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# What is a leap year?

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A leap year has 366 days instead of 365 days. The addition of this extra day to the Gregorian calendar occurs in the month of February.

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In a leap year, Feb. 29 is the extra day of the year, which is called either a leap day or an intercalary day. Leap years occur approximately every four years. The addition of an extra day to the Gregorian calendar occurs so that it aligns and correctly matches the length of a solar year. A solar year is the time it takes for the Earth to make one revolution around the sun. It is approximately equal to 365.242199 days. Without this correction, a calendar year is shorter than a solar year.

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## Related Questions

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The number of school days in a year depends on the state; 30 states have 180 school days, according to Education Commission of the States, 2013 update. Two states set minimum school days higher than 180 days, and 11 states have a minimum that falls between 160 and 179 days.

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One year is measured by the time it takes a planet to orbit the sun, and 365 days is the best estimate for how long it takes Earth to complete a full trip around the sun. Years on other planets are measured in comparison with the Earth year, and one year on most planets is longer than one year on Earth.

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The days start getting longer every year after the winter solstice, which falls on the first day of winter, the shortest day of the year. The first day of winter is typically December 21 or 22 in the Northern Hemisphere.