A Brief History of Timekeeping (with apologies to Stephen Hawking)

September 2006: Part 1
October 2006: Part 2
November 2006: Part 3
December 2006: Part 4
January 2007: Part 5
January 2007: Antikythera Mechanisim

Part1 - September 2006

Stonehenge

Many expats living in Andalucia take some time to become used to the difference between local noon, i.e. when the sun is at its zenith and due south, and 12 noon by the clock. For the record our distribution area lies between 5o 9' West (Estepona) and 5o 22' West (Gibraltar). The sun travels 1 degree every 4 minutes so local noon should be a few seconds after 12.20pm GMT, between the last Sunday in October and the first Sunday in March and around 1.20pm BST for the remainder of the year. Spain, although technically within the same time zone as Greenwich (0o to 15o West), opts to have an extra hours light in the evenings so is one hour ahead of Greenwich. So local noon is around 1.20pm during the winter and 2.20pm during the summer. Apart from this small discrepancy there is a great deal of co-operation between the UK and Spain. We have the same number of seconds in a minute, minutes in an hour, and hours in a day, the same number of days in a week, the same number of days in the same months and the same method of numbering years with the same starting date, i.e. 1st January AD1. Quite remarkable when you look at the fascinating history of time keeping.

Before written records began it was important to know, initially, on which day the sun dipped to its lowest point so that sacrifices could be made to ensure the sun started getting higher in the future. European ice age hunters created the first calendars about 20,000 BC. These consisted of notches cut into bone recording the number of days between phases of the moon. It was a rapid development, during Neolithic times, to then mark the start of the planting season, the start of the harvesting season and any other regular events that affected life. Incredibly accurate 'calendars' were constructed using stone pillars and inscriptions. Stonehenge is thought to be, originally, a calendar. Most pre-historic civilisations in the world made their own independent calendars based on observations of the sun and, or, moon, with varying degrees of accuracy.

The Hindu calendar of 1000 BC for instance calculated the length of the year as 360 solar days divided into 12 lunar months, each of 27 days and introduced a leap month every 60 months. The Chinese calendar about the same time was also a solar/lunar calendar but the Chinese, being Chinese, also developed a set of horrendously complicated mathematical equations to 'adjust' the year at varying intervals.

The earliest Egyptian calendar was based on the moon's cycles but then they realised that the star Sirius rose next to the sun every 365 days and that coincided with the flooding of the Nile. So, around 1000 BC the Egyptians are thought to be the first to have had a 365 day year. As civilisations became more advanced and started communicating between themselves it became more important for there to be a 'common calendar', something that does not actually exist today since not every nation can agree on its form. The first to have a stab at this concept were the Romans who of course created an overseas empire that encompassed many peoples, and many calendars. The problem was, before Julius Caesar, the Roman calendar was in total disorder.

The Roman calendar had been borrowed from an earlier Greek lunar calendar that had ten months of 30 or 31 days, resulting in a year of 304 days with 61 days of winter not falling within the calendar at all. This was variously modified by adding two months until by around 713 BC the Romans had a calendar that would have initially seemed fairly familiar with months of Martius (31 days) Aprilis (29 days), Maius (31 days), Iunius (29 days), Quintilis (31 days), Sextilis (29 days), September (29 days), October (31 days), November (29 days), Ianuarius (29 days) and Februarius (28 days), a total of 12 months with 355 days.

A Brief History of Timekeeping (with apologies to Stephen Hawking) - Part 2

The first part of this article took us to the pre Julian Roman calendar.

The Roman calendar now resembled a solar calendar but the leap year was similar to that of a lunisolar calendar so every other year was a leap year with an extra month, called Intercalaris, inserted after Februarius that had either 27 or 28 days. This resulted in a four year cycle of 1,465 days when, in fact four years has 1,460.969 days. The calendar also used an intricate pattern to name the days. There were special days called Kalendae (the first day of the month and the root of our word calendar), Nones (the fifth or seventh day depending on whether the month had 29 or 31 days) and Ides (the 13th or 15th day of the month). In between these special days the Romans counted the days backwards, including the special days, so the second day of Ianuarius (January) was designated 'day IIII before the nones of Ianuarius', bad enough in English but in Latin becomes ' ante diem IIII nonas Ianvarius'. In addition the day preceding kalendae, nones and ides was simply called 'pridie' instead of day II before.. Not surprisingly people became confused especially when the pontifices (who were in charge of the calendar) for political reasons, suddenly inserted an Intercalaris.

