A leap year occurs almost every four years, and it has 366 days instead of the usual 365 days. This extra day is added to the month of February as February 29, called leap day. The reason for a leap year is to keep the calendar year synchronized with Earth's orbit around the Sun. Earth takes approximately 365.242189 days to orbit the Sun, which is about 365 days, 5 hours, 48 minutes, and 45 seconds. The extra nearly six hours accumulate each year and, without correction, our calendar would drift out of sync with the seasons. Leap years correct this by adding an extra day roughly every four years. The rules for determining a leap year in the Gregorian calendar are:
- The year must be divisible by 4;
- If the year is divisible by 100, it is not a leap year, unless;
- The year is also divisible by 400, then it is a leap year.
For example, the year 2000 was a leap year, but 1900 was not. The last leap year was 2024, and the next will be 2028. This system keeps our calendar aligned closely with Earth's revolutions and seasons.
