"Bissextile years" is a term used to describe leap years, which occur every four years to account for the extra fractional day in the Earth's orbit around the sun. The spelling of "bissextile" may seem confusing, as it includes the rare and archaic word "sextile," meaning "occurring every sixth year," but also the prefix "bi-," meaning "two." However, the pronunciation is straightforward when written in IPA phonetic transcription: bɪˈsɛkstaɪl jɪərz.
Bissextile years, also known as leap years, are those which contain an additional day, known as leap day, inserted in order to keep the calendar year synchronized with the Earth's revolutions around the Sun. This practice is necessary because the Earth's orbit around the Sun takes slightly longer than 365 days, approximately 365.24 days. Therefore, to maintain accuracy and prevent the calendar from falling behind the astronomical year, the addition of an extra day is implemented every four years.
The name "bissextile" is derived from the Latin word "bissextus," meaning "twice sixth," as the leap day is inserted as the sixth day before the Kalends of March, which is February 29th in the modern Gregorian calendar. This practice traces back to the Julian calendar, wherein leap years were determined by the rule that any year divisible by four would have a leap day.
The purpose of bissextile years is to ensure that the seasons remain aligned with the calendar year. Without the added day, the dates of events tied to specific seasons, such as solstices and equinoxes, would gradually shift over time. By inserting the leap day, a balance is maintained, allowing the calendar to accurately reflect the Earth's position in its orbit and enabling predictability in various fields, including agriculture, astronomy, and everyday life.
The word "bissextile" comes from Latin "bissextus", which means "the twelfth day before the Calends of March". In the Roman calendar, this day was added every four years to align the lunar cycles with the 365-day solar year.
The origin of "bissextus" can be broken down as follows:
- "bis" meaning "twice" or "double"
- "sextus" meaning "sixth"
"Bissextile" refers to the addition of an extra day in the month of February (the sixth month in the Roman calendar) every four years. This additional day is now known as February 29th in the Gregorian calendar. Bissextile years are also commonly referred to as "leap years".