What Is a Leap Year?

Why We Need Leap Years00:00:00

The Earth takes approximately 365.25 days to orbit the sun. Because our standard calendar uses 365 days, those extra 0.25 days accumulate annually, causing our calendar to drift out of sync with the stars. Leap Day corrects this by adding an extra day every four years.

Historical Context: Egyptians and Julius Caesar00:01:41

The ancient Egyptians were the first to identify the 365.25-day astronomical year by observing the star Sirius. Julius Caesar later adopted this knowledge to create the Julian Calendar to address the synchronization issue.

Refining the System: The Gregorian Calendar00:02:23

The Julian Calendar was slightly inaccurate because the astronomical year is actually 365.2422 days. Pope Gregory introduced the Gregorian Calendar, which includes specific rules: years divisible by 100 are not leap years unless they are also divisible by 400.

Future Adjustments00:03:31

Due to the Earth's rotation slowing down by roughly 0.005 seconds per year, further calendar revisions will be necessary in the distant future to maintain accuracy.