Galileo's Moon Mountain Documents
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The Galileo's Moon Mountain Model illustrates the method used by Galileo to measure the height of a mountain on the Moon. Using his improved telescope design, Galileo was able to see spots of light in the otherwise dark potion of the Moon. He interpreted these spots as mountain peaks which caught the rays of the sun even though the sun did not illuminate the Moon's surface at the base of the mountain. He measured the distance of the bright spot from the terminator (the line separating the lit and unlit portions of the Moon) as a fraction of the Moon's radius. Then he was able to use a geometrical argument to determine the height of the mountain as a fraction of the Moon's radius. Galileo knew that the Moon's radius was approximately 1600 km (he didn't use those units, of course), which allowed him to determine the absolute height of the mountain. (Note that the modern value for the Moon's radius is about 1740 km.)
Last Modified June 6, 2014
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