hydrogen line

(redirected from 21 centimetre radiation)
Also found in: Wikipedia.

hydrogen line

(21 cm line) See H I region.

hydrogen line

[′hī·drə·jən ‚līn]
(spectroscopy)
A spectral line emitted by neutral hydrogen having a frequency of 1420 megahertz and a wavelength of 21 centimeters; radiation from this line is used in radio astronomy to study the amount and velocity of hydrogen in the Galaxy.