Bits and Beyond...
The Gregorian Calendar was introduced in 1582, when
Pope Gregory XIII modified the Julian calendar. The purpose of this
modification is to restore the date of Easter to
spring. Unlike the Julian Calendar, the years divisible by 100 in
the Gregorian Calendar are not leap years, unless they are divisible by
400. Thus, the years 1700, 1800 and 1900 were not leap years, while
the years 1600 and 2000 were.