A leap year is a year that has 366 days instead of the usual 365.

We add this extra day as February 29th to keep our calendar in sync with the Earth's orbit around the sun.

Here’s why it happens:

1. The Earth actually takes about 365.2422 days (or 365 days, 5 hours, 48 minutes, and 45 seconds) to circle the sun once.
2. That's roughly 6 hours longer than a standard 365-day year.
3. If we ignored those extra 6 hours every year, our calendar would drift. After 100 years, we'd be off by about 24 days. After a few centuries, summer would feel like winter!
4. To fix this, we add an extra day every 4 years to catch up. Those 6 extra hours per year × 4 years = about 24 extra hours (one full day).

How to know if it's a leap year:

Leap years are usually divisible by 4 (like 2020, 2024, 2028).

Exception: Century years (like 1900, 2100) are not leap years unless they are divisible by 400. For example, 2000 was a leap year, but 1900 was not. This extra rule fine-tunes the calendar so we don't over-correct.

So in short: A leap year adds one day in February every 4 years to make up for the extra quarter-day it takes Earth to orbit the sun.

A leap year is a year with 366 days instead of 365. An extra day is added to February to account for the extra time Earth takes to orbit the Sun.