Background
The Gregorian calendar is widely used in many countries such as the United States. This was introduced in 1582 by Pope Gregory XIII. The Julian calendar that had been in use until then was slightly inaccurate, causing the vernal equinox to move backwards in the calendar year. The Gregorian calendar was not accepted everywhere and some churches, particularly with origins in Eastern Europe, still use other calendars. According to the Gregorian calendar, the first day of the year is January 1.