The Sun's passage through the equinox was invented by the Chinese
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The festivals are dependent upon agriculture; but agriculture and astronomy were interwoven from the very beginning, not only in legend and mythology, but for very precise practical purposes. The very word "season" means "to sow" and spring was considered the season, par excellence. In most calendars the year commenced at the moment when the Sun crossed the equator, northward bound; but the starting point of the year was a matter of great dispute, and the word "summer," coming from Sanskrit around through Anglo-Saxon, also means year, and gives evidence of a different type of calendar.
The contrariness of the seasons in the Southern Hemisphere was mentioned early in classical times, and, once the theory of the spherical earth was established, the rumor grew into a certainty, though few people had peered over the equator to prove its truth. The Roman poet Lucan told of some Arabs (by whom he probably meant Ethiopians) who had been brought north about the time of the summer solstice. They marveled that the shadows cast by the grove did not fall to the south. "You Arabs come to a world unknown to you," said Lucan; but he did not seem unduly surprised at their bewilderment. By his time the scientists had duly calculated the movements of the Sun. But before such calculations were possible, man had to anticipate the seasonal changes close to his own home.
The first instrument which would mark the Sun's passage through the equinox was invented by the Chinese. It consisted of a flat ring, set in the ground in the plane of the equator. On one side the Sun shone during the autumn and winter months; on the first day of spring, the light touched the other side, and continued there until the fall. This simple device was useless for anticipating seasons; but at least it was more accurate than the weather in proclaiming that a season had arrived.
So practical was this ring, that the Greek astronomer, Eratosthenes, used it about 240 B. C. We cannot tell whether it was invented separately by his countrymen, or whether it came from China in a wonderful oriental cargo which seems to have included the abacus and the Chinese dragon as well. Certainly the Chinese brought it into Rome a little later, and the Romans marveled at it. Obviously the circle was too large for a ring, so they called it a "bracelet" or "armilla," and the name stuck. All the magnificent developments common during the Middle Ages were known as armillary spheres.
The Chinese had kept their instruments very simple. The Greeks and Romans added a multitude of accessories. Eratosthenes fixed another ring in the plane of the meridian, and used it to determine the solstices. Ptolemy, fifty years later, complicated the bracelet with rings for zones and a graduated sliding scale, until it more nearly resembled a spherical astrolabe than a simple seasonal dial. From that time on, the armillary sphere became tremendously useful. It had a variety of purposes, and the medieval models were extraordinarily beautiful; but, unlike some bracelets, the beauty was always subdued to the practicality of the design.
The Greeks, the Romans, the Chinese, were all interested in knowing when spring began, and the armilla was invented to suit their needs. The needs of the Egyptians were quite different and their inventions differed accordingly.
In all the Egyptian year the most important event for the people was the regular overflowing of the Nile. Their crops, their water, the actual personal safety of their lives, depended upon their knowing the summer solstice, when this great event occurred. What did it matter to them when the Sun was only halfway north? They wanted to know when the Sun had reached its most northerly point, for then they could say that the river was about to overflow.
For this purpose they observed the Sun at sunrise, and sunset. The Sun sets farthest to the north of west, and rises farthest to the north of east, at midsummer. At that time, as at the time of the winter solstice, the Sun appears to stand still for a while before it begins its journey back. Its movement resembles a great pendulum, pausing for an instant at the end of its swing, and hence the name for the occasion is "solstice"; that is, "the standing of the Sun."
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