英语听力文摘 English Digest 249、视差

　　Parallax
视差就是从有一定距离的两个点上观察同一个目标所产生的方向差异。从目标看两个点之间的夹角，叫做这两个点的视差，两点之间的距离称作基线。只要知道视差角度和基线长度，就可以计算出目标和观测者之间的距离。同位置看同一天体的方向之差。比如，当你伸出一个手指放在眼前，先闭上右眼，用左眼看它；再闭上左眼，用右眼看它，会发现手指相对远方的物体的位置有了变化，这就是从不同角度去看同一点的视差。视差可用观测者的两个不同位置之间的距离（基线）在天体处的张角来表示。
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. Astronomers¹ use parallax to calculate the distance to stars. Do you need a gigantic computer-based observatory² 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 forth³ 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 discrepancy⁴ 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 pointed⁵ in exactly the right direction? By aligning⁶ it with the so-called “fixed stars(恒星)”–stars so far away they show no parallax motion whatsoever⁷. Against that unmoving background, the closer stars can be picked out.
译文：
视差
视差是我们目测事物的距离时所产生的现象。天文学家利用视差来计算我们到恒星的距离。你需要使用一个庞大的以计算机为基础的天文台吗？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，闭上一只眼睛，然后换另一只眼睛。你的手指似乎在两个位置之间来回移动。这是因为每只眼睛的角度稍有不同，大脑合成的这些影会给你一种三维空间感。
但是，请注意，你的手指放得越远，这些图像之间位置的差异就越小。视差会随着距离增加而减少。这是一个令人兴奋的发现，因为我们可以利用视差来判断与外太空物体的距离。下面我们来说说怎样做到。
因为地球围绕太阳公转一圈是一年的时间，每六个月后它的位置离六个月前最远。这之间的距离就像你两眼之间的距离一样。在一月拍摄的远距离物体可与六月拍摄的相比较，根据视差所表现的物体的明显运动轨迹能够告诉我们它离地球有多远。
但是等等，你怎么知道你的望远镜是指向的正确的方向？通过对准所谓的“恒星”-星星如此之远以至于它们没有视差运动的现象。与静止的背景形成对比，比较近的星星就可以被挑选出来。

1 astronomers   

n.天文学者，天文学家( astronomer的名词复数 )

参考例句：

• Astronomers can accurately foretell the date,time,and length of future eclipses. 天文学家能精确地预告未来日食月食的日期、时刻和时长。 来自《简明英汉词典》
• Astronomers used to ask why only Saturn has rings. 天文学家们过去一直感到奇怪，为什么只有土星有光环。 来自《简明英汉词典》

2 observatory   

n.天文台，气象台，瞭望台，观测台

参考例句：

• Guy's house was close to the observatory.盖伊的房子离天文台很近。
• Officials from Greenwich Observatory have the clock checked twice a day.格林威治天文台的职员们每天对大钟检查两次。

3 forth   

adv.向前；向外，往外

参考例句：

• The wind moved the trees gently back and forth.风吹得树轻轻地来回摇晃。
• He gave forth a series of works in rapid succession.他很快连续发表了一系列的作品。

4 discrepancy   

n.不同；不符；差异；矛盾

参考例句：

• The discrepancy in their ages seemed not to matter.他们之间年龄的差异似乎没有多大关系。
• There was a discrepancy in the two reports of the accident.关于那次事故的两则报道有不一致之处。

5 pointed   

adj.尖的，直截了当的

参考例句：

• He gave me a very sharp pointed pencil.他给我一支削得非常尖的铅笔。
• She wished to show Mrs.John Dashwood by this pointed invitation to her brother.她想通过对达茨伍德夫人提出直截了当的邀请向她的哥哥表示出来。

6 aligning   

n. (直线)对准 动词align的现在分词形式

参考例句：

• There are signs that the prime minister is aligning himself with the liberals. 有迹象表明首相正在与自由党人结盟。
• ToolTips provide textual hints that assist in drawing lines and aligning objects. 工具提示提供了协助画线和对象对齐的文本提示。 来自About Face 3交互设计精髓

7 whatsoever   

adv.（用于否定句中以加强语气）任何；pron.无论什么

参考例句：

• There's no reason whatsoever to turn down this suggestion.没有任何理由拒绝这个建议。
• All things whatsoever ye would that men should do to you,do ye even so to them.你想别人对你怎样，你就怎样对人。