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The Question

(Submitted December 01, 1996)

I am looking for the right person to explain to me why the Moon looks much larger near the horizon (at Moonset) than in the middle of the sky.

The Answer

This is a psychological effect --- when the Moon is high on the sky, there is nothing to compare the size with except for the whole sky, and it seems small. When it is near the horizon, your mind compares it with the detailed features on the horizon, and the Moon appears to be bigger.

You can perform an experiment yourself to confirm this. See, for example, http://www.ucolick.org/~mountain/AAA/education/moonsize.html. (http://www.ucolick.org/~mountain/AAA/education/moonsize.html)

Koji Mukai
for Imagine the Universe!

Questions on this topic are no longer responded to by the "Ask an Astrophysicist" service. See http://imagine.gsfc.nasa.gov/docs/ask_astro/ask_an_astronomer.html for help on other astronomy Q&A services.

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