The Calendar Read Online Free PDF

10,000 years ago the Sahara was covered not with sand but with savannah. Then 7,000 or 8,000 years ago the savannah died as the earth waned and the people of the north-eastern Sahara were forced into the valley of the Nile. There they abandoned their Palaeolithic life of hunting and gathering and adapted to the cycles of the river. This provided a deep-set regularity to the Egyptian culture, which began farming and building settlements by about 7000 BC. Three millennia later Egyptians established what may be the first known date in human history, which chronographers have calculated to be as early as 4241 BC. A thousand years later the kingdoms of the Nile united politically, launching a complex and homogeneous civilization with a central authority and religion that persisted with few breaks for three thousand years, until the death of Cleopatra, all the while depending on the rhythms of the great river.
    The Nile is a gift of life; but it also is an enormous clock and calendar stretching over four thousand miles, the second-longest river in the world. Fed by rainfall and melting snow in the Ethiopian highlands and to a lesser extent by watersheds as far south as Uganda, the Nile floods with a predictability that Egyptians understood long before stone temples and pyramids began to rise on the river’s shoreline--or before anyone thought about a formal calendar. All an early Egyptian farmer needed to do was plant a tall reed in the mud along the river bank, cut a notch to measure the high point of the floods, and then count the days until the next high-water mark, which would occur almost exactly one year later. This simple device, called a Nilometer, was then the most accurate calendar in the world, based on the seasons as regulated by the earth’s orbit and the tilt of its axis rather than on the phases of the moon.
    Egyptian astronomers supplemented the Nilometer with another discovery that made their solar year even more accurate: that Sirius, the Dog Star and the brightest star in the sky, ascends in the dawn sky once a year in a direct line with the rising sun. Sirius’s appearance happened to coincide with the Nile’s annual flood; it also became the first day of the month of Thoth, the Egyptian New Year’s Day, commemorated annually with elaborate ceremonies that began when Sirius appeared on top of obelisks precisely aligned with observation points on the ground below. By timing Sirius’s appearance exactly from year to year, Egyptian astronomers eventually realized that the solar year was one fourth of a day longer than 365 days. Egyptians also used pyramids to measure shadows to determine the coming of the equinoxes.
    Adding a quarter of a day to the Egyptian year was a revolutionary discovery. It brought the Egyptian year within 11 minutes and 24 seconds (give or take a few seconds) of the true solar year at least two thousand years before Julius Caesar embraced the 365 1/4 day calendar for Rome, and over three millennia before Roger Bacon’s appeal to Pope Clement. Still, in a move Bacon would have ruefully understood, the priests who controlled Egypt’s calendar refused to alter their year to make the correction from 365 to 365 1/4 days. As orthodox and unbending as the Catholic Church in Bacon’s era, the white-kilted Egyptian priests with their shaved heads and painted faces considered their calendar too sacred to alter, leaving it to shift by six hours (a quarter of a day) each year. This launched the Egyptian calendar on a slow drift across the seasons in a cycle that repeated itself every 1,460 years. Called the Sothic cycle, this flaw was not corrected until the Ptolemaic era in Egypt. In 238 BC Ptolemy III* ordered a leap-year system by adding an extra day every four years. But even then the priests resisted the edict until 30 BC, when Rome conquered Egypt and Augustus forced the people of the Nile to add the extra quarter of a day to their calendar to bring it into line with the Julian calendar.