【英语时差8,16】什么是视差和如何计算它（上）（在线收听）

Parallax is a 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!