What is leap yearThe vernal equinox is the time when the sun is directly above the Earth’s equator, moving from the southern to the Northern Hemisphere.

The mean time between two successive vernal equinoxes is called a tropical year — also known as a solar year — and is 365.2422 days long.

The 365-day calendar results in a loss of 0.2422 days, or almost six hours per year. After 100 years, this calendar would be more than 24 days ahead, which is neither desirable nor accurate.

Leap years align the calendar with the seasons, making any difference as insignificant as possible.

CalendarsGregorian calendar (modern day)Introduced: 1582 A.D.Average year: 365.2425 days Error introduced: 27 seconds (1 day every 3,236 years)

The Gregorian calendar has a 400-year cycle until it repeats the same weekdays for every year — Feb. 29, is a Friday and Feb. 29, 2408, is a Friday.

The Gregorian calendar has 97 leap years during those 400 years.

Julian calendarIntroduced: 45 BCAverage year: 365.25 daysError introduced: 11 minutes (1 day every 128 years)

Long leapsThe longest time between two leap years is eight years — occurring last between 1896 and 1904. The next time will be between 2096 and 2104.

Sweden and Finland had a double leap year in 1712. Two days were added to February — creating a date of February 30, 1712. This was done because the leap year in 1700 was dropped and Sweden’s calendar was not synchronized with any other calendar. By adding an extra day in 1712, they were back on the Julian calendar.

SOURCE: www.timeanddate.com