Why Do Stars Twinkle?

The answer to why do stars twinkle at night is that they appear to twinkle when they are seen from the surface of the earth. So they don’t actually twinkle but because of the turbulence that is caused in the atmosphere, they appear to be twinkling. The light from the stars gets refracted as they pass through different mediums when they come in contact with the wind and different temperatures and densities in the atmosphere.

Why do stars twinkle?

When a ray of light travels from one medium to another it ‘bends’. This phenomenon is referred to as refraction. If it travels from a rare medium to a dense medium, it bends towards the normal and if it travels from a dense medium to a rarer medium, it bends away from the normal. The speed through which it travels changes depending on the medium and therefore this bending occurs.

Stars Twinkle

Watch this video to learn more about refraction and get a clear picture of this phenomenon:


This effect can be observed when light passes through a prism or a glass slab and even when light passes through water. The light ray actually travels from air to a medium of different density here.

So how are refraction and twinkling connected? The atmosphere of the earth is made of different layers. It is affected by winds, varying temperatures, and different densities as well. When light from a distant source (a star) passes through our turbulent (moving air) atmosphere, it undergoes refraction many times. When we finally perceive this light from a star, it appears to be twinkling! This is because some of the light rays reach us directly and some bends away from and toward us. It happens so fast that it gives a twinkling effect.

If you are in a large empty field such that the horizon is visible to you, you will notice that stars in this region appear to twinkle a lot more than stars right overhead. Why do you think this happens? Why do stars twinkle more when viewed from such places? It is because there are more layers of the atmosphere between you and the star in this direction. Therefore, more series of refractions!

Why Do Planets Do Not Twinkle?

Planets do not twinkle like stars because the distance between the planets and the earth is not far when compared to the distance between the stars and the earth. As the distance is less, the refraction of light won’t be much for planets. Thus, planets do not twinkle.

Watch interactive more videos, check out BYJU’S – The Learning App and you will always have the answer to questions like why do stars twinkle?

Practise This Question

What is the reason of the twinkling of stars?

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