Every civilization has its calendar that expresses its experience and unique perspective on time and the cycle of history, based on a set of values, standards, and cultural symbols in which it believes and from which it draws its existence. From here, we find that the values, symbols, and meanings that govern a specific civilization are reflected in the components of its calendar—whether in choosing the beginning of the year, the names of the months, or the seasons and festivals. Thus, the cultural-civilizational nature of the calendar is affirmed, meaning that the calendar is a cultural-civilizational matter before it is a matter of abstract astronomical calculation.

Among the most famous calendars known to the oldest civilizations, nations, and religions are:

1. The Syriac Calendar: which was adopted by the successor of Alexander the Great in ruling Syria—the commander Seleucus Nicator—in the year 312 B.C.

2. The Jewish (Hebrew) Calendar: a lunar-month, solar-year calendar, by which the Jews date the beginning of creation, which they place at 3761 B.C. It is still used within limited Jewish religious circles.

3. The Persian Calendar: the Persians fixed the start of its current era at the year 11 AH (632 Julian). The days of its months are similar to the old Coptic calendar.

4. The Hijri Calendar: a lunar calendar in which the year consists of 36 seconds, 48 minutes, 8 hours, and 354 days.

The Coptic Calendar

In the Coptic calendar, we find feasts with fixed dates and others with variable dates. For example, two feasts have fixed dates: 29 Kiahk (the Feast of the Nativity on January 7 AD) and 5 Abib (the Feast of the Apostles on July 12 AD). In between, comes Jonah’s Fast (variable), the Great Lent (variable), the Feast of the Resurrection (variable), and the Feast of Pentecost (variable).

Determination of the date of the Resurrection Feast

This is based on a long astronomical calculation called the “Epact Calculation,” referring to “the age of the moon at the beginning of the Coptic month of Tout each year.” This calculation was developed in the third century AD by the Egyptian astronomer Ptolemy of Pelusium (from the town of Pelusium between Port Said and Arish) during the time of Pope Demetrius the Vinedresser (the 12th patriarch between the years 189–232 AD). This calculation was attributed to the patriarch, and thus it was called “The Vinedresser’s Calculation.”

This calculation determines the date of the Christian Feast of the Resurrection so that it would be unified throughout the world. Indeed, all the bishops of Rome, Antioch, and Jerusalem at that time agreed to adopt it, based on what Pope Demetrius the Vinedresser wrote to them on this matter. When the Council of Nicaea was held in the year 325 AD, it approved this arrangement, and all Christian churches committed to it until the year 1582 AD, as we shall mention later.

This calculation ensures that the celebration of the Feast of the Resurrection adheres to the following conditions:

1. That it be on a Sunday because the Lord’s Resurrection took place on a Sunday.

2. That it comes after the vernal equinox (March 21).

3. That it be after the Jewish Passover because the Resurrection occurred after the Jewish Passover.

Since the Passover is on the 14th day of the first Jewish (lunar) month of the Jewish year, the celebration of the Feast of the Resurrection must come after the full moon in the second half of the Jewish lunar month. Since the Jewish Passover is linked to the harvest, according to the Lord’s command to Moses (Leviticus 23:4–12), and the harvest for the Jews always takes place between April and May (solar months), it was necessary to create a cycle that combines both the solar and lunar cycles, so that the Feast of the Resurrection falls between April and May—never before the first week of April, and never after the first week of May.

There is no space here to explain all the details, but the calculation as a whole is a cycle of nineteen years that repeats. Based on this calculation, the Feast of the Resurrection does not come before April 4 and does not come after May 8. The Feast of Sham El-Nessim follows it directly.

The celebration date of the Feast of the Resurrection remained unified among all Christian churches in the world according to this Coptic calculation until 1582 AD, when Pope Gregory XIII of Rome modified this arrangement. Under this adjustment, the Feast of the Resurrection in the Western churches came to fall after the full moon that follows the vernal equinox directly, regardless of the Jewish Passover—even though the Resurrection of Christ occurred after the Jewish Passover, as recorded in the four Gospels. Therefore, the Feast of the Resurrection in the Western tradition sometimes coincides with the celebration of the Eastern tradition, and sometimes comes earlier (by one to five weeks at most), and never comes after the Eastern tradition celebration.

It is worth mentioning that the Protestants were not pleased with the Catholic modification of the date of celebrating the Feast of the Resurrection. They continued to observe the Feast of Resurrection according to the Eastern Epact calculation until the year 1775 AD But with the increase of Western influence, they were forced to abandon the original calendar.

Thus, the purpose of the Epact calculation is to determine the date of the Feast of the Resurrection in consideration of the Jewish Passover. Then, the following feasts which are tied to it can also be determined. On this foundation, the entire Christian world could celebrate the Feast of the Resurrection on one unified and variable day from year to year, according to the precise Epact calculation and the canons of the First Ecumenical Council of Nicaea.

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