The current Coptic Calendar, which has been in use for nearly two millennia, and the even more ancient Egyptian Calendar on which it is based, are marvels of ancient ingenuity. Ancient Egyptians were able to estimate the length of the tropical year with stunning accuracy, given the rudimentary tools they had at their disposal. The Church of Alexandria prided itself on its astronomical prowess, and thus guided the world in calculating Easter after the Council of Nicaea.
As time has passed, astronomical tools and mathematical modeling improved, and with them came refinements to the estimates for the duration of the year. The current calendar that is in use by the Coptic Orthodox Church is based on a refinement to the more ancient Egyptian Calendar. Once it was realized that the year in the Ancient Egyptian Calendar was about ¼ day shorter than the tropical year, circa 25 BC an additional epagomenal day was added every 4 years to prevent the calendar from drifting.
Since that time, further refinements have occurred to other calendars that rely upon the tropical year, as estimates for its true duration have become more accurate. Most important to our discussion was the change instituted by Pope Gregory XIII of the Roman Catholic Church in 1582 AD. Advancements in astronomy revealed that the tropical year is actually slightly shorter than 365.25 days. Thus a new system was put in place for calculating leap years, to bring the average duration of the calendar year to 365.2425 days.
The point of the prior discussion is this: calendars change. They don't change often, but when they do, they do so based on advances in science and mathematics.
The Need for Change
It is a factual, true statement to say that the average duration of the year in the Coptic Calendar — 365.25 days — is not correct. The Coptic Calendar never underwent the one-time correction of the Gregorian Calendar, which is the most used civil calendar around the world today. As a result, the Coptic Calendar will continue to drift away from the Gregorian Calendar.
To illustrate why this is a problem, consider the Feast of the Nativity. In the year 1583 AD, 29 Kiahk in the Coptic Calendar corresponded to 4 January in the newly minted Gregorian Calendar (as opposed to 25 December, as it used to). These days, 29 Kiahk corresponds to 7 January (most of the time). That means since 1583, the Coptic Calendar has already drifted by 3 additional days from the Gregorian Calendar. Why?
Because while the Coptic Calendar has continued to add a leap day every 4 years without exception, the Gregorian Calendar did not do so in the years 1700, 1800, and 1900 AD. Looking forward, after the year 2100 AD, 29 Kiahk — the Feast of the Nativity — will occur on 8 January. And after 2200 AD, it will correspond to 9 January. The drift will never cease.
A Respectful Approach
A careful, holistic, one time change that permanently fixes these issues, and synchronizes the calendars in perpetuity is possible, all while applying the necessary honour and dignity due to this venerable calendar. Doing so would allow the Coptic Orthodox Church to celebrate fixed feasts, such as the Feast of the Nativity, at the same time as other churches in Christendom that rely on the Gregorian Calendar.
A more complex topic is the question of when to celebrate the Feast of the Resurrection / Pascha / Easter. In 2017, His Holiness Pope Tawadros II and His Holiness Pope Francis of the Roman Catholic Church expressed a desire to unify the date for all Christendom. What would be a proper, methodical way of answering this desire?
Here we turn, once again, to current scientific tools, as our forebears did to improve the calendars previously. Abiding by the rule of the Council of Nicaea for calculating Easter, while at the same time leveraging the most accurate astronomical modeling afforded to us by our modern observational and computational capabilities, we obtain a refinement which we believe can gain the consensus of all Christendom.
The Coptic Orthodox Church once embraced contemporary astronomical sciences to guide its liturgical calendar. It is time for Her to embrace contemporary methods once again.