BA PART II : PAPER 5.7

History of the Calendar

Introduction

It's the year 2000. We stand at the dawn of a new century, a new millennium. We can't even begin to imagine what the next thousand years will bring, but if the last thousand years are any guide, the third millennium will hold wonders.
But wait a moment, and ask yourself: why 2000? Why is this year so special? And why are we celebrating its birth on January 1st?
Our lives are bound up with the calendar. We use it to plan our future: the annual round of work, meetings, appointments, holidays, birthdays and all of the other events in life. We write them in our diaries so that we won't forget.
Our diaries also tell us of the other events of the coming year: public holidays, religious festivals, weekends, the waxing and waning of the Moon.
The calendar helps us to look back, too. The date of our birth is our personal milestone in the calendar. The historian looks further - to 1945 or 1812 or 1066. They seem to be just numbers, but we know instinctively that they are more than that. Each event, public or personal, great or small, has a day and a month and a year which fixes its place in time.
We take the calendar for granted because it's always been there, day following day, month following month, year following year. We know that it has rules - every fourth year is a leap-year and so we add an extra day to February. But the lengths of the months are irregular, some 31 days, other 30 and poor February only 28 days in three years out of four. Easter seems to move at random. The days of the week provide some kind of regularity, but why do we have seven, and why are they named after a mixture of planets and Norse gods? And why do the British pay their taxes on April 5th?
Our calendar can trace its roots back over 6000 years to ancient Egypt. Its story features Julius Caesar, the Council of Nicaea (which gave us the Nicene Creed), a small Russian monk called Denis, the Venerable Bede and Pope Gregory XIII.

Squaring the Circle

The lives of our ancestors were governed by the cycle of night and day, the waxing and waning of the Moon and the passage of the seasons.
Thus the story of the calendar begins with astronomy, with the Earth, the Sun and the Moon. To be precise, it begins with the length of the day, the year and the lunar month, and the fact that neither the year nor the lunar month is an exact number of days, nor the year an exact number of lunar months.
The cycle of the seasons - Spring, Summer, Autumn, Winter, and Spring once more - is known to astronomers as the tropical year and it can be measured very precisely. It is 365.2421896698 days long, although it is gradually getting shorter by about half a second per century.
The lunar month is measured by the phases of the Moon - New Moon, First Quarter, Full Moon, Last Quarter, and New Moon again. It is 29.5305888531 days long, but getting longer by a little less than a fiftieth of a second per century.
There are 12.36826639275 lunar months in a tropical year.
The history of the calendar is largely about the attempts of astronomers, priests and mathematicians to force the tropical year and the lunar month to fit into a scheme comprised only of whole numbers. Like the geometers who dreamed of ``squaring the circle'' and the alchemists who sought to turn lead into gold, they faced an almost impossible task, but that didn't deter them.
Most ancient calendars, including those of Greece, were based upon lunar months, but in order to keep the calendar in step with the seasons, it was necessary to insert extra months now and then, because 12 lunar months are 10.8751234326 days short of a tropical year. Each of the Greek city-states kept its own calendar, however, and the insertion of the extra, or intercalary, months was left to the public authorities.
In around 432 B.C., Meton of Athens noticed that 235 lunar months were almost exactly equal to 19 tropical years (the discrepancy is about 2 hours) and proposed a 19-year cycle of intercalation. Calippus, a century later, made 940 lunar months equal to 76 years each of 365.25 days. Hipparchus, the father of modern astronomy, suggested a further cycle which made 304 years equal to 3760 lunar months and 111035 days.
The Metonic cycle again became important in the early Christian church, which tied the date of Easter to the phases of the Moon, but it is significant that although the Greeks made many profound contributions to Western culture, their calendar is not one of them.

