Sure, sure, everyone knows that stars twinkle. You look up at the night sky, and pretty much any star you look at appears to fluctuate in its brightness and intensity very rapidly, giving it a "twinkling" appearance.
Why does this happen? It definitely doesn't have anything to do with the star itself, because "our" star, which you call the Sun, definitely doesn't twinkle the same way:
Not only that, but there are a few objects in the night sky that don't twinkle: the Moon, planets, and satellites.
Why is that? Why do stars twinkle, and nothing else? Well, there were two theories.
One was that the Earth's atmosphere was causing the twinkling. As pockets of turbulent air, both warm and cold, move around, they cause the light to move unevenly, causing relative brightness and dimness. Planets, satellites, and the Moon and Sun wouldn't do this because their apparent size is too big to be affected by such slight variations, but tiny, point-like stars could be.
The other theory is that the Sun, Moon, satellites and planets are all close to us, but something happening at the edge of the Solar System causes the twinkling. Molecular gas clouds that live at the outskirts of the Solar System -- as part of the Oort cloud -- could cause the twinkling. As the starlight passes through them, the turbulence there causes the twinkling, and it's only because the other, closer objects are inside the Oort cloud that we don't see it.
So, which explanation is it? Well, this is one piece of science that we were able to test via manned spaceflight! How's this? Well, all you have to do is go up in a spacecraft beyond the Earth's atmosphere, and look.
Well, former astronaut Walt Cunningham wrote a book about this. The title?
Importance of Observation that Stars Don't Twinkle Outside the Earth's Atmosphere.And there you have it. The Earth's atmosphere, and not gas clouds, cause stars to twinkle. You can find a much more detailed explanation at Astroprof's page, but this is one of the neatest little bits of information to come from manned spaceflight. Hope you enjoy it!
Physical Science
Comments
Why do stars twinkle?
Because they are angels flapping their wings???
Oh, no, I suppose you have some scientific explanation.
Posted by: Greg Laden | July 29, 2009 3:48 PM
http://sciencelife.ning.com/
Posted by: AAA | July 29, 2009 4:58 PM
Except for pulsars. That's not why pulsars twinkle.
Posted by: t-sup | July 29, 2009 11:23 PM
Except for pulsars. That's not why pulsars twinkle.
Posted by: t-sup | July 29, 2009 11:25 PM
Except for scienceblogs. That's not why scienceblogs causes double posts.
Posted by: t-sup | July 29, 2009 11:31 PM
T-sup,
Pulsars pulse, it's true. But it's not like you can see them with your eye, or even with a telescope. They're neutron stars, and we can detect them in radio and X-ray frequencies, but not with light.
And yes, ScienceBlogs is pretty bad about the double posts.
Posted by: Ethan Siegel | July 29, 2009 11:47 PM
T-sup,
Pulsars pulse, it's true. But it's not like you can see them with your eye, or even with a telescope. They're neutron stars, and we can detect them in radio and X-ray frequencies, but not with light.
And yes, ScienceBlogs is pretty bad about the double posts.
Posted by: Ethan Siegel | July 29, 2009 11:50 PM
So it's not because they are up above the world so high, like a diamond in the sky?
Posted by: Sigmund | July 30, 2009 12:10 AM
Of course, video cameraed spaceflight would have done the job too :)
Posted by: Bijan Parsia | July 30, 2009 2:19 AM
here is another question:
why do stars have spokes on them? for instance, in the top photo above, all the stars have 4 spokes that point up, down, left and right.
Posted by: rob | July 30, 2009 7:40 AM
Ethan, I think t-sup is referring to pulsar scintillation due to the turbulent ionized interstellar medium.
rob, those are diffraction spikes caused by the telescope.
Posted by: Anthony | July 30, 2009 10:24 AM
Anthony: yup. that is what they are. i was trying to find a link to another photo that shows 6 spikes, put APOD was kinda acting flakey for me.
Posted by: rob | July 30, 2009 11:42 AM
If you scroll to the bottom of this page, there is a nice example of multiple spikes.
Posted by: Anthony | July 30, 2009 12:20 PM
Sure you can see pulsars in optical.
Not all of them, but some.
Famously the Crab pulsar: http://messier.obspm.fr/Pics/Jpg/m1psr_k.jpg
but others are also seen.
Posted by: Steinn Sigurdsson | July 30, 2009 1:17 PM
Wow, Steinn! That picture is amazing!
Posted by: Ethan Siegel | July 30, 2009 1:22 PM
This page has a movie of those pics of the Crab.
Posted by: Anthony | July 30, 2009 2:36 PM
Anthony: yeah! that's what i was looking for. very cool.
Steinn: way cool!
Posted by: rob | July 30, 2009 2:58 PM