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Why Do Stars Twinkle?

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Last updated date: 16th May 2024
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An Overview of Twinkling of Stars

In simple words, the twinkling of stars is due to the passing of light from the stars to our eyes through the different layers of our atmosphere. Usually related to temperature gradient there is the change in density of air and due to this change in density when the light rays travel through layers having different densities only then the twinkling of stars is caused in most cases.


The twinkling of the stars is one of the most beautiful phenomena we come across in our life since our childhood. We learn rhymes on the twinkling of stars from the very beginning of our student life, since kindergarten. But as a matter of fact, these stars don't twinkle. Yes, indeed they don't. We shall discuss the whole topic of the twinkling of stars in detail here.


The twinkling of stars is due to the large distance between them and Earth. Even when viewed with the help of a large telescope, they appear as pinpoints easily disturbed by the Earth's atmosphere.


Basically, the twinkling of stars is caused when light rays travel through different layers of the atmosphere and then finally reach the Earth's surface. This twinkling is due to the refraction of light rays. It is generally related to the temperature gradients. As light rays from any star race through the atmosphere, it deviates and deflects through different

layers, causing it to bend before you see it. In the atmosphere, there is a regular change in the density of air that increases as we travel towards the surface.


Once the light from a star enters the Earth's atmosphere, each of its rays get refracted, causing a slight change in the direction due to various temperature and density layers of the atmosphere. You can visualize that light moves in a zig- zag path instead of a straight path to your eyes in case the Earth didn't have an atmosphere.


Explain the Phenomenon of Twinkling of Stars

The atmospheric refraction causes the twinkling of the stars. In other words, the air above us is like a big ocean and is not very dense fluid, which has a small bending effect on light that passes through it. If it were to be perfectly still, the light from the star would follow a straight path, and the star's image would have appeared stable.


But in reality, the atmosphere is always moving, and winds at every level will cause slight differences to shift around, and different densities bend light at different amounts. This will result in the light from the star as a zig-zag movement as they come close to our eyes making it appear to twinkle.A little bit of more apparent disk will take a lot more bending of the incoming light for the rays from all parts of the disk to get bent away from your direction so that large objects would appear to blink momentarily and so appear to twinkle. To prevent twinkling, it doesn’t take much of an apparent disk.


It also depends upon the condition that happens in the air above you at any given time. During clear nights, there will be a lot of rolling in the atmosphere, and the stars will appear to twinkle more. On other nights, when the upper air is calm, twinkling will not happen as it ought to be.


The whole effect can be compared to what you see when you are at the bottom of a swimming pool during bright sunlight. If the water surface is wavy, there will be a lot of moving light and dark patterns on the pool floor. If there is no disturbance and the surface of the water is smooth, and there is no wind, then the moving pattern will disappear.


Atmospheric Refraction

Atmospheric refraction is the phenomenon where the light rays or other electromagnetic waves that pass through the atmosphere if the Earth deviates due to the variation in the density of air and function of height. Atmospheric refraction not only deviates the visible light rays that come from the stars but also deviates the electromagnetic waves in different directions. Not only the light, but the sound waves also get refracted when they pass through the different atmospheric layers. Atmospheric refraction can help you to locate the celestial bodies and the distant objects in the universe. This is due to this phenomenon only that the celestial bodies or other distant objects in the sky appear to be at a much higher position than they actually are.


Why do Stars Twinkle and Planets do not?

When the light from the stars enters the atmosphere, it collides with gas molecules and scatters (reflection and interference). Planets are a collection of a large number of point sources of light, whereas stars are considered to have a point source.


We are able to see a tiny beam of light from it as the star is so far away from it. This light will get scattered from our eyes and then back into them, almost like it is blinking on and off. The process is so fast it appears like twinkling.


As compared to stars, planets are closer to us and send more light; even if some light beams get scattered away, others get to us. So, planets do not usually twinkle.


Explain Why Planets do not Twinkle

Planets do not twinkle because of the following reasons:

  • Planets reflect the low-intensity light reaching them; they are not the source of light.

