radio astronomy

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The branch of astronomy that uses observations of emissions in the radio part of the electromagnetic spectrum to study extraterrestrial sources such as stars, planets, galaxies, interstellar gas, and dust clouds.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The branch of astronomy which utilizes radio waves through the use of radio telescopes to study celestial bodies and occurrences.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the branch of astronomy that detects and studies the radio waves emitted by celestial bodies