Kara Byers 1CHtutor: Dr. Gerard McCartan
Our View of the Universe
?It took several thousand years to establish a satisfactory calendar. Even in this century not all the countries in Europe kept the same calendar. Why was it so difficult? Do we really need an accurate means of recording civil time?
Astronomy originated earlier in human history than the other natural sciences. In the earliest civilisations, the divine or occult was used to explain the movement of the stars and the Sun: the Aztecs, for example, believed that the Sun had to be nourished with a sacrifice of blood and a beating human heart, or else it would vanish. In those dark days there was no conflict between science and religion: a priest, magician or shaman would jealously guard scientific knowledge of the seasons and calendar. Knowledge, regarded as a sign of divine work in the world, conferred immense status on priests in their community, because they were able to foretell the future with some success. Astronomy meant power over people. It guided Man through the seasons, showing when to plough, to harvest or to move herds. Religious and sacrificial acts also had to be performed on specific occasions, for example, to coincide with the phases of the Moon or solar solstices. Astronomy also helped to guide the traveller.
With the rise of the calendar, human activities could be linked more accurately with the seasons and thus better co-ordinated. Three of the periods used in calendars ? days, months and years ? are based on astronomical cycles that have the greatest bearing on human life. The very earliest calendars relied on the Moon, which not only rose and set but changed its shape over a period of around a month that is convenient for describing the seasons. Later calendars evolved to take account of the Sun?s annual cycles. The ancient Egyptians are credited with one of the most advanced solar calendars of ancient times. Astronomy was their key to predicting the great annual event, the inundation of the Nile which coincided with the pre-dawn appearance on the eastern horizon of Sothis (Sirius), the brightest star in the sky. To the ancient Egyptians the event was so important that they dubbed the rising of Sirius the ?Opener of the Year?, and the calendar was arranged around this event.
Many ancient calendars had twelve months based on the average period of around thirty days between new moons, making a year that fell short of the solar year and had to be extended: the original Egyptian calendar had twelve months and, being linked to the Moon?s thirty-day cycle, produced a three hundred and sixty day year. Later it had additional five days added at the end of the year to keep the lunar month and the solar-based seasons co-ordinated and thus the calendar in step with the ?Opener of the Year?.
We thank the Egyptians for the twenty-four hour day, running from sunrise to sunrise. A twelve-hour cycle fitted the movement of the stars across the sky, with an hour marking out the time between each star, or group of stars, rising on the eastern horizon. In this way, the twelve hour night evolved and, probably for the sake of symmetry, a twelve hour day. The Egyptians measured the passing daylight hours with the water clocks, where the flow of time was measured by water trickling through a hole in a stone vessel, and with sundials and shadow clocks, where a sweeping shadow showed the passing hours. The last two furnished merely ?temporal hours?; they were not equal and varied according to the seasons. In Japan, temporal hours were still in use in the nineteenth century and mechanical clocks were adapted accordingly, but in Europe, the day was carved in to twenty-four equal hours in the fourteenth century, when towns introduced mechanical clocks.
Our own calendar is derived from that employed by the Romans. They used a lunar month, squeezing in a month every so often to make up a solar year. By the time Julius Caesar ruled, this process had fallen into such disarray that the winter months fell in the autumn. Pontiffs, state administrators who determined the intercalary month for political reasons to prolong a term of office or to bring an election froward, had abused it. By 47BC the calendar was out of step with the solar year by three months. The following year, under the guidance of the Greek astronomer Sosigenes, Caesar not only made the usual intercalation of twenty-three days but also inserted two additional months, amounting to a total of four hundred and forty ?five days. It became known as the ?year of confusion?. Form that time, each of the twelve months has had its present duration.
Unfortunately, the Julian calculation of 365 ? days to a year was too long by eleven minutes and fourteen seconds. As the centuries advanced, the shifting of the calendar dates of the seasons meant that the equinox, which occurred on 25 March in the time of Caesar, fell on 11th March 1582. That year, Pope Gregory XIII introduced a new and more accurate calendar, directing that the day after 4th October be designated 15th October. Protestants, however, were reluctant to fall into line with a Catholic innovation. In England it was not until 1752 that the Gregorian calendar replaced the Julian. Then a belated 11-day correction was necessary, provoking riots in the streets of London and Bristol, where several people died. Workers demanded to be paid for the days they had lost; many thought they had lost part of their lives. The change also had implications for Newton?s birth, which the modern Gregorian calendar now puts at 4th January 1643. However, it was not until 1924 that Orthodox Churches moved to the Gregorian calendar, though some fairs and local festivities still adhere to the Julian. Muslims have a lunar calendar, which explains why their holy month of Ramadan moves forward considerably each Gregorian year.
