hydrogen line

(redirected from 21-cm line)

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.
References in periodicals archive ?
As a consequence, this radiation is called 21-cm line radiation.
So any redshift in the 21-cm line's wavelength tells us how far away the HI-filled galaxy is.
SETI researchers have long favored frequencies close to this "21-cm line" for two reasons.