New Measurement of the Solar Gravitational Red Shift

The red shift of the solar potassium absorption line at 7699 Å has been measured by means of an atomic-beam resonance-scattering technique. The shift at the center of the solar disk, corrected for Earth's motion, is ${\left(\Delta \lambda \right)}_{\exp }=(1.01\mathrm{}\pm 0.06){\left(\Delta \lambda \right)}_{\mathrm{theor}}$, where the theoretical value, based on the principle of equivalence, is 16.3 mÅ. Further data show negligible center-to-limb wavelength variation for this line.