Every four years we have an extra day added at the end of February and this is all because of our orbit around the Sun and the Gregorian calendar. The Gregorian calendar replaced the Julian calendar around 1582 because it had become out of sync with the equinoxes and solstices.

Adding an extra day realigns the calendar with the Earth’s movement around the Sun. It takes 365.242199 days for Earth to orbit the Sun. The extra 5 hours, 48 minutes and 46 seconds needs to be accounted for, that’s why we get the extra day.

Timeanddate.com clarifies the criteria for a leap year:

  • The year number must be able to be divided by 4
  • If a century year can be evenly divided by 100, it is not a leap year, unless the century year is also evenly divisible by 400. Then it is a leap year.

Adding an extra day every four years means that every four centuries, there are three extra days. So those days are removed, one day in the three century years that cannot be divided by 400.

So, what are you going to do with your extra day?

How long to orbit the Sun?

Mercury

87.96 days

Venus

224.68 days

Earth

365.26 days

Mars

686.95 days

Jupiter

11.862 years

Saturn

29.546 years

Uranus

84.07 years

Neptune

164.81 years