<p>Planets do definitely twinkle sometimes, and stars don't always twinkle as much. It's not a binary yes-or-no, it's a continuum.</p>

<p>Even Venus can be seen twinkling if it's close to the horizon and the atmospheric turbulence (a.k.a. "seeing") is bad.</p>

<p>As for why stars twinkle more easily than planets, you've received some answers already.</p>

CC BY-SA 4.0
2018-11-06T19:35:53.113Z
2018-11-06T19:35:53.113Z
Florin Andrei
<p>Thought I'd add on the above. Starlight is like a very narrow laser beam pointed at you. A planet is like a bunch of those arranged in a circle all pointed at you. Any one of those lasers can be deflected by the atmosphere. There is only one to deflect in the case of star light. There's several in the case of a planet. If any few lasers deflect, there's still plenty that are undisturbed.</p>

<p>Light from both stars andcplanets deflect. The planet is less like a point source. Still deflects, but the spread of source points compensates.</p>

<p>Apparently both planets and stars can twinkle when closer to the horizon. There is more deflection. This works to offset  the spread effects. Can't say I've  witnessed this personally though.</p>

CC BY-SA 4.0
2018-11-06T01:20:34.437Z
2018-11-06T13:10:13.353Z
2018-11-06T13:10:13.353Z
R. Romero
<p>The answer to this is that stars are effectively point sources, but planets have disks.  Borrowing the <a href="http://skyandtelescope.com/astronomy-resources/why-do-stars-twinkle" rel="noreferrer">link to Sky and Telescope's explanation</a> from @N. Steinle's comment.</p>

<p>The way I envision it is to think of the light from a celestial object as a fiber optic cable, continually being snipped at with scissors (which stand in for atmospheric turbulence changing the path of light traveling through it).  The cable from a star is a single glass fiber with a very bright beam shining down it.  The cable from a planet is a thick bundle of fibers with a much dimmer beam shining down each fiber in the bundle (compare the surface brightness of Mars with the surface brightness of the Sun)-- the total amount of light coming through the cables is comparable.  The scissors can cut through the single-fiber cable completely, but they can only take out a few strands of the thick bundle.  So atmospheric turbulence can cause the light from a star to be drastically interrupted, while the change for a planet is much less.  Therefore, there is visible twinkling from stars, but not from planets.</p>

CC BY-SA 4.0
2018-11-06T16:33:45.323Z
Besides which, on a gusty enough night, even planets twinkle.
Wayfaring Stranger
CC BY-SA 4.0
2018-11-05T18:01:21.973Z
2018-11-05T18:01:21.973Z
antlersoft
<p>Many people say that stars twinkle because of Earth's atmosphere. However, the atmosphere is still there when we look at planets and don't see they twinkling.</p>

<p>Is there a clear scientific consensual explanation for the twinkling of some objects but not for others?</p>

<p><strong>Note:</strong> <em>just as a metter of distinction, my question is different from <a href="https://astronomy.stackexchange.com/questions/14082/why-doesnt-the-moon-twinkle">this one</a>. In fact, the moon is obviously different from stars, while my question is based on the fact that the only actual difference between stars and planets is that planets move across the sky, differently from stars (since they are the sky's reference). Proof of my words is the late distinction of Uranus as a planet due its extremely slow motion, although it also doesn't twinkle.</em></p>

CC BY-SA 4.0
2018-11-05T17:58:00.227Z
Here: https://www.skyandtelescope.com/astronomy-resources/why-do-stars-twinkle/
Daddy Kropotkin
CC BY-SA 4.0
2018-11-05T19:03:39.480Z
Just to be pedantic: some stars "blink" for real, e.g., Cepheid variables.  But I know that's not what you're asking here.
Carl Witthoft
CC BY-SA 4.0
2018-11-06T09:36:50.017Z
I've always thought "twinkle" is a more accurate term for this than "blink".
Fattie
CC BY-SA 4.0
2018-11-06T19:02:10.957Z
I would agree with you, @Fattie. But there is a huge difference between my question and that one you point at (and which I didn't see before your comment). The difference is that the Moon is a clearly different from stars and planets. However, planets can only be distinguished from stars after following their relative motion across the sky. Proof of my words is the late distiction of Uranus as a planet, instead of a star, due to its very slow motion as seen from Earth (although it also doesn't twinkle). Capiche?
Brasil
CC BY-SA 4.0
2018-11-07T00:35:33.837Z
hi @brasil!  you may have meant pela??   By the way planets can be very, very, easily distinguished from stars - you just look through even a pair of binoculars.
Fattie
CC BY-SA 4.0
2018-11-07T12:13:56.140Z
@Brasil You're right that, in this respect, the Moon is very different from planets. But the answer I linked to also discusses planets: "_The same is even true for planets. The planets you can see with the naked eye span from several arcsec up to almost an arcmin. Although they look like point sources (because the resolution of the human eye is roughly 1 arcmin), they aren't, and you will notice that they don't twinkle (unless they're near the horizon where their light goes through a thicker layer of atmosphere)_."
pela
CC BY-SA 4.0
2018-11-07T19:31:18.303Z
Hi, Fattie. Yes, I meant @pela. Sorry for the mistake. I can't edit the comment (no option shows to me)... now, "pela", the important point you highlight is the need of use optical devices (besides the very eyes) to distinguish planets from stars. My question is based on the fact that If I don't have such apparatuses, I wouldn't realize any other difference in a short period of observation.
Brasil
CC BY-SA 4.0
2018-11-08T10:16:12.827Z
@Brasil Hmm… I'm not sure I understand. I don't think I've mentioned optical devices. Using only your eyes, stars twinkle because they're "point sources", i.e. much smaller than the seeing (the region inside which the atmosphere will make a point source "jump around", roughly 1 arcsec. Planets (and of course the Moon) are much larger, so although they also jump around, the change in position is very small compared to their size, so you don't see it. But planets are still roughly the size that your eye can resolve (~1 arcmin), so they _look_ like point sources to you. Does this make sense?
pela
<star><planet><observational-astronomy><planetary-atmosphere>
Why do stars twinkle but planets don't
Brasil
# Why do stars twinkle but planets don't

(Asked by: username_0 on 2018-11-05)

Many people say that stars twinkle because of Earth's atmosphere. However, the atmosphere is still there when we look at planets and don't see they twinkling.

