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 Why does stars twinkle but planets do not?

Stars emit their own light and they twinkle due to the atmospheric refraction of light. Stars are very far away from the earth. Hence, they are considered as point sources of light. When the light coming from stars enters the earth’s atmosphere, it gets refracted at different levels because of the variation in the air density at different levels of the atmosphere. When the star light refracted by the atmosphere comes more towards us, it appears brighter than when it comes less towards us. Therefore, it appears as if the stars are twinkling at night

Planets do not twinkle because they appear larger in size than the stars as they are relatively closer to earth. Planets can be considered as a collection of a large number of point-size sources of light. The different parts of these planets produce either brighter or dimmer effect in such a way that the average of brighter and dimmer effect is zero. Hence, the twinkling effects of the planets are nullified and they do not twinkle

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As the light from a star enters the atmosphere, it hits gas molecules and scatters(reflection and interference).
Since the star is so far away, we only see a tiny beam of light from it.
This beam gets scattered away from our eyes and then back into them almost like it is blinking on and off.
It happens so fast that it just looks like it is twinkling.
(Planets are closer to us and send more light; if some of the light beams are scattered away, others still get through to us, so planets don't usually twinkle.)

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A distant star can be thought of as a point source of light. The twinkling of a star is due to atmospheric refraction of starlight. The starlight, on entering the earth’s atmosphere, undergoes refraction continuously in layers of atmosphere before it reaches the earth. The continuously changing atmosphere refracts the light from the star by different amounts from one moment to the next. The star light reaching our eye increases and decreases continuously due to atmospheric refraction and hence the star appears to twinkle.
Planets are much closer to the earth compared to stars and thus can be considered as extended sources. If we consider a planet as a collection of a large number of point sources of light the total variation in the amount of light entering our eye from all the independent point sources will average out to zero and hence the twinkling effect is cancelled.
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Why star Twinkle but the planet doesn't

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stars twinkle  because of atmospheric refraction but in planets they are close to earth in comparison to stars so we receive more  light from planets  and in planets atmospheric refraction also take place but it is not noticeable then in stars
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Atmospheric layer closest to the earth's surface has maximum refractive index which gradually decreases as we go higher up.Since the light rays travelling from rarer to denser medium bend towards the normal, the apparent position of the stars is slightly different from the actual postion.This apparent position keeps on changing slightly since the physical conditions of atmosphere are not stationary.Due to these changes in light rays entering the eye, the stars appears to flicker,that is, sometimes it appears brighter and sometimes dim causing the twinkling effect.
Planets are much closer to earth as compared to stars and as such they are extended bigger source of light when observed from earth.A planet can be considered as a collection of a large number of point sized sources of light.Due to atmospheric refraction, each point source will send varying bright and faint light to the observer.If all the point size are taken together, the net variation in the amount of light entering eye average out to zero,nullifying the twinkling effect.Thus, the planets donot twinkle.
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Hello friend!!
Rajdeep here....

Compare the distance between a star and the Earth and a planet and the Earth.

A star is located far from the Earth. The light rays from the star has to suffer repeated refraction as it passes through each successive layer of the atmosphere. The upper layers of the atmosphere are rarer than the lower, hence, after each successive refraction, the light ray bends towards the normal. Now, the density of each layer continuously changes due to slight change in physical conditions like temperature and pressure, hence the apparent position of the Star continuously changes. Since the distance of the star is much, to our eyes, the change in position occurs twinkling; hence, we see stars twinkling.

On the other hand, planets are much closer to the Earth. Moreover, planets are not luminous by themselves, light from the Stars (like Sun) reflect from the planet. Thus, planets do not seem twinkling.

Thanks!
 
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NYC answers
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:)
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as planet so much closer to earth the amount of flight receive from the them is Greater and fluctuation to due to atmospheric refraction is less
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TWINKLING OF STARS IS DUE TO ATMOSPHERIC REFRACTION,CHANGING POSTION OF STARS AND MOVEMENT OF LAYERS OF ATMOSPHERE.SO LIGHT FROM STARS ARE SOMETIMES BRIGHTER AND SOMETIMES FAINTER/LIGHTER.PLANETS ARE VERY CLOSE TO THE EARTH THAN THE STARS.

LIGHT FROM STARS-POINT SOURCES OF LIGHT

LIGHT FROM PLANETS-EXTENDED SOURCES OF LIGHT
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Here is the answer of why stars twinkle but planets don't

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Planets don't twinkle bcoz

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Unlike stars, planets don't twinkle. Stars are so distant that they appear as pinpoints of light in the night sky, even when viewed through a telescope. Because all the light is coming from a single point, its path is highly susceptible to atmospheric interference (i.e. their light is easily diffracted).

The much closer planets appear instead as tiny disks in the sky (a distinction more easily discerned with a telescope than with the naked eye). Their apparent sizes are usually larger than the pockets of air that would distort their light, so the diffractions cancel out and the effects of astronomical scintillation are negligible.

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The twinkling of stars is due to atmospheric refraction.Since the stars are very distant objects they are considered as point sized sources of light.As the path of light coming from sun goes on varying slightly.Since the physical conditions of atmosphere are not stationary,the apparent position of star keeps on changing.Due to this intensity of star light entering the eye flickers giving an twinkling effect. Planets being of larger size close to the earth can be taken as the collection of a large number of points size of objects/sources of light, which nullify the twinkling effect of each other
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@Tushar Singh  From what book is the first image you have given ??
 
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