astrology (n.)
late 14c., "calculation and foretelling based on observation of heavenly bodies," from Latin astrologia "astronomy, the science of the heavenly bodies," from Greek astrologia "astronomy," literally "a telling of the stars," from astron "star" (from PIE root *ster- (2) "star") + -logia "treating of" (see -logy).

Originally identical with astronomy and including scientific observation and description. The special sense of "astronomy applied to prediction of events" was divided into natural astrology "the calculation and foretelling of natural phenomenon" (tides, eclipses, dates of Church festivals, etc.), and judicial astrology "the art of judging occult influences of stars and planets on human affairs." Differentiation between astrology and astronomy began late 1400s and by 17c. this word was limited to the sense of "reading influences of the stars and their effects on human destiny."