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Julian calendar

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Julian calendar

Edited and enhanced from the original Wikipedia entry.

The Julian calendar was introduced by Julius Caesar in 46 BCE, taking force in 45 BCE or 709 ab urbe condita. It was chosen after consultation with Sosigenes and was obviously designed to approximate the tropical year as it was known at the time. It has a regular year of 365 days divided into 12 months, and a leap day is added every 4 years. The calendar remained in use into the 20th century in some places. However with this scheme too many leap days are added with respect to the astronomical seasons, which on average occur earlier in the calendar by about 11min per year. It is said that Caesar was aware of the discrepancy, but felt it was of little importance. In the 16th century the Gregorian Calendar Reform was introduced to improve its accuracy with respect to the time of vernal equinox, but the changes are relatively minor. Sometimes the reference Old Style or O.S., as opposed to 'New Style' for the Gregorian Calendar, is used when there is a confusion about which date is found in a text.

Roman Calendars

The previous Roman calendar contained various rules including two different lengths for leap month, plus modifications to the length of February during some leap years. This was further complicated by politics in which the calendar was modified to lengthen ones term in office. This resulted in the calendar becoming 90 days from its original intended definition. In order to re-align the calendar to what the Romans thought of as the correct seasons, 90 days were inserted. Because of its unusual length, the extra-long year was, and is, referred to as the Year of Confusion. The first year of operation of the new calendar was 45 BCE, which was deemed to begin on January 1.

Despite the new calendar being much simpler than the older Roman calendar, those tasked with implementing the calendar -- the Pontiffs, not the Pope, but a group of priests who were responsible for keeping the calendar in Roman society, apparently misunderstood the algorithm. They added a leap day every 3 years. This resulted in too many leap days. Augustus Caesar remedied this discrepancy by skipping several leap days after 36 years of such mistakes.

Looking for Leap Years

The historic sequence of leap years (i.e. years with a leap day) in this period is not given explicitly by any ancient source, although the existence of the triennial cycle is confirmed by an inscription that dates from 9 or 8 BCE. The chronologist Joseph Scaliger established in 1583 that the Augustan reform was instituted in 8 BCE , and inferred that the sequence of leap years was 42 BCE, 39 BCE, 36 BCE, 33 BCE, 30 BCE, 27 BCE, 24 BCE, 21 BCE, 18 BCE, 15 BCE, 12 BCE, 9 BCE, 8 CE, 12 CE etc. This proposal is still the most widely accepted solution. Other solutions have been proposed from time to time. Kepler proposed one in 1614 that the correct sequence of leap years were different. In 1883 the German chronologist Matzat proposed another ignoring year zero based on a passage in Dio Cassius that mentions a leap day in 41 BCE that was said to be contrary to Caesar's rule . It has also sometimes been suggested that 45 BCE was a leap year. In the 1960s Radke argued the reform was actually instituted when Augustus became pontifex maximus in 12 BCE , suggesting the sequence 45 BCE, 42 BCE, 39 BCE, 36 BCE, 33 BCE, 30 BCE, 27 BCE, 24 BCE, 21 BCE, 18 BCE, 15 BCE, 12 BCE, 4 CE, 8 CE, 12 CE etc. In 1999, an Egyptian papyrus was published which gives an ephemeris table for 24 BCE with both Roman and Egyptian dates. From this it can be shown that the most likely sequence was in fact 44 BCE, 41 BCE, 38 BCE, 35 BCE, 32 BCE, 29 BCE, 26 BCE, 23 BCE, 20 BCE, 17 BCE, 14 BCE, 11 BCE, 8 BCE, 4 CE, 8 CE, 12 CE etc., very close to that proposed by Matzat.

The Romans eventually named months after Caesar and Augustus, renaming Quintilis [Fifth month, with March = month 1] as Iulius (July) and Sextilis [Sixth Month] as Augustus (August). Other months were renamed from time to time (e.g. Septembris [Seventh Month] was renamed Germanicus) but these changes did not survive long.

According to the 13th century scholar Sacrobosco , the original scheme for months in the Julian Calendar was very regular, alternating long and short with an exception at the end of the year at the end of February. From January through December, the month lengths according to Sacrobosco were originally:

31, 29(30), 31, 30, 31, 30, 31, 30, 31, 30, 31, and 30

Augustus is said to have changed this to:

31, 28(29), 31, 30, 31, 30, 31, 31, 30, 31, 30, and 31

giving us the irregular month lengths which we still use today, so that the length of Augustus would not be shorter (and therefore inferior) than the length of Iulius .

