  The geocentric universe, in its most developed form as set out by Ptolemy,
was a remarkably successful and coherent theory. It did not, however, specify
the order of the planets, that is, which was closer to Earth and which farther
away. One would naively think that seeing one planet pass in front of another
would settle the matter. In practice such mutual phenomena happen too rarely
for them to have been useful. Even in principle, it turns out that most
naked-eye observations of a central event would show nothing conclusive, with
the exception of some occultations by Venus that would demonstrate it to be the
lowest (nearest) planet. However, if one's theory were good enough to allow
conclusions from {\it not} seeing changes, one could find that Mars is probably
lower than Jupiter and Saturn, and possibly that the overall order is
Venus-Mars-Jupiter-Saturn-Mercury.
