The intrinsic visual oblateness of the sun

Solar oblateness observations are reported which yield a value of 18.4 plus or minus 12.5 milli-arcsec for the difference between equatorial and polar diameters. These observations were conducted when the time-varying excess equatorial brightness was markedly reduced, greatly simplifying the interpretation of the apparent solar oblateness. The experimental scheme for defining the 'edge' of the sun and monitoring the shape of the extreme limb-darkening function is summarized along with a description of the instrumentation. Sources of systematic error are exhaustively surveyed to extract the intrinsic visual oblateness of the sun. The result further strengthens the conclusion of Hill et al. (1974) that the grave consequence of the Dicke-Goldenberg (1967) work for Einstein's general theory of relativity is removed. This result excludes an oblateness as large as that required by the rapidly rotating interior models used to explain the low neutrino flux.