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The term “Babylonian astronomy” is used to refer to a diverse range of practices undertaken by people in ancient Babylonia and Assyria including what in modern English would be referred to as astronomy, astrology and celestial divination, and cosmology. The earliest astronomical or astrological texts preserved from Babylonia and Assyria date to the early 2nd millennium bce, although some basic astronomical knowledge such as the identification of a regular cycle of the moon, the identification of the planets as a distinct type of celestial object from the stars, and the grouping of stars into constellations dates back much earlier, perhaps even before the development of writing in the 4th millennium bce. Astronomical and astrological texts were still being written around 2,000 years later during the 1st century ce. These texts are some of the latest known texts written in cuneiform. Babylonian astronomy encompassed a range of practices, including the cataloguing of stars and constellations, the regular observation of celestial phenomena, the development and use of methods of predicting those same phenomena, and the interpretation of observed and computed astronomical data through various forms of astrology.

During the Hellenistic and Roman periods, tables were extensively employed in Graeco-Roman astronomy to present structured, quantitative astronomical data for reference, calculation, and display of patterns of data. Media for tables included papyrus, in roll or codex format, wooden boards, and occasionally inscriptions. Aside from their didactic function in writings on theoretical astronomy such as Ptolemy’s Almagest, the chief practical applications of astronomical tables were in astrology. Tables for calculating celestial positions and phenomena of the heavenly bodies represented two distinct traditions: an originally Babylonian tradition based on arithmetical operations and a Greek tradition, best known from Ptolemy’s works, based on trigonometry relating to geometrical theories for the motions of the Sun, Moon, and planets. Both traditions made use of sexagesimal place-value notation. Additionally, almanacs and calendrically structured ephemerides presented celestial positions calculated over long spans of dates as a convenient tool for horoscopy and the astrological evaluation of days.

The Antikythera Mechanism (National Archaeological Museum, Athens, inv. X 15087) was a Hellenistic gearwork device for displaying astronomical and chronological functions. Substantial but highly corroded remains of the instrument were recovered from an ancient shipwreck (see Figure 1).

The most complex scientific instrument to have survived from antiquity, it resembled the sphaerae or planetaria described by Cicero (1) and other Greco-Roman authors. The date of its construction is in dispute but must have been earlier than the middle of the 1st centurybce and can scarcely have been before the end of the 3rd centurybce. It is an invaluable witness for ancient mechanical technology at its most advanced level (see mechanics) as well as for Hellenistic astronomy.