This year, for the first time in four years, February will have 29 days instead of the typical 28. In other words, it is going to be a leap year. Most of us are familiar with the concept of leap years, but why does this happen?

A typical calendar year consists of 365 days. However, this is not the exact number of days that it takes for the Earth to complete an orbit around the sun. It actually takes about 365.24 days for the Earth to finish the cycle. Though this may not seem like much, the extra quarter of a day per year accumulates over time. If there was no leap year, the seasons would begin to drift out of sync with the calendar year. After about 700 years without leap years, the summer weather expected in July would occur in December. In order to prevent this, an extra day is added to the typical 365-day year once every four years.

This system is still not precise enough, though. The length of the day is also not exactly what it is thought to be. Earth takes approximately 23.26 hours to complete a rotation, not 24 hours. Because of this, the added leap years actually make the non-rounded year too long by around 44 minutes. To account for this, we skip leap years on years that are divisible by 100 but not 400. For example, the year 1900 was not a leap year, while 2000 was a leap year; thus, the year 2100 will be our next skipped leap year.

As the 29th of February is such an interesting date, many superstitions are associated with the day. Some cultures associate the day with bad luck, while others think that being born on the 29th means you are uniquely gifted. In the past, leap days were thought to be the only days when women could propose to men. Leap year babies are called “leapers” or “leaplings,” and as much as having a one-in-four-year birthday is special, the 29th of February is technically the first day of March in non-leap years.