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Why Do Stars Twinkle - A Complete Guide

Why Do Stars Twinkle - A Complete Guide

Edited By Vishal kumar | Updated on Jul 02, 2025 05:01 PM IST

Looking upwards in the night sky, a star appears twinkling in the sky because of the phenomena atmospheric refraction. In this article, we will know why do stars twinkle at night, optical phenomenon included in twinkling of stars, why do stars twinkle but planets do not, why do stars seem higher in the sky than they actually are.

Why Do Stars Twinkle - A Complete Guide
Why Do Stars Twinkle - A Complete Guide

Why stars twinkle/shine at night

In class 10, we will find, which reason is responsible for twinkling of stars that is , why do stars twinkle.

We will first explain atmospheric refraction and will see a daily life example to see the wonders of this phenomenon.

A starry night sky with a light in the middle

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Atmospheric refraction

When we observe objects seen through a turbulent stream of hot air rising above a fire or a heat radiator, the objects appears to be flickering. The air just above the fire becomes hotter than the air farther up. The hotter air just above the fire is lighter than the cooler air above it. Thus, the hotter air just above the fire has a refractive index which is slightly less than that of the cooler air farther up. Since the air(I.E the refractive medium) is not stationary, the apparent position of an object as seen through the hot air fluctuates and causes flickering of the object, this wavering is an example of atmospheric refraction in the local environment of our laboratory .

Now, I hope that this phenomenon of atmospheric refraction is very clear to you after this example.

A close-up of a fire

Coming back to,

why do stars flicker?

When we look at a star on a clear night, the intensity of light coming from it appears to be continuously fluctuating (twinkling of stars in normal language).

At one moment, a star appears to be quite bright but at a very next moment, the star becomes dim and so on, this random fluctuation in observed brightness of a star is known as twinkling of stars.The twinkling of a star is on account of atmospheric refraction of light coming from the star.

When light coming from a star enters the earth’s atmosphere, it undergoes atmospheric refraction on account of varying optical density of air at different heights. The continuously changing atmosphere refracts the light from a star by different amounts in different atmospheric layers.

A group of stars in space

When the atmosphere refracts more light coming from a star to an observer, he feels star to be bright however when the atmosphere reflects less light to an observer, he feels the star to be dim so the star light reaching an observer’s eye changes randomly due to atmospheric refraction and the stars appears to be twinkling.

Related Topics Link,

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Why do stars twinkle but planets do not?

So, the question arises why not planets twinkle like stars at night. The star is the situated very distant from the earth and behaves approximately as a point-sized source, goes on varying slightly due to atmospheric refraction, the amount of light entering the eye flickers and the star twinkles.

A starry night sky with trees

The planets are much closer to the earth and thus seen as extended sources so a planet may be considered as a collection of a large number of points sized sources of light although amount of light coming from each point sized source flickers on account of atmospheric refraction yet the total amount of light entering our eye from all the individual point sized sources of the extended source will practically remain unchanged therefore planets do not twinkle but stars do.

Now let’s see how the phenomena of atmospheric refraction also changes the apparent position of a star and hence appears slightly higher than its actual position.

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Why do stars seem higher in the sky than they actually are?

We now know that refractive index of atmospheric air is maximum just near the surface of the earth and gradually decreases as one goes above the earth.

When starlight enters the earth’s atmosphere the light rays are travelling from optically rarer layers to optically denser layers. As a result, on Account of atmospheric refraction.

Diagram Description automatically generated

The light rays bend more and more towards the normal as they approach an observer on the earth. As a result of this bending of light towards normal, a star appears slightly higher or above then its actual position when viewed near the horizon.

Now, we have studied why do stars twinkle or twinkling of stars occurs due to which phenomena, atmospheric refraction and it’s example from our routine, why planets do not twinkle and why do stars seem higher in the sky.

Also check-

NCERT Physics Notes:

Frequently Asked Questions (FAQs)

1. What is a star? Is sun also a star?

A star is a huge sphere of celestial luminous body made up of gaseous (hydrogen and helium) plasma. Nuclear reactions inside the stars make stars alive and a luminous body. As soon as this fuel for nuclear reaction is used up, stars die because of their own gravitational force.

Yes, sun is our nearest star and the only star of our solar system.   

2. Are all stars of white colour?

No, the colour of a star depends upon the intensity of heat at the core that is its temperature. Hotter the star, more blue rays it emits. As temperature goes down its colour shifts towards red.Though most of the stars emits colour of all wavelengths. Stars appears to be white because are eyes are senistive to this only for blue rays.

