Introduction
The ancient Egyptian civilization lasted longer than any other. The Egyptian calendar, the oldest in history, originated three millennia before Christ. The exact date of its origin is unknown. It is believed that Imhotep, the supreme official of King Djoser c.2670 BC. had a great impact on the construction of the calendar. The Egyptian calendar is a solar calendar whose year consists of 12 months of 30 days (3 decans of 10 days each) and 5 additional yearly days (epagomenes), for a total of 365 days.
The myth was that Nut, goddess of the Sky, was separated from her lover Geb, god of the Earth, and cursed with barrenness: She could not give birth in any month of the year. Thoth, moon-god of time, measurement and wisdom, decided to help Nut and Geb. In a game of dice with the reigning gods, he won 5 extra days not belonging to any particular month, which Nut used to produce 5 children, including Isis and Osiris.

Helical Rising of Sirius
"Sirius is the one consecrated to Isis, for it brings the water." ~Plutarch
Historically, ancient Egyptians initially used a civil calendar based on a solar year that consisted of 365 days only, without making any adjustment for the additional quarter of a day each year. However, in the mean time, they knew an astronomical calendar which is based on an astronomical concept, namely the heliacal rising of Sirius, the brightest star in the sky, at the dawn of the eastern horizon. A heliacal rising of a star is defined as its appearance above the horizon just before sunrise. The day on which the heliacal rising of Sirius occurs marks the first day of the year and the beginning of the actual Inundation (as opposed to the calendrical one). Sirius or Spdt in Ancient Egyptian is characterized by high luminosity and is a member of the constellation Canis Major. It lies about 8.6 light years from earth. The first day coincides with the arrival of the highest point of the Nile flood at Memphis, south west of Cairo, the capital of Egypt during the early dynastic period of the Old Kingdom.
Discrepancies in year length underwent complex calculations considering stellar, solar and lunar cycles. Ancient Egyptians realized that the helical rising of Sirius coincides with the new year's day of the civil calendar precisely every 1460 years. Hence, 1461 Egyptian years are equal to 1460 years of 365¼ days (the length of what would become the Julian year). This period of 533265 days has been dubbed a Sothic Cycle, because Sothis is the Greek name of Sirius. The Egyptian civilization lived through several such cycles. A record exists by the 3rd century A.D. grammarian Censorinus that, in A.D. 139, the first day of the Egyptian Civil Year coincided with the helical rising of Sirius, marking the end of a Sothic cycle. This phenomenon was celebrated by issuing coins on the back of which appears the Greek inscription A ION, indicating an end of an Era. Egypt then was under the Roman Rule of Emperor Antoninus Pius. The notion of eternal time was personified and deified. A relief of the deity Aion was found in Oxyrhnichus , present day el-Bahnasa in middle Egypt. This notion, found its way into Persian Mithraism and into Gnosticism.
Before the construction of the Aswan High Dam in 1961, the inundations of the Nile were a yearly phenomenon, caused by the summer rains over the Ethiopian highlands, which are drained by 2 of the 3 major tributaries of the Nile, the Blue Nile and the Black Nile. The Blue Nile (Gihon) flows from lake Tana and joins the White Nile at Khartoum to form the Nile proper, whereas the Black Nile (Atbarah or Atbara) is the only tributary of the Nile after Khartoum. The Black Nile is dry for most of the year, but in a few short months it provides over 20% of the Nile's total yearly volume of water, loaded with about 11 million tons of this black mud which once made Egypt fertile, but is now settling in Lake Nasser, behind the Aswan Dam. The White Nile carries only half the total flow of the Blue Nile but it's much more regular. It flows from Lake Victoria, under a succession of names. The Kagera River flows into Lake Victoria, and has an upper branch, the Ruvyironza River of Burundi, whose source is now considered to be the ultimate source of the Nile.
The exact day when an heliacal rising is observed may depend on the longitude and latitude of the observer. The altitude is somewhat relevant too (on the equator, a star rising due east would be seen from a 100m cliff about 76.8s earlier than from the beach). The brightness of the star is important as well, since fainter objects disappear earlier at dawn.

