The Gregorian calendar, also called the Western calendar and the Christian calendar, is the internationally accepted civil calendar. It was introduced by Pope Gregory XIII, after whom the calendar was named, by a decree signed on 24 February 1582; the decree, a papal bull, is known by its opening words, Inter gravissimas. The reformed calendar was adopted later that year by a handful of countries, with other countries adopting it over the followi...
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The Gregorian calendar, also called the Western calendar and the Christian calendar, is the internationally accepted civil calendar. It was introduced by Pope Gregory XIII, after whom the calendar was named, by a decree signed on 24 February 1582; the decree, a papal bull, is known by its opening words, Inter gravissimas. The reformed calendar was adopted later that year by a handful of countries, with other countries adopting it over the following centuries.
The motivation for the Gregorian reform was that the Julian calendar assumes that the time between vernal equinoxes is 365.25 days, when in fact it is presently almost exactly 11 minutes shorter. The error between these values accumulated at the rate of about three days every four centuries, resulting in the equinox being on March 11 (an accumulated error of about 10 days) and moving steadily earlier in the Julian calendar at the time of the Gregorian reform. Because the spring equinox was tied to the celebration of Easter, the...
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