[Physics Class Notes] on Why Do Stars Twinkle? Pdf for Exam

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.