Merriam Webster
noun. as·trol·o·gy \ə-ˈsträ-lə-jē\
The study of how the positions of the stars and movements of the planets have a supposed influence on events and on the lives and behavior of people.

Urban Dictionary
The practice of predicting one’s attributes, past, and future from looking at the stars, planets, planetoids, moons, and pretty much anything in the sky.