of intercalations and is clearly inadequate for a lunar calendar; it has also been
argued that the other rules in MUL.APIN (e.g. that of the Pleiades) are
similarly inaccurate and possibly derived from the three-year rule, which
may suggest that these rules belonged to a simplified or idealized astronomical
scheme typical of MUL.APIN that was not intended for practical calendrical
use.^94 In practice, however, the conjunction of the moon with the Pleiades
could still have afforded a reasonably accurate criterion for intercalation,
provided it was determined through empirical observation rather than by
relying on the simplified, schematic calculations of MUL.APIN.^95 Similar
intercalation rules are also implicit in theBabylonianDiviner’s Manual;^96
whilst Balasî, in the letters cited above, uses Jupiter and the stars to determine,
very much in practice, the intercalations.^97
The use of astronomical criteria for setting intercalations was not always
driven by a concern for calendrical accuracy; in most cases, it was driven
rather by astrological concerns. A number of sources, such as the letters of
Balasî, suggest that intercalations were primarily made to prevent certain
astronomical events from occurring in inappropriate (hence unpropitious)
months, where they would have been interpreted as bad omens (Brown 2000:
121 – 2, 150–1, 195–6). These astrological motivations, however, would have
resulted in maintaining the lunar calendar, through intercalation, in a stable
relationship with the stellar year. Indirectly, astrology would thus have played
an important part in the regulation of the Babylonian calendar.^98
another intercalation scheme in MUL.APIN II i 22–4 (pp. 76–7), which states:‘assess how many
days are in excess’. They interpret this as meaning the excess of days in a solar year over a lunar
year, which brings about the need for intercalation. However, it is equally possible (and perhaps
more likely) that this passage refers to the excess of days between the ideal, 360-day year (see
above, near n. 56) and the lunar year, or between the solar year and the 360-day year; calculation
of these excesses would have been necessary for translating the ideal astronomical information
contained in MUL.APIN into real astronomical data (on this procedure see Brack-Bernsen 2007:
97 – 8).
(^94) Brown (2000) 119 n. 304. Similar arguments apply to the‘Astrolabe’texts: for a summary,
see Lehoux (2007) 103 95 – 6.
If accurately followed, this rule would lead to an average drift from the seasons of about
one day in 70 years (because of the precession of equinoxes), which is arguably not excessive. 96
Britton andWalker (1996) 46; Brown (2000) 120–1 (the date of this work is similar to
MUL.APIN). 97
For an explanation how Jupiter could have been used to regulate intercalation, see Brown
(2000) 196, and 121 and 197 for the suggestion that true equinoxes were observed for the
purpose of calendar regulation; but explicit evidence is lacking (the mention, in the context of
intercalation, of the‘first appearances of the sun and moon in months XII and VI’in the
BabylonianDiviner’s Manualis not necessarily a reference to the equinoxes; the significance of
these months is only that they can be intercalary).
(^98) PaceBrown, who argues that the use of astrological criteria would, if anything, have
disrupted the calendar.
98 Calendars in Antiquity