What does astronomy mean?
Astronomy is the scientific study of celestial bodies — stars, planets, moons, comets, asteroids, nebulae, and entire galaxies — together with the phenomena that originate outside Earth's atmosphere. As one of the oldest natural sciences, it began with naked-eye observations of the night sky by ancient civilizations who used the heavens to mark time, navigate, and build calendars. Today it spans observational work with ground-based and space telescopes across the electromagnetic spectrum, as well as theoretical modelling of cosmic structures and origins. Astronomy is closely related to but distinct from astrophysics, which applies physical laws to explain astronomical observations, and it should not be confused with astrology, the non-scientific practice of divining human affairs from planetary positions. Practitioners are called astronomers. The word carries no emotional connotation; it is a neutral, learned term common in education, journalism, and scientific writing.
nounThe scientific study of celestial objects such as stars, planets, comets, and galaxies, and of phenomena originating beyond Earth's atmosphere.
- The branch of science that studies celestial objects, space, and the physical universe beyond Earth's atmosphere.
"She has loved astronomy ever since her father showed her Saturn's rings through a small telescope."
"Advances in radio astronomy have revealed structures invisible to optical telescopes."
"Ancient civilizations used astronomy to track the seasons and navigate at sea."
For most of history, 'astronomy' and 'astrology' were the same word — the split between science and star-signs only hardened a few centuries ago.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of astronomy
Astronomy derives from the Greek astronomia, formed from astron ('star') and nomos ('arrangement' or 'law'), so literally the 'law or arrangement of the stars'. The word passed into Latin as astronomia and entered English via Old French in the Middle Ages, becoming well established by the early modern period. It shares its Greek root astron with cognates such as astronaut, asteroid, and astrology, which originally denoted much the same body of knowledge before the two fields diverged.
Related word forms
How astronomy is actually used
A formal, neutral term used in both academic and popular contexts. It is an uncountable noun referring to the discipline as a whole; individual practitioners are astronomers. In everyday speech it is often loosely contrasted with astrology, though historically the two words overlapped considerably.
Easily confused with astronomy
Astronomy is the science of studying celestial objects, while astrology is the pseudoscientific practice of predicting human affairs from the positions of stars and planets.