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History of the Calendar

Updated on May 26, 2010

The calendar is a method of dividing time into fixed intervals, such as years, months, weeks, and days. The principal calendar in use today is the Gregorian named after Pope Gregory XII, who established it in 1582. Frequently called New Style to distinguish it from the earlier Julian, or Old Style, calendar, the Gregorian calendar is the one most generally used by Western nations, including the United States. It has also been officially adopted by the Soviet Union, Turkey, Japan, China, and India. A New Style (N.S.) year begins on January 1 and usually contains 365 days. These are divided into 12 months, 7 of them with 31 days, 4 with 30 days, and 1 with either 28 or 29 days, depending on whether the year is a leap year. Other calendars in current use include the Muslim calendar, which is followed throughout the Near and Middle East, and the Hebrew calendar.

Most of the time divisions of the calendar are based on the movements of the earth and the appearances of the sun and moon. The rotation of the earth on its axis gives man his basic unit of time, the day. The year is calculated from the revolution of the earth around the sun and is variously referred to as the solar, seasonal, or tropical year. In ancient times the lunar month was determined by the number of days between full moons. In most modern calendars, however, the length of tHe different months is arranged by man to fit into the solar year and has no relation to the phases of the moon. This is called the civil month, as opposed to the lunar month.

Other divisions of time, such as the week and the day, were decided arbitrarily. According to the Judeo-Christian tradition, the origin of the week, or seven-day interval, is found in the story of the Creation in the Old Testament. There it is stated that God created Heaven and earth in six days and rested on the seventh.

The Romans named the days of the week for the moon, the sun, and the planets Mercury, Venus, Saturn, Mars, and Jupiter. The names of these gods can still be found in some weekday names in the Romance languages. For example, the Roman god Mars, who was honored on Tuesday, gave his name to mardi in French, martes in Spanish, and martedi in Italian. In English only Saturday takes its name from a Roman god (Saturn), whereas Tuesday, Wednesday, Thursday, and Friday derive from the names of Germanic and Norse gods. Sunday and Monday honor the sun and the moon.

Origins of the Calendar

Man's first measurements and records of time probably developed from his observations of the moon. It was noticed that on successive nights the moon diminished in size from a full circle to a thin crescent and then disappeared. A few nights later it reemerged in crescent form and gradually became a full circle again. In nomadic societies the phases of the moon formed the basis of crude calendars. However, when people learned to farm and settled in communities, the measuring of time and the accurate forecasting of the seasons became highly important. The calendar was used to establish the most favorable time for tilling the soil and planting crops.

More advanced farming required a calendar that indicated the occurrence of the months and the seasons in a fixed order, which was repeated in subsequent years. To use a lunar calendar for this purpose presented certain problems. Accurately measured, the lunar month has approximately 29.5 days, and 12 lunar months contain 354 days. A lunar year, therefore, is about lli/4 days short of the solar year, which consists of about 365V4 days. This slight discrepancy accumulates and becomes considerable over a period of time. As a result the months eventually do not correspond to the natural seasons in the lunar year.

To keep the months in harmony with the seasons the early calendar makers adopted a device to reconcile the lunar and solar years. They intercalated, or added, an extra month or period of days when it became necessary to prevent the seasons from drifting. This type of calendar is called a lunisolar calendar, in contrast to the lunar type, which is based solely on the moon's phases, and the solar type, which is calculated from the solar year.

Historic Calendars

The Egyptian Calendar. The original Egyptian calendar was probably based on the changes of the moon, but it also divided the year into three natural seasons, marked by floods, planting, and harvesting. Later, Egyptian astronomers conceived the idea of replacing the lunar calendar with one based on the solar year, because it was better suited to the Egyptian agricultural economy. They measured the solar year and devised a calendar consisting of twelve 30-day months and a period of five extra days following the last month. The months were no longer determined by the phases of the moon. This calendar was introduced in about 4240 B.C. and was used in Egypt for several thousand years. However, since this 365-day year was one-quarter of a day short of the actual solar year, a discrepancy between the calendar and the seasons gradually developed.

