History of the Calendar
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History of the CalendarThe purpose of the calendar is to reckon past or future time, to show how many days until a certain event takes place—the harvest or a religious festival—or how long since something important happened. The earliest calendars must have been strongly influenced by the geographical location of the people who made them. In colder countries, the concept of the year was determined by the seasons, specifically by the end of winter. But in warmer countries, where the seasons are less pronounced, the Moon became the basic unit for time reckoning; an old Jewish book says that “the Moon was created for the counting of the days.” Most of the oldest calendars were lunar calendars, based on the time interval from one new moon to the next—a so-called lunation. But even in a warm climate there are annual events that pay no attention to the phases of the Moon. In some areas it was a rainy season; in Egypt it was the annual flooding of the Nile River. The calendar had to account for these yearly events as well. The Egyptian CalendarThe ancient Egyptians used a calendar with 12 months of 30 days each, for a total of 360 days per year. About 4000 B.C. they added five extra days at the end of every year to bring it more into line with the solar year.1 These five days became a festival because it was thought to be unlucky to work during that time. The Egyptians had calculated that the solar year was actually closer to 3651/4 days, but instead of having a single leap day every four years to account for the fractional day (the way we do now), they let the one-quarter day accumulate. After 1,460 solar years, or four periods of 365 years, 1,461 Egyptian years had passed. This means that as the years passed, the Egyptian months fell out of sync with the seasons, so that the summer months eventually fell during winter. Only once every 1,460 years did their calendar year coincide precisely with the solar year. In addition to the civic calendar, the Egyptians also had a religious calendar that was based on the 291/2-day lunar cycle and was more closely linked with agricultural cycles and the movements of the stars. 1. The correct figures are lunation: 29 d, 12 h, 44 min, 2.8 sec (29.530585 d); solar year: 365 d, 5 h, 48 min, 46 sec (365.242216 d); 12 lunations: 354 d, 8 h, 48 min, 34 sec (354.3671 d).
Lunar CalendarsDuring antiquity the lunar calendar that best approximated a solar-year calendar was based on a 19-year period, with 7 of these 19 years having 13 months. In all, the period contained 235 months. Still using the lunation value of 291/2 days, this made a total of 6,9321/2 days, while 19 solar years added up to 6,939.7 days, a difference of just one week per period and about five weeks per century. Even the 19-year period required adjustment, but it became the basis of the calendars of the ancient Chinese, Babylonians, Greeks, and Jews. This same calendar was also used by the Arabs, but Muhammad later forbade shifting from 12 months to 13 months, so that the Islamic calendar now has a lunar year of about 354 days. As a result, the months of the Islamic calendar, as well as the Islamic religious festivals, migrate through all the seasons of the year. The Roman CalendarWhen Rome emerged as a world power, the difficulties of making a calendar were well known, but the Romans complicated their lives because of their superstition that even numbers were unlucky. Hence their months were 29 or 31 days long, with the exception of February, which had 28 days. However, four months of 31 days, seven months of 29 days, and one month of 28 days added up to only 355 days. Therefore the Romans invented an extra month called Mercedonius of 22 or 23 days. It was added every second year. Even with Mercedonius, the Roman calendar eventually became so far off that Julius Caesar, advised by the astronomer Sosigenes, ordered a sweeping reform. 46 B.C. was made 445 days long by imperial decree, bringing the calendar back in step with the seasons. Then the solar year (with the value of 365 days and 6 hours) was made the basis of the calendar. The months were 30 or 31 days in length, and to take care of the 6 hours, every fourth year was made a 366-day year. Moreover, Caesar decreed the year began with the first of January, not with the vernal equinox in late March. This calendar was named the Julian calendar, after Julius Caesar, and it continues to be used by Eastern Orthodox churches for holiday calculations to this day. However, despite the correction, the Julian calendar is still 111/2 minutes longer than the actual solar year, and after a number of centuries, even 111/2 minutes adds up. The Gregorian ReformBy the 15th century the Julian calendar had drifted behind the solar calendar by about a week, so that the vernal equinox was falling around March 12 instead of around March 20. Pope Sixtus IV (who reigned from 1471 to 1484) decided that another reform was needed and called the German astronomer Regiomontanus to Rome to advise him. Regiomontanus arrived in 1475, but unfortunately he died shortly afterward, and the pope's plans for reform died with him. Then in 1545, the Council of Trent authorized Pope Paul III to reform the calendar once more. Most of the mathematical and astronomical work was done by Father Christopher Clavius, S.J. The immediate correction, advised by Father Clavius and ordered by Pope Gregory XIII, was that Thursday, Oct. 4, 1582, was to be the last day of the Julian calendar. The next day would be Friday, Oct. 15. For long-range accuracy, a formula suggested by the Vatican librarian Aloysius Giglio was adopted: every fourth year is a leap year unless it is a century year like 1700 or 1800. Century years can be leap years only when they are divisible by 400 (e.g., 1600 and 2000). This rule eliminates three leap years in four centuries, making the calendar sufficiently accurate. In spite of the revised leap year rule, an average calendar year is still about 26 seconds longer than the Earth's orbital period. But this discrepancy will need 3,323 years to build up to a single day. Reform Adopted GraduallyThe Gregorian reform was not adopted throughout the West immediately. Most Catholic countries quickly changed to the pope's new calendar in 1582. But Europe's Protestant princes chose to ignore the papal bull and continued with the Julian calendar. It was not until 1700 that the Protestant rulers of Germany and the Netherlands changed to the new calendar. In Great Britain (and its colonies) the shift did not take place until 1752, and in Russia a revolution was needed to introduce the Gregorian calendar in 1918. In Turkey, the Islamic calendar was used until 1926. Adoption of the Gregorian Calendar
A Better Calendar?Despite its widespread use, the Gregorian calendar has a number of weaknesses. It cannot be divided into equal halves or quarters; the number of days per month is haphazard; and months and years may begin on any day of the week. Holidays pegged to specific dates may also fall on any day of the week, and few Americans can predict when Thanksgiving will occur next year. Since Gregory XIII, many other proposals for calendar reform have been made, but none has been permanently adopted. In the meantime, the Gregorian calendar keeps the calendar dates in reasonable unison with astronomical events. #################################################### The Chinese CalendarThe Chinese lunisolar calendar is divided into 12 months of 29 or 30 days. The calendar is adjusted to the length of the solar year by the addition of extra months at regular intervals. The years are arranged in major cycles of 60 years. Each successive year is named after one of 12 animals. These 12-year cycles are continuously repeated. The Chinese New Year is celebrated at the second new moon after the winter solstice and falls between January 21 and February 19 on the Gregorian calendar. The year 2007 translates to the Chinese year 4704–4705. The year 2008 translates to the Chinese year 4705–4706.
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############################################# A Brief History of the Calendarby David Harper, Ph.D., F.R.A.S.Squaring the CircleThe 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.
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