Ground-based measurements of the solar diameter after the transit of Mercury on 9 May 2016.
Sigismondi C., Boscardin S.C., Andrei A.H., Penna J.L., Reis-Neto E., Radziszewski K., Rudawi P., Altafi H., Ricra J., Beisker W., Westfall J., Kattentidt B., Ayomamitis A., Kardasis M., Piccotti L., Docobo Durantez J.A., Castiglioni F., Cicogna D., Cardoso L.F., De Bernardis P., Brothers T., Ochner P.
The 2016 transit of Mercury occurred 100 years after the publication of the theory of General Relativity, based upon the anomalous precession of its perihelion studied since 1845. Our purpose was to exploit the slow angular velocity 0.06 arcsec/s of this planetary transit to define, from the external and internal contact times, the actual dimension of the Sun, supposed perfectly spherical. Comparing ephemerides and observed times obtained by analytical fits we recovered the solar diameters in the corresponding wavelengths. The history of this method, the black drop phenomenon and the results relevant to solar physics and solar metrology are considered.