【英语时差8,16】什么是视差和如何计算它（上）

Parallax is a 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!

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。