Twinkle, Twinkle, Distant Star

On chilly nights, the stars here at the beach are wonderful. Growing up, I was taught that the twinkle would let you tell the difference between a star and a planet, because planets don't twinkle. Why? Lets find out.

On a clear night, go to a fairly dark spot and look at the stars. Why do they twinkle? It has to do with turbulence in the atmosphere. Parts of the air above you are warmer than others. The difference in temperature causes the warm air to expand more than the cold air, producing different densities. As light travels from one density to another, it is bent, or refracted, causing distortions. You may also have seen similar distortions from the hot air rising off a road in the summer. The distortions in the atmosphere bend the light and cause the twinkle. In fact, if you placed your toaster oven outside and looked at the stars over the top, you should see increased twinkle. Just be careful not to toast your fingers while you are looking.

For most things, these distortions are too small so notice. You do not notice the moon wavering. Even the other planets in our solar system appear large enough that they usually do not twinkle, although if the turbulence is strong enough they can. Although the stars are much larger than Mars or Venus, they are also much farther away. They are so far away that they appear as bright, tiny dots, even when magnified. They appear small enough that even tiny distortions cause their appearance to change.

You should also notice that stars that are low in the sky seem to twinkle more than stars overhead. Why? Think about it for a minute. If turbulence in the atmosphere is causing the twinkle, then the more air the starlight passes through, the more it will be distorted and the more it will twinkle. Light from stars near the horizon has to pass through quite a bit more air, so they twinkle more. The amount of twinkle can also vary quite a bit, depending on atmospheric conditions.

Besides the twinkle, these distortions can also cause color changes. As the difference in air temperature and density bends the light, it bends some colors more than others. As the air moves, the amount of bending changes, so the color that you see from the star changes rapidly. This color changing is even easier to see when you look at the star through binoculars. It is well worth a trip outside on a chilly night to try it. Just be sure to have some hot cocoa waiting for you when you are done.

Have a wonder filled week.

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