The Anno Mundi era and the “missing years”

Anno Mundi

The Hebrew year number is the Anno Mundi (AM) year — years counted “from the creation of the world”. hebrewcal.eras.anno_mundi exposes this directly:

>>> from hebrewcal import HebrewDate
>>> from hebrewcal.eras.anno_mundi import anno_mundi_year
>>> anno_mundi_year(HebrewDate(5785, 7, 1))
5785

AM conversion is computationally exact and unambiguous — it is simply the Hebrew calendar arithmetic documented in Hebrew calendar internals.

The “missing years”

There is a well-known discrepancy between the traditional Hebrew chronology and the academic-historical one for the Persian period: the traditional reckoning compresses that era and ends up roughly 165 years shorter. (See the Wikipedia overview.)

hebrewcal takes a deliberate stance:

AM years are computed exactly and the discrepancy is documented, not silently corrected. This keeps the library correct for religious use (which follows the traditional count) while being honest for academic use.

>>> from hebrewcal.eras.anno_mundi import traditional_vs_academic_gap, MISSING_YEARS_NOTICE
>>> traditional_vs_academic_gap()
165
>>> print(MISSING_YEARS_NOTICE)
The traditional Anno Mundi reckoning differs from academic-historical chronology by about 165 years for the Persian period (the 'missing years'). hebrewcal computes AM years exactly and does not silently correct this discrepancy; consumers needing historical alignment should apply the gap explicitly. See the project specification for details.

How to use the gap

If you are aligning Hebrew AM years with secular historical dates in the first millennium BCE, apply traditional_vs_academic_gap() explicitly in your own code, and document that you have done so. hebrewcal will never apply it for you, because for the modern and medieval periods — and for all religious use — the traditional count is exactly what you want.