Why do we need leap years?by Earth Sky on February 29, 2016
The last leap year was 2012, and the next one is today, February 29, 2016! Leap days are extra days added to the calendar to help synchronize it with Earth’s orbit around the sun and the actual passing of the seasons. Why do we need these extra days?
The reason is that Earth takes approximately 365.25 days to orbit around the sun every year. It’s that .25 that creates the need for a leap year every four years.
During non-leap years aka common years – like 2014 – the calendar doesn’t take into account that extra quarter of a day actually required by Earth to complete a single orbit around the sun. In essence, the calendar year, which is a human artifact, is faster than the actual solar year, or year as defined by our planet’s motion through space.
Over time and without correction, the calendar year would drift away from the solar year and the drift would add up quickly. For example, without correction the calendar year would be off by about 1 day after 4 years. It’d be off by about 25 days after 100 years. You can see that, if even more time were to pass without the leap year as a calendar correction, eventually July would be a winter month in the Northern Hemisphere.
During leap years, a leap day is added to the calendar to slow down and synchronize the calendar year with the seasons. Leap days were first added to the Julian Calendar in 46 B.C.by Julius Cesar at the advice of Sosigenes, an Alexandrian astronomer.