Seasons and Calculations
Egyptian astronomers knew that a period of 365 days was about ¼ day short of an actual tropical year, but an intercalary day was never added, and the calendar was allowed to drift through the seasons. A drift of a fixed calendar date through the seasons is a flaw of a solar calendar called calendar creep. The Egyptian calendar had a severe case of this, but it was originally designed to match the 3 seasons of the Nile (4 months each):
· Akhet: Inundation.
· Proyet, Peret, or Poret: Emergence, Winter, or Growth Season.
· Shomu or Shemu: Harvest, Summer, or Low Water.
This subdivision possibly occurred during the Ramesside period of the 19th Dynasty.
Although the Egyptian months have specific names (tabulated below, in our discussion of the Coptic calendar), they are commonly denoted by their ranks within those fictitious calendar seasons, whose names are either transliterated or translated: Third month of Akhet, first month of Harvest, etc.
A period of 533265 days does not quite bring the Egyptian calendar back to the same point with respect to the actual seasons, because an actual tropical year is not exactly equal to 365.25 days: It's now closer to 365.2422 days, which would imply a period of 1508 Egyptian years (1507 tropical years) between successive returns of the Egyptian calendar to the same seasonal point. However, the braking effect of the tides continuously increases the length of the day (whereas the duration of any flavor of astronomical year is much steadier). As longer days mean fewer days in a year, the number of days in a year decreases with time, and was thus slightly greater in the past than now: In 3000 BC, the tropical year was about 365.24265 days, which would roughly reduce the ancient value of the above cycle down to 1505 Egyptian years (1504 tropical years).
Similar sightings were recorded in the 7th year of the reign of King Senuse'rt the third (1878-1841 B.C.) of the third Dynasty. The dating of the event was the 16th day of the 4th month of the 2nd season. Discrepancies between the yearly Stellar cycle and Solar cycle were realized along the course of centuries or millennia. The difference is very slight, however, along the course of time, it became visible and chaotic. A record from an inscription from the reign of King Amenemhet the 3rd (1842-1797 B.C.) describes a visit of his treasurer Harurre to Serabit `Lkhadem, in Sinai, to extract turquoise ore in the third month of what was, according to the civil calendar, winter. The fact was that, according to the inscription, the weather was that of high summer. Harurre describes how he and his men suffered badly from the mountains that brand the skin with the intense heat. The civil calendar, then, was out of phase with Solar cycles by about seven months. A papyrus of the Ramesside period describes in the 13th century B.C. "Winter is come in Summer, the months are reversed, the hours in confusion".
It should be noted here that ancient Egyptian Civil Calendar relates to regal years of each king and their Dynasties. By counting forwards and backwards the chronological order was then related to three helical risings of the star Sirius mentioned above. By the year 664 B.C., the beginning of the 26th Dynasty (Saite Period) Egyptian chronology became more accurate. However, in spite of the story mentioned above, the subdivision of the year into three seasons based on the regular River Nile flood and agricultural activities remained accurately observed along the millennia.

 

Introduction
The Coptic calendar, also called the Alexandrian Calendar, is based on the Ancient Egyptian Calendar. To avoid the calendar creep described above, a reform of the Ancient Egyptian calendar was introduced at the time of Ptolemy III (Decree of Canopus, in 238 B.C.) which consisted in the intercalation of a 6th epagomenal day every fourth year. However, the reform was opposed by priests, and the idea was discarded until 25 B.C., when the Roman Emperor Augustus formally reformed the calendar of Egypt to keep it forever synchronized with the newly introduced Julian 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 calendar.

The Coptic Year
The Coptic Year is the extension of the ancient Egyptian civil year retaining its subdivision into the three seasons, four months each. The three seasons are commemorated by special prayers in the Coptic Divine Liturgy. This calendar is still in use all over Egypt by farmers to keep track of the various agricultural seasons. The Coptic calendar has 13 months, 12 of 30 days each and an intercalary month at the end of the year of 5 or 6 days depending whether the year is a leap year or not. The year starts on 11 September in the Gregorian Calendar or on the 12th in the year before (Gregorian) Leap Years. The Coptic Leap Year follows the same rules as the Gregorian so that the extra month always has 6 days in the year before a Gregorian Leap Year. The Coptic Year is divided as follows:

