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Basic Astronomy Concepts

Radio Astronomy

quasars, radio galaxies, celestial objects, Radio Astronomy, Cosmology

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Radio Astronomy, branch of astronomy in which celestial objects and astrophysical phenomena are studied by examining their emission of electromagnetic radiation in the radio portion of the spectrum.


Because radio galaxies and quasars are such powerful radio sources, they can be detected from a great distance. Because of the long time it takes for signals to reach the Earth from distant radio sources, radio astronomers are able to see the universe as it appeared more than 10 billion years ago, or far back in time toward the origin of the universe—the so-called big bang. Unfortunately, determining the distance to a radio source is not possible from radio measurements alone, so that distinguishing between a powerful distant source and a relatively weak nearby one is impossible. The distance may be determined only if that source is optically identified with a galaxy or quasar that has a measurable redshift. Nevertheless, from studies of the statistical distribution of large numbers of radio sources, it appears that when the universe was only a few billion years old, the number of intense radio sources was much greater and their dimensions smaller.


Kellermann, K.I., Ph.D.

Senior Scientist, National Radio Astronomy Observatory. Coeditor, "Galactic and Extra-Galactic Radio Astronomy".

Article key phrases:

quasars, radio galaxies, celestial objects, Radio Astronomy, Cosmology, Earth, great distance, origin, galaxy, universe, signals, dimensions, long time, studies, years old

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