Note the reading: 相 here is xiàng (look at, observe / appearance), not xiāng - same character as in 看相 (fortune-telling by appearance). 星相术 is the older, traditional term; for Western zodiac astrology people usually say 占星术.
history
Imperial Chinese astronomy and astrology were inseparable for most of history - court 太史 officials watched the sky to predict dynastic fortunes, with eclipses and comets read as direct messages about the emperor's mandate.
