A measure of the width of a line in a spectrum, either emission or absorption. It is simply the width of the line at a point that is half the line’s peak value. FWHM is usually quoted in nanometres, but can also be given as a velocity by applying the Doppler effect, since motions in the gas govern the width of the line. The absorption-line equivalent is full width at half depth. See also Beamwidth.
Subjects: Astronomy and Astrophysics.