Because of their extreme conservatism, Egyptian priests resisted any calendar reforms. In about 238 B.C., however, King Ptolemy III made an important calendar change. He ordered the addition of an extra day every fourth year, similar to our leap year. Until the time of Julius Caesar the Egyptian calendar was the only one in which the length of each year and of each month was prescribed by definite rules.

Other Ancient Calendars. The calendar has existed in some form or other for more than 6,000 years, and most early peoples had some type of time record. The unisolar calendar of the ancient Babylonians consisted of 12 lunar months, usually 30 days long, plus another month that was added whenever necessary to reconcile the lunar and solar years and to keep the calendar free of error. The Babylonian calendar- was later adopted by the Assyrians in about 1000 B.C. and by the Jews in the 6th century B.C.

The Hebrew calendar is lunisolar. Of ancient origin, it is still used by Jews all over the world for dating religious observances, and it is the official calendar in modern Israel. Hebrew chronology begins with the assumed date of the Creation, estimated at 3761 B.C. in terms of the Gregorian calendar. The rules for regulating the Jewish calendar were fixed in the 4th century A.D. Its 12 months are lunar months and generally have 29 or 30 days. The months are adjusted to the seasons, however, by such devices as lengthening the 8th month, shortening the 9th, or intercalating a 13th month when necessary. The Jewish year, therefore, varies from 353 days to 385 days. The purpose of modifying the basic year is to make sure that the Jewish New Year will be celebrated in September and the Passover holiday in the spring.

The Muslim calendar was instituted by Mohammed in the 7th century A.D. to reform the old Arab lunisolar calendar. His new calendar was based solely on the moon's phases and contained 12 lunar months, totaling about 354 days. No attempt was made to bring it into line with the solar year or take account of the seasons. If the solar year is used as a reference, the Muslim calendar accumulates an error of about 11 days annually, or about a year in every 33 years. The months therefore begin at a different part of a season each year, and it takes 33 years before they are back to their original position. The Muslims date events from the year of the hegira, or Mohammed's flight from Mecca to Medina, a date equivalent to the year 622 A.D. in the Christian calendar.

In the New World the Mayans of Mexico amazed their Spanish conquerors by the precision of their elaborate and ancient calendar. Their 365-day year consisted of 18 months, each of 20 days, with a supplementary period of 5 days. This created an error of one-quarter of a day per year. Instead of correcting the error hy altering the length of the year, the Mayans readjusted their dates and holidays to the calendar. The Aztecs of Mexico used a similar system. An impressive artistic representation in stone of the Aztec calendar is on exhibit in Mexico City.

The Roman Calendar. The original calendar used in ancient Rome consisted of 10 months with 304 days. According to tradition, the second King of Rome, Numa Pompih'us, introduced a lunar calendar in about 700 B.C. By adding January and February, he increased the number of months to 12.

Under the Roman republic the year averaged 355 days. March, May, Quintilis (later called July), and October had 31 days. The other months had 29, except February, which had 28. A month was added when necessary, usually every other year or at the discretion of the pontifex maximus, who was in charge of the calendar. The Romans began their chronology with the year of the founding of Rome, which is traditionally set at 753 B.C. in terms of the Christian calendar. The initials "A.U.C.," an abbreviation of the Latin word meaning "in the year of the founding of the city," preceded the year number.

Unfortunately, the pontifices often adjusted the calendar to lengthen or shorten an official's term or to manipulate elections. By 46 B.C., when Julius Caesar became pontifex maximus, calendar dates were unrelated to the seasons. Caesar realized the need to end the abuses of the calendar and saw the great advantages of using a. uniform and consistent calendar throughout the Roman Empire. After consulting the Greek astronomer Sosigenes of Alexandria, Caesar decided on a purely solar calendar and adapted the calendar of Egypt to suit Rome's needs. His system is referred to as the Julian calendar. It was introduced on Jan. 1, 45 B.C., and was used in Europe until the 16th century.

