A leap year is a year that contains an extra day—February 29th—instead of the usual 28 days. This occurs every four years to help synchronize the calendar year with the solar year (the time it takes the Earth to complete one orbit around the Sun).
Why is it necessary?
A standard year, with 365 days, is slightly shorter than the time it actually takes the Earth to complete one orbit around the Sun. This period is about 365.2422 days, which means that if we only had 365 days every year, we would lose about 0.2422 days per year. Over time, this discrepancy would add up and throw off the seasons.
To correct this, an extra day (February 29) is added every four years, making the year 366 days long. This adjustment keeps the calendar year more closely aligned with the Earth’s orbit around the Sun, ensuring that seasons (such as summer and winter) stay consistent over the long term.
However, there’s a slight exception to the rule: A year is a leap year only if it is divisible by 4. But if it’s divisible by 100, it must also be divisible by 400 to be a leap year. This extra adjustment ensures the calendar stays even more accurate over centuries.
So, leap years help maintain the accuracy of our calendar system, keeping it in sync with the Earth’s movement.