The year 2000, like the years 1996 and 2004, is a leap year - with 29 days in February; but the years 1900, 1999, 2001, 2002, 2003, 2005 and 2100 are not leap years - and have only 28 days in February.
Canada uses the "Gregorian" calendar through the heritage of the British Act of 1750:
"An Act for regulating the Commencement of the Year, and for correcting the Calendar now in use"
(24 Geo. 2 c. 23).
First introduced in 1582 by Pope Gregory XIII as a replacement for the Julian calendar, this calendar is now in worldwide use for civil purposes. The Gregorian calendar's rules for leap years have three parts:
- If divisible evenly by 4, a Gregorian year is a leap year, with a February 29 and 366 days (e.g. 1996/4 = 499, so 1996 is a leap year), UNLESS
- If divisible evenly by 100, a Gregorian year is a normal year with 365 days (e.g.1900/100=19, so 1900 is a normal year of 365 days; as is 2100), UNLESS
- If divisible evenly by 400, a Gregorian year is a leap year; so the year 2000 is a leap year.
These three rules are trying to keep the seasons near fixed dates on the calendar, with the first day of spring (the vernal equinox) near March 21.
Although other rules have been proposed in attempts to improve on the rules of 1582, none has been adopted for civil purposes. The history of the rules is rather involved.