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.
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.