intercalation

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February 29, leap day, leap year, happens every four years

Leap Day, February 29

Moonrise over Tucson, Arizona

Why Doesn’t Arizona Observe Daylight Saving Time?

Calendar marking march 15th

22 Questions About Time and Timekeeping Answered

Ancient Mayan Calendar

Our Days Are Numbered: 7 Crazy Facts About Calendars

Lead image for "A Timeline of the World in 8 Maps"

A Timeline of the World in 8 Maps

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Gutzon Borglum. Presidents. Sculpture. National park. George Washington. Thomas Jefferson. Theodore Roosevelt. Abraham Lincoln. Mount Rushmore National Memorial, South Dakota.

9 Memorials and Monuments in the United States

Ethel Rosenberg arrested in August 1950. Photograph dated Aug. 8, 1950. American civilians executed for espionage. Spies, communists, Julius Rosenberg

Spies Like Us: 10 Famous Names in the Espionage Game

Berries and leaves of the bittersweet nightshade (Solanum dulcamara) plant. Poisonous plant

7 of the World’s Deadliest Plants

Aurochs. Bos primigenius. Skeleton. Extinct animal. Skeleton of an Aurochs, an extinct wild ox.

6 Animals We Ate Into Extinction

Happy, smiling, flying pig

7 Everyday English Idioms and Where They Come From

US Marines firing at Fallujah, Iraq, during the Second Battle of Fallujah in November 2004. Operation Iraqi Freedom, Iraq War.

Timeline of the 2000s

Illustration for Demystified "How Dangerous is Quicksand"

How Deadly Is Quicksand?

intercalation: Related Content

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Topics

leap second leap year calendar International Date Line quarter days Dionysian period clock sundial Advent calendar dynamical time chronometer chronograph Standard Time

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calendar: Time determination by stars, Sun, and Moon