Viewed from earth's surface, why does light from planets not "twinkle" the same as stars?

Answer 1

The scientific name for the twinkling of stars is stellar scintillation (or astronomical scintillation). Stars twinkle when we see them from the Earth's surface because we are viewing them through thick layers of turbulent (moving) air in the Earth's atmosphere.

Stars (except for the Sun) appear as tiny dots in the sky; as their light travels through the many layers of the Earth's atmosphere, the light of the star is bent (refracted) many times and in random directions (light is bent when it hits a change in density - like a pocket of cold air or hot air). This random refraction results in the star winking out (it looks as though the star moves a bit, and our eye interprets this as twinkling).

Stars closer to the horizon appear to twinkle more than stars that are overhead - this is because the light of stars near the horizon has to travel through more air than the light of stars overhead and so is subject to more refraction. Also, planets do not usually twinkle, because they are so close to us; they appear big enough that the twinkling is not noticeable (except when the air is extremely turbulent).

Stars would not appear to twinkle if we viewed them from outer space (or from a planet/moon that didn't have an atmosphere).


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Stars, except for the Sun, although they may be millions of miles in diameter, are very far away. They appear as point sources even when viewed by telescopes. The planets in our solar system, much smaller than stars, are closer and can be resolved as disks with a little bit of magnification (field binoculars, for example).

Since the Earth's atmosphere is turbulent, all images viewed up through it tend to "swim." The result of this is that sometimes a single point in object space gets mapped to two or more points in image space, and also sometimes a single point in object space does not get mapped into any point in image space. When a star's single point in object space fails to map to at least one point in image space, the star seems to disappear temporarily. This does not mean the star's light is lost for that moment. It just means that it didn't get to your eye, it went somewhere else.

Since planets represent several points in object space, it is highly likely that one or more points in the planet's object space get mapped to a points in image space, and the planet's image never winks out. Each individual ray is twinkling away as badly as any star, but when all of those individual rays are viewed together, the next effect is averaged out to something considerably steadier.

The result is that stars tend to twinkle, and planets do not. Other extended objects in space, even very far ones like nebulae, do not twinkle if they are sufficiently large that they have non-zero apparent diameter when viewed from the Earth.
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I can be more specific, sure. Remember that just like a computer screen, your eye is composed of a certain number of "pixels," each represented by a single light-receptor cell in your retina. If two (or more) points of light are close enough such that they are focused on the same receptor cell in your eye, you will experience them as a single point of light. This is referred to as the "resolution" of your eye, or any telescope for that matter.


Now, a star on the sky is in a true sense a single point of light. All the light comes through the atmosphere in exactly the same direction, through exactly the same atmospheric turbulence, and thus is bent in exactly the same way. So when it gets to your eye, the amount of light you see coherently varies. It also strikes (primarily) only a single receptor in your eye.


On the other hand, light from a planet is different. Each of a few receptors in your eye sees a large number of light rays coming from the planet, each of which has been bent differently be the atmosphere (since the planet has size on the sky, they are arriving in slightly different directions). Some of these rays will become brighter, some dimmer. But because they all illuminate the same receptor in your eye, that receptor only sees the total amount of light hitting it. There will be about the same number of enhanced rays as dimmed rays, so you experience a steady light, not a twinkle.

No, planets never twinkle to the naked eye for exactly this reason. If you look at one through a magnifying telescope, though, the telescope can have better resolution than the coherently refracting length of the atmosphere. In this case, you can see the edges of the planet "wiggling."

Answer 2

Stars give off their own light where as planets do not give off their own light, they reflect the light of stars. That could account for what you see to be a difference, however if I am right the twinkle you might be talking about does not apply to every star. This twinkle is actually two stars that rotate around each other and when the bigger one is in front it looks brighter than when the little one is in front giving a twinkle effect. It is called a binary star system. It is actually very interesting stuff and it was one of the only times I stayed awake during Astronomy at the university.

Answer 3

First of all they're brighter than the stars. Secondly most of them are a disk rather than a point like the stars are. If you look at the planets through a telescope and the air is not perfectly clear and free of turbulence, you'll see the planets blur all over the place and change in clarity which is the same thing the stars are going. Since the stars are basically a point of light, it's more obvious.

Answer 4

you're speaking as if the absolutely existence contained in the universe in on earth. i imagine in a distinct way. There must be existence accessible it rather is extra wise than what we see in this dirt ball of a planet.Bernard's renowned individual is off target. And there are supernovas. Does that advise that this is the right of the international. And in case you imagine God made the universe, perhaps you ought to examine the bible and end wondering God. i position self belief in evolution, the massive bang, and the universe will strengthen invariably. You seem at one galaxy, with three hundred billion stars in it and tell me ,what number ineffective stars are in that galaxy?

Answer 5

Because planets is different than stars, planets not produce rays, hence stars do, the nearest star is your sun.