- Vatican Post Office issued for the fourth centenary of the Gregorian calendar Day Cover.
The Gregorian calendar, also known as the Western calendar, or Christian calendar, is the internationally accepted civil calendar.[1][2][3] It was introduced by Pope Gregory XIII, after whom the calendar was named, by a decree signed on 24 February 1582, a papal bull known by its opening words Inter gravissimas.[4] 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 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 occurring 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. Since the Spring equinox was tied to the celebration of Easter, the Roman Catholic Church considered that this steady movement in the date of the equinox was undesirable. The Gregorian calendar reform contained two parts, a reform of the Julian calendar as used up to Pope Gregory's time, together with a reform of the lunar cycle used by the Church along with the Julian calendar for calculating dates of Easter. The reform was a modification of a proposal made by the Calabrian doctor Aloysius Lilius (or Lilio).[5] Lilius' proposal included reducing the number of leap years in four centuries from 100 to 97, by making 3 out of 4 centurial years common instead of leap years: this part of the proposal had been suggested before by, among others, Pietro Pitati. Lilio also produced an original and practical scheme for adjusting the epacts of the moon for completing the calculation of Easter dates, solving a long-standing difficulty that had faced proposers of calendar reform. wikipedia read
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Keywords: calendar, chalcography, collecting, engraving, gregorian, lugris2, office, philately, post, reform, stamp, stamps, vatican
