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.
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.
I adapted it for my purposes by designing electronics and a prime-focus feed to receive the 21-centimeter line.