Gregorian calendar

From The Catholic Guide

The Gregorian calendar is the most widely used calendar in the world. A modification of the Julian calendar, it was first proposed by the Calabrian doctor Aloysius Lilius, and was decreed by Pope Gregory XIII, for whom it was named, on February 24 1582 via the papal bull Inter gravissimas. Years in the calendar are numbered from the traditional birth year of Jesus, which has been labeled the "anno Domini" (AD) era, and is sometimes labeled the "common era" or the "Christian era" (CE).