Tomorrow, February 29th, is leap day! Every four years, an extra day is added to the end of February. Non leap years have exactly 365 days, but it actually takes a little more than that for Earth to completely go around the Sun. It actually takes 365 and 1/4 days, which is why leap year is every four years. Every year that is divisible by four is a leap year!
Without leap years, every four years, the seasons would start an entire day yearly on the Gregorian Calendar. Without the leap years, it would become hard to keep track of the start of seasons! The Gregorian Calendar is what most of the world uses to keep track of dates. It is a solar calendar which means that days are marked using the sun. This calendar was introduced in 1582 by Pope Gregory XIII.
How will you be spending your extra day?