SUMMARY
Many chronologies exist, or have existed, for the numbering of years. But that we in the west now number the current year as 2011 is due to one Dionysius Exiguus - a Roman friar who instituted the present system in what we now term 525 AD.
THERE ARE 7 UNITS OF TIME MEASUREMENT
“To measure” is to “determine extent by counting out standard units”. Hence metres or miles for distance, litres or gallons for liquid volumes, and so on.
Likewise nature has provided us with 3 standard units – day, moonth and year -for the measurement of time. These were all largely fixed when the Earth solidified and assumed its orbital parameters around the sun some 4.3 billion years ago, though hey have altered slightly over the intervening aeons.
Much later came humanity’s 3 subdivisions of the day into hours, minutes, seconds. But this finer set of time units is entirely artificial, originating around ancient Babylon about 2,000 BC.
To these 6 basic units of time measurement we must also add the week – a parcel of days originating in ancient astronom,y but which also serves our human habits well.
In any case, and whether we realise it or not, our 7 main methods for time measurement must also strongly influence our temporal ideas overall. And so they merit further consideration at this early stage....
Time measurement as practiced by us also falls neatly under 3 headings – chronology, calendars and chronometry. Chronology means the numbering of years arranged in proper past-to-future sequence. Calendars involve rather untidy procedures for subdividing each year into moonths, weeks, days. And chronometry is a much more exact branch of science – dividing each day into finer units by wholly artificial means.
Each of these 3 main systems of time measurement I will then consider briefly in their turn....
CHRONOLOGY – THE COUNTING OF YEARS
Most primitive societies have no real system for keeping count of the years: they depend on personal memories or oral tradition hardly stretching back more than a few centuries at most. Beyond that the tribal memory is of certain “peak moments” - like ancient battles or heroes - all gradually merging into a legendary and quite undated “once upon a time”.
For example when Homer or his contemporaries sang of The Siege of Troy, they were likely dealing with real events from perhaps 300 years before. This event likely took place around 1150 BC, but its exact date remained unknown then as now.
Likewise the Ancient Egyptians - who formed the first organised civilisation that we know of from 3,000 BC onwards - were to our eyes remarkably casual with the dates of history. What passed for chronology then was largely regnal , or based on the reigns of individual monarchs.
Each new Egyptian ruler therefore regarded his own arrival on the throne as that all-important First Event of history. This chronological egotism was also recorded on all monuments. So modern Egyptologists now have some difficulty with ordering the reigns of the early Pharaohs into proper historical sequence.
Regnal dating was also common in other major ancient societies like the Chinese and the Roman, and seems to have been a common early chrono-cultural constraint.
In contrast the Jewish story of Creation in the Bible emphasised that time clearly had a beginning – a tenet which may have influenced modern Big Bang cosmologists more than they might care to realise. And because the Bible also recorded the ages of all the patriarchs from Adam and Eve onwards, it seemed to offer a firm chronology from the start.
So, logically enough, the ultimate First Event in the Jewish AM (Anno Mundi) chronology was the Creation of the world. This they dated to what we now term 3761 BC , meaning also that it is now AM 5772 in such terms (Add 2011 to 3761...).
Around 700 BC however the Greeks began to emphasise rationality without recourse to religion, so further requiring a new sequencing of years. They based their novel chronology on the relatively new Olympic Games, a regular recurrence which conveniently took place triennially. So for them that crucial First Event became the year of the First Olympics, which took place in what we now term 772 BC.
But early Olympic records seem to have been not wholly accurate, so causing problems for Herodotus and Thucydides when they assembled the first true histories in the 5th century BC.
The Romans succeeded the Greeks, and copied them closely in many ways. Naturally however they regarded their own history as more important than one dated by mere games. So for them the greatest First Event was obviously the foundation of their capital at Rome. Hence came their AUC chronology (Ab Urbe Condita: from the foundation of the city) ,commencing in what we now term 753 BC.
Surprisingly however the AUC system was never much used throughout the height of Empire, being largely applied by later scholars who wrote up its history. Instead, as in Egypt, regnal dating was still very much the norm. Each year in Roman history was therefore usually identified by the names of those two consuls who happened to be in power then.
THE AD SYSTEM
1300 years after the city was founded however, the new Christian religion had grown largely dominant in the fading Roman Empire. So Friar Dominus Exiguus (470-540AD) proposed that the birth of Christ be regarded as that all-important First Event. He was a mathematically skilled computus whose main function was to determine the date of Easter, member of a respected profession from which the modern term computer comes!
Exiguus was chosen by the pope to determine the date of Christ’s birth in Roman terms. This he reckoned to be 753 AUC - which he also renamed as Year 1 in the new Christian AD chronology (AD = Anno Domino, Year of the Lord).
Exiguus may have been four years out in his calculations, since most people now think that Christ was born in 4 BC. Still his system was adopted by the Venerable Bede, a monk at Jarrow whose great History of the English People was finished in 731 AD. Thereafter AD chronology spread during the ninth century through Mediaeval Europe, and so was long prevalent when western science and commerce started to flourish there after about 1500 AD.
Bede also occasionally used BC (before Christ) chronology, which counted backwards – though with no Year Zero - from 1 AD. But this usage then largely lapsed until the 16th century, when again it became important for Biblical calculations of the ultimate Creation date.
AD and BC abbreviations naturally emphasise the part played by Christianity in our current chronology, an historical role which some people don’t like to recognise. So around the mid-19th century Jewish scholars began to adopt CE {Common Era) instead of AD when numbering the years. Likewise BCE (Before Common Era) can be used in preference to the BC term.
OTHER CHRONOLOGIES
Although AD (or CE) counting of years is now the preferred practice in science and commerce, many other systems are still in use. For example Muslim chronology dates the First Event to the flight of Muhammad from Mecca in 622 AD. Uniquely however the Muslin year is reckoned as the sum of 12 lunar months, and so approximately 11 days shorter than our own.
This also means that Muslim chronology is slowly gaining on the AD system in terms of yearly totals: the western year 2011 is now reckoned as 1432 in most Islamic lands.
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