Although this calendar was introduced in 45 BC, it seems to be the solar calendar used by the Chronology of Man during its reckoned periods from the first day after the fall of Adam!
It differs from the Gregorian Calendar in its treatment of leap years and Easter. The Gregorian Calendar was introduced because by the sixteenth century, the date of the spring equinox had moved 10 days since the Council of Nicea in 325 AD. Then, the dating of Easter had been standardised using 21 March as the date of the vernal equinox and the Metonic cycle as the basis for calculating lunar phases.
Leap Years
Leap years always occur if the year is divisible by 4, whereas the Gregorian Calendar does not include all century years as leap years.
History
The Julian Calendar was introduced on 1 January 45 BC by Julius Caesar.
First he inserted 90 days to bring the months of the Roman Calendar back to their traditional seasons. The previous Roman Calendar had been luni-solar but its months no longer followed the lunar phases and its year got out of step with the seasons. On the advice of Sosigenes, an Alexandrian astronomer, Caesar introduced a solar calendar with twelve months of fixed lengths and a provision for a leap day to be added every four years.
Unfortunately, after the death of Caesar the Roman authorities misapplied the leap-year rule by adding a day every three years instead of every four. It seems that Emperor Augustus put this right by omitting the extra days from 8 BC to 4 AD.
During the Middle Ages the Julian Calendar acquired local differences. There were variations in the initial epoch for counting years, the date for beginning the year and the method of specifying the day of the month. Sometimes different methods were used for dating ecclesiastical records, fiscal transactions and personal correspondence.
The most common variations to the start of the year were 1 March, 25 March and 25 December.
Days within months were originally reckoned from designated points in the month called Kalends, Nones and Ides:-
- The Kalends is the first day of the month
- The Nones is always eight days before the Ides
- The Ides is the thirteenth day of the month, except in March, May, July and October when it is the fifteenth day of the month
Dates in between these points were designated by inclusively counting backwards from the points. Leap days were inserted by repeating VI Kalends March, i.e. by inserting a day between VI Kalends March (24 February) and VII Kalends March (23 February).
By the eleventh century, days were generally being counted consecutively from the beginning of the month. However, local variations continued, such as counting days from dates that commemorated local saints. It was not until the inauguration of the Gregorian Calendar that the adoption of a uniform method of recording dates came about.
Christmas Day
Christmas Day is celebrated on 25 December.
Until 1923 Eastern Orthodox Churches celebrated Christmas on 25 December in the Julian Calendar, but then the Ecumenical Patriarch Meletios IV convened a congress at which it was decided to use the Gregorian date instead for this one festival.
Easter Day
Easter Day was fixed in 325 AD by the Council of Nicea to occur on the first Sunday after the first full moon (14/15 days after the new moon) occurring on or after the vernal equinox. This causes it to be delayed for one week if the full moon is on Sunday to reduce the chances of it occurring on the same day as the Jewish Passover. The full moon is not the true astronomical full moon but "the Paschal moon" or "the ecclesiastical Full Moon" based on tables that do not take into account the full complexity of lunar motion.
The date of Easter as enacted by Dionysius Exiguus in 525 AD is based on the assumption that the vernal equinox is always on 21 March, and on lunar epacts which are ecclesiastical approximations of the lunar phases based on the 19-year Metonic cycle that is named after the Greek astronomer Meton who in 432 BCE published his observation that 19 solar years contain almost exactly 235 lunations.
The calculation of Easter in the Gregorian Calendar differs from that in the Julian Calendar by incorporating a more accurate approximation to the lunar phases developed by the German Jesuit astronomer Christoph Clavius from the suggestions made by Lilius. There are two corrections and two adjustments not made in the Julian Calendar.
Other festivals
Start of Lent
Start of Lent is 46 days before Easter Day.
Passion Sunday
Passion Sunday is the Sunday 14 days before Easter Day.
Palm Sunday
Palm Sunday is the Sunday before Easter Day.
Good Friday
Good Friday is the Friday before Easter Day.
Ascension Day
Ascension Day is 39 days after Easter Day.
Pentecost (Whitsunday)
Pentecost (Whitsunday) is 49 days after Easter Day.
First Sunday in Advent
The First Sunday in Advent is the Sunday closest to November 30.
