On this day in history, Hattie McDaniel won an Oscar for her role in Gone With the Wind. The founder of the Shaker religion, Ann Lee was born, and South Korean troops began withdrawing from the Vietnam War.
But as you well know, this day in History has no anniversary date most years. Figuring out which years will have a bonus day in the Gregorian calendar isn’t as simple as counting to four. Yes, the year must be divisible by four, but there are other caveats.
The year cannot be evenly divided by 100— unless it is also divisible by 400. So as timeanddate.com points out, the years 2000 and 2400 contain a leap, while 1800 and 1900 were not leap years.
The Western calendar of today was first introduced by Pope Gregory XII in 1582. Gregory tweaked the calendar to realign the calendar year with the Equinox, but he did not invent the concept of a leap. He developed the last two caveats, but Julius Caesar incorporated a February leap into his calendar, that was introduced at about 45 BCE. Caesar’s calculations were was adapted from the ancient Egyptian Civil calendar, according to History.com.
Other cultures with leap days occuring every few years include Ethiopians, Persians, and separately, those who observe the Islamic Hijri calendar. Another Middle Eastern religious group, the Bahai, also have a leap day calendar.