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Tuesday, November 21, 2006

History of the Calendar

Not sure what I was doing, but in the progress of trying to get the internet to do tricks for me over lunch, I stumbled on an interesting history of calendaring. It was clearly prepared just before the Y2K roll-over. Here's an excerpt covering the interesting bit before it goes into Y2K stuff.
Rioting Over a Calendar?
By Mary Mullett

The year was 1582, and Pope Gregory had spoken: the Julian calendar had outlived its usefulness. Come October, it would be replaced in Catholic countries by the more accurate Gregorian calendar.

The Julian calendar ran slowly, like a watch with a weak battery. True, it lost only 11 minutes and 15 seconds a year, but those minutes and seconds had been piling up for centuries.

By 1582, the vernal equinox was 10 days off from where it should have been on the calendar, and if the vernal equinox fell on the wrong date, so did Easter, the holiest of Christian holidays.To the pope and his advisers it seemed obvious a change was long overdue.

But the public wasn't so sure. People rioted in the streets, and many others were equally unhappy. It wasn't that the rioters objected to having a new calendar--they didn't much understand calendars anyway. But the pope had decreed that the day after Thursday, October 4, 1582, would become Friday, October 15, 1582! They understood that someone was stealing 10 days from their lives.

Nevertheless, the change was made--on schedule in a few countries, later in most--and eventually accepted.

Protestant England and her colonies clung to the creaky Julian calendar for another 170 years. By the time Parliament adopted the new calendar, the old one was 11 days behind. The day after Wednesday, September 2, 1752, became Thursday, September 14, 1752, in England and America.

Once again, angry mobs took to the streets. "Give us back our 11 days!" they demanded. If 11 days were being taken from them, they at least wanted wages for the lost days. But employers refused to pay them for days they hadn't worked.

Actually, by historical standards the Julian calendar had been a very good one. The first calendars were lunar--based on phases of the moon and were not very accurate. A major difficulty with calendars in general is the length of the seasonal year, an awkward 365 days, 5 hours, 48 minutes and approximately 45 seconds. Weeks, days, hours, minutes, seconds--none of these divides evenly into a year. Neither does the lunar month, an equally awkward 29 days, 12 hours, 44 minutes and 2.9 seconds.

An Egyptian scientist and physician named Thoth created the precursor to the Julian calendar in 4236 B.C. Ancient Egyptians lived and grew their crops on a narrow strip of fertile land along the Nile River, surrounded by desert. The Nile flooded about the same date every summer, bringing life-giving silt to the area as well as water. With a calendar, it was possible to predict when the floods would come--and move people and belongings to safety. Thoth's calendar had twelve 30-day months, plus five extra days at the end of the year, six in leap years. The new year began on our September 23. Flood waters were receding then, and it was time to plant seeds in the wet ground.

In 47 B.C. the Roman conqueror Julius Caesar came to Egypt and discovered Thoth's calendar. Its accuracy impressed him. Rome's old lunar calendar was off 80 days from the seasonal year by then. Caesar took the Egyptian calendar back to Rome and modified it, creating the original Julian calendar.

The Roman lunar calendar began with March, so Caesar started making his changes there. He gave the first 11 months 31 or 30 days, in an alternating pattern, but by the time he got to February, the last month, he was down to 29 days, or 30 in leap years. He began the Julian calendar year in January. So February wasn't the last month any more, but it remained the shortest. Later, February was shortened by another day so that August, named for the emperor Caesar Augustus, could be made as long as July which had been named for Julius Caesar.

The original Julian calendar numbered years from the founding of Rome. Our practice of numbering from the birth of Christ was started in the sixth century A.D. by a monk called Dionysius Exiguus, or Dennis the Short. Unfortunately no one understood zeroes in the sixth century. Instead of beginning with the year zero, Dennis began with the year one--throwing each century off one year forever after. Because of his error, the 21st century will begin, not in the year 2000, but in 2001.

Dennis apparently made another error too. Most experts now believe Christ was born around four B.C., instead of one A.D.

The Julian calendar made every fourth year a leap year--no exceptions. The more accurate Gregorian calendar handles century years differently. All century years are divisible by four, but only those divisible by 400 are leap years.

The Gregorian calendar is better--not perfect. It runs fast by about 26 seconds relative to a seasonal year. In the year 4909, the Gregorian calendar will be one day ahead of the seasonal year and will need adustment. Perhaps the day after October 4, 4909, will become . . . October 4, 4909?

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