Another important function of a calendar is to establish a start date. During the early part of the Roman Republic the years were not counted, they were named after the consuls who were in power. The first day of the consular term effectively became the first day of the year. This day changed a few times during the history of this early Roman calendar. Before 153 BC the first day of the year was the 15th March, then it became 1st January. Earlier start dates are less certain and still the subject of heated discussion in some circles. In the later Republic, years were counted from the founding of Rome but even that date is contentious. The most widely accepted date is 753 BC.

By the time Julius came along in 46 BC to sort it out, the Roman calendar was 90 days ahead of the sun and nobody knew what day it was. The astronomer Sosigenes of Alexandria was charged with finding a realistic alternative. The result was a calendar with 365 days divided into 12 months and a leap day added to February every 4 years. This calendar was so successful that it remained in use in many countries right through to the 20th Century and is still used by many national Orthodox churches however it does have an inbuilt defect. On average the astronomical solstices and the equinoxes advance by about 11 minutes per year against the Julian year. Not much in the short term but enough to significantly accumulate over hundreds of years. Before the Julian calendar could be put in place the 'lost' days from the previous calendar had to be replaced. In 46 BC 23 days were added to February and two new months of 67 days in total were inserted between November and December. The majority of the Roman Empire viewed this as a good thing; Julius had, in one stroke, increased their life spans by 90 days! The new Julian calendar was then introduced in 45 BC.

In 44 BC Julius was assassinated so was unable to inform the pontifices that a leap year occurred every 4 years. They were still in the habit of counting inclusively, at least according to Macrobius, the pontiff called upon to explain the error, so added a leap year every 3 years. Since the algorithm is very simple a more likely explanation is that they were miffed at not being included in the decision making process so deliberately sabotaged the new calendar. After 36 years Caesar Augustus remedied the discrepancy by insisting on the correct leap year frequency and skipping leap years until the year was realigned. Meanwhile, shortly after Julius's demise, the old month of Quintilis was renamed Iulius, and in 8 BC Sextilis was renamed Augustus. The month names and days within the month would now be very familiar to anybody today. However the Roman Emperors were not yet finished. Caligula renamed September as Germanicus, Nero renamed April as Neroneus, Maius as Claudius and Iunius as Germanicus. Domitian renamed October as Domitianus. Commodus uniquely renamed all 12 months after his own adopted names; Amazonius, Invictus, Felix, Pius, Lucius, Aelius, Aurelias, Commodus, Augustus (through gritted teeth), Herculeus, Romanus and Exsuperatorius. Fortunately none of these changes lasted long.

Longer lasting were the name changes introduced by Charlemagne (ironically entitled the first Holy Roman Emperor). He gave all the months Old High German agricultural names, a system that lasted until the 15th Century and, slightly modified, until the late 18th Century in Germany and the Netherlands.

Anyhow, back to the Julian calendar. Following its introduction, years continued to be named after the two consuls who took office in it. They happened to take up office on the 1st January. This system was used until our 541 AD. Historians, who wanted to work out the time between events, referred back to the founding of Rome in 753 BC, that being year 1, so the year 541, then was actually year 1294 as far as the Romans were concerned; you see how confusing it can be? It was not until 525 that a bright chap called Dionysius Exiguus proposed the system of anno Domini which spread throughout the western Christian world once it was adopted by the historian Bede (673 to 736 AD).

Give us our eleven days

All would have been well if the Julian calendar had been ultra accurate but, as we have seen, it 'gains' 11 minutes each year. By 1582 the error had grown to such an extent that it was embarrassing for the Catholic Church. Easter just could not be calculated properly. (The story of the Easter calculation is another fascinating tale.) Pope Gregory XIII promulgated the Gregorian calendar, which was soon adopted by most Catholic countries. Anno Domini was formerly fixed at the perceived birth year of Christ. To correct the Julian error leap years remained every four years, with the exception of those years divisible by 100 but not those divisible by 400 (1900 was therefore not a leap year but 2000 was). Spain immediately adopted the new calendar on the 15th October 1582. England and other Protestant countries naturally objected to adopting a Catholic invention until, in England's case, 1752, by which time it was necessary to introduce an 11 day correction. The 2nd September 1752 was followed by the 14th September. This naturally caused a bit of unrest, people thinking the Government had 'stolen' 11 days of their life. It did not however lead to riots. That apocryphal tale arises from a painting by William Hogarth made during the 1754 elections when the 11 missing days were still a political hot potato. He wrote 'Give Us Our Eleven Days' at the foot of the painting. The Gregorian calendar is accurate to one day per 3,300 years. Not bad but it does not solve the problem of calendar seasonal error.

