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Introduction to Babylonian Astronomy


(De Jong 2016; Ossendrijver 2012:3f.)

Astronomical texts were first understood by J. Epping who had been working with Late Babylonian texts copied and sent to him by J. N. Strassmaier. Their collaboration led to the first book on Babylonian astronomy (Epping 1889). Still mostly based on copies by Strassmaier, F. X. Kugler could successfully decode more and more observational and computational texts (Kugler 1900; 1907-24).

These works provided secure identifications of the names of planets and stars. This made it possible to see more of the astronomical reality on which celestial omens were based (as far as they were). Hundreds of these omens were published in the last part of the 19th century, mainly from the excavations in Nineveh and other tablets in the British Museum. An edition of what was available then was produced by Ch. Virolleaud (1905-12). Much of the astronomy involved was explained by F. X. Kugler and J. Schaumberger. In the meantime, many more sources were identified, especially by E. Weidner. New editions of some of the omens were done by E. Reiner and D. Pingree (1975-2005), F. Rochberg (1988), W. van Soldt (1995), L. Verderame (2002), and others.

Continuing the work of Kugler on mathematical-astronomical texts, O. Neugebauer began to prepare an edition of all of them in the 1930ies; it appeared in 1955. He described Babylonian astronomy in the larger context of ancient mathematical astronomy in 1975. With more material again, new readings, and improved interpretations, M. Ossendrijver edited and explained the procedure texts within this corpus in 2012.

Numerous articles on details of the astronomical texts were also published. References can be found on the website, or e. g., in Ossendrijver 2012.


Astral phenomena occurring in Mesopotamian astronomical texts:

a) Stars: Lists of stars (or constellations) according to their place in the sky; rising and setting (calendar dates of first and last visibility, stars rising simultaneously); culmination

b) Planets: First and last visibilities, stationary points (where applicable), periods, path among the stars

c) Moon: Path among the stars; first and last visibilities; length of month; eclipses

d) Sun: Length of daylight, shadow of a stick in the course of the day, path among the stars

Lexical texts:

Celestial bodies are included in the thematic list ḪAR-ra = ubulluTablet XXII (p. 30f. in Reiner and Civil 1974; von Weiher 1988 No. 114A v 10-67); a new parallel Fadhil and Hilgert 2007:98-100 IM 132506 v 4´-vi 22´ has a similar but often deviating sequence of entries. The sequence of both sources is partly parallel to Mul-Apin.

The list is nevertheless far from being a complete star catalogue.

Most preserved exemplars of this part of HAR-ra are from the 1st millennium, but forerunners from Nippur (Reiner and Civil 1974 p. 107f.:387-410) and other places (ibid. p. 133f. ix 1-10; p. 136 rev. ii´ 1´-8´; p. 137 r. ii 1´f.; p. 143 x 13-28; p. 144 iii 1-9) show that it is based on lists from Old-Babylonian  times.

Texts describing the sky and its phenomena – apart from omens – first appear in the second half of the 2nd millennium BC. We have the star lists of the so-called Astrolabes (Horowitz 2014), of which the earliest exemplar P281769 dates to the 12th century. Other texts (Mul-Apin and similar) are preserved on tablets P479385 from the 8th and 7th century onwards, but probably go back to the 14th century (see the article on Schematic Astronomy).

Description of constellations:

There is one published text from Assyria (8th – 7th c. BC) that describes constellations in words (VAT 9428, Weidner 1927). In Hellenistic times, pictures of constellations were drawn on a few tablets (Weidner 1967). In some texts, relations between stars are expressed by geometrical figures (in a loose sense); these are only partly understood (Pingree and Walker 1988; Walker, Welt des Orients 26, 27-42). Whether K 8538 P397674 with its drawings has an astronomical or rather a magical purpose, is disputed (Koch 1989).

Time measurement

a) Calendar:

The Babylonian calendar is based on two clearly defined units: the day and the month. The Babylonian day begins at sunset. It can be divided into daylight and night; each of these, into three watches. The Babylonian month begins with the evening on which the crescent moon is seen for the first time after the conjunction of sun and moon. Such a month has either 29 or 30 days. Apart from day and month, the Babylonian calendar uses years. A year contains an integer number of months, usually 12. But 12 lunar months add up to only about 354 days. Such a year  is very quickly out of step with the course of the sun, and therefore with the seasons. In order to keep the seasonal events at the same place in the calendar year, a month was added to the year whenever it was thought to be necessary. Therefore some years had 13 months. The decision when a month had to be intercalated lay with the king. Until about 500 BC, intercalation was slowly becoming more and more regular. Then, an intercalation cycle of 19 years was introduced which contained 7 additional months in a fixed pattern so that one could know in advance which years would be intercalary. See Steele 2011:334f. – There are no weeks in Mesopotamia.

In Assyria, the calendar is a lunar calendar as in Babylonia. There are however different month names. It is likely but not completely proven that there was no intercalation in Assyria, at least in some periods. By the time of Tiglat-pileser I (12th century), intercalation appeared in Assyria too, and both calendars were synchronized.

b) Subdivision of the day:

Time is measured either in units of weight or of length. In weight, 1 mana  = 60 šiqil (about ½ kilogram) measures 4 of our hours. In length, 1 bēru = 30 UŠ (about 10,8 km) is 2 hours. 1 UŠ = 1 šiqil is therefore the equivalent of 4 minutes. UŠ (of unknown reading) is also a measure for 1 degree of arc.

There is one text using seasonally varying hours (of which there are 24 in one day) inscribed on an ivory prism from Neo-Assyrian times (Smith 1969).

The variation of the length of daylight is first described in an Old Babylonian tablet (Hunger and Pingree 1989:163f.). There the longest day is assumed to be twice as long as the shortest. This ratio 2 : 1 remains the norm throughout most of Babylonian history. Only some astronomical texts from the 1st millennium BC use 3 : 2, which corresponds better to the situation in Mesopotamia.

For details, see the article on Schematic Astronomy.



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