Michael Kwayisi

Proleptic Gregorian (and Jewish) Calendar

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Proleptic Gregorian calendar from 5000 B.C.E. to 5000 C.E.Proleptic Gregorian calendar from 5000 B.C.E. to 5000 C.E.

When Pope Paul III took the papal throne in 1534, he employed several astronomers to come up with a new calendar system.[1] However, it was not until just about three decades later, during the papacy of Pope Gregory XIII, that Christopher Clavius’s proposal was chosen among several others to be implemented. The Pope then issued a papacy bull named Inter Gravissimas on February 24, 1582, whose intent was to bring the date for the celebration of Easter to the time of the year in which the Roman Emperor Constantine had enacted at the First Council of Nicaea in 325. Later that year, Pope Gregory decreed that the day following October 4, 1582 would be known as Friday, 15th October, 1582. Thus we came to have the so-called Gregorian calendar.

Below is a proleptic Gregorian calendar produced by extending the Gregorian calendar backward to dates preceding its official introduction, in order to make it possible to identify particular dates prior to October 15, 1582. In addition, the calendar accurately extends forward as well, to as far as the year 5000! I don’t think you and I will live till then, will we?

List of Centuries

The years from 5000 B.C.E. to 1 B.C.E. have been grouped into periods of 100 years, that is, centuries. Likewise, the same has been done for the years ranging from 1 C.E. to 5000 C.E. This is to make it easier to browse the years by era and centuries.


  1. ^ The Church was then using the Julian Calendar, a calendar system that Julius Caesar had implemented in 45 BC. The length of a year in the Julian calendar was 365 days with an additional day added every 4 years. Hence, the average length of a year in this calendar was exactly 365.25 days. This figure, however, is significantly different from the mean vernal equinox year (i.e., the real length of a solar year) of 365.2424 days. In other words, the Julian calendar year was 10.944 minutes longer, which by the close of the 15th century had accumulated to nearly 12 days! This evidently proved that the Julian calendar was inaccurate with regards to the seasons and so needed a reform.

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