leap-year

Context:

2020 will have February 29, a date that comes approximately once every four years .

Rationale of Leap Year:

  • Our solar calendar is supposed to reflect one orbit of Earth around the Sun. This helps in anticipating the seasons, maintaining crop cycles, setting school schedules, etc.
  • Compensation of extra time:
    • Earth takes nearly 365 days and a few hours to orbit the Sun, which is why a year is usually 365 days long. 
    • But to be more precise, the Earth completes one orbit in 365 days, 5 hours, 48 minutes and 46 seconds.
    • To compensate for this extra time we have a leap year every four years that has 366 days.

Failure in Overcoming Deviation:

  • Still no accurate compensation:
    • However, with three years of 365 days and one leap year of 366 days, the average length of a year was 365 days and 6 hours. 
    • This was longer, if ever slightly so, than 365 days, 5 hours, 48 minutes and 46 seconds.
  • Leap years were introduced because the calendar year was short, but they ended up making the average calendar year longer than the solar year. The difference is a small matter of 11 minutes and 14 seconds.
  • Eventually, the reform led to the Gregorian calendar, which we follow today. 

Rules and Exceptions::

  • A year that is a multiple of 4 is a leap year; except:
  • A year ending with 00 is not a leap year; except:
  • A “00 year” in which 00 is preceded by a multiple of 4 (1600, 2000, 2400 etc) remains a leap year. That is why 1900 and 2100 are not leap years, but 2000 is one.