The Ethiopian calendar, also called the Ge'ez calendar, is the principal calendar used in Ethiopia and also serves as the liturgical calendar for Christians in Eritrea belonging to the Eritrean Orthodox Church, Eastern Catholic Church and Lutheran Evangelical Church of Eritrea. It is based on the older Alexandrian or Coptic calendar, which in turn derives from the Egyptian calendar.
also known as the Western calendar, or Christian calendar, is the internationally accepted civil calendar.
It was introduced by Pope Gregory XIII, after whom the calendar was named, by a decree signed on 24 February 1582, a papal bull known by its opening words Inter gravissimas.
Because of the Protestant Reformation, however, many Western European countries did not initially follow the Gregorian reform, and maintained their old-style systems.
Britain and the British Empire (including the eastern part of what is now the United States) adopted the Gregorian calendar in 1752.
or Muslim calendar or Hijri calendar is a lunar calendar consisting of 12 lunar months in a year of 354 or 355 days. It is used to date events in many Muslim countries (concurrently with the Gregorian calendar), and used by Muslims everywhere to determine the proper day on which to celebrate Islamic holy days and festivals. The first year was the year during which the emigration of the Islamic prophet Muhammad from Mecca to Medina, known as the Hijra, occurred.
began in 45 BC as a reform of the Roman calendar by Julius Caesar. It was chosen after consultation with the astronomer Sosigenes of Alexandria and was probably designed to approximate the tropical year (known at least since Hipparchus).
or sometimes called Iranian calendars are a succession of calendars invented or used for over two millennia in Greater Iran. One of the longest chronological records in human history, the Iranian calendar has been modified time and again during its history to suit administrative, climatic, and religious purposes.
The Religious Society of Friends (also known in some places as Friends Church or Quakers) is a Christian denomination focusing on the priesthood of all believers, which encompasses a range of belief from evangelicalism to liberalism.
The "plain calendar," sometimes called the "scriptural calendar," differs from what Friends referred to as the "world's calendar" in that it uses numbers to denominate the names of the months and days of the week. The plain calendar does not use names of calendar units derived from the traditional names due to their derivation from pagan deities.