Did Neolithic humans build this structure to celebrate Pi Day? Not likely. Pi Day is a relatively recent phenomenon—invented by a physicist in 1988 and designated by Congress a national holiday in 2009. But it"s already almost certainly the most popular holiday celebrating a mathematical constant. While Pi Day is a young tradition, the number π (pi) itself has been a fascination since antiquity, when it was first calculated as the ratio of a circle"s circumference to its diameter.
Pi Day
Today in History
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Over and under the delta
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Audubon Christmas Bird Count
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World Environment Day
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Old Town in Prague, Czech Republic
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Freeze frame
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Svolvaer, Lofoten Islands, Norway
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Tough turf
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Wild garlic in bloom at Hainich National Park, Germany
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Ah Shi Sle Pah Wilderness, New Mexico
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Christmas Eve
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Goðafoss waterfall, Iceland
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Composite image of a lunar eclipse
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Perseid meteor shower over Nevada
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It s World Bee Day
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The Great Blue Hole, Belize
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Katahdin Woods and Waters National Monument, Maine
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The artists come to Venice
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Happy World Photography Day!
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Autumnal equinox
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World Lizard Day
Bing Wallpaper Gallery

