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Why do stars twinkle?
Question Date: 1999-06-03
Answer 1:

If you were looking from the Space Shuttle in orbit, you wouldn't see the stars twinkle at all. What makes the view different from here on earth is that the light from the stars must pass through our atmosphere, just as the sun's rays do.

The atmosphere can bend or distort light traveling through it when it is moving or heated. You can see this when looking down a long road on a hot day and the horizon shimmers, or when you look at something beyond a candle flame.

So it's not the stars that twinkle, really, but the air we look through that makes them appear that way.

Here's another effect of the atmosphere you may want to investigate: why is the sky blue?

Answer 2:

Stars appear to twinkle because the light that they emit is bent back and forth just a little as it comes through the atmosphere to your eyes.

Answer 3:

Your question is a good one. Stars twinkle because of irregularities in our atmosphere. Sometimes you hear or read about "crystal nights" or "nights when the stars were so vivid" and you might note that these descriptions come from remote places or places that are well above sea level. The amount that a star shifts with the atmosphere will depend on what's in the atmosphere and how much atmosphere there is between you and space. Close to sea level, or in polluted areas, there are a lot of particles in the atmosphere and the atmosphere is dense. Although hard to see normally, the atmosphere can be observed and when you're looking through a lot of atmosphere to see a star, the smallest perturbations from wind will make the atmosphere appear to ripple. A very good example of this is when it is really hot and you can see objects ripple in the air because of the differences in air density between you and the object. If you go to very high altitudes, there is less atmosphere obstructing your vision so the effects are less severe and the stars seem crisper, almost like little crystals.
Why do you think astronomers often like to build telescopes in remote places and on mountains?

Answer 4:

Stars 'twinkle' due to the Earth's atmosphere. A volume of gas in the atmosphere can delay light arriving from a distant star compared to light that did not pass through the gas, and also the gas can change the direction that the light travels. (Can substances here on Earth do the same things to light?) If the atmosphere never changed, the stars would not seem to twinkle. However, winds in layers of the atmosphere move the gasses around and change their densities, delaying and deflecting light by different amounts. Light traveling from a distant star will take different paths over time to reach the Earth, and due to the different densities of gasses in these paths, will hit different locations on the Earth's surface and will have its intensity changed. So, if you stand in one place, you will see the star light seem to come and go, or 'twinkle'.
If you knew where the star light was going, and could correct for the changing intensity, could you see stars without them appearing to twinkle? No human could, because the atmosphere typically changes the light over 100 times a second, and no human can react that fast. On the other hand, computers can, and are now being used to adjust mirror segments in large telescopes. These 'adaptive optics' systems are now being installed in many of the world's Earth-based telescopes. In a few years, we should start to see much clearer pictures of stars and galaxies taken from Earth.

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