Question
Thu February 02, 2012 By:

why don't planets twinkle? because in my opinion planets do not twinkle because they do not have their own light, but it totally different given in my text book?

Expert Reply
Thu February 02, 2012

Stars always twinkle because they’re so far away from Earth that, even through large telescopes, they appear only as pinpoints. And it’s easy for Earth’s atmosphere to disturb the pinpoint light of a star.

As a star’s light pierces our atmosphere, each single stream of starlight is forced by the atmosphere to zig and zag this way and that. . . . and so stars appear to twinkle. On the other hand, planets don’t twinkle (usually) simply because they’re closer to Earth. You’d know they’re closer if you looked through a telescope. Through telescopes, planets don’t look like pinpoints. Instead, they look like tiny disks. And while the light from one edge of a planet’s disk might be forced to “zig” by Earth’s atmosphere, light from the opposite edge of the disk might “zag” in an opposite way. The zigs and zags cancel each other out . . . and that’s why planets appear to shine steadily.

planets don’t twinkle – you might see them twinkling a little if you spot them low in the sky. That’s because, in the direction of any horizon, you’re looking through more atmosphere than when you look overhead. Even planets can’t withstand too much atmosphere, because it’s the atmosphere that makes them twinkle!
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