This article originally appeared in the Winter 1999 issue of the local astronomy club's publication "Inside Orbit."

Calendars and the New Millennium

by Will Millar

Do you believe the news media when it says we are beginning a new millennium in a few days? Do you think the news media and advertising agencies can get their stories straight? Do you think they can count beyond three? Think again. Some years ago, the Russian-American physicist George Gamow (the major proponent of the Big Bang theory) published a book called, "One, Two, Three, Infinity..." In this book he talks about primitive cultures dealing with the concepts of counting. Whenever I hear of the new millennium starting in 2000, I think of this book and the people who can not count beyond three. The new century and the new millennium begin on 1 January 2001. Here is a history of calendars and the reason why the new millennium begins in 2001.

The Julian Calendar

All cultures and civilizations now or in the past have used the lunar phases as the basis for their calendars. The word month has as its root, the word moon. The Greeks, Romans, Egyptians, Hebrews, Hindus, Chinese and Muslims used (or use) a calendar based on the lunar cycle. The design of these calendars has been the work of politicians and priests.

Our modern Gregorian calendar is a modified version of a calendar developed by the early Romans. There is some controversy about exactly how this calendar was structured, but there are some obvious remnants of the calendar within our own. The original Roman calendar started the new year in March, probably on the first day of spring, and had only ten months. The seventh, eighth, ninth and tenth months are now named (based in Latin), September (septem for seven), October (octo for eight), November (novem for nine), and December (decem for ten). Even numbers were considered unlucky, so all (at least at first) the months had an odd number of days. The eleventh (Januaris) and twelfth (Februaris) months were added in 712bc, by King Numa. Confusion reigned over this calendar, because it was the subject of political and priestly patronage. If one religious sect was in favor, its religious month was made longer than the others. Since favoritism came and went, the calendar was unstable.

Julius Caesar ended the confusion. He appointed the Greek-Egyptian astronomer, Sosigenes, to make a new calendar that started on the day Roman magistrates took office, on January 1. January is named after the Roman two-faced god, Janus. Janus had a face on both the front and back of his head. He could see in front and behind. This is perhaps symbolic of our tendency to look forward to the new year, and behind at the past. Caesar extended the year 46bc to 466 days to bring the old and new calendars into step. The first day of spring was March 25.

The seven days of the week probably originate from the seven wandering celestial objects: the Sun, the Moon, Mercury, Venus, Mars, Jupiter and Saturn. This is evident in the English names of the days: Monday for the Moon, Sunday for the Sun, Saturday for Saturn. Other languages (especially the romance languages) show even stronger evidence for this suggestion. It is also possible that the seven-day week is based on the Jewish Shabbat (Sabbath day), or on the Babylonian-Torah-Biblical creation story. There is a great deal of disagreement between scholars on this subject.

This new Julian calendar (named after Julius Caesar), had twelve months with each month alternating in length of 30 and 31 days except February, which had only 29. This gives a total of 365 days. However, it was known even then, that the year is actually 365¼ days long. (The Egyptian calendar of Sothis.) To make sure the astronomical (astrological?) events, like the first day of spring, occurred on the same day of each year, a leap day was added to the end of February every four years. Thus, every fourth year, February was 30 days long. This calendar design of three years with 365 days and one year of 366 days was first suggested by the Greek mathematician, Eudoxus, who was also the first to create a working geocentric model of the universe. Julius Caesar was assassinated on March 15, 44bc. ("…beware the Ides of March…") The calendar he commissioned worked so well, and thus was so impressive, that after his death, the month in which he was born was renamed in his honor. It is now called July.

After the reign of Julius Caesar, came his nephew, Augustus Caesar. Augustus was probably the greatest of the Caesars. He lived a long life, and the Roman Empire prospered under his rule. Upon his death, the month containing the greatest number of days celebrating his achievements as Caesar was renamed in his honor, as "Augustus" (now, August). At this time, July was 31 days long, and August was only 30 days long. The month honoring Augustus could certainly not be shorter than that for Julius. So, August became a 31-day month. This made the year too long. To fix this problem, the remaining months (following August) were swapped in length and the extra day was taken from (the already abused) month of February. February became, and is now, only 28 days long. However, leap day is still added to February. So much for the politicians.

