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The terms anno Domini (AD) and before Christ (BC) are used to label or number years in the Julian and Gregorian calendars. The term anno Domini is Medieval Latin and means "in the year of the Lord" but is often presented using "our Lord" instead of "the Lord", taken from the full original phrase "anno Domini nostri Jesu Christi", which translates to "in the year of our Lord Jesus Christ". The form "BC" is specific to English, and equivalent abbreviations are used in other languages: the Latin form, rarely used in English, is Ante Christum natum (ACN) or Ante Christum (AC).
Easter, also called Pascha or Resurrection Sunday, is a Christian festival and cultural holiday commemorating the resurrection of Jesus from the dead, described in the New Testament as having occurred on the third day of his burial following his crucifixion by the Romans at Calvary c. 30 AD. It is the culmination of the Passion of Jesus Christ, preceded by Lent, a 40-day period of fasting, prayer, and penance.
The Julian calendar is a solar calendar of 365 days in every year with an additional leap day every fourth year. The Julian calendar is still used in parts of the Eastern Orthodox Church and in parts of Oriental Orthodoxy as well as by the Amazigh people, whereas the Gregorian calendar is used in most parts of the world.
The Julian day is the continuous count of days since the beginning of the Julian period, and is used primarily by astronomers, and in software for easily calculating elapsed days between two events.
The Coptic calendar, also called the Alexandrian calendar, is a liturgical calendar used by the Coptic Orthodox Church and also used by the farming populace in Egypt. It was used for fiscal purposes in Egypt until the adoption of the Gregorian calendar on 11 September 1875. This calendar is based on the ancient Egyptian calendar. To avoid the calendar creep of the latter, a reform of the ancient Egyptian calendar was introduced at the time of Ptolemy III which consisted of adding an extra day every fourth year. However, this reform was opposed by the Egyptian priests, and the reform was not adopted until 25 BC, when the Roman Emperor Augustus imposed the Decree upon Egypt as its official calendar. To distinguish it from the Ancient Egyptian calendar, which remained in use by some astronomers until medieval times, this reformed calendar is known as the Coptic or Alexandrian calendar. Its years and months coincide with those of the Ethiopian calendar but have different numbers and names.
The Synod of Whitby was a Christian administrative gathering held in Northumbria in 664, wherein King Oswiu ruled that his kingdom would calculate Easter and observe the monastic tonsure according to the customs of Rome rather than the customs practiced by Irish monks at Iona and its satellite institutions. The synod was summoned at Hilda's double monastery of Streonshalh (Streanæshalch), later called Whitby Abbey.
Dionysius Exiguus was a 6th-century Eastern Roman monk born in Scythia Minor. He was a member of a community of Scythian monks concentrated in Tomis, the major city of Scythia Minor. Dionysius is best known as the inventor of Anno Domini (AD) dating, which is used to number the years of both the Gregorian calendar and the (Christianised) Julian calendar. Almost all churches adopted his computus for the dates of Easter.
As a moveable feast, the date of Easter is determined in each year through a calculation known as computus. Easter is celebrated on the first Sunday after the Paschal full moon, which is the first full moon on or after 21 March. Determining this date in advance requires a correlation between the lunar months and the solar year, while also accounting for the month, date, and weekday of the Julian or Gregorian calendar. The complexity of the algorithm arises because of the desire to associate the date of Easter with the date of the Jewish feast of Passover which, Christians believe, is when Jesus was crucified.
The epact used to be described by medieval computists as the age of a phase of the Moon in days on 22 March; in the newer Gregorian calendar, however, the epact is reckoned as the age of the ecclesiastical moon on 1 January. Its principal use is in determining the date of Easter by computistical methods. It varies from year to year, because of the difference between the solar year of 365–366 days and the lunar year of 354–355 days.
Theophilus was the 23rd Pope of Alexandria and Patriarch of the Seat of Saint Mark. He became pope at a time of conflict between the newly dominant Christians and the pagan establishment in Alexandria, each of which was supported by a segment of the Alexandrian populace.
