Astronomy Terms

Astronomy terms are used to describe the various phenomena in space. In this section you can learn what every astronomy term means and how it helps us to better understand the cosmos.


Scientists are still trying to figure out the essence of dark matter. If they do, will it lead only to greater understanding, or can we develop new technologies?

Everyone knows that nothing travels faster than the speed of light, but how does the speed of dark compare? Read on to find out!

If you have a theory that potato chips are making you fat (with the proof being your expanding waistline), you've just used two scientific terms in a very unscientific way.

You've heard of the big bang, of course, but do you have any idea as to what was happening during that massive flurry of activity billions of years ago?

So much of our cosmological history starts with the much-discussed big bang, but what led up to that cataclysmic moment? And did time even exist back then?

Every day, astronomers unravel a little more of the universe's inner workings, but the jury is still out on 95 percent of its contents.

Quasar, or Quasi-stellar Object (QSO), a starlike object displaying an unusually large red shift.

Magellanic Clouds, three irregularly shaped galaxies that lie some 150,000 to 200,000 light-years from earth.

Aberration of Light, a phenomenon in which a star or other celestial body, as viewed from the earth, appears to be slightly displaced from its true position.

Albedo, in astronomy, the reflecting power of a celestial body that is not self-luminous.

Andromeda Galaxy, a spiral galaxy that is larger than the Milky Way (the galaxy to which Earth belongs) but similar to it in structure, and the closest to ours.

Eros, a small asteroid (minor planet) discovered in 1898. It was the first asteroid known to come closer to the earth than the planet Mars.

Astrogeology, the science that applies the principles of geology to the study of solid bodies of the solar system other than the earth.

Transit, in astronomy, the passage of one celestial body across the disc (face) of a larger, more distant body, or across the observer's meridian.

Astrophysics, the application of the theories and techniques of modern physics to astronomy.

Autumn, or Fall, the season of the year that follows summer and comes before winter.

Azimuth, the horizontal direction of an object, measured clockwise in degrees, minutes, and seconds of arc from true north or south along the theoretical horizon.

Bolometer, an instrument used to measure infrared, or heat, radiation. The bolometer is essentially a very sensitive thermometer.

Brown Dwarf, a celestial object more massive than a planet but less massive than a star.

Chronology, the science of measuring time. Chronology divides time into regular divisions or periods, and assigns events their proper place and sequence by giving them dates.

Chronometer, a timepiece that is exceptionally accurate. Traditionally, the term refers to the marine chronometer, a rugged mechanical instrument used at sea to keep time for navigational purposes.

Cosmogony, the study of the origin and development of the universe as a whole and of the individual bodies that compose it.

Cosmology, the study of the universe. It is both a scientific subject and a philosophical one.

Day, in astronomy, the average length of time between successive noons. Noon is defined as the instant when the sun is highest in the sky.

Double Star, a pair of closely-spaced stars that to the unaided eye usually appear as a single star.