@database "Brief History of the Calendar"
@author "Mathew Wilson"
@wordwrap

## $VER: CalendarHistory v2.10 (21.03.97)

@node main "A Brief History of the Calendar."

	@{b}A BRIEF HISTORY OF THE CALENDAR@{ub}

The calendar is a very big part of our everyday life yet we often forget the centuries of patient study, trial and error that went into creating the thing that now controls our lives. This method of recording the passage of time started with the Babylonians and has evolved through centuries of change to emerge as the modern day calendar we use today.

The first calendars were based on the movements of the moon. This gave direct correlation between the length of the year and the cycles of the moon. This was due to the fact that man had no real perspective on his local solar neighbourhood. Later when man learned that the Earth revolved around its star, the Sun, the moon based systems were found to be an inaccurate measure of a true year. The Sun became the base for recording time as the lunar year did not match the cycle of the Earth around the Sun. However, there are still some calendars in use today that are based on the Moon cycle. These systems are usually well entrenched in tradition and would be difficult to change without affecting the culture; especially if a religion is involved. The current Jewish calendar is still based on the Moon's movements which begin with the year of Creation, set at 3760 BC. The Islamic calendar is also based on the Earth's meteorite impacted satellite. The Christian Calendars (Julian and Gregorian) are based on the movements of the earth around the sun (1 cycle = 1 year) and the months have no correlation with the movements of the moon. The Hebrew calendar's year is linked to the sun but its months are amazingly linked to the motions of the moon using a complex system.

The Egyptians were the first to adopt the Sun as a base for time keeping. Theirs is the long descendant of the Gregorian calendar we use today. The month became an arbitrary unit that was no longer related to the cycles of the moon. The Egyptians used a 365 day calendar year. It is thought that they first adopted this system in 4236 BC.

As man's knowledge of the stars increased, he learnt that the Earth revolved at a period of 365 and about a quarter days around the Sun. Pharaohs and other leaders made many attempts to alter their calendar to reflect this but failed either because of tradition or miscalculations from the priests that were assigned to look after the motions of the calendar.

The Romans were also responsible for major changes to the calendar. They had originally used a Moon based system that was very complicated. Its accuracy was entrusted to the College of Pontiffs who often misused this privilege to their own gain. By the time Julius Caesar became virtual dictator of Rome the calendar was in a mess. In 47 BC he called upon famous Greek astronomer Sosigenes to make corrections. After suggestion by Sosigenes, Caesar decided to adopt the Solar year as the Egyptians had done. He gave the calendar year a length of 365 and a quarter days. This quarter day was with held for 4 years and then added as a Leap Year. To honor Julius, the Senate changed the name of the month Quintilis to Julius (July). Julius also had to make some corrections due to the errors in the old calendar. The problems did not end there, for after he was assassinated in 44 BC the Pontiffs in charge of the calendar decided to insert the leap every third instead of every fourth year.

When Augustus Caesar came on the scene he restored the correct leap-year additions in 8 AD. As you may have guessed, the Senate also honored this change by renaming the month Sextilis to Augustus (August). This calendar is also referred to as the Julian calendar, for obvious reasons. Although the Julian Calendar began before 8AD, this date is regarded as the most reliable starting point for Julian based calculations.

In 321 AD the Emperor Constantine created the seven day week, discarding the old complicated system of Kalendaes the Romans had developed to make reference to days within a month.

As greater technology became available the length of the solar year was redefined as 365.25 days. This became known as the length of the Julian (calendar) year. But all was not well, for the Julian year was too long by about 11 minutes. After a few centuries this soon amounted to several days (1 day every 128 years). Again the calendar began drifting from the seasons. 

In 1582 Pope Gregory XIII commissioned the services of the mathematician Christopher Clavius  and the astronomer-physician Luigi Lilio Ghiraldi to fix the drift in the calendar. They found the error to amount to 10 days. A Papul Bull in February 1582 decreed that in October 1582, 10 days would be dropped from the calendar. The 4th day of October was followed by the 15th to enable the loss of the 10 days. This created problems for people born on the 5th but they made reference to those dates using either OS (Old Style) or NS (New Style) systems.

The leap-year rule was then changed to avoid further errors. Now any centurial year (ending in 00) was @{b}only@{ub} a leap year if it was divisible by 400. Therefore 1600 was a leap year but 1700,1800 and 1900 were not. This will give an error of 1 day in approximately 3300 years. This became the Gregorian calendar, the one we use today. The average length of a year as defined by the Gregorian calendar is 365.2425 days. The exact length of the year varies but currently it is 365.242190 days. It was 365.242196 days near 1900, and it will be 365.242184 days around the year 2100. However, it is important to realise that gravitation forces exterted on the earth from other planets can alter the length of the year by a matter of minutes.

All Roman Catholic countries immediately adopted the Gregorian reform, but others were slow to follow. The English didn't start using it until 1752. The French originally followed the Gregorian way but changed in 1792 and returned to it in 1805. Japan followed in 1873, China 1912, Greece 1924 and Turkey 1927. Russia had a similar experience to France during the Bolshevik revolution but returned to it in 1940

Since the introduction of the Gregorian Calendar, some have been dissatidfied and attempted reforms, but a major change has not been implimented because the entire world cannot agree on a new system. In 1923, 500 new reforms were heard at the League of Nations. Two new calendars emerged as favourites:the Thirteen Month Calendar and the World Calendar. But these did not get a majority acceptance by the nations due to conflicts with nationalistic dates of importance and the business community said it would complicate things too much.

So it seems we are to keep the Gregorian calendar for a while yet. Currently it is estimated that there are about 40 different calendars in use around the world.

On-Time uses the Julian method when performing its date calculations, although the program confines itself to the Gregorian Calendar (dates from 15th October 1582). A Julian day is the number of days that have elapsed since 1st January 4713 BC. True Astronomical Julian days are actually offset by 12 hours (beginning 12 noon) but we are not concerned with that in this application. Sometimes when referring to events in more modern times, a form of Julian day called the Modified Julian Date is used. It begins from the Julian day 2400000.

Because so many countries adopted the Gregorian reform at different times, it can be quite tricky to make correct calendars for each country. On-Time uses the Gregorian calendar based on the Roman Catholic date of change. For this reason, early dates cannot always be calculated by just subtracting a certain amount of days from today. Time is not linear in this sense because of all the changes that have been made. If people are really interested in calculating these dates then a library full of useful date functions (by Kai Hofmann) can be found on Aminet ->(Aminet:dev/c/date.lha) to assist you.

For more information of calendars visit http://www.juneau.com/home/janice/calendarland
@endnode