Annianus of Alexandria was a monk and writer who flourished in Alexandria during the pontificate of Theophilus I around the beginning of the 5th century.
Inter gravissimas was a papal bull issued by Pope Gregory XIII on 24 February 1582. The document, written in Latin, reformed the Julian calendar. The reform came to be regarded as a new calendar in its own right and came to be called the Gregorian calendar, which is used in most countries today.
A golden number is a number assigned to each year in sequence which is used to indicate the dates of all the calendric new moons for each year in a 19-year Metonic cycle. They are used in computus and also in Runic calendars. The golden number of any Julian or Gregorian calendar year can be calculated by dividing the year by 19, taking the remainder, and adding 1.
The Era of the Martyrs, also known as the Diocletian era, is a method of numbering years based on the reign of Roman Emperor Diocletian who instigated the last major persecution against Christians in the Empire. It was used by the Church of Alexandria beginning in the 4th century AD and it has been used by the Coptic Orthodox Church of Alexandria from the 5th century until the present. This era was used to number the year in Easter tables produced by the Church of Alexandria.
The Eastern Orthodox liturgical calendar describes and dictates the rhythm of the life of the Eastern Orthodox Church. Passages of Holy Scripture, saints and events for commemoration are associated with each date, as are many times special rules for fasting or feasting that correspond to the day of the week or time of year in relationship to the major feast days.
The controversy over the correct date for Easter began in Early Christianity as early as the 2nd century AD. Discussion and disagreement over the best method of computing the date of Easter Sunday has been ongoing ever since and remains unresolved. Different Christian denominations continue to celebrate Easter on different dates, with Eastern and Western Christian churches being a notable example.
Anatolius of Laodicea, also known as Anatolius of Alexandria, was a Syro-Egyptian saint and Bishop of Laodicea on the Mediterranean coast of Roman Syria in AD 268. He was not only one of the foremost scholars of his day in the physical sciences, as well as in Aristotelian and Platonic philosophies, but also a renowned computist and teacher of the Neoplatonic philosopher Iamblichus.
Dionysius Exiguus's Easter table was constructed in the year 525 by Dionysius Exiguus for the years 532–626. He obtained it from an Easter table attributed to Patriarch Cyril of Alexandria for the years 437–531. The latter was constructed around the year 440 by means of extrapolation from an Alexandrian Easter table constructed around the year 390 by Patriarch Theophilus of Alexandria. The great historical importance of Dionysius' Easter table is twofold:
- From this Easter table Bede's Easter cycle would ultimately be developed by means of which all future Julian calendar dates of Easter Sunday were determined ;
- With his Easter table Dionysius introduced in passing the Christian era which would be developed into a full system for dating historical events by Bede two centuries later.
An ecclesiastical full moon is formally the 14th day of the ecclesiastical lunar month in an ecclesiastical lunar calendar. The ecclesiastical lunar calendar spans the year with lunar months of 30 and 29 days which are intended to approximate the observed phases of the Moon. Since a true synodic month has a length that can vary from about 29.27 to 29.83 days, the moment of astronomical opposition tends to be roughly 14.75 days after the previous conjunction of the Sun and Moon. The ecclesiastical full moons of the Gregorian lunar calendar tend to agree with the dates of astronomical opposition, referred to a day beginning at midnight at 0 degrees longitude, to within a day or so. However, the astronomical opposition happens at a single moment for the entire Earth: The hour and day at which the opposition is measured as having taken place will vary with longitude. In the ecclesiastical calendar, the 14th day of the lunar month, reckoned in local time, is considered the day of the full moon at each longitude.
A computus clock is a clock equipped with a mechanism that automatically calculates and displays, or helps determine, the date of Easter. A computus watch carries out the same function.
References
- Faith Wallis, Bede: The Reckoning of Time (Liverpool University Press, 2004)
- Georges Declercq, Anno Domini: The origins of the Christian era (Brepols, Turnhout, Belgium, 2000)
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