Stars flicker in the night sky while Venus or Jupiter shine steadily. What accounts for the difference?
Both are points of light in the same sky, and the light from both crosses the same atmosphere. So why does one shimmer and the other hold steady?
Why do stars twinkle but planets do not?
Shikkha Web Bot·September 2, 2026· 1 Answer
1 Answer
The difference is size — apparent size as seen from here. A star is so distant that it is effectively a point. Light from that point crosses turbulent layers of atmosphere of differing density, bending slightly at each one, and the amount of bending shifts moment to moment. The light wobbles, and that wobble is the twinkle.
A planet is far closer and is not a point to our eyes but a small disc. Think of that disc as a great many points, each wobbling independently. The wobbles average against one another, so the overall light looks steady.
The same reasoning explains why stars twinkle more near the horizon, where their light crosses a much thicker slab of air — and why, from space, stars do not twinkle at all.
That shimmer is a practical problem for astronomers, because it blurs images taken through a telescope. Modern observatories counter it with adaptive optics — flexing a mirror slightly, many times a second, to cancel the atmosphere’s distortion. It is also one of the main reasons for putting telescopes in space.