Natural Knowledge in Ancient Mesopotamia 21That is, the gods were thought to communicate with humankind through
the behavior of physical phenomena, which in turn became intensely
signifi cant objects of observation and analysis. The results of such inquiry
in the realm of celestial phenomena were the development of empiricism,
mathematical theoretization of astronomical problems, and methods of
predicting the phenomena.
An important astronomical work preceding the development of the
late mathematical astronomy by many centuries is the two- tablet com-
pendium MUL.APIN, which compiles the astronomical material required
to understand Enu ̄ma Anu Enlil.^16 Stars and constellations were classifi ed
in accordance with paths in the sky in which they are seen to rise and set.
Three such paths were demarcated and named for the gods Anu, Enlil, and
Ea. In our terms, the Path of Anu is reckoned as the arc over the horizon
where stars roughly 15 degrees on either side of the celestial equator rise
and set, the Path of Enlil is to the north of this arc, and the Path of Ea is
to the south. MUL.APIN also lists the simultaneous rising and setting of
constellations and fi xed stars in the three paths, season by season, and
intervals of visibility and invisibility of planets.^17
Perhaps most clearly representative of a desire to render celestial
phenomena amenable to mathematical description in the period before
500 BCE, is Enu ̄ma Anu Enlil 14, which contains no omens but instead
provides an arithmetical scheme concerning the duration of visibility of
the moon each night.^18 Underlying the lunar scheme of Enu ̄ma Anu Enlil
14 was a simple scheme for the duration of daylight in relation to the
schematic calendar month of thirty days. The length of day was not un-
derstood to be a function of the motion of the sun in the ecliptic, but the
result of a division of the schematic year into four symmetrical “seasons”
organized around the two days when day and night are of equal length
(equinoxes) and the longest and shortest days (summer and winter sol-
stices) which differ from the length of daylight at the equinoxes (3 units)
by ±1 unit (that is, the length of day at equinox is 3, summer solstice is 4,
and winter solstice 2). The ratio of longest to shortest day was therefore
2:1. In relation to this daylight length scheme, the duration of visibility
of the moon at night, time between sunset and moon set for the fi rst half
of the month and between sunset and moon rise for the second half, was
arithmetically schematized.^19 Suffi ce it to say here that Enu ̄ma Anu Enlil
14 is signifi cant for the history of astronomy in that it represents the
development of a quantitative methodology applied to solving several as-
tronomical problems—here, the variation in the length of day (and night)
and the variable duration of visibility of the moon each night due to its
elongation from the sun as well as the variable length of night through-