Stars twinkle, while planets (usually) shine steadily. Why? Stars twinkle because Б theyБre so far away from Earth that, even through large telescopes, they appear only as pinpoints. And itБs easy for EarthБs atmosphere to disturb the pinpoint light of a star. As a starБs light pierces our atmosphere, each single stream of starlight is refracted Б caused to change direction, slightly Б by the various temperature and density layers in EarthБs atmosphere. You might think of it as the light traveling a zig-zag path to our eyes, instead of the straight path the light would travel if Earth didnБt have an atmosphere.
Planets shine more steadily because Б theyБre closer to Earth and so appear not as pinpoints, but as tiny disks in our sky. YouБd could see planets as disks if you looked through a telescope, while stars would remain pinpoints. The light from these little disks is also refracted by EarthБs atmosphere, as it travels toward our eyes. But Б while the light from one edge of a planetБs disk might be forced to БzigБ one way Б light from the opposite edge of the disk might be БzaggingБ in an opposite way. The zigs and zags of light from a planetary disk cancel each other out, and thatБs why planets appear to shine steadily.
You might see planets twinkling if you spot them low in the sky. ThatБs because, in the direction of any horizon, youБre looking through more atmosphere than when you look overhead. If you could see stars and planets from outer space, both would shine steadily. ThereБd be no atmosphere to disturb the steady streaming of their light. Can you figure out which objects are stars and which are planets just by looking for the twinklers vs the non-twinklers? Experienced observers often can, but, at first, if you can recognize a planet in some other way, you might notice the steadiness of its light by contrasting it to a nearby star.
Bottom line: Stars twinkle because they appear as tiny pinpoints as seen from Earth, even through telescopes. Planets donБt twinkle because they are closer, and thus appear larger in our sky, as tiny disks instead of pinpoints.
Everyone must be familiar with the famous poem : Twinkle Twinkle Little StarБ. Well, itБs not just a poemб for children, itБs actually referring to a particular scientific phenomenon that has fascinated observers from manyб years. They certainly appear to do so, Why do all the other stars in the night sky appear to twinkle, but Planet sб never does?
Why Do Stars Twinkle? Light from stars crosses a very long distance to reach us and also passes through EarthБs atmosphere, whichб vary in temperature and density. Our atmosphere is very turbulent, with streams and eddies forming, churning around, and dispersing all the time. Every layer of EarthБs atmosphere has air moving in different directions atб different intensities. When light from stars passes through the atmosphere, it is bent due to refraction, which is why stars seem to twinkle when we stare at them. If viewed from outer space, you would not see the stars twinkling.