I always get astronomy and astrology mixed up! Which is which? Can an astrologer do astronomy and vice versa?
Astrology is a pseudo-science which claims that the positions of the heavenly bodies have an effect on the lives of human beings and events on Earth.
A long time ago, astronomy and astrology were the same. People studied the motions of the planets and hoped to used them to predict not only the behavior of the heavens, but also wars, natural disasters, the rise and fall of kings, and other earthly matters. However, around the time of Johannes Kepler, Galileo Galilei and Isaac Newton, astronomers came to realize that astrology was basically bunk. From that time on, the primary job of an astronomer was to use physics to understand what was going on in the sky.
Some people stuck to astrology, though. Astrologers use computer programs that tell them the positions of the planets (using the work of real scientists, incidentally), and they do not look through telescopes or learn about stars and planets and galaxies and so forth like astronomers do--except perhaps for fun.
Astrology has many of the trappings of real science, like math and complicated diagrams and a specialized vocabulary, but astrologers do not follow the scientific method. Real scientists make careful measurements in well-controlled studies. Astrologers don't do experiments to prove their theories. Instead, they like to provide anecdotal evidence--stories people tell about how accurate they think astrology is. Anecdotal evidence is not acceptable in a real science because it's too easy to leave out all the negative experiences people have, and people not very good at recalling and accurately reporting experiences.
Don't refer to an astronomer as an astrologer!
This answer was last updated on June 17, 2015.