Need an extra day to catch up on sleep or to finish an assignment this month? Then you are in luck, because 2020 is a leap year, an event that occurs once every four years. This means that instead of the customary 365 days, the year will have 366 days. Since the extra day is tacked onto the shortest month of the year, February 2020 will have 29 days.
The leap day, as it is called, is necessary to account for the discrepancy between the lunar and the solar calendar. It takes our planet 365.2422 days to complete one revolution around the sun, which means that each year ends about a quarter day short of the complete orbit. While adding the extra hours to our annual year would make for a strange day, ignoring them is not a good idea either. That's because the extra quarter day each year adds up to a full 25 days every century. This means that at the end of the 100 years, our lunar seasons would lag behind our solar seasons by almost a month. If left unchecked for multiple centuries, the lunar and solar calendars would become entirely out of synch.
The ancient Egyptians are believed to be the first to correct the discrepancy by adding a leap-year system in the third-century BC. In 46 BC, after Rome's lunar calendar had diverged from the seasons by about three months, Emperor Julius Caesar decided to adopt the Egyptian calendar. He began by realigning the seasons with a 445-day-long year before adding an extra day every four years. Though this was a big improvement, rounding the extra 5 hours, 49 minutes, and 16 seconds to six hours, or a quarter of a day, meant that the calendar year ended up being about 11 minutes longer than its solar counterpart. As a result, the two diverged by an entire day every 128 years.
The Gregorian calendar, introduced by Pope Gregory XIII in 1582, solved the issue, albeit in a slightly confusing manner. It stipulates that years divisible by 100 are not leap years unless they are also divisible by 400. This means that 1700, 1800, and 1900 were not leap years, but 1600 and 2000 were. Thanks to this rule, every four hundred years, there are three times when leap years occur at an interval of eight years instead of the usual four! Since this will next happen in 2096, most of us can be assured of an extra day every four years during our lifetimes.
Leap day is particularly special for the over 4 million people worldwide who are born on February 29, and only get to celebrate their birthdays once every four years. Many hotels and retail chains go all out to make the day extra memorable for the leaplings by offering special deals and discounts. The twin cities of Anthony, Texas, and Anthony, New Mexico — the self-proclaimed leap day capital of the world — also stage a four-day Leap Year Festival, which includes a huge birthday party for all leap year babies!
Be sure to let us know how you plan on celebrating the bonus day by adding your comments below.
Resources: National Geographic.com, Vox.com