The Christian Calendar

The Christian Calendar was established by the sixth-century scholar Dionysius Exiguus. He compiled a table of dates for Easter and fixed the beginning of the calendar as January 1, 1ad, which was as near as he could estimate the birth of Jesus. It is important to note here that the number "zero" did not exist until at least 200 years after the work of Dionysius. "Zero," and "place value," are concepts credited to the Hindus, around 800ad. The Arabs then developed the mathematics surrounding the new numbering system developed by the Hindus, which is why we use Arabic numerals. Roman numerals were used in Europe until the mid-renaissance years. Thus, Roman numerals, without a zero, were used in all calendars of the Western World. The year 1ad is preceded by the year 1bc. This is the point where some people claim the year 2000 as the millennium, because they start counting the years at zero. However, as you now can plainly see, there is no year, "zero." The original Christian calendar is simply the Roman-Julian calendar with a shifted starting epoch.

The Gregorian Calendar

I say the original Christian calendar because we have since modified it. The tropical year (the amount of time it requires for the Sun to "travel" from the vernal equinox, around the celestial sphere and back to the vernal equinox) not is exactly 365.25 days long. (Because of the Earth's precessional motion, the vernal equinox moves to the west along the ecliptic line.) The tropical year is actually 365.242199… days long. A small error, but in the Julian calendar, this small error built up over sixteen centuries to about ten days. The first day of spring _ and thus the religious holidays that are scheduled according to the lunar months, like Easter _ were falling on the wrong days. In 1582, Pope Gregory XIII announced the creation of a new calendar. He eliminated the extra ten days by making the day after October 4 into October 15. This brought the first day of spring back to March 21. Only those countries with strong ties to the Church made this adjustment. In others, like England and her colonies (USA, etc.), the adjustment was not accepted until 1752. By that time it was necessary to adjust the calendar by 11 days. This caused riots in the streets in England because people were told they had to pay a full month's rent for a month, which was missing 11 days! To account for the tiny error in the length of the year, the rule for leap years was modified.

For a century year to be a leap year in this new calendar, it must be divisible by four and divisible by 400. This means the year 1900 was not a leap year. The year 1900 is divisible by four, but not by 400. The year 2000 is a leap year, because 2000 is divisible by four and 400. This adjustment makes the error in the length of the year about one day in 3,300 years. No further adjustment should be necessary until 5000ad. This new calendar is called the Gregorian calendar. The Christian World, and most governments and businesses use this calendar. In those cultures where they wished to avoid connecting the calendar with the birth of Jesus, they use CE (Common Era) in place of AD and BCE (Before the Common Era) in place of BC.

The New Millennium

The Hindu-Arabic number system, which includes the concept of "place values" and the number "zero," was not introduced to the Western World until at least the 13th century. Thus, as stated above, there is no year "zero." The year 1ad is preceded by the year 1bc. The first century begins with the year 1ad and runs to the year 100. The second century begins with the year 101 and runs to the year 200. The third starts with 201 and runs to 300, and so forth. Continuing this brings us to the twentieth century, which starts on January 1, 1901 and runs through 2000. The twenty-first century thus begins on January 1, 2001, not January 1, 2000. The year 2000 is the last year of the twentieth century.

Other Calendars of the World

The traditional Jewish calendar is based on the lunar phases. There are 354 days in twelve lunar months. Eleven days short of a seasonal year. To have the religious holidays fall on approximately the same day of the year, a thirteenth lunar month (an intercalary month, or leap month) is inserted every few years.

The Islamic calendar is based strictly on the phases of the Moon. No correction is made to align the Islamic calendar to the seasons. The holy month of Ramadan may come in any season. Islam started with desert peoples of the Middle East, where there was little concern for the seasons of the solar year.

The Chinese calendar is also based on phases of the Moon, and on a cycle of 12 years. The twelve-year cycle is linked to the position of Jupiter in the Zodiac. The Chinese Zodiac is different from the Western (Babylonian) Zodiac. Thus, the Chinese calendar has "The Year of the Dog," "The Year of the Dragon," etcetera.

The Mezzo-American civilizations had calendars based on the solar and lunar cycles, similar to the European calendar. Their observatories in Central America were built to very high precision. Their timings of astronomical events, such as the summer solstice, were nearly perfect. When Hernando Cortez arrived in Mexico in 1518 (just before the 1582 Gregorian calendar) he was surprised to see how accurately the Mayans had measured time. The Mayan calendar matched the European (Julian) calendar, except the Mayan calendar (according to the Europeans) was ten days too fast!

The millennium problem is one belonging to the Christian World. The rest of the world really doesn't care. Maybe we shouldn't either.

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