Name (Bohairic)	Name (Sahidic)	Modern Name (based on Greek)	Gregorian Calendar Dates	Season	Name Origin
:wout	:oout	Thout	11 September - 10 October	Akhet (Indundation)	Thoth, god of Wisdom
Paopi	Pawpe	Paopi	11 October - 10 November		Hapi, god of the Nile (Vegetation)
A;wr	Ha;wr	Hathor	10 November - 9 December		Hathor, godess of beauty and love (the land is lush and green)
<oiak	Koiak	Koiak	10 December - 8 January		Ka Ha Ka = Good of Good, the sacred Apis Bull
Twbi	Twbe	Tobi	9 January - 7 February	Proyet, Peret, or Poret (Growth)	Amso Khem, a form of Amun-Ra (growth of nature and rain)
Mesir	Msir	Meshir	8 February - 9 March		Mechir, genius of wind (month of storms and wind)
Paremhat	Par`mhotp	Paremhat	10 March - 8 April		Mont, god of war (high temps; month of the sun)
Varmou;i	Parmoute	Paremoude	9 April - 8 May		Renno, severe wind and death (vegetation ends; earth is dry)
Pasonc	Pasonc	Pashons	9 May - 7 June	Shomu or Shemu (Harvest)	Khenti, a form of Horus god of metals
Pawni	Pawne	Paoni	8 June - 7 July		?
Epip	Epip	Epip	8 July - 6 August		Apida, the serpent that Horus - son of Osiris - killed
Mecwri	Mecwry	Mesori	7 August - 5 September		Mesori, birth of the sun
Pikouji `n`abot	Kouji `n`abot	Little Month	6 September - 10 September		The Five Days over the Year

The Feast of Neyrouz marks the first day of the Coptic Calendar. Its celebration falls on the 1st day of the month of Thot, the first month of the Coptic year, which usually coincides with the 11th day of September. Coptic years are counted from 284 A.D., the year Diocletian became Roman Emperor, whose reign was marked by tortures and mass executions of Christians, especially in Egypt. Hence, the Coptic year is identified by the abbreviation A.M. (for Anno Martyrum or Year of the Martyrs) which is unfortunately also used for the unrelated Jewish year (Anno Mundi). To obtain the Coptic year number, subtract from the Julian year number either 283 (before the Julian new year) or 284 (after it).

Coptic Feasts and Fasts
Copts celebrate seven major Holy feasts and seven minor Holy feasts. The Coptic Calendar is also full of other feasts, usually commemorating the martyrdom of popular Saints from Coptic History.

