calendar months.^20 The purpose and function of month-length prediction,
indeed, was not necessarily calendrical: it may have fulfilled a purely astrolog-
ical or astronomical role. The ability of astrologers, particularly in the later
period, to predict month-lengths long in advance with a reasonable degree of
accuracy does not mean that this is how the calendar was reckoned in practice.
The extent, therefore, to which the Babylonian calendar month was regu-
lated by new moon sighting or by new moon prediction is a complex question
that will be addressed below. I shall argue that until the neo-Assyrian period
(eighth–seventh centuries) the month was determined on the sole basis of new
moon sightings; but later, new moon predictions—and hence, the possibility
of setting the calendar in advance—were introduced.^21
The neo-Assyrian period (eighth–seventh centuriesBCE)Although, as mentioned above, the practice of predicting new moons (or
month-lengths) was already well established in the neo-Assyrian period, in
this period it appears to have been intended only for astrological purposes, and
not for the determination of calendar months.^22 Astrological omen lists of the
early seventh centuryBCEsuggest, indeed, that the month only began when the
new moon had actually been sighted.
This can be inferred in more than one way. Firstly, the omen lists lay down
that if the moon was sighted on day 30 (i.e. on the evening preceding day 30 of
the outgoing month), it‘rejected’the day (by turning it into day 1 of next
month);^23 whereas if the moon was not sighted on day 30, the day was‘not
rejected’but‘completed’(i.e. kept within the old month).^24 But the possibility
(^20) The Astronomical Diaries suggest that the criterion used for predicting new moon visibility
could not have been based on the sunset–moonset lag on its own, and hence did not conform to
the rules of TU11 (see previous n.). Indeed, some new moon predictions in the Diaries are
recorded with predicted sunset–moonset lags as low as 8º or 9º, whereas some predicted sunset–
moonset lags higher than 10º appear elsewhere to have been disregarded as evidence of new
moon visibility. This apparent inconsistency suggests that the new moon visibility criterion, or
the criterion for determining month-lengths, was not dependent on the sunset–moonset lag
alone; this does not necessarily mean, however, that it was more accurate than the new moon
visibility criteria of TU11. See further Stern (2008) 37 n. 12.
(^21) For a detailed presentation of the argument and evidence, see Stern (2008).
(^22) They may also have been intended for cultic purposes, as well argued by Beaulieu (1993)
and Brown (2000) 161–207. The astrological purpose of month-length predictions is evident in
Hunger (1992) (above, n. 16).
(^23) e.g. Hunger (1992) no. 53, reporting that on two consecutive months the moon had
‘rejected the day’. The notion that the moon itself, somewhat anthropomorphically, rejected
the day by appearing on day 30, emphasizes that it was the actual appearance of the moon that
determined the beginning of the month. 24
Ibid. no. 3.
78 Calendars in Antiquity