21-centimeter line

21-centimeter line

[¦twen·tē¦wən ′sen·tə‚mēd·ər ‚līn]
(spectroscopy)
A radio-frequency spectral line of neutral atomic hydrogen at a wavelength of approximately 21 centimeters and a frequency of approximately 1420 megahertz, that results from hyperfine transitions between states in which the spins of the electron and proton are parallel and antiparallel.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
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References in periodicals archive ?
Radio Flyspeck "The total radio power striking our earth in the famous 21-centimeter line of neutral hydrogen is scarcely 20 watts.
November 1959: shooting the moon
"The clear aperture will allow very precise measurements of spectral lines, including the 21-centimeter line of atomic hydrogen." Image courtesy NRAO/AUI.
New Green Bank Telescope dedicated
I adapted it for my purposes by designing electronics and a prime-focus feed to receive the 21-centimeter line. The dish and feed, akin to the mirror and eyepiece in an optical reflecting telescope, ride on an altazimuth mount fixed toward due south.
A radio map of the Milky Way

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