Natural Knowledge in Ancient Mesopotamia 23fi rst invisibilities were ominous, as were the planets in retrograde, but not
their stationary points.
Probably before the formulation of mathematical predictive schemes,
goal- year texts exemplify a method of prediction by the use of synodic
periods. These tablets give dates of characteristic planetary (synodic) phe-
nomena and of planets’ passing by bright ecliptical stars for a certain year
(the goal year) by tallying those positions, culled from astronomical dia-
ries, an appropriate number of years before the goal year for the planet
(for example, Venus eight years before, or Jupiter seventy- one years). In
seventh- century BCE Assyrian sources as well, the use of planetary periods
as a way of anticipating certain celestial phenomena deemed ominous
is well documented in the scholars’ correspondence with the Sargonids.
This “nonmathematical” method of astronomical prediction was differ-
ent from that of the mathematical astronomy developed later, in which
the behavior of celestial phenomena was subject to more rigorous math-
ematical description. Aside from a few exceptional planetary daily motion
ephemerides, the Babylonian mathematical astronomical texts did not
tabulate positions of celestial bodies between synodic “events.”^25 Con-
sequently they do not appear to have been designed with horoscopy in
mind, since a horoscope requires the positions of the seven planets for an
arbitrary time, namely, the date of birth.
Because the zodiac provided the basic and primary reference point for
astronomical data recorded in horoscopes, the usefulness of astronomical
sources to those who wrote the horoscopes can be assessed in terms of
their use of this reference system. Because most of the planetary positions
recorded in the diaries represent observations, these are reckoned some
number of cubits (1 cubit = 2 1 / 2°) with respect to (in front of, behind,
above, and below) a group of about thirty ecliptical stars (e.g. “night of
the 7th beginning of the night, the moon was 2 / 3 cubit in front of ε Leo-
nis”)^26 A systematic relationship between such observational statements
and positions with respect to degrees of the zodiac, which are not strictly
speaking observable, has not been determined, and so we are not certain
if the ancients had a method of converting cubits with respect to the
“normal stars” to degrees of the zodiac.^27 The diaries, however, include an
enumeration of the zodiacal signs in which the planets are found during
a given month, with dates of entries into signs, and so could conceivably
have been practical for the construction of horoscopes.
Some horoscopes give planetary positions in degrees of the zodiac. The
only astronomical text genre in which data are given in this form are the eph-
emerides, although, as mentioned above, the methods employed in these