What is the difference of an astronomer and an astrologer?

Astronomy is about universe and physics (a science). whereas astrology is about horoscope. Astronomer is someone who studies the universe, whereas an astrologer is someone who studies horoscope.

Astronomer = looks at the stars and their position (usually science or physics related)

Astrologer = uses the findings from astronomy to relate back to horoscopes and psychic abilities. Also used to tell someone's future.