Because the Earth's rotational speed is slowing ever so slightly, each day is becoming slightly longer. The annual orbit of the earth around the sun however is remaining more uniform so the year remains the same length, at least for our purposes. The equinox therefore occurs a little earlier each year. In 1900 the winter solstice was at 0:18 on the 23rd December. In the year 2000 it was at 6:59 on the 22nd December and in 2100 it will be at 20:47 on the 20th December. Today is therefore very slightly longer than the day you were born. Why then do the days, months and years appear to pass faster as you get older? More next month

A Brief History of Timekeeping (with apologies to Stephen Hawking) - Part 3

Stone Pillar

The introduction of the Gregorian calendar, and its acceptance throughout the western world, should have resulted in a uniform system of calculating the day, month and year but today there are still a few places that think they have a better calendar. The Persian calendar was introduced as late as 1925 and replaced an 11th Century calendar. It is incredibly accurate with an error of one day every 3.8 million years but the year corresponding to our 2006 is 1385. The Indian Civil calendar was introduced in 1957. This calendar starts the year in our March and it is now 1928 in India. It is the year 5767 according to the Hebrew calendar in which system the day officially starts at sunset on the day before and Sunday is day one of the week. So day one begins at sunset on day seven (Saturday) and ends at sunset on Sunday. The Islamic calendar is similar to the Hebrew but starts on Friday, July 16th, 622 in the Julian calendar, the day Mohammed fled Mecca. In the Islamic world it is 1427 and let us not forget the Chinese calendar, a description of which would take the whole magazine.

Having now reached a more or less accurate method of determining what day it is and in which year, we now have to look at how the measurement of smaller divisions of a day, i.e. hours and minutes, has evolved and that again takes us right back to prehistoric times. Whilst erecting stone pillars to monitor certain days of the year prehistoric man noticed that on any particular day the sun rose at a particular point, rose to a certain height and then set at a particular point. The rising and setting point altered in an annual cycle but the sun always reached its highest point in the same direction, or at least the shadow of a pillar was always pointing in the same direction at what we now know as local noon. It was not until about 5 - 6,000 years ago that the measurement of time within a day, became important.

Our present system of measuring time within a day originates with the Sumerian sexagesimal numeral system that is based on the number 60. This was passed on to the Babylonians and copied by the Egyptians. Initially the system was not used to measure time it was used in geometry. The Egyptians divided the circle, and, crucially, the sphere into 360O and each degree had 60 minutes and each minute had 60 seconds.

The question here is why or how did the Sumerians come up with the sexagesimal system? Nobody really knows but the hypothesis is that they counted the knuckles on each hand, excluding the two on the thumb, giving a total on one hand of 12. This multiplied by the number of digits on one hand gives us sixty so the sexagesimal system is a combination of base 12 and base 5, or, if you like, base 12 and base 10. The Sumerians were superb mathematicians and probably realized that a base 12 numerical system is more useful than base 10 because multiplication and division is actually easier. There are many 'relics' of the inherited Sumerian sexagesimal system. 12 ins in 1 foot, 12 pennies in 1 shilling (until decimalization) and 6,000 feet in a nautical mile (dealt with more fully later). The first recorded clocks were stone pillars, or obelisks and the first are credited to the Egyptians about 3500 BC. Their moving shadows allowed the Egyptians to differentiate between morning and afternoon. Later, additional markers allowed sub divisions of morning and afternoon. By 1500 BC there were 10 sub divisions for daylight hours and 1 sub division for the twilight hour of dawn and one for the twilight hour of evening. The Egyptians had a 12 hour day. By 600 BC they could align two devices called merkhet with the Pole Star to establish a meridian and then mark off the night time hours by observing when certain other stars crossed that meridian. Since the day had 12 hours, so, the Egyptians reasoned, did the night. A complete day therefore had 24 hours. Furthermore, the Egyptians realised that one day represented one rotation, whether it was the sun rotating around the earth or vice versa, so a circle was involved. It was then only a matter of time before somebody realized they had already worked out a perfectly acceptable sub division of the hour, 1/60th i.e. one minute. So we have 60 seconds = 1 minute, 60 minutes = 1 hour. The length of the hour and its divisions was actually fixed a long time before we managed to fix the length of a year.

