Gregorian Calendar

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The Gregorian calendar, which is the calendar used today, was first introduced by Pope Gregory XIII  in February 1582 to correct an error in the old Julian calendar.

The error had been accumulating over hundreds of years so that every 128 years the calendar was out of sync with the equinoxes and solstices by one additional day.

As the centuries passed, the Julian Calendar became more inaccurate. Because the calendar was incorrectly determining the date of Easter, Pope Gregory XIII reformed the calendar to match the solar year so that Easter would once again fall upon the first Sunday after the first full moon on or after the Vernal Equinox.

Ten days were omitted from the calendar to bring the calendar back in line with the solstices, and Pope Gregory XIII decreed that the day following Thursday, October 4, 1582 would be Friday, October 15, 1582 and from then on the reformed Gregorian calendar would be used.

Many Catholic countries immediately observed the calendar change, but for almost two hundred years Protestant countries refused to change to the new calendar because it had reformed by a Catholic Pope. The Greek Orthodox countries didn't make the change until the start of the 20th century.

Those countries who changed to the Gregorian calendar in the 18th century removed eleven days from their calendar; those countries who changed in the 19th century removed 12 days, and those countries who changed to the reformed calendar during the 20th century removed 13 days.

Canada and the United Kingdom stopped using the Julian Calendar on Wednesday, 2 September 1752 so the following day on the Gregorian calendar was Thursday, 14 September 1752 - 11 days were lost.

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