Solar Oblateness from Archimedes to Dicke
  The non-spherical shape of the Sun has been invoked to explain the anomalous precession of Mercury. A brief history of some methods for measuring solar diameter is presented. Archimedes was the first to give upper and lower values for solar diameter in third century before Christ; we also show the method of total eclipses, used after Halley's observative campaign of 1715 eclipse; the variant of partial eclipses useful to measure different chords of the solar disk; the method of Dicke which correlates oblateness with luminous excess in the equatorial zone. 
Costantino Sigismondi and Pietro Oliva