Sacrobosco is almost certainly wrong on this point. One thing that was not changed by the switch from the old Roman calendar to the new Julian calendar was the dates of the Nones and Ides. In particular, the Ides are late (on the 15th rather than 13th) in March, May, July and October. This suggests that these months always had 31 days in the Julian calendar. Also, Sacrobosco's theory is explicitly contradicted by the third and fifth century authors Censorinus and Macrobius, and, finally, it is inconsistent with seasonal lengths given by Varro , writing in 37 BCE , before the Augustan reform, and with the 31-day Sextilis given by the new Egyptian papyrus from 24 BCE .

Various systems of year numbering were used with the Julian calendar, starting with ab urbe condita (from the supposed founding of Rome , as calculated by Varro ) or the reign year of the current ruler. Diocletian instituted anno Diocletiani, numbering from the beginning of his reign, which appears to have remained widespread after his death. In 525 CE Dionysius Exiguus proposed the system of anno Domini (AD), which gradually spread through the Christian world. Years were numbered from the supposed date of the "incarnation" or "annunciation" of Christ on March 25 of the new year 1 (preceding the Diocletian era by 284 years, and offset by 753 years from ab urbe condita). However, we're not all Christians.

Alternative Nomenclature for the Same Era

As a substitute for "Anno Domini", many people now use the abbreviation C.E. which is sometimes understood as meaning Common Era and rarely as Christian Era. Correspondingly, as a substitute for "Before Christ", the abbreviation B.C.E. is used, which is understood as Before the Common Era. This terminology is preferred by some academics for various reasons, but probably mainly because it need not be interpreted as making religious reference.

The term "Common Era" has been in use since the late 19th century . Indeed, in its article on "Chronology", the 1908 Catholic Encyclopedia uses the sentence: "Foremost among these [dating eras] is that which is now adopted by all civilized peoples and known as the Christian, Vulgar, or Common Era, in the twentieth century of which we are now living."

This terminology is seen by some Christians, and others, as a move by nonbelievers to make Christianity less visible. By contrast, many groups find the A.D. teminology to be objectionable for different reasons. For example, Jehovah's Witnesses find the term B.C./A.D. objectionable because it implies that Christ was born on 1 A.D. and their theology requires a different date, which they believe was prophesied in the book of Daniel. Jews, Muslim, and many academics object to the term A.D. because it implies that “Jesus Christ” is lord.

Gregorian Calendar

The Julian calendar was in general use in Europe from the times of the Roman Empire until 1582, when Pope Gregory XIII promulgated the Gregorian Calendar, which was soon adopted by most Catholic countries. The Protestant countries followed later, and the Eastern Orthodox ones yet later. England had Thursday 14 September 1752 follow Wednesday 2 September 1752. Sweden adopted the new style calendar in 1753 , but also for a twelve-year period starting in 1700 use a modified Julian Calendar. Russia remained on the Julian calendar until after the Russian Revolution (which is thus called the 'October Revolution' but occurred in November according to the Gregorian calendar). The Eastern Orthodox churches themselves continued using the Julian Calendar until 1923, when many adopted their own Revised Julian Calendar rather than the Gregorian one. Easter, Pentecost, and their associated holy days are still calculated according to the Julian calendar in the Eastern Orthodox churches, and some Eastern Orthodox churches continue to use the Julian Calendar for all their church calendar dates.

Proleptic Julian calendar

The proleptic Julian calendar is produced by extending the Julian calendar to dates preceding its official introduction in 45 BCE.

Historians since Bede have traditionally represented the years preceding AD 1 as "1 BC", "2 BC", etc. In this system the year 1 BC would be a leap year (although the leap years actually observed between 46 BCE and 4 CE were erratic: see the Julian calendar article for details). (Bede and later Latin writers chose not to place the Latin zero, nulla, between BC and AD years.)

To determine an interval in years across the BCE/CE boundary, it is more convenient to include a year zero and represent earlier years as negative. This is the convention used in the " astronomical Julian calendar ". In this system the year 0 (equivalent to 1 BCE) is a leap year.

Likewise, the Proleptic Gregorian Calendar is used to specify dates before its official introduction in 1582 . Because the Julian Calendar was actually used before that time, one must explicitly state that a given date is in the Proleptic Gregorian Calendar when that is used.

Proleptic Gregorian Calendar

The proleptic Gregorian calendar is produced by extending the Gregorian Calendar to dates preceding its official introduction.

When using the Latin numbering system, which does not include zero, it is traditional to represent the years preceding 1 as " 1 BCE " etc. In this system the year 1 BCE is a leap year (likewise in the Proleptic Julian calendar ).

When using a numbering system which includes zero, it is more convenient to include a year zero and represent earlier years as negative. This is the convention used in the "astronomical Gregorian calendar". In this system the year 0 is a leap year.

Note that because around this time the Julian calendar was in actual use, historians and astronomers prefer to use the Julian Calendar.

Likewise, the Proleptic Julian calendar is used to specify dates before its official introduction in 45 BCE.