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Heraclitusstudent says

That makes predicting the motion of planets kind of difficult.

Difficult, but not impossible. The Antikythera mechanism, thought to have been built by the workshop of Archimedes more than 2000 years ago, cranked out the apparent positions of the visible planets (plus the sun and moon) quite accurately. The moon was accurate to nine decimal places, particularly impressive considering its elliptical orbit. The success was especially surprising when you consider that the layout reflected the religious belief at the time (doubted by Aristarchos, who was condemned as a heretic) that the earth was at the center of the solar system.

http://video.pbs.org/video/2364988981/

curious2 says

Heraclitusstudent says

That makes predicting the motion of planets kind of difficult.

Difficult, but not impossible.

Basically impossible given enough time.
The Greeks achievements are certainly impressive. Too bad they fell into the dark ages.