Things you probably didn’t know about leap day - ScienceNerds

February 29, also known as the leap day. A leap day is added to several solar calendars, including the calendar Gregorian standard in most of the world.

February 29 only happens every four years unless that year is divisible by 100 but not by 400. This is to keep our calendar synchronized with the Earth's rotation around the sun. Without leap day, we would be out of sync about six hours a year.

Leap Year

Years that contain a leap day are called leap years. Years that do not contain a leap day are called common years. According to the Gregorian calendar, the year numericals that are divisible by 100, but not by 400, do not contain a leap day. Thus 1900, 1800 and 1700 did not contain a leap day; neither will 2300, 2200 and 2100. Because they are divisible by 100.

On the contrary, 1600 and 2000 had leap days, and 2400 will have leap days, even if they are divisible by 100 because they are also divisible by 400. Although most modern calendar years have 365 days, a complete revolution around the Sun (a solar year) takes approximately 365 days and 6 hours.

Therefore, an additional 24 hours are accumulated every four years, which requires that an additional calendar day be added to align the calendar with the apparent position of the Sun. Without the additional day, in future years the seasons would occur later in the calendar, which would eventually generate confusion on when to carry out activities that depend on the weather, ecology or daylight hours.

A leap day is observed to handle this. A leap day compensates for this delay, realigning the calendar with the position of the Earth in the Solar System; otherwise, the stations would occur later than expected in the calendar year. Adding a calendar day every four years results in an excess of about 44 minutes every four years, or about 3 days every 400 years. To compensate for this, three days are eliminated every 400 years. That is why the years that are divisible by 100 but not by 400, do not contain a leap day. Anyone born on leap day will not have the opportunity to celebrate their birthday every year. Were you born leap day? Share your birthday celebration experiences through comments.

~sciencefreak