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History of the Calendar

Julius CaesarIn the year 45 BC, a powerful man instituted a reform that would have a major impact on the advancement of civilisation. The man was Julius Caesar, and he had decided to change a Roman calendar that was woefully inaccurate. The calendar used at that stage was adjusted at the whim of the pontiffs (priests), who would often have hidden agendas and concerns other than accuracy. Farmers had to cope with a calendar where winter months could change to summer months within a period of a few years. Understandably, crop failures were a common result.

Had Julius Caesar not been so powerful, he probably would not have been able to get his calendar reforms past the establishment (the senate had appointed him as consul and dictator). Against subdued resistance from religious circles, he instituted the new calendar (currently known as the Julian Calendar). It covered all dates from January 1, 4713 BCE (before common era). For the first time there was a calendar that corresponded with the lunar and solar cycles and farmers could rely on it to determine when to sow crops.

It was a calendar based on astronomical observation and the calculated time the earth took to cycle once around the sun. It had 365¼ days and a leap year every four years, to compensate for the ¼ day. As a testament to its accuracy, the Julian Calendar remained in use unchanged, for over 1 500 years.

Pope Gregory XIIIBy 1582, however, the calendar was incorrect by 10 days. Under the instruction of Pope Gregory XIII, the calendar was changed by dropping the leap year at every turn of the century, except where the century is divisible by 400. He also adjusted the date by deleting the 10 days that the calendar was in error. This resulted in the good citizens going to bed on Thursday, 4 October 1582, and waking up on Friday, 15 October 1582. Many people thought that this was sacrilege and there was widespread discontent (mostly superstitious) about the changes. Several non-Catholic countries only adopted the so-called Gregorian Calendar two centuries later.

Since the Middle Ages scholars have strived to convert the calendar into an understandable mathematical equation that can apply to any date in the past or future (perpetual calendar). In 1882 a reverend by the name of Christian Zeller (1822 - 1899), a protestant minister in Markgröningen (20 km NW of Stuttgart) came the closest to simplifying a formula for a perpetual calendar, and his algorithm is named the Zeller Congruence. His algorithm is complicated and only comprehensible for mathematicians, though. An example of his equation is given below:

Zeller Congruence

In 1991, South African Etienne A. Marais developed a 12-digit calendar key that enabled any layman to calculate a perpetual calendar, using simple arithmetic. The technique, called the Marais Formula, is fully described on the Formula - page.

Interesting Facts:
* The year 46 BC had 455 days and is known as the last of the "Years of Confusion".
* The actual time the earth takes to revolve around the sun is 365.24219 days, so the Julian Calendar only had an error margin of 0.00781 days per year (approx. 11 minutes 25 seconds, or one day every 128 years).
* The Gregorian Calendar has an error margin of one day every 3 300 years.
* Russia only switched to the Gregorian Calendar after the "October Revolution" of 1917. The revolution actually happened on 7 November 1917, and not the celebrated 25 October 1917.

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Copyright © ZAbra December 2008