Is there a clear scientific consensual explanation for the twinkling of some objects but not for others?

**Note:** *just as a metter of distinction, my question is different from [this one](https://astronomy.stackexchange.com/questions/14082/why-doesnt-the-moon-twinkle). In fact, the moon is obviously different from stars, while my question is based on the fact that the only actual difference between stars and planets is that planets move across the sky, differently from stars (since they are the sky's reference). Proof of my words is the late distinction of Uranus as a planet due its extremely slow motion, although it also doesn't twinkle.*

**Tags:** star, planet, observational-astronomy, planetary-atmosphere

> **Comments:**
> **username_1**: Here: https://www.skyandtelescope.com/astronomy-resources/why-do-stars-twinkle/  
> **username_2**: Just to be pedantic: some stars "blink" for real, e.g., Cepheid variables.  But I know that's not what you're asking here.  
> **username_3**: I've always thought "twinkle" is a more accurate term for this than "blink".  
> **username_0**: I would agree with you, @username_3. But there is a huge difference between my question and that one you point at (and which I didn't see before your comment). The difference is that the Moon is a clearly different from stars and planets. However, planets can only be distinguished from stars after following their relative motion across the sky. Proof of my words is the late distiction of Uranus as a planet, instead of a star, due to its very slow motion as seen from Earth (although it also doesn't twinkle). Capiche?  
> **username_3**: hi @brasil!  you may have meant username_4??   By the way planets can be very, very, easily distinguished from stars - you just look through even a pair of binoculars.  
> **username_4**: @username_0 You're right that, in this respect, the Moon is very different from planets. But the answer I linked to also discusses planets: "_The same is even true for planets. The planets you can see with the naked eye span from several arcsec up to almost an arcmin. Although they look like point sources (because the resolution of the human eye is roughly 1 arcmin), they aren't, and you will notice that they don't twinkle (unless they're near the horizon where their light goes through a thicker layer of atmosphere)_."  
> **username_0**: Hi, username_3. Yes, I meant @username_4. Sorry for the mistake. I can't edit the comment (no option shows to me)... now, "username_4", the important point you highlight is the need of use optical devices (besides the very eyes) to distinguish planets from stars. My question is based on the fact that If I don't have such apparatuses, I wouldn't realize any other difference in a short period of observation.  
> **username_4**: @username_0 Hmm… I'm not sure I understand. I don't think I've mentioned optical devices. Using only your eyes, stars twinkle because they're "point sources", i.e. much smaller than the seeing (the region inside which the atmosphere will make a point source "jump around", roughly 1 arcsec. Planets (and of course the Moon) are much larger, so although they also jump around, the change in position is very small compared to their size, so you don't see it. But planets are still roughly the size that your eye can resolve (~1 arcmin), so they _look_ like point sources to you. Does this make sense?  

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## 3 answers

### Answer by username_7 on 2018-11-05. Score: 7 | Accepted answer

The answer to this is that stars are effectively point sources, but planets have disks. Borrowing the [link to Sky and Telescope's explanation](http://skyandtelescope.com/astronomy-resources/why-do-stars-twinkle) from @N. Steinle's comment.

The way I envision it is to think of the light from a celestial object as a fiber optic cable, continually being snipped at with scissors (which stand in for atmospheric turbulence changing the path of light traveling through it). The cable from a star is a single glass fiber with a very bright beam shining down it. The cable from a planet is a thick bundle of fibers with a much dimmer beam shining down each fiber in the bundle (compare the surface brightness of Mars with the surface brightness of the Sun)-- the total amount of light coming through the cables is comparable. The scissors can cut through the single-fiber cable completely, but they can only take out a few strands of the thick bundle. So atmospheric turbulence can cause the light from a star to be drastically interrupted, while the change for a planet is much less. Therefore, there is visible twinkling from stars, but not from planets.

> **Comments:**
> **username_8**: Besides which, on a gusty enough night, even planets twinkle.  

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### Answer by username_5 on 2018-11-06. Score: 7

Planets do definitely twinkle sometimes, and stars don't always twinkle as much. It's not a binary yes-or-no, it's a continuum.

Even Venus can be seen twinkling if it's close to the horizon and the atmospheric turbulence (a.k.a. "seeing") is bad.

As for why stars twinkle more easily than planets, you've received some answers already.


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### Answer by username_6 on 2018-11-06. Score: 2

Thought I'd add on the above. Starlight is like a very narrow laser beam pointed at you. A planet is like a bunch of those arranged in a circle all pointed at you. Any one of those lasers can be deflected by the atmosphere. There is only one to deflect in the case of star light. There's several in the case of a planet. If any few lasers deflect, there's still plenty that are undisturbed.

Light from both stars andcplanets deflect. The planet is less like a point source. Still deflects, but the spread of source points compensates.

Apparently both planets and stars can twinkle when closer to the horizon. There is more deflection. This works to offset the spread effects. Can't say I've witnessed this personally though.


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