What is the difference between the ancient Egyptian calendar and the Julian calendar?

In 46 B. C., Julius Caesar adopted the ancient Egyptian solar calendar, with the help of the Alexandrian astronomer Sosigenes . The original Roman calendar was lunar, and its year had 355 days. The Romans had reckoned thirty-one days in the months of March, May, Quintilis (July⁶³⁴ ), and October and twenty-eight days in February, while the rest of their months were twenty-nine days. In their new calendar, they added one day to each of April, September, and November, and two days to the months of January, Sextilis (August⁶³⁵ ), September, and December, bringing the Julian year to a total of 365 days. In the first thirtysix years from the inception of the Julian calendar, the extra day required in a leap year was added every three years instead of every four years, as per the ancient Egyptian calendar.

632 Herodotus. The Histories of Herodotus , trans., Henry Cary (D. Appleton and Company, 1904) 2.4: p. 86. 633

See entries on “Calendar, Gregorian” and “Calendar, Julian” in The Coptic Encyclopedia , vol. 2, pp. 436– 437; and Elisabeth Achelis, Of Time and Calendar (New York: Hermitage House, 1955). 634 Later named after the Emperor Julius Caesar.

635

Later named after the Emperor Augustus Caesar who changed its number of days from thirty to thirty-one.

The Julian calendar was adopted throughout the Western world. But around the year 325 A. D., its inaccuracy became apparent as it was realized that the Julian year of exactly 365.25 days was slightly longer than the actual solar year, which is precisely 365.24217 days long. This difference amounts to eleven minutes and fourteen seconds each year, which adds up to approximately a day and a half every two centuries or seven days every thousand years.

In 1582 A. D., Pope Gregory XIII of Rome omitted ten days from that year to correct for this accumulated error in the calendar. Thus, for that year only, the day after 4[th] October 1582 became 15[th] October. He further adjusted the calendar such that three times in every four hundred years (century years that are not divisible by 400), a leap year is omitted. The Gregorian calendar gradually replaced the Julian calendar in different parts of the Western world over the period from 1582 to 1924. For example, England adopted the Gregorian calendar in 1752. The Julian calendar is still used in the calculations of the Feast of the Resurrection and the moveable feasts that depend on it in the Orthodox Churches, which has resulted in the liturgical year of the Church today diverging from the Gregorian calendar by thirteen days.