Understanding Bissext: The Leap Week Concept Explained

Bissext, also known as leap week, is a calendar concept that allows for an extra day to be added to the calendar every four years. This extra day is added to the month of February, which normally has 28 days, making it a 29-day month in a leap year. The purpose of bissext is to keep our calendar aligned with the Earth's orbit around the sun, as the Earth takes approximately 365.24 days to complete one orbit.

The concept of bissext was first introduced by Julius Caesar in 45 BCE, as part of the Julian calendar. However, the Julian calendar had a small error, which added up over time, causing the calendar to drift away from the actual solar year. This error was corrected in 1582 by Pope Gregory XIII, who introduced the Gregorian calendar, which is the calendar used today. The Gregorian calendar has a leap year every four years, but it also skips three leap years every 400 years.

The word "bissext" comes from the Latin words "bis" meaning "twice" and "sext" meaning "sixth", as the extra day added to February is considered the sixth day of the week.