ECLIPSES IN HISTORY

Eclipses in history In ancient and medieval times, eclipses of both the Sun and the Moon were often regarded as portents; hence, it is not surprising that many of these events are mentioned in history and in literature, as well as in astronomical writings. Well over 1,000 individual eclipse records are extant from various parts of the ancient and medieval world. Most known ancient observations of these phenomena originate from three countries: Babylonia, China, and Greece. No records appear to have survived from ancient Egypt or India. Whereas virtually all Babylonian accounts of eclipses are confined to astronomical treatises, those from China and Greece are found in historical and literary works as well. Eclipses are noted from time to time in surviving European writings from the early Middle Ages. At this time only the Chinese, however, continued to observe and record such events on a regular basis, and this tradition continued almost uninterrupted down to recent centuries. Many eclipses were carefully observed by the astronomers of Baghdad and Cairo between about AD 800 and 1000. About AD 800 both European and Arab annalists began to include in their chronicles accounts of eclipses and other remarkable celestial phenomena. Some of these chronicles continued until the 14th or 15th century. Toward the end of this period, European astronomers commenced making fairly accurate measurements of the time of day or night when eclipses occurred, and this pursuit spread rapidly following the invention of the telescope. The value of ancient and medieval records may be classified as follows, although it should be emphasized that there is some overlap between these individual categories: (1) literary and historical, depending on the interest that these records aroused and their connection with historical events; (2) chronological, insofar as they make it possible to verify chronological systems resting on other evidence and to supply dates for events concerned with eclipses; and (3) astronomical, including the determination by ancient astronomers of the periods and motions of the Sun and the Moon and by modern astronomers of variations in the length of the mean solar day. The Sun is normally so brilliant that the casual observer is liable to overlook those eclipses in which less than about 80 percent of the solar disk is obscured. Only when a substantial proportion of the Sun is covered does the loss of daylight become noticeable. Hence it is rare to find references to small partial eclipses in literary and historical works. At various times, astronomers in Babylonia, China, and the Arab lands systematically reported eclipses of small magnitude but their vigilance was assisted by their ability to make approximate predictions. They thus knew roughly when to scrutinize the Sun. Arab astronomers sometimes viewed the Sun by reflection in water to diminish its brightness when watching for eclipses. The Roman philosopher and writer Seneca (c. 4 BCAD 65), on the other hand, recounts that in his time pitch was employed for this purpose. It is not known, however, whether such artificial aids were used regularly. When the Moon covers a large proportion of the Sun, the sky becomes appreciably darker and stars may appear. On those rare occasions when the whole of the Sun is obscured, the sudden occurrence of intense darkness, accompanied by a noticeable fall in temperature, may leave a profound impression on eyewitnesses. Total or near-total eclipses of the Sun are of special chronological importance. On average, they occur so infrequently at any particular location that if the date of such an event can be established by historical means to within about a decade, it may well prove possible to fix an exact date by astronomical calculation. The Full Moon is much dimmer than the Sun, and lunar eclipses of even quite small magnitude are thus fairly readily visible to the unaided eye. Both partial and total obscurations are recorded in history with comparable frequency. As total eclipses of the Moon occur rather often (every three or four years on average at a given place), they are of less chronological importance than their solar counterparts. There are, however, several notable exceptions to this rule, as will be discussed below. Literary and historical references Old Babylonian The earliest known references to eclipses for which dates can be established with reasonable confidence go back to the 21st century BC. These are recorded on the series of astrological tablets from Ur known as Enuma Anu Enlil. Several of these texts contain lunar eclipse ominawarnings of disasters that might follow an eclipse based on past coincidences between celestial and terrestrial occurrences. Some of the omina are so detailed that they are clearly based on observation of a specific eclipse. The example cited below is found on tablet 20 of the series: From a careful investigation of the historical and astronomical circumstances, it has been shown that the eclipse referred to here is very likely to have been associated with the murder of Shulgi by his son and the accession of Amar-Sin. The most probable date for the eclipse is April 4, 2094 BC. A further lunar eclipse 42 years later regarded as signaling the destruction of Ur has been dated to April 13, 2053 BC.