What is a leap year?

A leap year is a calendar year that contains an extra day, February 29th, making it 366 days instead of the usual 365 days. This adjustment is necessary to synchronize the calendar year with the astronomical year, which is the time it takes for the Earth to complete one orbit around the Sun. The leap year system helps to maintain alignment between the calendar year and the seasons.

The need for a leap year arises because the Earth’s orbit around the Sun is not precisely 365.25 days; it’s about 365.2422 days. If we didn’t add an extra day every four years, the calendar would gradually drift out of sync with the Earth’s orbit, causing seasonal misalignment over time.

The rules for determining leap years are as follows: A year divisible by 4 is a leap year, except for years that are divisible by 100 but not divisible by 400. For example, the year 2000 was a leap year because it is divisible by 400, but the year 1900 was not a leap year because, while divisible by 4 and 100, it failed the 400 criterion. This leap year system is known as the Gregorian calendar, widely used around the world today.