A. General Annual Feasts

Feast	Date	Type	Description
Annunciation	29 Paremhat	Major	We recall the fulfillment of the Old Testament prophecies, and the attainment which the men of God had longed for across the ages, namely the coming of the Word of God incarnated in the Virgin's womb (Matt. 13:17)
Nativity (Christmas)	29 Koiak	Major	It is preceded by a fast of 43 days. Its aim is to confirm the divine love, when God sent His Only-begotten Son incarnate. Thus, He restored to humanity her honor, and sanctified our daily life, offering His life as a Sacrifice on our behalf
Epiphany (Baptism)	11 Tobi	Major	It is preceded by one day of fasting. In the Epiphany He offered us what is His own. By His incarnation He became a true man while still the Only-begotten Son of God, and through Baptism we became children of God in Him while we are human being
Palm Sunday	Sunday before Easter	Major	It has its characteristic joyful hymns [the Shannon - Hosanna (Matt. 21:9)], and its delightful rite. The church commemorates the entrance of our Lord Jesus into our inward Jerusalem to establish His Kingdom in us and gather all in Him
Resurrection (Easter, Pascha, Passover)	Second Sunday after Spring's full Moon	Major	It is preceded by Great Lent (55 days) and is considered by the Coptic Church as the greatest Feast. Its delight continues for fifty days until the Pentecost. Easter is also essentially celebrated on every Sunday by participating in the sacrament of the Eucharist. For the church wishes that all believers may enjoy the new risen life in Jesus Christ (Rom. 6:4)
Ascension	Thursday, 40 days after Easter	Major	In this feast we recall Him who raises and lifts us up to sit with Him in heaven (Eph. 2:6)
Pentecost	Sunday, 50 days adter Easter	Major	It represents the birthday of the Christian Church. The Only-begotten Son paid the price for her salvation, He ascended to heaven to prepare a place for her. He sent His Holy Spirit in her, offering her existence, guidance, sanctification and adornment as the Heavenly Bride
Circumcision	6 Tobi	Minor	We remember that the Word of God who gave us the Law, He Himself was subjected to this Law, fulfilling it, to grant us the power to fulfill the Law in a spiritual manner. Thus we enjoy the circumcision of spirit and that of heart (Col. 2:11), instead of the literal circumcision of the flesh
Entrance of our Lord into the Temple	8 Meshir	Minor	We remember that the Word of God became man and does not want us to be careless about our lives, but to set our goals early since childhood. Thus we have to work and fulfill our goals regardless of people related to us, in spite of our love and obedience to them (Luke 2:24)
Escape of the Holy family to Egypt	24 Pashons	Minor	The Coptic Church is distinguished among all nations with this unique divine work, by the coming of our Lord to Egypt among the Gentiles
First Miracle of our Lord Jesus at Cana	13 Tobi	Minor	Our Lord changed the water into wine, as His first miracle, at the wedding in Cana of Galilee, confirming His eagerness for our attaining the heavenly wedding, and granting us the wine of His exceeding love
Transfiguration	13 Mesori	Minor	The unity of the two testaments was manifested in this feast, for Moses and Elijah assembled together with Peter, James and John. The glory of our Lord was revealed to satisfy every soul who rises up with Him to the mountain of Tabor to enjoy the brightness of His Glory
Maundy Thursday	Thursday before Easter	Minor	We commemorate the establishment of the Sacrament of the Eucharist by our Lord Jesus, when He offered His Body and Blood as the living and effective Sacrifice, capable of sanctifying our hearts, and granting us the eternal life
Thomas' Sunday	Sunday after Easter	Minor	We bless those who believe without seeing so that all might live in faith through the internal touch of the Savior's wounds (John 20:29)
Apostles' Feast	5 Epip	-	This is the feast of martyrdom of the Apostles SS. Peter and Paul. It is preceded by a fasting period which starts on the day following the Pentecost. In this feast, the liturgy of blessing the water takes place, in which the priest washes the feet of his people, commemorating what the Lord did for His disciples. Thus, the priest remembers that he is a servant who washes the feet of the people of God and not a man of authority
Neyrouz	1 Thot	-	The word Nayrouz has Persian roots, meaning the beginning of the year. This feasts commemorates the beginning of the Coptic Martyrs Year
First Feast of the Holy Cross	17 Thot	-	It commemorates the dedication of the Church of the Holy Cross which was built by Queen Helen, the mother of Emperor Constantine
Second Feast of the Holy Cross	10 Paremhat	-	It commemorates the discovery of the Holy Cross on the hands of Queen Helen in A.D 326

B. Annual Feasts concerning the Most Holy Theotokos

Feast	Date
The annunciation of her birth	7 Mesori
Her Nativity	1 Pashons
Her Presentation into the Temple	3 Koiak
Her Dormition	21 Tobi
The Assumption of her body	21 Paoni
The apparition of her body to the Apostle	16 Mesori
Her apparition over the Church of Zeitoon (April 2nd 1968)	24 Paremhat

C. Monthly Feasts

Feast	Date
Commemoration of the Annunciation, the Nativity and the Resurrection of our Lord Jesus Christ	29 of each Coptic month
Commemoration of the Most Holy Virgin St Mary Mother of God	21 of each Coptic month
Commemoration of the Archangel Michael	12 of each Coptic month

D. Weekly Feasts

E very Sunday stands as a true Sabbath (rest), in which we find our rest in the resurrection of Christ. To receive the Holy Eucharist, the faithful must abstain from all sort of food and drink for 9 hours prior to the receipt of the Eucharist. There is no abstention from food or drinking on Sundays after the celebration of the Eucharist, even during Great Lent.

E. Daily Feasts

There is a daily feast, commemorating the departure or martyrdom of a saint, so that the believers may live in perpetual joy and in communion with the saints.

