Eclipse: The science and history of nature's most spectacular phenomenon. J. McEvoy P.

       THE BABYLONIANS, CHRONICLERS OF ECLIPSES

       How much is one god beyond the other god?

      Old Babylonian astronomical text

      CLAY FROM BAGHDAD

      During the 1870s and early 1880s, numerous clay tablets from Babylonian archaeological sites found their way to antique dealers in Baghdad. The tablets had been found in the ruins of the ancient Assyrian city of Nineveh, where they had once formed part of the royal archive in the most famous library in the ancient Near East. The library was built by King Assurbanipal, who reigned during Assyria’s ascendancy in the eighth century BC. This historical treasure was preserved for future scholars when a combined force of Medes and Chaldeans sacked Nineveh in 612 BC destroying the library completely and burying the royal archive in the process.

      The Babylonian empire was situated between the two great rivers, the Tigris and the Euphrates, in an area historically known as Mesopotamia – the ‘land between two rivers’. Flowing south-eastward, the rivers converge to form a single valley, then proceed in parallel channels for the greater part of their course. Finally, they unite shortly before reaching the Persian Gulf. The joint delta of these rivers forms a plain about 275 km long. As in Egypt with the Nile, the delta offered many advantages to early people, continually attracting settlements for thousands of years. The fertile valley yielded abundant harvests, workable clay and the nutritious fruit of the date palm. Though large stone deposits were lacking, the early settlers used the local clay for building and even for writing material.

       Figure 2.1. The Near East: Mesopotamia, the valley ‘between the two rivers’.

      Wars were frequent in ancient Mesopotamia as tribes of hunters from the northern mountains and herdsmen from the south often tried to conquer this rich land. The Sumerians, the earliest inhabitants for whom there are written records, had entered the region by 3700 BC and gradually settled down to a life of farming. The Sumerians are credited with developing the earliest known form of writing.

      In the 1880s, the British Museum purchased virtually all the clay tablets from Baghdad via London antique dealers. It was soon realised that among this vast collection were stories of the creation of the world and the great flood, as well as thousands of short texts on mathematics and astronomy. The latter texts contained records of astronomical observations made over hundreds of years in Assyria and Babylonia, and dating back to the third millennium BC. Today over a hundred and thirty thousand of these tablets are still stored at the Museum. It is an astonishing collection that comprises at least 98 per cent of all extant records of Babylonian astronomy.

      One set of seventy tablets from Nineveh revealed a vast programme of astronomical observations which had been carried out in the second millennium BC. Known from its opening words as Enuma Anu Enlil (‘When Heaven and Earth …’), the set is a list, compiled over centuries, of celestial omens believed to have been sent to the king from the gods, warning him of impending disasters. Most of the tablets deal with interpretations of lunar and solar eclipses, conjunctions of planets, and comets, which the Babylonians took as dangerous omens.

      OLD BABYLONIAN PERIOD

      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.

      CELESTIAL OMENS AND DIVINATION

      However, developing a lunar–solar calendar was relatively simple compared with their deeper goal. Their aim in studying the motions