Solar rotation: The photospheric height gradient

For selected pairs of Fraunhofer lines the height of formation has been calculated corresponding to that portion of the profile intercepted by the magnetograph exit slits. A photospheric height discrimination of 150–300 km is realized. In 1971 simultaneous measurements of equatorial angular velocity from spectroscopic displacements of these line pairs indicate no height gradient in excess of 1%.The disturbing influence of telluric line blends is analyzed. It is proposed that undetected telluric lines could account, at least in part, for the photospheric height gradient which has been found in a number of photographic investigations.Operated by the Association of Universities for Research in Astronomy, under contract with the National Science Foundation.