21-centimeter line | Article about 21-centimeter line by The Free Dictionary
21-centimeter line[¦twen·tē¦wən ′sen·tə‚mēd·ər ‚līn]
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.
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.
"The clear aperture will allow very precise measurements of spectral lines, including the 21-centimeter line
of atomic hydrogen." Image courtesy NRAO/AUI.
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.