A large number of the astronomical observations in the Babylonian diaries are occurrences
of close conjunctions of moving objects, such as the Moon or planets with bright stars, in
the vicinity of the ecliptic. In 1995, Graßhoff proposed the hypothesis that the observations
fit best when one assumes that the Babylonians used an ecliptical coordinate system. In the
following we present a test that excludes an equatorial coordinate system as an alternative
system of measurement.