THE CALENDAR as we know it has evolved from a Roman calendar established by Romulus, consisting of a year of 304 days divided into 10 months, commencing with March. This was modified by Numa, who added two extra months, January and February, making a year consist of 12 months of 30 and 29 days alternately plus one extra day and thus a year of 355 days. This calendar required the use of an Intercalary month of 22 or 23 days in alternate years.
In the year 46 B.C. Julius Caesar asked for the help of the Egyptian astronomer Sosigenes, as he had found that the calendar had fallen into some confusion. This led to the adoption of the Julian calendar in 45 B.C. In fact, the year 46 B.C. was made to consist of 445 days to adjust for earlier faults and is known as the "Year of Confusion".
In the Christian system, years are distinguished by numbers before or after the Incarnation, being denoted by the letters B.C. (Before Christ) and A.D. (Anno Domini). The starting point is the Jewish calendar year 3761 A.M. (Annus Mundi) and the 754th year from the foundation of Rome. This system is said to have been introduced into England by St. Augustine about 596 A.D. but was not in general use until ordered by the bishops at the council of Chelsea in 816 A.D.
In the Julian calendar all centennial years were leap years (ie the years A.D. 1200, 1300, 1400 etc.) and for this reason towards the end of the 16th century there were found to be a difference of 10 days between the Tropical and calendar years. This was corrected in 1582 when Pope Gregory ordained that October 4th would be followed by October 15th, making the 10 day correction, and that only every fourth centennial year should be a Leap Year. This is known as the Gregorian calendar and is the one we now use.
It was adopted by Italy, France and Portugal in 1582 and other countries made the correction at various dates up to as recently as 1923. The change from the Julian to the Gregorian calendar took place in
Great Britain and her dominions in 1752 [Which included the pre-independent USA colonies], when the correction was made by the omission of eleven days; Wednesday, September 2nd being followed by Thursday, September 14th.
An Aztec calandar for the year 1790 [A1]
The Julian and Gregorian calendars are sometimes referred to as the Old Style and New Style calendars. It is interesting to note that these terms originally applied to the date of the beginning of the year (New Year's Day). In the Old Style this was March 25th and was changed to January 1st (New Style) in England in 1752 when changing from the Julian to Gregorian calendar. New year's day was changed to January 1st in Scotland in 1600.
The Equinoctial or Tropical Year is the time that the Earth takes to revolve around the Sun from one Spring Equinox to another. This is approximately 365.24219 mean solar days, or 365 days, 5 hours, 48 minutes and just over 45 seconds. The Equinox is the point where the Sun crosses the Equator making day and night equal.
The Calendar Year is 365 days except if the year number is divisible by four evenly, this being a Leap year of 366 days. The last year of a century is not a leap year unless its number is evenly divisible by 400. For example, 1800 and 1900 were not Leap Years, while 2000 is a Leap Year.
© The Australian EsE-2c Calendar 1998