<P> The Gregorian calendar is the most widely used civil calendar in the world . It is named after Pope Gregory XIII , who introduced it in October 1582 . The calendar spaces leap years to make the average year 365.2425 days long , approximating the 365.2422 day tropical year that is determined by the Earth 's revolution around the Sun . The rule for leap years is as follows : </P>
<P> The Gregorian calendar is the most widely used civil calendar in the world . It is named after Pope Gregory XIII , who introduced it in October 1582 . The calendar spaces leap years to make the average year 365.2425 days long , approximating the 365.2422 day tropical year that is determined by the Earth 's revolution around the Sun . The rule for leap years is as follows : </P>
when did we change from julian to gregorian calendar
when did we change from julian to gregorian calendar
October 1582
October 1582