What does the prefix astro- mean?
Astro- comes from the Greek astron, which means "star". It is used for anything related to stars, space and celestial bodies. If a word starts with astro-, you can assume it is about the sky and the universe.
ESEN
Prefix · stars / space
astro-
Signals relation to stars or outer space: astronaut, astronomy, astrophysics, asteroid.
Scientific
Written by Bryan López, English teacher · Updated
Astro- in science today
Today astro- attaches to other branches of science to mean "that, but applied to space": the physics, biology or chemistry of what happens beyond Earth. That makes it a very productive prefix in science news and documentaries, and one you can use to guess brand-new words.
How it is used
Attaches to scientific nouns:
- astro- + person/fieldnaut → astronautnomy → astronomyphysics → astrophysicsbiology → astrobiology
- astro- + object/processnomy → astronomylogy → astrologyid → asteroidlabe → astrolabe
Pronunciation: /ˈæstrəʊ/.
How it is pronounced
astro-/ˈæstrəʊ/
Tap the button to hear how the prefix sounds. Each word in the table has its own audio.
Examples
Root word
With astro-
In a phrase
- nautastronautThe astronaut spent six months aboard the space station.
- nomyastronomyAstronomy reveals that the universe is about 13.8 billion years old.
- logyastrologySome people check their astrology horoscope every morning.
- physicsastrophysicsAstrophysics studies the nature and behaviour of stars and galaxies.
- idasteroidScientists monitor the asteroid belt for objects approaching Earth.
- biologyastrobiologyAstrobiology searches for conditions that could support life in space.
- labeastrolabeMedieval sailors used an astrolabe to find their latitude at sea.
Common mistakes
astronomy and astrology are the same
astronomy = a science; astrology = a belief system with no scientific basis
"Astronomy" is a rigorous science studying celestial bodies with empirical methods. "Astrology" is a belief system claiming that the positions of stars affect human personality and fate. The scientific community does not recognise astrology as a science.
astronaut = directly "explorer of the stars"
astronaut = "sailor of the stars" (astro = stars + naut = sailor in Greek)
"Astronaut" combines "astron" (star) with "nautes" (sailor, navigator). The same root "-naut" appears in "cosmonaut" (Russian/Soviet term for space sailor) and "taikonaut" (the term for Chinese astronauts).
A trick to remember it
Look up at the night sky: astro- = stars, space. astronaut, astronomy.
Practise what you learned
Exercise 1 · Form the word
Exercise 2 · Pick the right one
"An ___ is a rocky body orbiting the sun, smaller than a planet but larger than a meteoroid."
Exercise 3 · Pick the right one
What is the key difference between "astronomy" and "astrology"?
Frequently asked questions
What does the prefix astro- mean in English?
The prefix astro- signals relation to stars or outer space: astronaut, astronomy, astrophysics, asteroid.
How do you pronounce astro-?
The prefix astro- is pronounced /ˈæstrəʊ/. For example, "astronaut".
Can you give an example of a word with astro-?
"naut" becomes "astronaut". It is a typical example of the astro- prefix.
Other useful prefixes
cosmo-
From Greek "kosmos" (universe, order): appears in words about the universe and the world, like cosmology and cosmopolitan.
geo-
Signals relation to the Earth or geography: geography, geology, geometry, geothermal.
helio-
Means "sun": heliocentric, helium, heliograph, heliotherapy, heliosphere, heliostat.
Learn every English prefix
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