The week does not have a basis in the motions of the heavens. As Michael Young, a leading sociologist, put it: ?The Sun has not been the only master. Humans can create their own cycles without having to rely on the ready-made ones. No other creature has demonstrated so much independence from astronomy. No other creature has the week.? The week probably arose from the practical need for societies to have a time unit smaller than a month but longer than a day. Communities run more smoothly when there are regular opportunities for laundry, worship and holidays. Ancient Colombia used to have a three-day week. The Ancient Greeks favoured ten-day weeks while some primitive tribes today prefer a week of only four days. The seven-day week derived from the Babylonians whom in turn influenced the Jews (though the former ended it with an ?evil day? rather than a Sabbath, when taboos were enforced to appease the gods ? perhaps the origin of the restrictions on Sunday activities). Its popularity has defeated a number of attempts at change. The French tried to decimalise it after the Revolution but their ten-day week was scrapped by Napoleon. In 1929 the Soviets attempted to introduce a five-day week and in 1932 extended it to six, but by 1940 the seven-day week had returned.
Just as the week ignores astronomy, so does the modern technology of time keeping. As modern societies have developed, time has been counted in smaller and smaller subdivisions. In fact, the division of hours into minutes and seconds, like the week, owes its origins to the earliest scientific astronomers, the Babylonians, who carried out all their reckoning in multiples of sixty when they compiled their star catalogues around 1800 BC. But it is only since the Industrial Revolution with its train timetables and other detailed working schedules that the minute has grown to its present importance. These trends to subdivide time continued with the rise of science, because of the need to cope with extremely rapid processes.
The Calendar has two main purposes, to fix dates and to act as an instrument for measuring out equal intervals of time. In its purpose of fixing dates the calendar provides us with a continuos register of days, months and years on which we can record the dates of past and future events and engagements. The dates to be recorded are usually physical or natural, civil or ecclesiastical. Physical events include the Ephemerides; the regular astronomical periodic phenomena, the equinoxes, solstices, eclipses, transits, appearances of comets etc; and terrestrial phenomena: tides, seasonal changes and harvests.
A proper record of dates is the true framework of civil history, without which no clear and adequate knowledge of human history is possible. As regards the future what we require is to record are chiefly cyclical or periodic events and appointments. The terms of possession of houses and lands, the terms of payment of rents and interests, salaries and wages, sessions of law courts, of Parliament and of local authorities, the terms of schools and universities, public holidays and festivals etc. With few exceptions these future civil events are recurrent and periodic.
A third class of dates is made up of the dates of the ecclesiastical calendar. These also may be divided into past and future recurring events, on a principle similar to that applicable to civil dates. The ascertainment of the date of Easter ? the principle future date of the ecclesiastical calendar ? has dominated the whole history of calendar construction, and involves a curious composition of physical and civil cycles.
The second purpose of the calendar is to measure intervals of time. Contracts of hiring, loan of money, or of labour or services, are usually made for a fixed interval of time and the remuneration is estimated by reference thereto. A uniform or standard interval is required for these purposes. Recurring intervals of uniform or standard length are desiderated also for the efficient use and comparison of statistics, the preparation of financial estimates and other similar purposes. It is consequently desirable and almost imperative that the necessary intervals should be furnished by and ascertainable to the calendar.
So, do we really need an accurate means of recording civil time? It appears that we do in order to maintain order and function in our society. What is required is a calendar which maintains a close approximation to its astronomical basis, and which is repeated in a stable, uniform, simple and regular order. The present calendar amply fulfils these requirements.
The Calendar. Its history, structure and improvement
UCL Press Limited 1998.R. Poole
The Fontana History of Astronomy and Cosmology
Fontana, 1994.J. North