As we all know, 2024 is a leap year, which means that there will be one more day in February this year. But why February? Why not put a leap day at the beginning of the year, such as January 0, or December 32?
It may seem like a strange choice, but the origins of February 29 are actually steeped in the long history of timekeeping, astronomy, and evolving attempts to combine the two through mathematics.
Inserting days into the calendar, it has been tried and tested in different civilizations to ensure that the lunar and solar schedules remain compatible and consistent with the season tracking. This practice varies from culture to culture: the ancient Egyptian calendar consisted of 12 30-day months, with an additional 5 days at the end of each year. In the lunisolar calendar, as in the Chinese calendar, one month is added every three years, allowing followers of those years to celebrate two springs to welcome the new year or "double spring". Similarly, in the Wickrean and Hebrew calendars, one month is added every three years or so, according to the moon's 19-year phase. The Islamic lunar calendar has a 30-year cycle, with 11 years added by one day.
But, as we know, the roots of the modern leap day can be traced back to ancient Rome. Rome's first king, Romulus, instituted the Roman republican calendar around 738 BC, stipulating that the year began with Mathius (now known as March), only10 months, and winter was not taken into account, because at that time people did not work. However, frustrated by the irregularities of the Roman calendar, and recognizing the differences between the Roman calendar and other calendars, by the 7th century BC, the second Roman king, Numa Pompilius, decided that it was time to start the official counting of the winter months. Therefore, it was added at the end of the calendar yearJanuary and February
Still, even with the addition of these two months, the Roman calendar often deviates from the seasons. So, about every two years, the Roman consuls wouldAdd a 27-day or 28-day month to the 13th month, as appropriate— Mercedonius, or leap months as they are sometimes called—resynchronize their time measurements with the sun. Usually, the extra month is inserted after February 23, shortening the month by five days, immediately following the celebration of Terminalia, an annual festival on February 23 in honor of Terminus, the god of borders in ancient Rome.
Then there was Julius Caesar, who created the new solar calendar, which was created with the help of the Greek astronomer Sosigenes. Sosignes was an advisor to Cleopatra in Egypt, with whom Caesar is known to have been allied. The new Julian calendar—which came into effect after 45 days of the revised Ultimus annus confusionis ("the last year of chaos") after 445 days BCE—is based on the mathematics that a year should consist of exactly 365 days and 6 hours, and that for every four 365-day years, this extra 6 hours will add up to an additional day.
Caesar's CalendarExtend February 24 to 48 hoursto add this leap day after February 23. Because this double sunset falls on the sixth day before the beginning of March, it is called a double sixth, and to this day, some cultures refer to leap years as double sixths.
The Julian calendar is also the year that officially begins on January 1, and as the Roman Empire expanded, the Julian calendar would be used throughout Europe for centuries, but its rule of inserting a leap day every four years was still 11 minutes longer than the solar year. By the 16th century, this difference would result in a difference of 10 days from the actual solar cycle, leading then Pope Gregory XIII to introduce a new calendar in the 1570s: the Gregorian calendar we use today, which adjusted the rule of every four years for leap years to exclude centurions (i.e. 1700, 1800, 1900), but those that were divisible by 400 (i.e. 1600, 2000, 2400).However, for various reasons related to the celebration of Easter and Saints' Day, the Catholic Church insists on repeating February 24 rather than adding a new day elsewhere.
To be sure, humanity has now perfected the art of tracking time, but from 1972 onwards there has been another adjustment: leap seconds, which help compensate for the slight differences between Coordinated Universal Time (UTC), which is based on the Gregorian calendar, which is closer to solar time and is slightly faster. But timekeeping is not an exact science – sometimes it causes so much trouble that experts decide to stop pursuing this precision, such as in 2022, when the world's most important metrology agency decided to abandon leap seconds altogether by 2035. Hotspot Engine Program
But not everyone adopted the Gregorian calendar quickly. Sweden even switched back and forth between the Julian and Gregorian calendars, which eventually took an extra two days to resolve in 1712, resulting in the rare observation of February 30 by the Swedes. At the same time, given the tensions between Britain and its American colonies and the Pope, it took them longer to fully adopt a more accurate Gregorian calendar, but they eventually made concessions as well. In 1752, the Calendar (New Style) Act was implemented, moving the British New Year from March 25 (the Anglican Feast of the Annunciation) to the more familiar January 1, and officially calling the quadrennial leap day February 29, which has since become an international standard.