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SIDIC Periodical XXXII - 1999/1
Toward a new millennium. A Jubilee of hope (Pages 13-16)

Other articles from this issue | Version in English | Version in French

Calendars: How Jews And Christians Measure Time
Westrheim, Margo


The Hebrew Calendar of the Jews

*The beginning of time for Jews is the date traditionally accepted as the day of the Creation of the world as recorded in the Book of Genesis. Scholars are not in agreement about when the first written Hebrew calendar appeared, but it would be safe to say that its development can be attributed to both to piety and political pressure.

It was vitally important to devout Hebrews, the ancestors of the Jews, to observe religious rites at the proper times. The sighting of the Rosh Chodesh, the new moon, marking the beginning of a new month was particularly important because it regulated the time of Shabbat, the Sabbath Day, and the dates for all festivals, holy days and fast days.

In Jerusalem the priests would climb the Mount of Olives and light a signal fire as soon as they had observed the crescent of the new moon. Their fire was the first in a chain of signal fires as priests, keeping watch on other summits in the distance, sighted the fire and lit their own signal. This process would continue until the news that the new month had begun was sent by signal fires as far north as the city of Safed, about 225 km (140 miles) from Jerusalem. At one time the chain of signal fires extended like a telegraph system all the way to Babylonia. Faithful believers eagerly watched for, and relied upon, the signal fires so they would be able to observe their religious rites at the proper times.

Imagine how distressed the people must have felt when it was discovered that enemies deliberately set false signal fires to trick them! And, to compound their distress, the Romans later prohibited the Jews from lighting any signal fires at all. The priests in Jerusalem then tried sending out special messengers with the news that the new moon had appeared, but because it took too long, a month could not be started everywhere at the correct time.

What could be done? The Hebrews were obliged to develop their own reliable written method of measuring time. It needed to be recorded so the priests and believers did not have to depend on signal fires or messengers. With a written calendar, the time of the new moon and the beginning of a new month could be shared by all the priests and believers.

The Hebrew priest-astronomers went to work. It is believed that the pre-Babylonian exile Hebrew calendar was a lunisolar one, but little else is known about it. Some scholars believe that the Hebrews began to use the Babylonian calendar about 586 BC and were much influenced by it. There certainly are similarities in some of the names of the months and in the basic design. If the Hebrews did adopt the Babylonian calendar, they seem to have added further important observations to its design resulting in a much more accurate method of measuring time. Significantly, the Hebrew calendar is still in use today while the Babylonian calendar has been relegated to the history books.

The Jewish day begins and ends at sunset, therefore its length varies with the seasons. It is believed that the Hebrews began the day at sunset because of the Bible verse, ďAnd God called the light Day, and the darkness he called Night. And the evening and the morning were the first dayĒ (Gen 1:5). The calendar day is a 24-hour period measured from 6 p.m. to 6 p.m. at the meridian of Jerusalem. Each hour of the day is divided into 1080 parts called chalakim.

The Hebrew calendar week, which is a group of seven days, is a man-made measure of time. It is not governed by the natural rhythms of the earth, sun, moon or stars. It is believed to be based upon the story of Creation as told in the Book of Genesis. According to the story in Genesis, God created the world in six days and on the seventh day He rested. The Hebrews named the seventh day Shabbat, which means a day of rest. The Jewish Sabbath day, a day set aside to honor God, became the pivotal point around which Jewish life and worship revolved. The seven-day week became a constant measure of time that established the regular recurrence of Shabbat. It not only established a rhythm of life for the Hebrews and their descendants, but it has also affected the lives of millions of Christians and Muslims.

So great is the respect given by Jews to Shabbat that in years when a conflict with other Jewish festivals may occur, precedence is always given to Shabbat. It is also significant that the other days of the week are designated only by a number, that is, first day, second day, third day and so forth. The only day of the week deemed worthy of a name was the seventh day, the day of God, Shabbat.

