Dating with the calendar reveals some strange facts

Lionel WIJESIRI

The other day, I was bringing down my 2009 calendar and hanging up the new one. This simple exercise made my mind wander through the adventures and tribulations of the concept of calendar down the ages. In essence it vividly shows us how the schedule of our lives is shaped by the movements of the earth, moon, and sun.

In ancient Rome, long time ago, a priest observed the sky and announced a new moon cycle to the king. For centuries afterward, Romans referred to the first day of each new month as Kalends (from their word calare, which means "to proclaim"). On that day, the pontiffs would announce the rest days for the upcoming month, and the dates the debtors had to pay off their dues that were inscribed in the calendaria, a sort of accounts book. The term calendar derived from this custom.

Today, we take the calendar for granted, whether we are in Colombo or London or New York. We know what day it is or which month of which year - give or take 12 hours. We all follow the same calendar. And that is such a big relief.

Pre-history

Little is known about the details of timekeeping in prehistoric eras, however, records and artefacts that are discovered show that in every culture, people were preoccupied with measuring and recording the passage of time. There are "Man made" lunar calendars that some scientists place as old as 32,000 years. Some recent archaeological findings are from the Ice Age where hunters carved notches and gouged holes into sticks, reindeer bones and the tusks of mammoths, depicting the days between each phase of the Moon. These artefacts are dated between 25,000 and 10,000 B.C. There are also surviving astronomical records inscribed on oracle bones dating back to the Shang dynasty of the fourteenth century B.C. that reveal a Chinese calendar, with intercalation of lunar months.

Five thousand years ago, Sumerians in the Tigris-Euphrates valley in today's Iraq had a calendar that divided the year into 30-day months, divided the day into 12 periods (each corresponding to 2 of our hours), and divided these periods into 30 parts (each like 4 of our minutes)..

In Egypt, the paths of the stars were recorded as early as 6,000 years before Christ. The wisest of the Egyptians were the Hermetic philosophers, who possessed a profound knowledge of the sky. They relied upon the predictable motion of these bodies through the sky to determine the seasons, months, and years. People began a preoccupation with measuring and recording the passage of time. There was a need for planning and for divination and prognostication; to maintain these cycles meant that records needed to be kept and observatories needed to be built to precisely measure these cycles. In the Egyptian calendar, over 4000 years ago, the year consisted of 365 days. The year was divided into 12 months equalling for 30 days in each; at the end of the year 5 holidays, which were not going into the month structure, were added. Thus, the Egyptian calendar year had the following structure: 365 = 12 ´ 30 + 5. Note that just the Egyptian calendar is the prototype of the modern calendar.

Evolution

And then the concept of zero arrived. The first evidence we have of zero is from the Sumerian culture in Mesopotamia, some 5,000 years ago. There, a slanted double wedge was inserted between cuneiform symbols for numbers, written positional, to indicate the absence of a number in a place (as we would write 102, the '0' indicating no digit in the tens column). However, the first recorded zero appeared in Mesopotamia around 3 B.C. Since then, it has played a vital role in mathematizing the world. This also meant that it was now possible to have a correct calendar. A calendar that was more accurate. This laid the foundation for a universally acceptable calendar.

But universal acceptance of calendar was not that easy. The dark ages of Europe did its best to suppress anything remotely challenging the authority of the Church. And then there was politics of the church and the kings. It required a tremendous political will and open mindedness to arrive at the calendar that we today take for granted.

Two personalities played key roles in making the calendar as it is today. Have you heard about a sage known Aryabhatta? He was the first in the line of great mathematician-astronomers from the classical age of Indian mathematics and Indian astronomy. His most famous works are the Aryabhatiya (499 CE, when he was 23 years old) and the

Arya-siddhanta. In Aryabhatiya, he divides his work into three parts: mathematics (ganita), time reckoning (kalakriya) and the sphere (gola).

In the section on time reckoning Aryabhatta describes the Hindu calendar, including measurements of the months, weeks and year. He estimates the length of the solar year at 365.356805 days, some 2 hours 47 minutes and 44 seconds off from the true year in Aryabhatta's era.

Everyone knows about the other - Nicolaus Copernicus (1473 - 1543). He worked quietly in Frauenburg: writing, taking astronomical observations, fulfilling his duties as a cathedral canon and tending to the occasional patient as medical doctor of renown. Copernicus came up with a remarkable accurate measurement of the tropical year: 365.2425 days. He also provided measurements and data that would become important 4 decades after the publication of his tome as Pope Gregory's calendar commission struggled to come up with an acceptable measurement of year.

Confusing term

So, we see that the calendar I hung up was not a new concept. It has a very long history. Calendar is also a confusing term. There are many systems of calendars - lunar calendar, solar calendar, luni-solar calendar etc. Calendars in widespread use today include the Gregorian calendar, which is the de facto international standard, and is used almost everywhere in the world for civil purposes. Hebrew calendar, Iranian (Persian) calendar, Islamic calendar. Chinese, Hebrew, Hindu, and Julian calendars are widely used for religious and/or social purposes.

For example, the Year 2010 will be 2763 according to the old Roman calendar, 2759 according to the ancient Babylonian calendar, 6336 according to the first Egyptian calendar, 1430 according to the Moslem calendar, 1388 according to the Persian calendar, 2554 according to the Buddhist calendar, 5129 according to the great Maya calendar. Confusing, isn't it?

Somebody asked me recently, why the Egyptians sectioned the calendar year into 12 months? I explained to him that there were calendars with other number of months in one year. For example, in the Maya calendar the year consisted of 18 months for 20 days in one month. He asked me some further questions concerning to the Egyptian system of time measurement, in particular concerning to selection of such units of time, as hour, minute, second. In particular, there is a question: why the unit of hour was selected so that it was packed 24 times in the day. Further, why 1 hour = 60 minutes, and 1 minute = 60 seconds? I didn't have answers. I just told him that these are mysteries we still do not seem to understand.