The Orthodox calendar, also known as the Eastern Orthodox calendar or the Julian calendar, is a liturgical calendar used by the Eastern Orthodox Church and some other Eastern Christian churches. It is based on the Julian calendar, which was introduced by Julius Caesar in 46 BC and was the predominant calendar in the Roman Empire until the 16th century. The Orthodox calendar differs from the Gregorian calendar, which is used in most of the world today, by 13 days. This means that Orthodox Christmas is celebrated on January 7th, while Western Christmas is celebrated on December 25th.
The Orthodox calendar is important for Orthodox Christians because it determines the dates of their religious holidays and festivals. It is also used to calculate the date of Easter, which is the most important feast in the Orthodox Christian year. The Orthodox calendar has a long and complex history, and it has been revised several times over the centuries. The current version of the calendar was adopted in 1582 by the Council of Constantinople.
