Glossary of Radio Astronomy Terms

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Light Waves:

Waves in the electromagnetic field. Examples include Gamma, X-Ray, Ultraviolet, Visible, Infrared, Microwave, and Radio.

Light Waves


The distance that light travels in one year in a vacuum. One light year is equivalent to about six trillion miles.


The amount of energy that a star emits per unit time. It is independent of distance or how bright or dim the star appears from Earth. It is measured in Watts (Joules/seconds) and is often given in terms relative to our Sun, L⊙ (about 3.846×10^26 W).



In astronomy, luminosity is an actual unit. It’s the amount of energy given off by a star or galaxy, or any other object — over a specific period of time. “Brightness,” in astronomy, is how apparently bright an object appears to an observer. Brightness goes down with distance. Luminosity does not.