The Hebrew calendar synchronizes a cycle of lunar years with solar years. In each cycle of nineteen years there are twelve common years and seven leap years. The leap years occur in the third, sixth, eighth, eleventh, fourteenth, seventeenth and nineteenth years of the cycle. In ancient times, the observations of the priest-astronomers in Jerusalem determined the length of the years. Later, observation gave way to calculation in determining if a year was a common year or a leap year. The sequence of common and leap years became fixed after the acceptance of Hillelís reforms.

The number of days in a year can vary from 353 to 385 because, in addition to the reckoning of time, the Hebrew calendar is also influenced by religious requirements. In terms of year length there are six types: regular (354 days), deficient (353 days) and abundant (355 days) common years; and regular (384 days), deficient (383 days), and abundant (385 days) leap years. During a deficient year the month of Kislev is shortened by one day and during an abundant year the month of Heshvan is increased by one day.

The reason for this complicated variation in the length of a year is the problem of fixing the dates of two special holidays, Yom Kippur (Day of Atonement) and Rosh Hashanah (Jewish New Year). It is considered undesirable to have Yom Kippur, a fasting day, fall on the day before or the day after Shabbat, and it is forbidden for Rosh Hashanah to occur on Shabbat. The timing of the first day of Tishri (the start of the religious year) is controlled by changing the length of the year preceding that month. By adding or subtracting a day to the year prior to Tishri 1, the date of Rosh Hashanah is controlled for the following year. Nisan, the Passover month, still marks the beginning of the civil and agricultural year which, at one time, was determined by the ripening of the barley.

Some Jews observe a grouping of seven years together, calling each seventh year a Sabbatical Year. In ancient times the year was commemorated by allowing the land to lie fallow, by setting slaves free and by canceling all debts. A grouping of seven times seven years, which was known as a week of Sabbatical Years, was celebrated by a Jubilee Year. In addition to the same obligations as in the Sabbatical Year, there was the further obligation to restore property to its original owners.

The Julian and Gregorian Calendars of Christendom

The Christian era begins with the date accepted as the year Jesus Christ was born. As the daily life of the early Christians was regulated by the Julian calendar of Rome, they adopted the Roman year of exactly 365 1/4 days, divided into twelve months, and retained the same names and lengths of each of the months. They did change the beginning date, counting the time from Jesusí birth instead of from the founding of Rome. Another change made by early Christians at the time they adapted the Julian calendar to their needs was the introduction of a seven-day week. Their desire for a seven-day week was prompted by the Creation story and the need to celebrate the Sabbath. Yet, strangely enough, the names they gave to the days of the week seem to have been more influenced by pre-Christian Teutonic gods than by the Bible.1

The Julian calendar was considered to be very accurate because the finest of the priest-astronomers of Rome had designed it under the authorization of Julius Caesar only fifty years before the birth of Christ. Therefore, the calendar the early Christians adapted to their needs had already been adjusted to bring the old lunar calendar into line with the solar year. Even so, it was not as accurate as had originally been hoped. It turned out to be eleven minutes and fourteen seconds too long per year. That may sound insignificant, yet that tiny error resulted in those few minutes adding up to one whole day every 128 years.

Over the years, the problem was discussed but no solution found. By AD 1582 the Julian calendar was ten days out of synchronization with the solar year, so Pope Gregory XIII ordered a study to be made on how the calendar could best be reformed. He recruited the most able scholars, priests, scientists and astronomers to conduct the study, which resulted in a calendar that measures time very accurately. The Gregorian reformers made a minor, but exceedingly important adjustment in calculating which years should be declared leap years. They decided that leap years should occur every four years except for three of every four century years ending in 00. For example, the year 1600 was a leap year. The years 1700, 1800, and 1900 were common years. The year 2000 will be a leap year. That subtle adjustment is the key to the accuracy of the Gregorian calendar. In honor of Pope Gregory XIII, the reformed calendar was named the Gregorian calendar.

