Solstices and Equinoxes in 1703 at the meridian line of St. Maria degli Angeli in Rome, and the stellar aberration of Sirius

Abstract: The 1703 was the first year of full operation of the meridian line in the Basilica of St. Maria degli Angeli in Rome. The instants of solstices and equinoxes, the \textit{Anni Cardines}, obtained by comparing transit timings of Sun and Sirius, also in daytime, are affected either by the East deviation of the meridian line of about 5' Eastward (geometrical effect), either by the stellar aberration of Sirius (relativistic effect). Similarly the seasonal shifts of Sirius' declination observed by Bianchini are here firstly recognized as depending on the stellar aberration in ecliptic latitude. The eccentricity of the Earth's orbit and the orientation of its axis in the space can be measured, since Ptolemy, by knowing the exact timing of the solstices and the equinoxes. The dates of 1703 equinoxes and solstices have been published by Francesco Bianchini in local roman mean time, referred to the local (roman) mean noon, i.e. after the solar meridian mean transit time. By using the observations of the three lunar eclipses of 1703 we found the equation of time for that year, and the UTC corresponding timings of the beginning of the seasons. This operation lead to find the contribution of the Sirius aberration to the instant calculated by Bianchini with respect to the current celestial mechanical models of IMCCE.