Why we need leap years

29th February:

According to the calendar has a year of 365 days. The earth needs but 5 hours, 48 ​​minutes and 45 seconds longer to orbit the sun. The leap day balances out the difference - but not quite…

According to the calendar lasts a year of 365 days. Astronomically, this is not correct. The tropical year - ie the time that the planet needs Earth to travel once around the sun - is longer: "It has about 365 days, 5 hours, 48 minutes and just over 45 seconds," says Hans-Ulrich Keller, professor of astronomy and chronology at the University of Stuttgart.” The Leap Years reduce the difference between the 365-day calendar year and the tropical year.” reduce them, but they can not completely compensate for them to have the numbers to round. After adding the extra hours, minutes and seconds, after four years to about 23 hours and 11 minutes -. So any day therein lays the crux. 

Since the Julian calendar reform in the days of Julius Caesar (100 BC to 44 BC), each year 365 days every fourth year was a leap year. This added uncertainty to the 16thCentury to ten days.” In 1582, prompted Pope Gregory, therefore, a calendar reform," said Keller. Gregory did turn out for ten days and clarified the rules. Since then, every smooth by four separable years is a leap year (egg 2004, 2008, and 2012), but not the full centuries (1900, for example, none) - unless the year is without rest by 400 divisible (1600 and 2000 Leap years)....