Twinkle, twinkle, little star, How I wonder what you are!

Stars are technically defined as massive celestial luminous bodies made of burning gases held by its own gravity. All stars have one thing in common; they all twinkle in dark night. On a clear dark night, the sky full of celestial bodies, we could see about 6000 or so twinkling stars. Have you ever been curious about what makes these stars to do twinkle? How do they twinkle and what is actually a twinkling of stars? Let’s find the answer-

This is all the refraction of light, what makes stars to twinkle:

Unlike other planets of our solar system earth is unique, it has all things necessary for a life. The most important of which is the presence of an atmosphere consisting of different layers of different composition, full of gases turbulently moving around. These gases in the atmosphere collectively form the air. Different layers of the earth’s atmosphere heat differently and form moving air pockets of cold and hot airs in the atmosphere.

Refraction is the change in direction of wave propagation due to a change in its transmission medium.

Refraction is the change in direction of wave propagation due to a change in its transmission medium. When a light ray passes through earth’s atmosphere, it bends and changes its path. This phenomenon of bending of light is known as refraction. If light rays enter from a thinner to denser medium the light bends slightly inwards, while in the case of a light entering from a denser medium to thinner medium it bends outwards. Similar things happen when the light rays coming from the sun passes through the earth’s atmosphere. The only difference, in this case, is- earth’s atmosphere consists of several air pockets each one having a different temperature. Hence these air pockets in different layers of atmosphere not only works like little prism or lens but also moves turbulently.

the movement of light refracting air pockets in the atmosphere makes the bending of light a random process, causing star’s light flicker randomly. This random flickering changes the brightness as well as the position of stars in our view, giving us an appearance of twinkle. This process of change in brightness and position of luminous bodies; i.e stars when viewed through a medium (earth’s atmosphere in this case)is what astronomers call stellar scintillation or astronomical scintillation.

Star’s distance from earth also plays a role:

If we leave the only star of our own galaxy which we call the sun, all other stars are so far away from the earth. In fact, the closest one after our sun is about 4.37 light year away and is the part of Alpha Centauri triple-star system. Being so distant from the earth these stars appears to us not more than a tiny little shining dot in the night sky. The change in brightness and position due to refraction by the earth’s turbulent atmosphere becomes so evident for these tiny shiny spots, making them appear as they are winking or twinkling. But in reality, these stars are burning normally like our sun, so far away from the earth.

The stars closer to the horizon appear to twinkle more than others which are overhead to us. This is because of the fact that the light rays coming from the stars near the horizon travel more distance through the atmosphere than the light rays coming from an overhead star. Hence causes more refraction, which means more flickering in brightness and position of the star, making them twinkle more than the overhead one.

Stars on horizons twinkle more in comparison to overhead stars.

What about planets, do they twinkle?

Hmm, so now this is the time for Planets. Planets usually do not twinkle except when the atmosphere is extremely turbulent. In comparison to stars, planets are so close to us and appear bigger than stars. Most of the planets in the sky do appear like a disk than a tiny dot like stars.  As Planets do not twinkle and it could be a good way to figure out if a particular celestial object we see in the sky is a planet or a star. The reason why these planets do not twinkle lies in the fact that they have a finite size and so close to the earth that their size in a sense “averages out ” the refraction caused by the turbulent air pockets of atmosphere, forming a relatively stable image in our eyes.

Stellar scintillation of a star and a planet.

Stars from the space:

This is not hard now to guess that stars from the space do not appear to twinkle. They just appear like a small round disk or circle. If you are on another planet where there is no atmosphere, stars surely will not twinkle as they do on earth. As the moon do also not have any atmosphere so there is no chance of twinkling stars on the moon. They will simply look like tiny little shiny dots. Lack of atmosphere in space is also one of the reasons for space telescopes, like Hubble, capture a better image of stars because there will be no twinkling in stars in absence of atmosphere

Simply explained:

Twinkling of stars, also known as stellar scintillation or astronomical scintillation is a phenomenon of slight change in brightness and location of stars while looking them through a medium. It happens because of their distance from the earth and presence of an atmosphere on the earth. Being so distant from the earth, most of the stars looks like a tiny dot. Light rays coming from a star get bent in one or another direction (anomalous refraction) by small air pockets of hot and cold air in earth’s turbulent atmosphere.  These air pockets act like prism and lenses slightly diverting the path of light rays making a change in brightness and position of stars. The small dot-like appearance of stars makes the change in brightness and position more evident, as stars are winking or twinkling. If you are in space or on another planet or on the moon where there is no atmosphere, I am sorry to say but stars do not twinkle there.


This is all about twinkling stars, we hope there is no wonder left for you in why these shiny bodies twinkle? They do also not blink their eyes because they don’t have any 😉 Do you have any queries or curiosity wanna get answered by us? Don’t forget to tell us by commenting down below. Want to say something in private, use our contact page.


  2. Starchild Nasa
  3. Alden, Harold L. (1928). “Alpha and Proxima Centauri”. Astronomical Journal. 39 (913): 20–23.
  4. Born and Wolf (1959). Principles of Optics. New York, NY: Pergamon Press INC. p. 37.



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