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Differential Measurements of ΔUT1 at the Meridian Line of Santa Maria degli Angeli in Rome and the Rediscovery of the Boscovichian Sinus

JOA 2022, Vol. 12, No. 3, Page 12

Author(s): Costantino Sigismondi, Silvia Pietroni

Abstract: The meridian line of Santa Maria degli Angeli (1702) has been inspected with modern observing methods. The IGEA (Informatized Geometrical Ephemerides for Astrometry) observational campaign 2018-2021 has been completed by ZIA (Zenithal Image Analysis) measurements in 2022 to allow us to determine exactly the local deviation from the North direction on many positions on the line, with respect to the pinhole, a source of the sunlight for the measurement of the solar position, over the 45 m-long meridian line built in Santa Maria degli Angeli basilica (Rome) in 1701-1702. A partial historical documentation on the so-called Boscovichian sinus (claimed but not localized on the line) has been supported with precise measurements of that deviation in the equinoctial sector of the meridian line during the ZIA 2022 campaign, and we rediscovered the exact locations of such deviation with the submillimetre accuracy limited by the atmospheric turbulence. It is as large as 4.7 mm and 2.3 s of extra delay in the meridian passage just near the equinoxes. The comparison between 10 and 13 observations made on the same dates separated by 3 years 2019-2022 (from April 25th to June 2nd) yields results of ΔUT1=UT1-UTC in good agreement with the IERS service of Paris for the same dates.