The leap year was introduced to synchronize our calendar and orbital motion in Rome, under the command of Julius Caesar, advised by the mathematician and astronomer Sosigenes of Alexandria. Caesar decided that, in the Julian calendar (named after him), one in four years would have 366 days , one more than common years. In this way he ensured that the months of the year kept pace with the seasons. In principle, the “extra” day of the leap year was interspersed between the days that today correspond to February 23 and 24.
The desynchronization was solved only approximately :, since the Earth does not reach the same point in its orbit in exactly a whole number of days (365) plus a quarter of a day. Specifically, an extra 44 minutes and 56 seconds are added every four years, that is, almost eight days per millennium. The difference accumulates with each revolution of the Earth around the Sun, and it became important several centuries after Julius Caesar devised his calendar. Hence, in the year 1582 AD, Pope Gregory XIII, advised by the astronomers Christopher Clavius and Luigi Lilio, chose to introduce a reform that consisted of adjusting the leap years so that the years divisible by one hundred but not by four hundred ceased to be be 366 days old . In this way, the lag that was taking place by inserting excessive leap years was avoided, since three days were eliminated every four centuries.
Thus, 1600 was a leap year and 2000 was also leap (all two are divisible by four hundred), but they were calendar years 1700, 1800 and 1900, and it will be 2100.
Leap day also observes another important day
Since February 29 is a “rare” date, it is also home to Rare Disease Day, which began in 2008 to raise awareness of diseases that affect fewer than 1 in 2,000 people. But don’t worry: if it’s not a leap year, the celebration takes place on the last day of February.
As a curiosity, in the past, workers advocated for leap day to become a holiday.
Over the years, some smart members of the world’s workforce realized that they were working an extra day every leap year without additional pay. This has sparked a legitimate campaign to make February 29 a public holiday. Makes sense right?
An important set of literary characters does not observe leap years, for example. While leap day helps keep our orbital timeline on track as we’ve seen, some literary characters don’t seem to need it. The hobbits of the writer JRR Tolkien have a calendar that includes a 30-day month of February each year. What if the weather works slightly differently on Middle-earth?