The Roman Catholic countries of Europe adopted the reformed calendar by the year 1587, five years after it was first declared by the Pope. Non-Roman Catholic countries were more reluctant to adopt a calendar that had been reformed under the auspices of the Roman Catholic Church and continued using the Julian calendar. It took the British government 165 years before it finally adopted the Gregorian calendar in 1752, and this only after the calendarís name was changed to the New Style calendar to increase its acceptability.

At the time Pope Gregory XIII inaugurated the reformed calendar, it was necessary to drop ten calendar days. He declared that the day following 4 October 1582 would be known as 15 October 1582. Because the Pope had decreed it, Roman Catholics accepted the adjustment without question. It was not so easy in Great Britain. By 1752, when the British Parliament decided to adopt the New Style (Gregorian) calendar, the Julian calendar was eleven days out of synchronization with the solar year. It was necessary, therefore, for the British Parliament to decree that the day following 2 September 1752 would be known as 14 September 1752.

The use of the New Style (Gregorian) calendar spread around the world quickly because the European nations imposed it upon all their colonies. Acceptance of the New Style (Gregorian) calendar was slower in Asia. It was adopted by Japan in 1873, by Egypt in 1875, by China in 1912, by Turkey in 1917 and by the U.S.S.R. in 1918. In 1923 Greece adopted it, becoming the last European country to do so. Both the United Kingdom and Japanese governments maintain the practice of dating government documents according to the year of their present monarchís reign despite adoption of the New Style (Gregorian) calendar for civil purposes.

The Julian calendar is still the official calendar used by many Eastern Orthodox Churches, such as the Orthodox Churches of Greece, Russia, Serbia and Romania. It is also the calendar used by scientists and historians for referring to dates prior to AD 1582. Christian holy days celebrated by both the eastern and western Churches do not fall upon the same day because of the time difference between the Julian and Gregorian calendars.

The early Christians adopted the Roman custom of beginning a day at one minute after midnight. Each day was a 24-hour period measured from midnight to midnight including a period of darkness split by a period of light. The dayís length was divided into two units of twelve equal hours by some countries and into 24 equal hours by others. The custom of using a seven-day week as a measurement of time for keeping the Sabbath day was not legalized until AD 321 when it was declared law by the Christian Emperor Constantine.

No one is sure who decided how to name the days of the week.. The influence upon the very early Christians of the pagan names for the days of the week is obvious when the pre-Christian and current Christian names are compared. Today the majority of Christians regard Sunday, the first day of the week as their Sabbath Day to commemorate the resurrection of Jesus Christ on the third day after He was crucified. A minority of Christians recognize and celebrate Saturday as the Sabbath Day in strict adherence to Judaic law.

When the old Roman calendar was reformed during the reign of Julius Caesar, the division of the year into twelve months was retained but the number of days assigned to some of the months changed. This was to help keep the year synchronized with the solar seasons. However, in doing so the months were no longer synchronized with the waxing and waning of the moon. The months as they were adopted by the early Christians retained the names of the Roman months, some of which were named after gods ((e.g., the gods Janus, Mars, Juno) and some derived their names from numbers which reflected the position the months had held when the year was only ten months long (e.g., Quintilis, Sextilis, Septembris, Octobris, Novembris, Decembris).

The Julian calendar year is exactly 365.25 days long and the Gregorian calendar year 365.24 days long. Both calendars use the system of having regular years interspersed with leap years to help balance the lunar year with the solar year. Regular years have 365 days and leap years have 366 days.


* This article, with a few minor modifications, consists of excerpts from pages 49-55 and 66-72 of Calendars of The World: A Look at Calendars and The Ways We Celebrate by Margo Westrheim, 1993,1994. With permission granted from Oneworld Publications, Oxford, England and Rockport, Md.
1 Sun, Moon, Tiw, Woden, Thor, Frigg, Saturn.


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