)度，就可以計(jì)算出目標(biāo)和觀測(cè)者之間的距離。同位置看同一天體的方向之差。比如，當(dāng)你伸出一個(gè)手指放在眼前，先閉上右眼，用左眼看它;再閉上左眼，用右眼看它，會(huì)發(fā)現(xiàn)手指相對(duì)遠(yuǎn)方的物體的位置有了變化，這就是從不同角度去看同一點(diǎn)的視差。視差可用觀測(cè)者的兩個(gè)不同位置之間的距離(基線)在天體處的張角來(lái)表示。

You may have heard of parallax, but what is it? Find out on this Moment of Science.

Parallax is phenomenon by which we can judge the distance to things just by looking at them. Astronomers use parallax to calculate the distance to stars. Do you need a gigantic computer-based observatory to use it? Not at all. Your finger will do nicely.

Put one finger up in front of your face and close one eye, then the other. Your finger seems to jump back and forth between two positions. That’s because the perspective from each eye is slightly different, and your brain combines these images to give you a sense of three dimensional space.

Notice, however, that the farther you move your finger away the less discrepancy there is between the images. Parallax must decrease with distance! This is an exciting discovery, because we can now use parallax to judge the distance to objects out in space. Here’s how.

Because the earth moves around the sun in one year’s time, every six months it is as far away from where it was six months ago as it can get. That distance is like the distance between your eyes. Images taken of a far-off object in January can be compared with images of the object in June. The apparent motion of the object due to parallax tells us how far away it is from earth.

But wait! How do you know that your telescope is pointed in exactly the right direction? By aligning it with the so-called “fixed stars(恒星)”–stars so far away they show no parallax motion whatsoever. Against that unmoving background, the closer stars can be picked out.

譯文：

視差

視差是我們目測(cè)事物的距離時(shí)所產(chǎn)生的現(xiàn)象。天文學(xué)家利用視差來(lái)計(jì)算我們到恒星的距離。你需要使用一個(gè)龐大的以計(jì)算機(jī)為基礎(chǔ)的天文臺(tái)嗎?根本不用。你的手指就可以做得很好。

放一只手指在你的面前，閉上一只眼睛，然后換另一只眼睛。你的手指似乎在兩個(gè)位置之間來(lái)回移動(dòng)。這是因?yàn)槊恐谎劬Φ慕嵌壬杂胁煌?，大腦合成的這些影會(huì)給你一種三維空間感。

但是，請(qǐng)注意，你的手指放得越遠(yuǎn)，這些圖像之間位置的差異就越小。視差會(huì)隨著距離增加而減少。這是一個(gè)令人興奮的發(fā)現(xiàn)，因?yàn)槲覀兛梢岳靡暡顏?lái)判斷與外太空物體的距離。下面我們來(lái)說(shuō)說(shuō)怎樣做到。

因?yàn)榈厍驀@太陽(yáng)公轉(zhuǎn)一圈是一年的時(shí)間，每六個(gè)月后它的位置離六個(gè)月前最遠(yuǎn)。這之間的距離就像你兩眼之間的距離一樣。在一月拍攝的遠(yuǎn)距離物體可與六月拍攝的相比較，根據(jù)視差所表現(xiàn)的物體的明顯運(yùn)動(dòng)軌跡能夠告訴我們它離地球有多遠(yuǎn)。

但是等等，你怎么知道你的望遠(yuǎn)鏡是指向的正確的方向?通過對(duì)準(zhǔn)所謂的“恒星”-星星如此之遠(yuǎn)以至于它們沒有視差運(yùn)動(dòng)的現(xiàn)象。與靜止的背景形成對(duì)比，比較近的星星就可以被挑選出來(lái)。