F. Fasting Periods
The Copts have seasons of fasting matched by no other Christian community. Out of the 365 days of the year, Copts fast for over 210 days. During fasting, no animal products (meat, poultry, fish, milk, eggs, butter, etc.) are allowed. Moreover, no food or drink whatsoever may be taken between sunrise and sunset. These strict fasting rules are usually relaxed by priests on an individual basis to accomodate for illness or weakness. Lent, known as "the Great Fast", is largely observed by all Copts. It starts with a pre-Lent fast of one week, followed by a 40-day fast commemorating Christ's fasting on the mountain, followed by the Holy week, the most sacred week (called Pascha) of the Coptic Calendar, which climaxes with the Crucifix on Good Friday and ends with the joyous Easter. Other fasting seasons of the Coptic Church include, the Advent (43 days, also called Fast of the Nativity), the Fast of the Apostles, the Fast of the Most Holy Virgin Saint Mary Mother of God (14 days), and the Fast of Nineveh (3 days). In addition, Copts fast every Wednesday and Friday of the year, except during the 50 days period following Easter.

This is a link to a program that calculates the dates of all Coptic feasts between 1902 and 2037:
www.copticchurch.net/easter.html#Easter

Julian Calendar
An early form of the Julian Calendar was introduced by Julius Caesar in 46 B.C., on the advice of the Egyptian astronomer Sosigenes. That early form was based on the Ancient Egyptian Calendar system. Officially, the first day of the Julian Calendar was the Kalends of Januarius, 709 AUC (January 1st, 45 B.C.) At first, there was a leap year every third year, but this was soon recognized to be a mistake: In 8 B.C., the calendrical reform of Augustus gave the months their modern names and lengths, and returned the calendar year back to the seasonal point intended by Julius Caesar. This was done by shunning leap years until 8 A.D., which would be a leap year like every fourth year thereafter. (5 BC, 1 BC and AD 4 were ordinary years.)
The so-called proleptic Julian Calendar extends backward in time the regular pattern which has been in force since March of 4 A.D. This may mean a discrepancy of several days from the historical calendar used between 45 BC and AD 4 and it's all but fictitious before that.
The Julian calendar is in complete harmony with the Coptic calendar. For instance, 25 December of the Julian calendar, the day of Christmas, always falls in 29 Koiak of the Coptic calendar. However, the Julian 25 December is what we know as January 7th, because today we use the Gregorian calendar, which is shifted 2 weeks in advance in comparison with both the Julian and the Coptic calendars.

AD = Anno Domini
Dionysius Exiguus was a Russian monk who had been commissioned by pope St. John I to work on calendrical matters, including the official computation of the date of Easter. The story goes that he was confronted with the Coptic calendar in the course of his work with Alexandrian data. He liked the idea of a continuous count of years based on a Christian milestone, but was disturbed by the choice of the Egyptians, who were honoring their greatest persecutor by counting from the year Diocletian became emperor (284 CE). Dionysius had the idea to count years from a joyous event instead, the birth of Christ. In 527, he formally declared that Jesus was born on December 25 in the year 753 AUC, equating the year 754 AUC with the year AD 1 (Anno Domini = Year of the Lord).

The Date of Christmas
The choice of 25 December to celebrate the Nativity of our Lord Jesus Christ was first proposed by St Hippolytus of Rome (170–236), but was apparently not accepted until 336 or 364 A.D. Dionysius of Alexandria emphatically quoted mystical justifications for this very choice:
"March 25th was considered to be the anniversary of Creation itself. It was the first day of the year in the medieval Julian Calendar and the nominal vernal equinox (it had been the actual equinox at the time when the Julian calendar was originally designed). Considering that Christ was conceived at that date turned March 25 into the Feast of the Annunciation which had to be followed, 9 months later, by the celebration of the birth of Christ, Christmas, on December 25th."
There may have been more practical considerations for choosing 25 December. The choice would help substitute a major Christian holiday for the popular pagan celebrations around the winter solstice (Roman Saturnalia or Brumalia). The religious competition was fierce. In 274, Emperor Aurelian had declared a civil holiday on December 25 (Sol Invicta, the Unconquered Sun) to celebrate the birth of Mithras, the Persian Sun-God whose cult predated Zoroastrianism and was then very popular among the Roman military. Finally, joyous festivals are needed at that time of year, to fight the natural gloom of the season.
Whatever the actual reasons were for choosing a December 25 celebration, the scriptures indicate that the birth of Jesus of Nazareth did not even take place around that time of year, since there were in the same country sherperds living out in the fields, keeping watch over their flock by night (Luke 2:8). During cold months, shepherds brought their flocks into corals and did not sleep in the fields. That's about all we know directly from scriptures, besides wild speculations.
Until the 16th century, 25 December coincided with 29 Koiak of the Coptic calendar. However, as described above, upon the introduction of the Gregorian calendar in 1582, December 25th shifted 2 weeks earlier in comparison with the Julian and Coptic calendars. This is the reason why Old-Calendrists (using the Julian and Coptic calendars) celebrate Christmas on January 7th, 2 weeks after the New-Calendrists (using the Gregorian calendar), who celebrate Christmas on December 25th.