Ancient Egypt

The civilisation of ancient Egypt left to posterity some of the greatest wonders of the world. The pyramids, the Sphinx and the Valley of the Kings still haunt us, and the golden face of Tutankhamun has been seen around the world. The Pharaohs sought immortality, and after 4000 years they found it.
The ancient Egyptians also bequeathed to us the idea which is at the heart of our calendar. Unlike the Babylonians, the Greeks and early Romans, they based their calendar upon the Sun alone. As the earliest great farming civilisation, Egypt was dependent upon the annual flood of the Nile which brought water and rich silt to the river's flood plain. Life in Egypt was controlled by the seasons, and hence by the Sun. The Moon played no part in the calendar.
The Egyptian year had twelve months, each of thirty days, plus an extra five days at the end of the year. These five days were associated with the birthdays of the greatest gods of the Egyptian pantheon and were given over to celebrations.
Thus the year was 365 days long. The Egyptians made no attempt to force their calendar to keep step with the actual seasons, as we do by adding leap-days. Instead, they accepted that the seasons would gradually become later and later with respect to the calendar, in a cycle that would take 1460 years to complete.
The Egyptians checked the relation of their calendar to the natural year not by observing the equinoxes and solstices but by the heliacal rising of Sirius, the Dog-star. This was the first sighting each year of Sirius in the morning sky just before sunrise.
Until the time of Julius Caesar, the Egyptian calendar was the only civil calendar in the ancient world in which the length of each month and year was fixed by rule instead of being determined by the discretion of priests or by the observations of astronomers. As such, it is the direct forerunner of our modern calendar.

Rome and the Julian Calendar

The calendar of ancient Rome, like that of the Greek city-states, was essentially a lunar calendar with an extra, or intercalary, month inserted occasionally to keep the months more or less in step with the seasons. There were twelve months, and they were named, in order: Martius, Aprilis, Maia, Junius, Quintilis, Sextilis, September, October, November, December, Januarius and Februarius. Apart from Quintilis and Sextilis, these names have come down to us almost unchanged in over 2500 years. The names of Quintilis to December are based on the Latin words for ``five'' to ``ten'', and we can therefore deduce that the Roman year began with March.
The Romans were very superstitious. They regarded odd numbers as lucky and even numbers as unlucky, and so all of the months except February had an odd number of days: March, May, Quintilis and October had 31, February had 28 and the remainder had 29. This gave 355 days, roughly equal to 12 lunar months. The intercalary month was added, when needed, at the end of February, and on such occasions, February itself was shortened to 23 days.
Each month had three special days: the Kalends, the Nones and the Ides. The Kalends was the first day of the month, and this is the origin of the word ``calendar'' itself. The Nones was the 5th day of most months, but the 7th day of the long months (March, May, Quintilis, October). The Ides was the 13th, except for the long months, in which it was the 15th. Anyone who knows a little Shakespeare will remember that Julius Caesar was warned to beware the Ides of March - the 15th of March.
The Romans did not count the days of the month in the way that we do. Instead, they always counted towards the next of the three named days. Thus the day after the Kalends of March was not called March 2nd, but ante diem sextum Nonas Martias or ``day six before the Nones of March'', abbreviated to a.d. VI Non. Mar. March thus progressed like this:
1st
Kalendis Martiis
2nd
ante diem VI Nonas Martias
3rd
ante diem V Nonas Martias
4th
ante diem IV Nonas Martias
5th
ante diem III Nonas Martias
6th
pridie Nonas Martias
7th
Nonis Martiis
The 6th, the day before the Nones, was pridie Nonas Martias, literally ``the day before the Nones of March.'' The Nones itself was included in this countdown, which is why the 5th is called the third day before the Nones and not the second.
After the Ides, the dates were counted down towards the Kalends of the following month, so that March 16th was named ante diem XVII Kalendas Aprilis or ``the 17th day before the Kalends of April,'' even though it was recognised as part of the month of March.
The Romans believed that certain days were more auspicious than others for carrying out important events such as business contracts, religious rites and even battles. Only the priests, led by the Pontifex Maximus, could tell a Roman citizen whether a given day was auspicious or not, and naturally they made a charge for each inquiry.
The priests also decided when intercalary months were needed, so they had complete control over virtually every aspect of public and private life through the calendar. However, they had no formal rules to tell them when intercalation was required, and in any case they were rather careless, so that by the time that Julius Caesar became Pontifex Maximus, the calendar had slipped by almost three months with respect to the seasons.
In order to bring the calendar back into line with the seasons, Caesar ordered that three intercalary months should be added at the end of the year which we know as 46 B.C. He also re-arranged the lengths of the months, giving each month its present duration.
But Caesar's most significant reform was to reject the lunar month completely and to adopt a solar year whose average length was 365.25 days. He introduced the four-year cycle of leap years which we still use today. The extra day was added at the end of the Roman year, after the last day of February.
Once again, carelessness prevailed. The priests applied the intercalation every three years, not four. Perhaps it arose from the superstition: 4 is an even number, and hence unlucky. Whatever the cause, the result was that the year 8 B.C. began three days late.
Augustus Caesar corrected the error by omitting leap-years until 8 A.D., and the Julian calendar was observed without further change until the great reform of Pope Gregory XIII in 1582.