Short · Sky
Why do stars twinkle but planets don't?
Moving pockets of warm and cool air bend starlight like lenses. A star is a single point, so it flickers; a planet is a tiny disk of many points, and their flickers average out.
Try it yourself
Opens Twinkle Lab. Change the same thing yourself.
Transcript
Why do stars twinkle, but planets don't? Starlight crosses the whole atmosphere, through pockets of warm and cool air that bend light like moving lenses. A star is so far away it's a single point, so each wobble shifts all of its light at once. It flickers. Now grow the dot into a planet. Jupiter is a tiny disk: many points, each wobbling its own way. The flickers average out, so it shines steady. Try it yourself at Explainer Tools dot com.