The Date of Easter
According to Christian scriptures, Jesus Christ resuscitated on a Sunday that fell on the Jewish Spring festival of Pesach (Pascha or Passover, April 15th), which is always near a full moon. At the First Ecumenical Council of the Christian Church, held in 325 A.D. in Nicea, it was decided to celebrate Easter on the Sunday following the so-called Paschal full moon.
The Paschal full moon is an arithmetical approximation to the first full moon after the vernal equinox. It may be expressed as follows in terms of the so-called Golden number (G) and Century term (C):
. Paschal full moon (PFM) = (April 19, or March 50) - (C+11G) mod 30
Except in two cases where the PFM is one day earlier than this, namely:
· When (C+11G) is 0 modulo 30, PFM = April 18 (not April 19).
· When (C+11G) is 1 modulo 30, and G=12, PFM = April 17 (not 18).
The Golden number (G) is the same for both Julian and Gregorian computations, but the Century term is constant (C = +3) in Julian computations:
· G = 1 + (Y mod 19) in year Y (Julian or Gregorian).
· C = -H + ëH/4û + ë8(H+11)/25û with H = ëY/100û (Gregorian year Y)
C is -4 from 1583 to 1699, -5 from 1700 to 1899, -6 from 1900 to 2199, -7 from 2200 to 2299 etc...
As the Sunday following the PFM, Easter is one week after the PFM when the PFM happens to fall on a Sunday. One must work with the Julian calendar (C = +3) to find when Easter is celebrated by Orthodox churches.
At the Council of Nicea, it became one duty of the Pope of the Coptic Church of Alexandria to determine the exact dates of Easter and to announce it to the rest of the Christian churches. With its renowned School of Alexandria and its bright scientists, the Coptic Church was suited for that duty. The precise rules are rather involved, but Easter is usually the first Sunday after a full moon occurring no sooner than March 21, which was the actual date of the vernal equinox at the time of the First Council of Nicea. Shortly before Julius Caesar reformed the calendar, the vernal equinox was occurring on the "nominal" date of March 25. This was rightly discarded at Nicea, but the reason for the observed discrepancy was all but ignored (the actual tropical year is not quite equal to the Julian year of 365¼ days, so the date of the equinox keeps creeping back in the Julian calendar).

More Readings
The establishment of what came to be known as the Gregorian or New Calendar by Pope Gregory of Rome upset the harmony, which existed between all Christian Churches concerning the celebration of the major feasts of the Church. Today, most Orthodox Churches remain Old-Calendarists and use the Julian Calendar to determine all of their feasts. Some Orthodox are New-Calendrists, using the Julian Calendar to determine the date of Easter while using the Gregorian Calendar to determine the dates of all other fixed feasts. All Catholics and Protestants follow the Gregorian Calendar. Here are some useful links that tackle that issue:
1. New vs Old Calendar
www.stjohndc.org/what/9608ca.htm
2. Determining the date of Easter
www.smart.net/~mmontes/ortheast.html
3. Determining the date of Christmas
www.suscopticdiocese.org/messages/nativitydate.html

Sources
www.copticchurch.net/easter.html
www.coptic.net/EncyclopediaCoptica
www.geocities.com/remenkimi/calendar1717.htm