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Twinkles
This week's experiment is
the result of my evening walks with Shelby
the Dog. On chilly nights, the stars here are wonderful. Looking at them
tonight, I thought it would be fun to so something about stars.
You will need:
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. Two weeks ago, we looked at flame shadows
(exp. # 354). Besides the shadow of the flame, you probably saw a wavering
shadow above the flame. This was caused by the difference in the way light
passes through air at different temperatures and densities. You may also have
seen similar distortions from the hot air rising off a road in the summer, and
we also saw them in experiment #237 (Heat Waves). 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
stars are much larger than our planets, 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 them 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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