Fixed Feasts and Observances
The proposal does not modify the dates of fixed feasts and observances in the liturgical calendar of the Coptic church. By adhering to this principle, there is no need to modify the daily readings from the Katamerous and the Synaxarium. For example, the date of Feast of the Theophany remains as 11 Tobi without change. What does change is its corresponding date in the Gregorian calendar.
The proposal does not solely focus on realigning the date of The Feast of the Nativity/Christmas to 25 December in the Gregorian calendar while neglecting a holistic change to the entire calendar. There is no decoupling of a single feast from the totality of the architecture of the liturgical calendar of the Church.
The actual date for the Feast of the Nativity in the Coptic Orthodox Church is 29 Kiahk. Therefore, shifting 29 Kiahk in the Coptic Calendar to 25 December in the Gregorian calendar requires a similar shift to all other dates in the entire Coptic Calendar.
The proposal maintains alignment between the New Coptic Calendar and the Gregorian Calendar in perpetuity, which necessitates a new method of computing leap years for the Coptic Calendar. This way, 1 Thout in the New Coptic Calendar always corresponds to 29 August in the Gregorian calendar, in perpetuity.
Accurate Astronomical Modeling for Calculating Easter
The proposal does not change the rule set forth by the Holy Fathers of the First Ecumenical Council of Nicaea for computing the date of the Feast of the Resurrection/Easter: Easter is the first Sunday after the first full moon on or after the Vernal Equinox.
To this day, the Coptic Orthodox Church relies on the brilliant Easter calculation first devised by our father among the saints, Pope Demetrius I in the year 214. The calculation utilizes the lunar epacts and the Metonic cycle to estimate the date of the Paschal Full Moon, and uses March 21 as a fixed date for the Vernal Equinox.
While the epacts and the Metonic cycle are astonishing in their accuracy given the time period in which they were devised, they do differ substantially from the accuracy afforded to us today by precise astronomical observation and computer modeling.
Therefore, the proposal for the New Coptic Calendar relies on accurate astronomical modeling for the dates and times of the Vernal Equinox and the Paschal Full Moon, in place of the ancient tables of the epacts. The dates for these celestial events are computed from freely available data sets created by the Jet Propulsion Laboratory (JPL) at NASA - the National Aeronautics and Space Administration of the United States.
It is important to note that while the Vernal Equinox and the Paschal Full Moon occur at one instant astronomically, the corresponding date and time of that instant depends on the location where the observation is made. Two observers in different time zones would observe the Paschal Full Moon at the same instant, but the local date and time for that observation would correlate with their time zones
Given that Christians are dispersed across the world, the proposal uses the dates and times for the Vernal Equinox and the Paschal Full Moon as observed from the Great City of our God Jerusalem.
The intention is for the New Coptic Calendar to be used by the entirety of the Coptic Orthodox Church across the whole world, including Egypt. It is not intended for use by Copts in Western societies only.