3. How colour of stars describes about the age or distance of the stars from us?

At younger age there is plenty of fuel in stars the emit enormous energy hence less wavelength or more frequency waves are emitted. This is the reason why younger stars look bluish and old stars look reddish in colour. 

According to the, doppler effect in light as we go farther than the source. Wavelength of the object decreases with respect to the source. Hence, as stars go farther from us, they appears to be red in colour.

4. How is the approximate life of a star measured and its approximate temperature?

Actual age of the star cannot be calculated precisely. Hence, can be estimated only. Also, the age of stars are categorised on the basis of the type of stars. 

Total number of rays coming out of star per unit area is calculated to find the luminiousity and hence, the temperature of the stars is estimated.

5. How stars are born?

Stars nursery or stellar nursery is the space filled with dust and clouds of gases of dead stars through the fusion of elements. Here, is the stars born in middle of outburst of stars called supernovas.

Generally, nebula are known to be the birthplace of the stars. 

6. Why do stars appear to twinkle?
Stars appear to twinkle due to atmospheric turbulence. As starlight passes through Earth's atmosphere, it encounters layers of air with different temperatures, densities, and movements. These variations cause the light to refract (bend) slightly and randomly, making the star's position and brightness appear to change rapidly. This phenomenon is called atmospheric scintillation.
7. Do stars actually twinkle in space?
No, stars do not twinkle in space. The twinkling effect is only observed from Earth due to our atmosphere. Astronauts in space or observers on the Moon would see stars as steady points of light without any twinkling.
8. Why don't planets twinkle like stars?
Planets generally don't twinkle because they appear as small discs rather than point sources of light. The light from different parts of the planetary disc gets refracted differently by the atmosphere, averaging out the twinkling effect. However, very bright planets like Venus can sometimes appear to twinkle slightly.
9. How does the atmosphere affect starlight?
The atmosphere affects starlight in several ways:
10. What is atmospheric scintillation?
Atmospheric scintillation is the scientific term for the twinkling of stars. It refers to the rapid variations in apparent brightness, position, and color of celestial objects when viewed through Earth's atmosphere. This phenomenon is caused by turbulence and temperature fluctuations in the air, which affect the path of light as it travels to our eyes.
11. What is speckle interferometry and how does it relate to star twinkling?
Speckle interferometry is an astronomical imaging technique that takes advantage of atmospheric turbulence. It involves:
12. Can star twinkling be used to detect exoplanets?
While star twinkling itself isn't used to detect exoplanets, related concepts are employed:
13. How does the twinkling of stars affect radio astronomy?
While "twinkling" is primarily an optical phenomenon, similar effects occur in radio astronomy:
14. Can the study of star twinkling provide information about exoplanet atmospheres?
While challenging, the study of star twinkling can potentially inform us about exoplanet atmospheres:
15. How does altitude affect star twinkling?
Stars appear to twinkle less at higher altitudes. This is because there's less atmosphere for the light to travel through, resulting in less turbulence and refraction. Observatories are often built at high elevations to minimize atmospheric effects and provide clearer views of celestial objects.
16. Why do stars sometimes appear to change color when twinkling?
The color changes in twinkling stars are due to atmospheric dispersion. Different wavelengths (colors) of light are refracted by slightly different amounts as they pass through the atmosphere. This can cause momentary separation of colors, making a star appear to rapidly change between red, blue, and other hues.
17. What is the difference between scintillation and seeing in astronomy?
Scintillation refers to the rapid changes in brightness of a star due to atmospheric turbulence. Seeing, on the other hand, describes the overall steadiness and clarity of the atmosphere for astronomical observations. Good seeing conditions mean less atmospheric disturbance and sharper images of celestial objects.
18. Can the twinkling of stars be used for any practical purposes?
Yes, the twinkling of stars can be useful:
19. How does the twinkling of stars relate to the concept of refraction?
The twinkling of stars is directly related to refraction. As starlight enters Earth's atmosphere at an angle, it bends (refracts) due to the change in medium density. The constantly changing atmospheric conditions cause this refraction to vary rapidly, resulting in the twinkling effect we observe.
20. Why do stars twinkle more near the horizon?
Stars twinkle more near the horizon because their light has to travel through more of Earth's atmosphere to reach our eyes. This longer path means the light encounters more atmospheric layers and turbulence, leading to increased refraction and scintillation effects.
21. How does temperature affect star twinkling?
