Gregorian Calendar

A solar calendar established by Pope Gregory XIII in 1582 and now widely used throughout the world.

The changes made by Gregory corrected the drift in the civil calendar which arose because the mean Julian calendar year (exactly 365 1/4 days) was slightly too long, causing the vernal equinox, and consequently the date on which Easter was being celebrated, to drift slowly forward in relation to the civil calendar and the seasons.

Years in the reformed calendar continue the numbering system of the Julian calendar, which are numbered from the traditional Incarnation year of Jesus, which has been labelled the "anno Domini" (AD) era.