Twinkle, Twinkle, Little Star.


Look at a scene through a wavy plastic shower stall door to get the idea of how the atmosphere distorts our view of the stars.


A Minimag light or other bright point source of light. A sheet of wavy plastic meant to be used as shower door or window material,
at least 10 cm x 10 cm (4" x 4").
Get the clearest, least wavy sheet you can find.
(I found pieces in the scrap bin at my local plastic store: TAP plastics in Mountain View California.)


Remove the bulb cover from the Minimag light to make it a point source.

To Do and Notice

View the Minimag light through the plastic sheet.

Move the plastic sheet slowly back-and-forth or up-and-down.

Notice that the light seems to move about and grow brighter and dimmer.

It seems to twinkle.

What's Going On?

The view of the stars from the surface of the earth is through a turbulent atmosphere. The atmosphere has small regions of warmer and cooler air.
These regions have different indices of refraction and bend light like the bathroom shower plastic.
This causes stars viewed through the atmosphere to twinkle.

Going Further

Get a piece of the plastic bigger than your face.

Stand face to face with a friend. Stand a handshake distance apart.

Hold the plastic in front of your face touching your nose.

Move it away from your face. When it gets half way to your friend have them grab the plastic and bring it toward their face until it touches their nose.

Notice that when the plastic is near you it greatly distorts your view of your friend.
However, when it is near them, your view is clearer.

Thus the temperature fluctuations in the atmosphere which are greatest near the surface of the earth distort our view of the universe more than they distort the view that spy satellites have of us.

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Scientific Explorations with Paul Doherty

© 2001

19 April 2001