  The variation of the solar diameter in time and in position angle has
implications in astrophysics and in general relativity, as the long series of
studies attest. The Transits of Venus in 2004 and 2012 have been carefully
studied because of the rarity of the phenomenon and its historical importance
due the AU measure and to the discovery of Venus atmosphere. The
characterization of Venus atmosphere and the measure of the solar diameter to
the milliarcsecond level of precision have been studied also from satellite
images. The results of the solar diameter measurements made with the
observations in Athens (2004) and at the Huairou Solar Observing Station in
China (2012) are presented. The topic of the oblateness of the Sun at sunset
and its intrinsic value is drafted to introduce the general public to the
relativistic relevance of measuring the solar figure, in the occasion of the
International Year of Light 2015.
