Theology Feast of Annunciation Medieval Feast of the Circumcision of Jesus Christ date Gregorian calendar circumcision spring equinox December 25th secular religious Christian Bible standardize Jesus Christ birth Politics Gospel of Luke Ancient Roman timekeeping Christian calendar deity tradition Janus Pope Gregory XIII 8 days Biography Cultural Anthropology Sociology Roman calendar Anthropology Mythology January 1st Julian calendar Jewish Protestant celebrate Ancient History 1582 New Year's Day History Agriculture sacred catholic March 25th transition new year Graphology Etiology Europe observance reformation christmas Iconography Chronology