Julian Calendar

Julian Calendar

Julius Caesar's Reform

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Gaius Julius Caesar Sosigenes

In 46 B.C. the supreme Priest Julius Caesar by his decision carried out calendar reform. Introduced by Caesar, the calendar is still called Julian, though its elaboration was made by a group of Alexandria astronomers at the head of Sosigenes. The year with the length of 365.25 days was made the basis of the new calendar. Three Julian years out of every four have 365 days each (non leap years) and one � 366 days (leap year). The year is divided into 12 months, the names of which came from the old Roman calendar.

Ordinal number
of the month		 Latin name
of the month		 English contemporary
name of the month		 Number of days
in the non leap year		 Number of days
in the leap year
1 Januarius January 31 31
2 Februarius February 28 29
3 Martius March 31 31
4 Aprilis April 30 30
5 Maius May 31 31
6 Junius June 30 30
7 Quintilis July 31 31
8 Sextilis August 31 31
9 September September 30 30
10 October October 31 31
11 November November 30 30
12 December December 31 31
Total days in the year: 365 366
Medium length of a year in the 4 years cycle: (3 * 365 + 366) / 4 = 365.25

Caesar decided to start counting of days of the new calendar from the New Moon, happened on Januarius 1, 45 B.C., thus moving the beginning of the year from Martius 1. The first year of the Julian calendar was a leap year.
In gratitude for the calendar reform and taking into account outstanding merits in the state and military spheres, the Senate decided to rename the month of Quintilis, when Caesar was born, into the month of Julius.

Julian calendar is the solar calendar. Its basic is the tropical year, and its months are in no way coordinated with the Moon. But the length of the year of 365.25 days, which is its basis, does not coincide with the length of the tropical year of 365.242 days, and there is no mechanism in the calendar's algorithm to correct this inaccuracy. As a result, every 128 years and 68 days one more divergence of one day is added, and the Julian year does not coincide more and more with the tropical year.

It is interesting, that Romans did not name the month's days by numbers, how it is adopted now, but used specific method of naming the days by calends, nones and ides. First days of month were called Calends, days in the middle of the month (always odd days) were called Ides, the ninths days before ides were called Nones. Days before Calends, Nones and Ides were called Eves. Below on the table the names of the days are given in relation to calendas, nones and ides depending on the number of days in the month.

Ordinal
number
of days
in the
month		 The number of days in the month and month's names
31 days in the month 31 days in the month 30 days in the month 28 days in the month
Januarius, Augustus, December Martius, Maius, Julius, October Aprilis, Junius, September, November Februarius
Latin names of days in the months
1 Kalends Kalends Kalends Kalends
2 Ante Diem IV Nones Ante Diem VI Nones Ante Diem IV Nones Ante Diem IV Nones
3 Ante Diem III Nones Ante Diem V Nones Ante Diem III Nones Ante Diem III Nones
4 Pridie Nones Ante Diem IV Nones Pridie Nones Pridie Nones
5 Nones Ante Diem III Nones Nones Nones
6 Ante Diem VIII Ides Pridie Nones Ante Diem VIII Ides Ante Diem VIII Ides
7 Ante Diem VII Ides Nones Ante Diem VII Ides Ante Diem VII Ides
8 Ante Diem VI Ides Ante Diem VIII Ides Ante Diem VI Ides Ante Diem VI Ides
9 Ante Diem V Ides Ante Diem VII Ides Ante Diem V Ides Ante Diem V Ides
10 Ante Diem IV Ides Ante Diem VI Ides Ante Diem IV Ides Ante Diem IV Ides
11 Ante Diem III Ides Ante Diem V Ides Ante Diem III Ides Ante Diem III Ides
12 Pridie Ides Ante Diem IV Ides Pridie Ides Pridie Ides
13 Ides Ante Diem III Ides Ides Ides
14 Ante Diem XIX Kalends Pridie Ides Ante Diem XVIII Kalends Ante Diem XVI Kalends
15 Ante Diem XVIII Kalends Ides Ante Diem XVII Kalends Ante Diem XV Kalends
16 Ante Diem XVII Kalends Ante Diem XVII Kalends Ante Diem XVI Kalends Ante Diem XIV Kalends
17 Ante Diem XVI Kalends Ante Diem XVI Kalends Ante Diem XV Kalends Ante Diem XIII Kalends
18 Ante Diem XV Kalends Ante Diem XV Kalends Ante Diem XIV Kalends Ante Diem XII Kalends
19 Ante Diem XIV Kalends Ante Diem XIV Kalends Ante Diem XIII Kalends Ante Diem XI Kalends
20 Ante Diem XIII Kalends Ante Diem XIII Kalends Ante Diem XII Kalends Ante Diem X Kalends
21 Ante Diem XII Kalends Ante Diem XII Kalends Ante Diem XI Kalends Ante Diem IX Kalends
22 Ante Diem XI Kalends Ante Diem XI Kalends Ante Diem X Kalends Ante Diem VIII Kalends
23 Ante Diem X Kalends Ante Diem X Kalends Ante Diem IX Kalends Ante Diem VII Kalends
24 Ante Diem IX Kalends Ante Diem IX Kalends Ante Diem VIII Kalends Ante Diem VI Kalends
25 Ante Diem VIII Kalends Ante Diem VIII Kalends Ante Diem VII Kalends Ante Diem V Kalends
26 Ante Diem VII Kalends Ante Diem VII Kalends Ante Diem VI Kalends Ante Diem IV Kalends
27 Ante Diem VI Kalends Ante Diem VI Kalends Ante Diem V Kalends Ante Diem III Kalends
28 Ante Diem V Kalends Ante Diem V Kalends Ante Diem IV Kalends Pridie Kalends
29 Ante Diem IV Kalends Ante Diem IV Kalends Ante Diem III Kalends —
30 Ante Diem III Kalends Ante Diem III Kalends Pridie Kalends —
31 Pridie Kalends Pridie Kalends — —

At the time of Emperor August the seven days week started to be used in Rome.

Week day in Latin Week day patrons
Dies Saturni Day of Saturn
Dies Solis Day of Sun
Dies Lunae Day of Moon
Dies Martis Day of Mars
Dies Mercurii Day of Mercury
Dies Jovis Day of Jupiter
Dies Veneris Day of Venus

Anno Domini Era

Counting of years in Rome was according to consuls and emperors years of government. For example the 1st, 2nd etc. year after consul Vassily's assumption, or the 15th year of Diocletian's era. Counting of years from Rome foundation was not popular because of disputes on the age of the City.

The A.D. (Anno Domini) Chronology was introduced by the Roman monk and Pope archivist Dionysius Exiguous (in English known as Denis the Little). It happened in 525 A.D. Dionysius explained nowhere the course of his considerations and calculations and how he determined the year, when Christ was born on December 25. Introducing the account of years from the era of the Christ Birth, Dionysius rejected adopted at his time account of years from the era of Diocletian (Persecutor of Christians). However, the dating from the Christ Birth became widely used only in VIII—IX centuries, and only from 1431 A.D. it has been used to date Pope's encyclicals and documents of the Pope's office.

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