Why Do Stars Twinkle?
Written by Fraser Cain
Sirius. Image credit: Hubble
Head outside on a nice dark, clear night and look up. If you're away from the glare of the city lights, you should be able to see lots of stars. But if you notice, the stars seem to be twinkling. What's going, why do stars twinkle?
If you could fly up into space and do the same experiment, you wouldn't see the stars twinkle at all. They would be unchanging points of light in all directions. Something's changed from when you were on the surface of the Earth to when you were in space. That thing is the Earth's atmosphere.
Stars twinkle because of turbulence in the Earth's atmosphere. Light from distant stars passes through various layers in the Earth's atmosphere, and it gets refracted depending on the temperature and density of the air at that point. So light will pass through one layer, be refracted at one angle, and then pass through a different layer and be refracted at a different angle. When you see a twinkling star, you're seeing the accumulated refractions from all those layers, which change the position and size of the star – many times a second.
This twinkling is a big problem for astronomers, who need the clearest possible view of the sky. That's why observatories are built at the top of mountains, where there's less atmosphere in between the telescope and the vacuum of space. And to have the clearest view, you really want to launch a space telescope that can get above the Earth's atmosphere and see the stars as they really are.
We have written many articles about stars here on Universe Today. Here's an article about that talks about a technique astronomers use to minimize the twinkle of the Earth's atmosphere.
Want more information on stars? Here's NASA's World Book on Stars, and more information from NASA's imagine the Universe.
We have recorded several episodes of Astronomy Cast about stars. Here are two that you might find helpful: Episode 12: Where Do Baby Stars Come From, and Episode 13: Where Do Stars Go When they Die?
Filed under: Astronomy
