What is "anno mundi"

a. (context of a year English) count from the creation of the world.

( Latin for "in the year of the world"; Hebrew: , "from the creation of the world"), abbreviated as AM or A.M., or Year After Creation, is a calendar era based on the biblical accounts of the creation of the world and subsequent history. While numerous efforts have been made to determine the biblical date of Creation, yielding varying results, two in particular have established epochs for significant calendars, including one that is still in use today.

The Hebrew calendar epoch is based on twelfth-century CE rabbinic estimates for the year of creation, which are calculated from data obtained in the Hebrew Masoretic text. This calendar is used within Jewish communities for religious and other purposes. On the Hebrew calendar, the day begins at sunset. The calendar's epoch, corresponding to the calculated date of the world's creation, is equivalent to sunset on the Julian proleptic calendar date 6 October 3761 BC. The new year begins at Rosh Hashanah, roughly in September. Year anno mundi , or AM , began at sunset on on the Gregorian calendar.

The Byzantine calendar, used for over 1000 years in the Byzantine Empire and many Christian Orthodox countries and Eastern Orthodox Churches, based its epoch on seventh-century (or earlier) calculations from data found in the Septuagint text, an early Greek translation of the Hebrew Bible that was made by Alexandrian Jews and adopted by Christians. That calendar is actually the Julian calendar itself, except for the eastern-derived epoch of year counting in place of the western AD/BC epoch, and a different new year's date, 1 September. It proposed that the creation occurred 5509 years before the Incarnation, so its epoch is equivalent to 1 September 5509 BC on the Julian proleptic calendar.

While differences in biblical interpretation or in calculation methodology can produce some differences in the creation date, most results fall relatively close to one of these two dominant models. The primary reason for the disparity seems to lie in which underlying Biblical text is chosen (roughly 5500 BC based on the Greek Septuagint text, about 3750 BC based on the Hebrew Masoretic text). Most of the 1,732-year difference resides in numerical discrepancies in the genealogies of the two versions of the Book of Genesis. Patriarchs from Adam to Terah, the father of Abraham, are said to be older by as much as 100 years or more when they begat their named son in the Greek Septuagint than they were in the Latin Vulgate (; ) or the Hebrew Tanakh (; ). The net difference between the two major genealogies of Genesis is 1466 years (ignoring the "second year after the flood" ambiguity), 85% of the total difference. (See Dating creation.)