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!