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Eclipse Demo: Moon-Earth Model on Telescope

To depict the moon's shadow crossing the earth during a solar eclipse, mount two balls to scale on a stick, and then attach the stick to a telescope on an equatorial mount. Once you align the shadow so it falls on your model earth, you can repeatedly slew the scope to demonstrate the shadow's path.

The telescope mount is vastly easier than trying to manipulate it by hand, and you can repeat the demonstration readily if you have a crowd taking turns with it. Place a white board behind the rig so you can follow the shadows "out in space" behind your telescope. Do this in the real sunshine instead of inside a lit room.

My original model had some tape holding the moon ball on top of a nail, so the tape imperfection shows up slightly in the shadow. In the demo you can discern a slightly dark central shadow (the umbra) while the fainter yet broader penumbral shadow extends further across the earth ball.

More eclipse activities are at The Astronomical Society of the Pacific has a Yardstick Eclipse Activity available as kits for purchase.

Image: Astronomischer Bilder Atlas by Ludwig Preyssinger, plate 8,ca. 1852. (scan with moire pattern)


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