  • Compared to stars, the planets are much closer to Earth, due to which the shift in atmospheric refraction is smaller.

  • Since the planets are closer, they appear larger than stars, so the shift is not enough for planets to twinkle.


The planets should twinkle if they are spotted low in the sky. This is because you are looking through more atmospheres in the direction of any horizon than when you look overhead.


If you are able to see stars and planets from outer space, both will shine steadily since there will be no atmosphere to disturb the steady streaming of their light.


Based on twinklers and non-twinklers, can one determine which object is a star and which is the planet? The observers who have an experience they can, but for the first time to recognize a planet, would be noticing the steadiness of its light by contrasting it to a nearby star.


Do You know?

Stars don’t usually twinkle, but when seen from the surface of the Earth, they just appear to twinkle. Due to the effects of Earth's atmosphere, the stars twinkle in the night sky. When starlight enters the atmosphere, it is affected by winds in the atmosphere and by areas with different densities and temperatures. These are the causes due to which light from the star appears to twinkle when seen from the ground.


Conclusion

The twinkling of light is just due to the refraction of light through different layers. They don't actually twinkle but just appear to be so, because of the different densities of the different layers of light. Due to different densities and different temperatures in different layers of our atmosphere, the light ray is refracted, or bent, many times which results in the twinkling of the light.

FAQs on Why Do Stars Twinkle?

1. Why do Planets Shine More Steadily?

As the distance between the Earth and planets is small; they don't appear as pinpoints but tiny disks in our sky. One can see planets as a disk when observed through a telescope while stars remain pinpoints. The lights from these little disks are also refracted from the Earth's atmosphere, as it travels towards our eyes.  But while light from one edge of a planet disk might be forced to zig in one direction; light from the opposite edge of the disk might be zagging in an opposite way. The planet appears to shine steadily since the zigs and zags of light from a planetary disk cancel each other out.

2. Why are Some Stars Bright and Others Dim?

All stars are not equidistant from us, some are close, and some are farther. The star will appear brighter the closer they are to us. The stars also come in various sizes and brightness. Compared to smaller stars, larger stars shine brightly. So, the brightness of the star depends upon the size and how far it is from us. If the star is away from us then there is more refraction and it takes more time for the light rays to reach our eyes. This is the main reason the far one appears to be less bright.

3. What are Constellations?

A group of objects that make an imaginary shape in the night sky is known as the constellation. This is usually named after mythological characters, people, animals, and objects. Different shapes from the same group of bright stars have been made by different people in different parts of the world. It is similar to the game of connecting dots. In the past, it was useful for navigation and keeping track of the seasons. Since all the stars are at a different distance, the constellations would appear totally different to inhabitants of another planet orbiting another star.

4. Are there moving stars also?

We know about the phenomenon of the twinkling of stars but do you know that stars are not fixed but are constantly moving. If you factor in the moving of the stars along with the rotation of the earth, you are going to get the same pattern of the stars in many places that seem never changing at all. They are constantly moving but the thing is that they are so far from us, like thousands of light-years away, and so we are not able to see their movement from our naked eyes. The stars are farther away from us, even than mountain tops, so the motion in their field of view is very minute but still, they are moving.

5.  Why do stars appear in different colours while twinkling?

This is because of the twinkling of stars only, we know when the light rays travel from the stars to the earth surface they cross a number of layers. In each layer there occurs the refraction of light. Due to the refraction of light, there is bending of light at each layer due to which when it reaches our eyes, we consider stars to be twinkling. Along with this when the air moves in and out, the light of stars is refracted, and often different colours are transmitted in different directions. Due to this particular property of chromatic aberration the stars may appear to change their colour when they are twinkling very strongly.

6. Are stars present during the day also?

Yes, the stars are still there during the day. During the day, stars are present but the strong rays of the sun and the bright light that the sun gives out overpowers the faint light that is given out by all the other stars. At night when the sun moves to the other side of the earth due to the rotation of the earth, it is possible for us to see the stars that were present in the sky all the time but their light was just masked up or covered up by the light that is emitted by the sun.

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