Why do stars twinkle? – Put simply, stars do not twinkle! They just appear to twinkle. The question should not be why do stars twinkle rather it should be why does this happen? It is because of the earth’s atmosphere. Before getting into this process, you should have a basic understanding of refraction.
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.
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 atmosphere between you and the star in this direction. Therefore, more series of refractions!
Watch this video to learn more about refraction and get a clear picture of this phenomenon:
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