19-year cycle

NINE-teen yeer SY-kuhl

babylonian: 19-year cycle (modern scholarly term; cuneiform texts encode the relation as 235 synodic months ≡ 19 years with a 7-in-19 intercalation pattern)

Definition

The 19-year cycle is the Babylonian luni-solar period relation that 235 synodic months agree closely with 19 years, so a lunar calendar is kept in step with the seasons by adding seven intercalary thirteenth months across every 19-year span. The same relation later named the Metonic cycle in Greek tradition is, in its earlier Babylonian form, equated with 19 sidereal years rather than 19 tropical years.

In Tradition

Neugebauer, Rochberg, and Hunger-Pingree concur in treating the 19-year cycle as a Babylonian achievement of the Achaemenid period — Britton, cited by Rochberg, places its first attested use under Cyrus in 530 BCE and its standardization under Xerxes in 484 BCE. Rochberg notes that the cycle is mathematically equivalent to the later Uruk solstice-scheme used in horoscopes for computing solstice and equinox dates.

In Practice

For the reader of the cuneiform astronomical corpus, the 19-year cycle is the chronological skeleton on which Late-Babylonian calendar computation rests: a fixed pattern of 7 intercalary years in 19 (the arithmetic 19·12 + 7 = 235) keeps the new year inside a narrow window of vernal longitude, where before its introduction irregular intercalations had let the year-start drift widely. Neugebauer, in essay [7], names the 19-year cycle together with the Seleucid Era as one of the greatest advances in practical chronology, supplying for the first time a precise era in which dates could be established by simple computational rules. The cycle is the recurrence period of the Seleucid-period observation-text scheme for computed solstices and equinoxes, and the same period the medieval Golden-Number Easter calendar inherits via the Jewish Passover calendar. The Babylonian astronomers themselves, Neugebauer emphasises in essay [41], were aware the cycle was approximate and used refined non-cyclic methods for true lunations, retaining the cycle as a convenient civil-calendar arrangement.

Historical Origin

Attested in cuneiform calendar practice from the Achaemenid period (first occurrences c. 530 BCE under Cyrus; standardized c. 484 BCE under Xerxes) through the Seleucid-Parthian mathematical-astronomy programme. Modern treatments: Neugebauer, *The Exact Sciences in Antiquity* (1957/1969) Ch. I p. 7; *Astronomy and History: Selected Essays* (1983) essays [7] p. 161, [34] p. 390, [41] p. 515, [43] p. 532; Rochberg, *The Heavenly Writing* (2004) p. 56 and pp. 154+163-164; Hunger-Pingree, *Astral Sciences* (1999).

Definition

In Tradition

In Practice

Historical Origin

Further Reading