The Seven and Nine Day Planetary Weeks

Seven-day groupings may have been present as quarters of the 28-day lunar mansion sequence or for other reasons at a fairly early date. This is suggested, for example, by the seven days of creation of the Hebrew Bible or the seven fires of Agni in Indian Vedic texts. However, the existence of a series of seven days directly associated with the planets in a fixed sequence is first clearly attested (in the Mediterranean) in the last century b.c. The sequence was Saturn, Sun, Moon, Mars, Mercury, Jupiter, and Venus. The structural reasons for the sequence were discussed in §4.1.3, and the order of the days of the week was illustrated in Figure 4.11. Their associated deities are given in Table 2.7, and a comprehensive survey of the names of the week is to be found in F.G. Richards (1998). Even in Mesoamerica, what seems to be the same arbitrary sequence of the planets appears on the lid of Pacal's coffin (see §12.5).

The image of the Sun as a charioteer (or driven by a charioteer) spread throughout the Mediterranean world, even to such unlikely places as the Beth-Shan synagogue. Presumably, the image derives from the regular pattern of movement in a chariot race, rather than from irregular movements of, say, engaged war chariots. Increasingly, there was a feedback effect from the creation of ever more elaborate racecourses designed as cosmic images. During the Byzantine period, astrological images seemed to dominate the design of hippodromes (Lindsay 1971, pp. 239-243). All planets were conceived at least by the 4th or 5th century a.d. to be drawn in chariots.

Indian planetary diagrams also show the planets in chariots drawn by animals (by no means always horses) and in China, the mythical Hsi-Ho (cf., §10.1.2) was sometimes regarded as the charioteer of the Sun and sometimes as the mother of the Sun (Needham 1959, p. 188).

When the seven-day week spread to India, it was adopted both in the seven-day form found elsewhere and in a unique nine-day form, incorporating two additional postulated invisible planets, Rahu and Ketu. The introduction of these additional planets, conceived as the causes of eclipses, implies a slightly more scientific interpretation than does an older view, in which eclipses were caused by a giant dragon whose head was called Rahu and tail was called (perhaps later) Ketu. Still later, they were interpreted as the ascending and descending nodes of the lunar orbit. In creating the nine-day week, the days Rahu and Ketu were simply added on to the normal sequence of the seven-day planetary week, although this nullified the mathematical basis on which the seven-day sequence had been constructed (see §4.1.3).

This nine-day week, with the seven-day week, was introduced to China in a translation of an early Indian Buddhist text and became a regular feature of Chinese calendrics. Despite its invention in India, the nine-day week never seems to have achieved the importance in India that it did in China.

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