Temperature variations in the atmosphere play a crucial role in star twinkling. Warm and cool air pockets have different densities, which affects how light travels through them. Greater temperature differences between air layers lead to more pronounced refraction and, consequently, more noticeable twinkling.
22. What is the Airy disc and how does it relate to star twinkling?
The Airy disc is the central bright spot in the diffraction pattern of a point source of light when viewed through a circular aperture, like a telescope. Star twinkling can cause the Airy disc to rapidly change shape and position, affecting the resolution and quality of astronomical observations.
23. Can modern technology eliminate the effects of star twinkling for astronomers?
While we can't eliminate atmospheric effects entirely, modern technology has developed ways to mitigate them:
24. How does the twinkling of stars affect astrophotography?
Star twinkling can significantly impact astrophotography by:
25. What is a scintillometer and how is it used in astronomy?
A scintillometer is an instrument used to measure the intensity fluctuations of light caused by atmospheric turbulence. In astronomy, it's used to:
26. How does the size of a telescope affect the perception of star twinkling?
Larger telescopes tend to reduce the apparent twinkling of stars. This is because they collect light over a wider area, averaging out some of the atmospheric effects. However, larger telescopes are still affected by seeing conditions and may require advanced adaptive optics systems for optimal performance.
27. Why don't we see stars twinkle during the day?
We don't see stars twinkle during the day primarily because we can't see stars at all due to the brightness of the scattered sunlight in our atmosphere. If we could see stars during the day, they would still twinkle, but the effect would be masked by the bright sky background.
28. How does air pollution affect star twinkling?
Air pollution can exacerbate star twinkling by:
29. What is the connection between star twinkling and mirages?
Both star twinkling and mirages are caused by atmospheric refraction. While star twinkling involves rapid, small-scale refraction changes high in the atmosphere, mirages are typically caused by larger-scale temperature inversions closer to the ground. Both phenomena demonstrate how light can be bent by variations in air density.
30. How does the wavelength of light affect twinkling?
Different wavelengths (colors) of light are refracted by slightly different amounts as they pass through the atmosphere. This differential refraction can cause:
31. Can star twinkling be observed on other planets with atmospheres?
Yes, star twinkling could be observed on other planets with atmospheres. The extent and nature of the twinkling would depend on:
32. How does the Earth's rotation affect our perception of star twinkling?
The Earth's rotation doesn't directly cause star twinkling, but it does affect our perception of it:
33. What is the relationship between star twinkling and astronomical seeing?
Star twinkling and astronomical seeing are closely related:
34. How does the concept of coherence length apply to star twinkling?
Coherence length in optics refers to the distance over which a wave maintains a consistent phase relationship. In the context of star twinkling:
35. How does the twinkling of stars relate to the concept of turbulent flow in fluid dynamics?
The twinkling of stars is a direct result of turbulent flow in the atmosphere:
36. What is the difference between chromatic and achromatic scintillation?
Chromatic and achromatic scintillation refer to different aspects of star twinkling:
37. How does the concept of Fried parameter relate to star twinkling?
The Fried parameter (r0) is a measure of the quality of optical transmission through the atmosphere:
38. Can artificial stars be used to study atmospheric effects on starlight?
Yes, artificial stars (like laser guide stars) are used to study atmospheric effects:
39. How does the twinkling of stars relate to the concept of wavefront distortion?
Star twinkling is directly related to wavefront distortion:
40. What is the role of Kolmogorov turbulence theory in explaining star twinkling?
Kolmogorov turbulence theory is fundamental to understanding star twinkling:
41. What is the connection between star twinkling and the concept of optical turbulence?
Star twinkling is a direct manifestation of optical turbulence:
42. How does the presence of water vapor in the atmosphere affect star twinkling?
Water vapor in the atmosphere can significantly impact star twinkling:
43. What is the relationship between star twinkling and the concept of isoplanatic angle?
The isoplanatic angle is closely related to star twinkling:
44. How does the twinkling of stars relate to the phenomenon of astronomical refraction?
While related, twinkling and astronomical refraction are distinct:
45. How does the concept of coherence time relate to star twinkling?
Coherence time is crucial in understanding and mitigating star twinkling:
46. What is the connection between star twinkling and the phenomenon of limb darkening?
While not directly related, both phenomena involve how we perceive starlight:
47. How does the twinkling of stars relate to the concept of atmospheric extinction?
Atmospheric extinction and star twinkling are both atmospheric

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