New absolute spectroscopic measurement of the solar equatorial rotation rate

An atomic-beam resonance-scattering technique applied to the 7699 A solar potassium absorption line is used to make an absolute spectroscopic determination of the solar equatorial rotation rate. This is believed to be a new method which has not previously been used for studying solar rotation. The measurements were made during 1979-82, initially with a permanent apparatus at Oberlin College and more recently with a portable apparatus installed at the Snow Telescope on Mt. Wilson. After carefully allowing for possible systematic errors, it is concluded that the solar sidereal equatorial rotation rate is 13.8 + or - 0.3 deg/day and that it has not varied significantly over the period of these observations.