Seleucid Era

Definition

The Seleucid Era, abbreviated SE in Assyriological convention, is the continuous chronological dating system used throughout the Late-Babylonian astronomical cuneiform corpus — Astronomical Diaries, Babylonian Horoscopes, and the ACT mathematical-astronomy tablets — counting years from the regnal start of Seleucus I in 312 BCE. Year 1 SE corresponds to 311/310 BCE, and subsequent years are reckoned by adding to that base; the conversion convention used in modern editions is year X SE = (-312 + X)/(-311 + X) in the astronomical chronology.

In Tradition

Neugebauer, Rochberg, and Hunger-Pingree concur in treating the Seleucid Era as the standard internal dating system of the cuneiform astronomical corpus and the principal documentary anchor for the absolute chronology of Late-Babylonian astronomy. Neugebauer describes the era together with the 19-year cycle as one of the greatest advances in practical chronology — for the first time supplying a precise era in which dates could be established by simple computational rules rather than by the cumbersome counting of individual reigns.

In Practice

For the reader of Late-Babylonian astronomical texts and modern critical editions, the Seleucid Era is the chronological framework against which every observation, ephemeris-row, and horoscope is dated. Rochberg gives anchor equivalences SE 0 = 312/311 BCE, SE 50 = 262/261 BCE, and SE 400 = AD 89/90, and notes Ptolemy himself dated the Babylonian observations he reports in Almagest IX 7 "according to the Chaldeans" — i.e. in the Seleucid Era — confirming the era's role as the bridge through which Babylonian astronomy entered Greek tradition. Hunger and Pingree use SE dating pervasively (e.g. section one of a Jupiter ephemeris at 69 SE = -242/1; double-year notation reflects that the Babylonian year crossed two Julian years, beginning near spring equinox). Modern historians of the Hellenistic age inherit their chronology in part from Father Epping's decipherment of the Babylonian astronomical-text terminology in its relation to the Seleucid Era. Islamic astronomers continued to use the era — or the Era of Philip — into the medieval period.

Historical Origin

Adopted officially in the cuneiform astronomical corpus from approximately SE 9 onward and used continuously through the Seleucid and Parthian periods (c. 311 BCE to first century CE). Modern critical treatments: Otto Neugebauer, *The Exact Sciences in Antiquity* (1957/1969); *Astronomy and History: Selected Essays* (1983) essays [4] p. 81 and [7] p. 161; Francesca Rochberg, *The Heavenly Writing* (2004) Chronological References p. xxiii; Hermann Hunger & David Pingree, *Astral Sciences in Mesopotamia* (1999) p. 189.

Further Reading

• Otto Neugebauer, Astronomy and History: Selected Essays
• Francesca Rochberg, The Heavenly Writing: Divination, Horoscopy, and Astronomy in Mesopotamian Culture
• Hermann Hunger & David Pingree, Astral Sciences in Mesopotamia