Leap Year

A leap year occurs every four years and is an additional day in the month of February, meaning there are 29 days in the month instead of the usual 28. This allows the calendar year to keep synchronised with the astronomical or seasonal year as the year doesn’t last a whole number of days, it last 365 days and a quarter. So every four years an extra day is added.

On 1st January 45 BC by edict, Julius Caesar reformed the historic Roman calendar to make it a consistent solar calendar, thus removing the need for frequent intercalary months. His rule for leap years was a simple one, add a leap day every for years. A Julian year lasts 365.25 days, a mean tropical year is about 365.2422 days. Consequently even this calendar drifts out by about three days every 400 years. The calendar continued unaltered for about 1600 years until the Catholic Church became concerned about the widening divergence between the March Equinox and 21st March. This meant the Gregorian Calendar was created, and to stop the calendar becoming out of sync, leap days on every 3 out of 4 centuries are missed unless the century is divisible by 400. So 2000 has a leap day, but 2100, 2200 and 2300 don’t. This is because every 400 years an extra three days is added to the calendar, so omitting those three days means it is back in sync.

There are some traditions on a leap day. In Ireland and Great Britain it is tradition that women may propose marriage. A person born on a leap day may be called a “leaping” or “leaper”.