Wednesday, January 7, 2015

Tonight's Sky for January 7: Galileo Discovers Jupiter's Moons

It was on this date in 1610 that Galileo Galilei turned his primitive telescope on Jupiter and shattered the notion that everything orbits the Earth. Having recently constructed a telescope that he had based off of a Dutch design, Galileo turned it on the heavens and made discoveries that re-shaped the universe.

At the time, it was widely believed that everything orbited the Earth, a belief held virtually unchallenged since Classical Greece and only recently challenged (in theory only) by Copernicus. Turning his telescope in Jupiter, Galileo noted 4 small stars near the planet, nothing unusual. However, in the coming nights, Galileo noticed that the 'stars' moved relative to each other while remaining with the planet. The only conclusion: the 'stars' were moons. Now known as the Galilean Moons, they are, in order from Jupiter: Io, Europa, Ganymede (largest moon in the solar system), and Callisto. An easy way to remember this fact: I(Io) Eat(Europa) Green(Ganymede) Caterpillars(Callisto)!

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