About 325 BC the Greeks started using clepsydras, or water clocks, to measure the passage of time. These were stone vessels with sloping sides that allowed water to drip from a hole near the bottom. The sloping sides were a clever attempt to make the drip equal no matter what the water pressure within the vessel. If you imagine the vessel full, the water pressure is high but the hole is a constant size so more water will flow through the hole than when the water level is low. Therefore if the amount of water available at high pressure is greater than that at low pressure, with the proper calibration, it is possible to achieve a steady drop in water level from the first drip to the last. Other clepsydras worked the opposite way and were calibrated on the inside and measured the passage of time as they filled. Similar devices were still used in North Africa in the 20th Century.

Clepsydras became more elaborate with trap doors opening to display figures, bells ringing at regular intervals and so on. The ultimate clepsydra must be the Su Sing water clock tower built in China in 1088. It was 30 feet tall and incorporated a water driven bronze sphere for observations, a rotating celestial globe and five panels with doors that opened to display rotating manikins that rang bells and gongs and held tablets indicating the hour. Elaborate sundials were the height of time keeping technology right up until the 14th Century. One 10th Century English version even compensated for seasonal changes of the sun's altitude and since the 10th Century there had been several 'pocket' sundials available. Then, in the 14th Century, large mechanical clocks started to appear adorning the outside of towers in Italy. They were driven by weights. Unfortunately there is no record of the developments that suddenly led to this technology. Spring powered clocks were invented between 1500 and 1510 and these mechanisms were the first to be used in pocket watches that were very popular with the wealthy.

A Brief History of Timekeeping (with apologies to Stephen Hawking) - Part 4

Greenwich

Our history to date has covered the invention of the calendar and various methods of calculating the hours, minutes and seconds that make up a day. We have also covered the history of the timekeeper right up to the first pocket watches in the early 16th Century.

With one notable exception there was no pressing need to have more accurate time keeping devices until it became possible to travel at substantial speeds. For instance, between the easternmost point of Spain (3o 10 E), near the French border, and the westernmost point of the Iberian peninsula near Lisbon (9o 40 W) there is a total of 12 degrees 50 minutes which represents a local time difference of less than 1 hour. Since it took many days to accomplish that journey the exact time of the day did not really matter. The early traveller was not likely to suffer from jet lag. The exception is nautical navigation, in particular the determination of longitude, i.e. where exactly you are east or west of a fixed line between the north and south poles. This became important in the early 16th Century as the maritime nations started the 'Age of Discovery'. The UK Admiralty became the driving force behind the efforts to accurately determine longitude.

Since sundials and clepsydras could not be used on a pitching, rolling vessel, the hourglass was used to record the passage of time on ships. This could be used in two ways. One could be kept at the local time for the port of departure and one could be set daily to ship's local time depending on the ship's longitude. Although notoriously inaccurate at least mariners had some idea of how far east or west (longitude) they were of their home port. Unfortunately either 'local' time, ship or home port, did not have to be far out for the mariner to end up far from his calculated position. In terms of distance. At the equator the earth is 24,901 land miles in circumference. A nautical mile is the distance on the surface of the earth subtended by one minute of arc at the centre of the earth and works out to 6,086.91 feet reduced to 6,000 feet or 2,000 yards for easy reckoning. The average circumference of the earth is therefore 21,600 nautical miles (360 x 60). The sun's shadow, at dawn for instance, therefore travels at 900 knots (1 knot = 1 nautical mile per hour) across the surface of the earth. That is 15 nautical miles per minute. And that is about how far out our mariner would be for every minute his hourglasses were incorrect. At our latitudes the error would be about three quarters of that.

