On January 7, 1610, Galileo was the first person to train a telescope on Jupiter—and what he saw surprised him. Strung in a line beside the planet were three tiny stars, one to the left of the planet and two to the right. But when he observed the formation the next night, he saw that now all three were on the same side of Jupiter. Over the following week, he watched as the tiny stars (now joined by a fourth) changed their position relative to the planet while remaining beside it. By January 15, he had it figured out: he was observing four moons orbiting Jupiter.
Jupiter and the Galilean moons
Today in History
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An uncommonly cool critter
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Celebrating 30 years of eye-opening images
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Chilling out in the Arctic
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High seas commerce
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National Park Week begins
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Sparkling ice diamonds on a black sandy beach
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The desert blooms
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Birch trees, Drammen, Norway
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Vietnam’s new bridge deserves a big hand
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Monarch butterflies migrate south
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A cozy winter village
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Longer days mean warmer sand
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Wedded Rocks, Japan
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World Bamboo Day
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Atop the Needle of Chamonix
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Hoh Rain Forest, Olympic National Park, Washington
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International Sloth Day
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Red-necked grebes during breeding season
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Who left the tub running?
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There was gold in them there hills…
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Thomas Jefferson Memorial, Washington, DC
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Blue-footed booby, Galápagos Islands
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Feelin groovy on Record Store Day
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Lake Tai s cherry trees in bloom
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Chicagohenge
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To Sua Ocean Trench
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Mexican giant cardon cactus
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Oh, happy day!
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Freshwater plants in Aquário Natural, Brazil