An Etymological Dictionary of Astronomy and Astrophysics
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In solar calendars the year that contains 366 days, instead of 365, in order to keep the calendar in pace with the real solar time.

→ leap; → year.

The three criteria that identify → leap years in the → Gregorian calendar: 1) The year must be evenly divisible by 4; 2) If the year can be evenly divided by 100, it is not a leap year, unless; 3) The year is also evenly divisible by 400. This means that in the Gregorian calendar, the years 1600, 2000, and 2400 are leap years, while 1700, 1800, 1900, 2100, 2200, 2300 and 2500 are not leap years.

→ leap; → year; → rule.