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Which Babylonian years received intercalary months in the 19-year cycle?
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First complete printed title page for the Kalendarium (“Calendar”) by Regiomontanus, 1476.
In the 19-year cycle established around 380 BCE, Babylonian calendar calculators implemented a system of intercalation to reconcile the lunar year with the solar year. Within this cycle, an extra month was added in the 3rd, 6th, 8th, 11th, 14th, 17th, and 19th years.1
The specific intercalary months used were as follows:
- Adaru II: This month was intercalated in six of the seven designated years (the 3rd, 6th, 8th, 11th, 14th, and 19th years of the cycle).1
- Ululu II: This month was inserted specifically in the 17th year of the cycle.1
This regularized system ensured that the beginning of the year, Nisanu 1, remained aligned with the spring equinox.21