New Measurement of the Solar Gravitational Red Shift

The red shift of the solar potassium absorption line at 7699 {} 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 (Δλ)ₑₓₚ=(1.01±0.06)(Δλ)ₜₕₑₒᵣ, where the theoretical value, based on the principle of equivalence, is 16.3 m{}. Further data show negligible center-to-limb wavelength variation for this line.