Hands-On Astronomy

Full Moon Illusion

Everyone has experienced the huge size of a full (or nearly full) moon when it is low on the horizon. Is it really bigger than when the same moon is high in the sky? It sure looks bigger!

We decided to put this to a test. Using a Kodak DS260 digital camera set at its maximum telephoto zoom (3X), we took photos of the moon very low on the horizon (7:00 PM), and about 2 1/2 hours later (9:30 PM) when the moon was relatively high and appeared much smaller. (The photos were taken on 1/21/00, so the moon was actually 1 day past full.)

In PhotoShop, we superimposed the two images. Despite the subjective appearance, the moon's diameter was identical.

The animated GIF below shows the "high" moon superimposed (50% opacity) on the "horizon" moon. We did not manipulate the images sizes! The strange green sky color is an artifact of (1) the limitations of the GIF format and (2) limiting the image to "web-safe" colors to avoid dithering as much as possible.

The "low" moon was behind some tree branches, which can be seen across the face of the moon. Overexposure is caused by the camera's limited manual exposure control.

Lunar Eclipse, 1/20/00

Using a Kodak DS260 digital camera and PhotoShop, this composite photo shows the progession of the January 20, 2000 lunar eclipse. Overexposure is caused by the camera's limited manual exposure control.

Books and Other References for Hands-On Astronomy

In 1994 I taught a 2-week summer course on astronomy to rising 2nd-6th graders. The following references were very helpful. (And I've added a few new ones since then.)