Astronomy is the science of objects in space — stars, planets, galaxies — studied by observation and physics. Astrology is the belief that the positions of those objects influence human lives and events. They share an ancient history and a Greek root, but astronomy is a science and astrology is not.
The core difference
- astronomy — the scientific study of celestial objects: what they are, how they move, what they are made of. Tested by observation and prediction.
- astrology — the belief that the positions of those objects at a given moment bear on human character and events.
Why they are so easily confused
For most of recorded history they were the same activity. Charting the sky accurately was necessary for both, and the same people did both work — Kepler cast horoscopes while deriving the laws of planetary motion. They separated as the scientific method took hold and astrology's predictions failed to survive testing.
The words themselves
Both take the Greek astron, star. The endings mark the split: -nomy from nomos, law — the laws governing the stars; -logy from logos, account or discourse — talk about the stars. The distinction is neatly encoded, though it postdates the split rather than causing it.
Using them correctly
Calling astrology "astronomy" or vice versa is a straightforward error. A horoscope is astrology. A telescope observation is astronomy.
Frequently asked questions
Is astrology a science?
No. It is a belief system. Its predictions have not held up under controlled testing, which is the line that separates it from astronomy.
Were astronomy and astrology ever the same thing?
Effectively yes, for centuries. Accurate sky-charting served both, and figures such as Kepler practised both before the two separated.
What do the words literally mean?
Both come from Greek astron, star. Astronomy adds nomos, law; astrology adds logos, discourse. So: the laws of the stars, and talk about the stars.