Leap Year

• 01 Mar 2024

Source: IE

Why in News?

In 2024, February 29^th marks Leap Day, an additional day added to the calendar during leap years. This extra day, known as Leap Year Day, extends the year to a total of 366 days.

What is a leap year?

• Leap Year:
  • A leap year has 366 days in a year as opposed to the regular 365 days. The extra day is added to February, the shortest month of the year, as February 29.
  • A solar calendar signifies one complete orbit of the Earth around the Sun. The Earth's orbit takes about 365 days, 5 hours, 48 minutes, and 46 seconds to simplify, a regular year is rounded to 365 days.
    • To account for the extra time, rounded up to six hours, 24 hours (one full day) are added to every fourth year.
  • Without leap years, the calendar would become out of sync with the seasons over time.
    • The extra day keeps calendars and seasons from gradually falling out of sync and impacting harvesting, planting and other cycles based on the seasons.
• Evolution of Leap Years:
  • The Julian calendar's approximation of the solar year led to accumulating errors over time, primarily due to a slight overcompensation.
  • By the 16th century, the calendar was approximately 10 days ahead of the solar year, prompting the need for reform.
  • Pope Gregory XIII initiated calendar reform in 1582, removing ten days to realign the calendar with the solar year.
  • To prevent future errors, the Gregorian calendar introduced a refined leap year rule, omitting three leap years every 400 years.
• Math of Leap Year:
  • Leap years are always multiples of four like 2016, 2020, 2024, but a year that is a multiple of four is not always a leap year.
  • The Gregorian leap year rule states that the year number must be divisible by four, except for end-of-century years (ending in '00'), which must be divisible by 400.
    • This means that the year 2000 was a leap year, although 1900 was not. 2024, 2028, 2032 and 2036 are all leap years.
  • This extra rule is needed because adding a leap day every four years actually overcompensates for the slight difference in the solar year. It turns out that adding a leap day every four years adds a little too much time, about 44 minutes more than necessary.
    • So, by skipping leap years for centuries that aren't divisible by 400, we fine-tune the calendar to stay even closer to the actual solar year and keep the seasons in check.