On this date in 1610, Galileo wrote a letter..

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Source: Garrison Keillor, Writer's Almanac

 Excerpt: On this date in 1610, Galileo wrote a letter describing his discovery of three of Jupiter's moons. He had recently made some improvements to his telescope, and he discovered them in December. As he continued to observe them over the next few months, a fourth celestial body appeared, and he realized that they were actually orbiting the giant planet.

 writersalmanac.publicradio.org/index.php

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