Latitudes, positions north or south of the equator, were easier to calculate. It had been known since the Phoenicians that at any particular latitude, on any particular day, the sun would be at a certain altitude at local noon. In fact there were tables to help mariners locate themselves. It was common for sailors, until the invention of an accurate chronometer in the 18th Century, to sail north or south until they reached the latitude of their destination and then simply sail east or west until they arrived. Not always the safest method. The Royal Observatory was founded by Charles II in 1675 with a brief to find a method of solving the longitude problem. The concept of Greenwich Mean Time was established, and then, in 1714 the British Government offered a £20,000 prize for anybody who came up with a solution that would provide longitude to within half a degree. A watchmaker, John Harrison, eventually found the solution. Cook took his chronometer, known as H4, on his second voyage of discovery. When he returned in 1775 after a voyage of three years, it was found that the daily rate of H4 had never exceeded 8 seconds, three times as accurate as had been specified.

Meanwhile, on land, local apparent time, obtained from a sundial, was used for all practical matters. There were even pocket sundials. Then came the horse drawn coach. Once the pocket watch had been invented guards carried time pieces so that they could regulate arrival and departure times. Because of local time differences these timepieces were manually adjusted to gain 15 minutes every 24 hours when travelling west to east and to lose 15 minutes every 24 hours when travelling east to west. This method survived until the early 19th Century when two technological advances were made, the railways and the telegraph.

The telegraph allowed time signals to be transmitted to various stations so that clocks could be synchronised with London time to allow accurate railway timetables to be published. Station clocks were then used by local clock and watch makers as 'control' time pieces but it was not until 1880 that a 'standard' London time was used throughout the whole of Britain.

In 1833 a red 'time ball' was installed on the roof of the Royal Observatory at Greenwich. This dropped daily at precisely 1pm, the astronomers being busy taking observations at noon. Navigators on the River Thames could now set their ships clock to Greenwich Mean Time. Other ports soon adopted the practice, dropping balls and firing cannon in response to a time signal from London.

All the ingredients were now in place for a major international political row. Ideally there should be one meridian from which all others were calculated and, ideally, all nations should adopt a standard time depending on how far east or west they were of that meridian. In that way communications and navigation could be regularised. Unfortunately many nations were trying to claim the honour of having the 'prime meridian', preferably through their capital city. In addition, many charts had a prime meridian that ran anywhere but through Greenwich.

A Brief History of Timekeeping (with apologies to Stephen Hawking) - Part 5

We have now covered the history of timekeeping from prehistoric times right up to the 19th Century when it became ever more pressing to have international agreements fixing a common zero for longitude and time reckoning throughout the globe.

In 1871 the first International Geographical Congress (IGC) took place at Antwerp. The view expressed was that for passage charts for all nations, not necessarily coastal or harbour charts, the Greenwich meridian should be adopted as the common zero for longitude, and that this should become obligatory within fifteen years. It was also recommended that, whenever ships exchanged longitudes at sea, they should be based on Greenwich. This did not apply to land maps and coastal charts, these should keep their own prime meridian.

However, the 2nd IGC in Rome in 1875 discussed the whole matter again without coming to any further conclusions. France did intimate that if the UK were to accept the metric system, then they would accept the Greenwich meridian. Eventually, it was agreed internationally that a prime meridian was needed, and that it should be Greenwich and, after years of discussion, the conference hoped that if the entire world was to accept Greenwich as the prime meridian, Great Britain might be prepared to conform to the metric system. Implementing that agreement would have to wait a while.

In the early 1880s many countries still used prime meridians that did not run through Greenwich. Spain used a line running through Cadiz for its marine charts and through Madrid for land charts. France used Paris for both marine and land charts and Portugal similarly used Lisbon. Ships passing in the night had to be very careful if they exchanged positions (a common courtesy at sea), that they each knew to which prime meridian the other was working.

In 1884 Chester A. Arthur, the 21st President of the United States called the first International Meridian Conference. Twenty seven nations were represented and eventually agreed to adopt a system very similar to the one used today where there are 24 standard meridians of longitude (lines running from the North Pole to the South Pole at right angles to the equator) starting from the prime meridian running through Greenwich, London. These meridians are theoretically the centres of 24 standard time zones but in practice, in many cases, the zones have been subdivided or altered in shape for the convenience of inhabitants. Time is the same throughout each zone differing from Greenwich Mean Time by an agreed, integral, number of hours. Minutes and seconds are the same.

