What is a Leap Year?
A leap year is a year containing one additional day added to keep the calendar year synchronized with the astronomical year or seasonal year. Because the Earth doesn't orbit the sun in exactly 365 days, we add an extra day (February 29th) every 4 years to account for the extra 6 hours.
However, adding a day every 4 years actually overshoots slightly. To correct this, the Gregorian calendar introduced a specific set of rules.
The Leap Year Rules
Not every 4th year is a leap year. The system is slightly more complex:
- Rule 1: The year must be evenly divisible by 4.
- Rule 2: If the year is divisible by 100, it is NOT a leap year...
- Rule 3: ...unless the year is also evenly divisible by 400. Then it IS a leap year.
For example, 2000 was a leap year (Rule 3), but 1900 was not (Rule 2).