Читать книгу Eclipse: The science and history of nature's most spectacular phenomenon - J. McEvoy P. - Страница 20

In the early part of the second millennium BC, Hammurabi, the Semitic king from Arabia, conquered the Sumerians. With this victory he completed the unification of the region ‘between the two rivers’, and he made Babylon the capital city of his kingdom. Located on the left bank of the Euphrates, some 110 km south of modern Baghdad, for the next four hundred years Babylon was ruled by the Hammurabi dynasty during what is now called the ‘Old Babylonian period’, from 2000 to 1600 BC. It was not until after this golden age, however, when the fabled city became the leading centre and capital of the region, that the whole area became known as Babylonia.

The rich heritage of literature, religion and astronomy from the Old Babylonian period found in the ruins of the ancient cities of Babylonia would never have been preserved without a durable medium for recording. The practice of using clay tablets, inherited from the Sumerians, was perfect. These tablets were made from soft clay and written upon with a wedge-shaped stylus, which gave its name to the style of writing, cuneiform: the Latin word cuneus means ‘wedge’. For permanent records, a completed tablet was dried or baked until hard and usually protected by a clay case or envelope. Practically indestructible when dried, these tablets have provided modern scholars with a wealth of information about this period. Among some of the numerous treasures are thousands of astronomical and mathematical records. For example, the ancient site of Nippur, once the location of an astronomical observatory established by the Assyrian kingdom, has alone yielded some fifty thousand tablets.

Another legacy from Sumeria and the Old Babylonian period was the sexagesimal number system. Thousands of tablets dating from about 1800–1600 BC illustrate a number system that would seem unfamiliar to the modern reader. Instead of the decimal system based on the number 10, the Babylonians used the number 60 as the base (hence the name ‘sexagesimal’). Many historians have tried to explain the use of this unusual system of numbers. One theory is that the predominant role of astronomy in Babylonian society was instrumental in the adoption of the sexagesimal system. For example, the solar year is approximately 360 days, a figure which can easily be expressed as 6 x 60. Whatever the origin, the sexagesimal system of numeration has enjoyed a remarkably long life. Remnants survive even today in our units of time, 60 minutes in an hour, and angular measure, 360 degrees in a circle, in spite of the nearly universal acceptance of the decimal system for other counting schemes.

The Old Babylonian period was a time of great advancement for the development of what could be called the ‘sciences’. Yet it was one ‘science’ in particular that characterised the Babylonians’ world view – astrology. From early on in this period these people looked to the heavens and attempted to discover some kind of order in the skies. By the beginning of the first millennium BC, the Babylonians had developed skywatching skills and utilised them in the making of a calendar and a system of mathematics, based on the sexagesimal system, to track and simulate the motion of the Sun and Moon.

The regularity of celestial events provided early civilisations with the best means for bringing order and understanding to the cosmos. Their cataloguing of the heavens enabled them to identify celestial cycles of time and thus to develop calendars. Their knowledge of the recurrence of the seasons for agriculture and of reference points in the sky for navigation was essential for a developing culture.

Other ancient civilisations, such as the Egyptians and the Chinese, had impressive constellation maps, and developed schemes for tracking the motions of the Sun and the Moon in their attempts to solve the problem of how the Moon’s motion was synchronised with the Sun’s. Though the Moon provides a very convenient time cycle for dividing up the year, it has no bearing on the all-important seasons, which depend on the Sun.

The Babylonians went further than others in their efforts to use the Moon’s cycle as a universal timekeeping device. They did this by studying the motion of the Moon as it orbits the Earth. Their observations were accurately and systematically recorded over long periods of time. Next, they searched their records for repeating patterns of the Moon’s motion, such as the phases it passed through in the course of a month, and the succession of positions on the horizon where it rose and set. Finally, they simulated these patterns using mathematical models to predict future positions. All this bears a surprising similarity to modern applied mathematical science. It may be hard to believe, but this is how the Babylonians studied the motion of the Sun and the Moon over three thousand years ago.