It would take many years for all nations to adopt hourly time zones. Most had done so by 1929 but even today not all apply the concept as it was originally conceived. Parts of Australia for instance use half hour deviations from standard time and some use 15 minute deviations. The result is that there are actually 39 time zones, not 24. Furthermore the time between adjacent time zones is not always one hour. The greatest difference between political boundaries is that between China and Afghanistan, where, travelling from China you would have to set your watch back 3.5 hours as you entered Afghanistan.

Meanwhile, back in the UK, in 1924, the first six pip Time Signal was broadcast by the BBC in conjunction with the Greenwich Time Service. It is the sixth pip that signals the start of the new minute, the pips are at 55, 56, 57, 58, 59 and 00 seconds. The Greenwich Time Service transmitted its last pips in 1990 since when the BBC have originated their own pips based on signals from the GPS satellite network and from the 60kHz radio transmitter at Rugby, operated by BT Aeronautical and Maritime under contract to the National Physical Laboratory.

Speaking Clock

In 1936 a new service, the speaking clock, was introduced by the GPO (who then operated the telephone service in the UK). The service was originally known as 'TIM' because those were the first letters represented by the numbers 1,2,3 on the dialler telephones. It was evident that accurate time keeping was perceived as becoming ever more important in everyday lives but this was by no means the end of the story.

Readers of this series since September last year will have realised that the history of timekeeping was a quest to accurately measure increasingly small units of time, the year, month, day, hour and minute. Today the important unit is the second.

From the earliest days of timekeeping it had been known that the sun was not the most accurate method of measuring simple daily time. Because of the way the Earth circles the Sun the apparent time at midday, when the Sun is at its highest point, may vary by up to 14 minutes late or 16 minutes early from the real time depending on the time of year. In fact there are only four days in the year when the two coincide, on or about the 25th December, 15th April, 14th June and the 31st August.

GPS

Until the 20th century with the introduction of supersonic travel, space travel, global positioning satellites and computers this was not too much of a problem but eventually, a more accurate method of measuring small divisions of time had to be devised. In 1958 atomic time entered the scene. This was based on clock data from numerous countries and in 1968 became based on the radiation patterns of the element caesium. The concept of the leap second was born and in 1986 Co-ordinated Universal Time (UTC) replaced GMT. However Earth time still rules so, on the last day of June and December between 23:59 and 00:01, leap seconds are added or subtracted to keep atomic time and Earth time in step. However, for all everyday purposes, GMT and UTC are synonymous and GMT remains the standard time zone for the prime meridian.

Is that the end of the story? I very much doubt it for one very good reason. Time is not consistent on Earth, never mind throughout the Universe. For instance, gravity affects the passage of time. In low gravity situations, like on the moon, or even on top of a mountain, time actually passes at a slower rate than on the surface of the earth. GPS satellite clocks have to be corrected because they run slightly slower than earth clocks. For an explanation of that phenomenon though I will definitely hand over to Stephen Hawking.

Antikythera Mechanism

One of the reasons history is such a fascinating subject is that new pieces of information appear now and again that neatly slot into the historical jigsaw. Often that new discovery about something incredibly old can only be made by using very modern technology. In November 2006 a report was released concerning a wreck find made in 1901 that neatly fits into this series about timekeeping.

Bronze fragmant

In 1901 a Greek sponge diver found fragments of bronze on a Roman era shipwreck including 30 gear wheels of different sizes. The device, known as the 'Antikythera Mechanism' was correctly identified as being an ancient Greek astronomical clock made around 100 - 150 BC. Modern X ray technology used to detect flaws in turbine blades was used over the last year to learn far more and the results were published on the 1st December 2006.

Reconstruction

The calculator could accurately follow the movements of sun and moon, predict eclipses and recreate the irregular orbit of the moon as seen from earth. It may also have predicted the position of some planets. Some gears covered cycles of as many as 80 years and could indicate at which point the Earth was in two important cycles, the Saros cycle, the period of approximately 18 years separating the return of the sun, moon and earth to the same relative positions, and the Callipic cycle which is a period of 76 years, a function of the tropical year and synodic month, that produced, in 330 BC a very accurate calendar.

(Thanks to Peter Hilton for finding this report)