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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Sonoma Coast State Park, California
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Why does this panda cub look so happy?
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National Park Week: Canyonlands National Park, Utah
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Misool, Raja Ampat Islands, Indonesia
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It s tree-climbing season
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A long path to freedom
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Bridge to infinity
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Arenal Volcano, Costa Rica
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Global commerce in motion
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World Art Day
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Bavljenac Island
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Lakeside serenity in Finland
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Alaska National Interest Lands Conservation Act marks 42 years
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Happy Lunar New Year!
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Mount Field National Park, Tasmania, Australia
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Watch your step
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In Sicily, history is everywhere
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An historic forest
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Celebrating Bike to Work Week, May 14-18
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National Panda Day
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Hollywood s big night
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Glass footbridge in Zhangjiajie, China
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Celebrating National Park Week, April 21-29
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At the shore of an inland sea
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National Take a Hike Day
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River otters at Acadia National Park, Maine
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America s Playground by Derrick Adams
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Craig Goch Dam in the Elan Valley of Wales
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Gazing down on planet Earth
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Paradise Cave, Phong Nha-Ke Bang National Park, Vietnam
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