Authorities disagree about the precise nature and extent of Julius Caesar's reforms. There is good reason to believe, however, that Caesar divided the year into 12 months, giving 31 days to January, Sextilis (later called August), and December and 30 days to April, June, September, and November. He left March, May, Quintilis (July), and October with the 31 days they already had and February with its 28 days. His arrangement of the number of days in each month and the order of the months still survives in present-day calendars. Some historians, however, attribute some of these reforms to Augustus, who succeeded Julius Caesar.

Caesar was also concerned about the discrepancy between the solar year of 365V4 days and the 365-day period provided by the 12 months. He solved the problem of the extra day by decreeing that in every fourth year, which is now referred to as a leap year, an extra day was to be added. Following Julius Caesar's death in 44 B.C., the Roman month Quintilis was named July for him. Later the month Sextilis was renamed August for Emperor Augustus.

The Gregorian Calendar. The Julian calendar's year was 11 minutes and 14 seconds longer than the actual solar year, so that by 1582 the calendar had accumulated an error of ten extra days. As a result, Christian holidays, such as Easter, were being moved out of their traditional seasons. In order to correct this displacement, Pope Gregory XIII decreed in 1582 that ten days be dropped from that year. To prevent the error from happening again, the Pope further prescribed that leap year be omitted every 100 years, except when the number of years was divisible by 400. Therefore, the year 1600 would be a leap year, whereas 1700 would not.

The Gregorian calendar was immediately adopted in most Catholic countries, including Spain, Portugal, and parts of Italy. Protestant countries accepted it somewhat later, as, for example, Germany in 1694 and England in 1752.

Since it uses the birth of Jesus Christ as its starting date, the Gregorian calendar is generally considered the Christian calendar. Dates within the Christian period are often given with the initials A.D., standing for Anno Domini ("in the year of [our] Lord"), and earlier dates are usually followed by B.C., standing for Before Christ. The dating of the Christian era from the birth of Christ was first proposed by Dionysius Exiguus, a Christian abbot of the 6th century a.b. This suggestion was formally adopted by Charlemagne in 800 A.D. An interesting example of the controversies centered around the calendar concerns the date of Christ's birth. Originally it was set at Dec. 25, 1 B.C., but modern scholarship places it at Dec. 25, 4 B.C.

Calendar Reform

Although the Gregorian calendar is, on the whole, satisfactory, it still has defects. It divides the year into unequal halves, quarters, and months, thereby creating problems for statisticians and accountants. Moreover, because of the extra day in what would otherwise be an even 52-week year, each date falls one day later than it did in the preceding year. As the days shift, the number of working days per month also changes, and businessmen have no precise way of comparing production from one year to the next. Businessmen and educators also waste much time on adjusting operations and schedules to the shifts of the calendar. In addition, holidays with fixed dates, such as Christmas on December 25, fall on a different day of the week each year. On the other hand, there are holidays, such as Thanksgiving Day and Labor Day, that fall on the same day but on a different date each year.

To overcome these defects, other calendars have been proposed. The International Fixed Calendar would divide the year into 13 months of 28 days each, with each month beginning on a Sunday. An extra day, called Year Day, would follow the end of the last month to effect a 365-day year. In leap years a Leap Day would be added following June 28. While this calendar is uniform, the main objection to its use is that it has an uneven number of months and does not divide the year into the even quarters and halves required in business and statistics.

A second proposed calendar, the World Calendar, would divide the year into identical quarters of 3 months, each containing 13 weeks, with an extra day, called World Day, as the last day of each year. In leap years a second World Day would follow June 30. The first months of each quarter, January, April, July, and October, would have 31 days, while all other months would have 30 days. Each date would fall on the same day of the week. Holidays, birthdays, and anniversaries would always occur on the same day, making it easier for people to plan and schedule the use of time.

The World Calendar was brought before the United Nations in 1954. Its leading supporter was India, which wanted an orderly system to replace its 30 different calendars. Many countries, however, including the United States, disapproved of it because the World Day at the end of the year would interfere with the regular procession of Christian and Jewish Sabbaths, as well as with other religious observances. A similar system, the Perpetual Calendar, has also been proposed without success. Since the calendar is intricately involved in man's social, economic, and religious activities, people have generally resisted calendar changes.

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