Lo Gnomone Clementino: Astronomia Meridiana in Chiesa dal '700 ad oggi

TL;DR

The paper explores the historical and modern significance of the Clementine Gnomon in Rome, analyzing its precision, distortions, and potential for modern astrometry through historical review and contemporary measurements.

Contribution

It provides a detailed analysis of the Clementine Gnomon's historical accuracy, optical properties, and potential for modern astrometric applications, including a proposal for restoring the original pinhole.

Findings

The azimuth of the Gnomon is accurately referenced with respect to celestial North.

Local deviations from a perfect line are known with better than 0.5 mm accuracy.

Seeing effects on the solar image are studied using video analysis.

Abstract

The Clementine Gnomon is a giant pinhole dark camera dedicated to meridian solar astrometry operating in the Basilica of Santa Maria degli Angeli in Rome. Pope Clement XI ordered Francesco Bianchini (1662-1729) to build this instrument in 1701-1702. It renders solar images distortion-free, because the pinhole is optics-less. The azimut of the Clementine Gnomon has been referenced with respect to the celestial North pole, and it is 4'28.8"\pm0.6" Eastward. Also the local deviations from a perfect line are known with an accuracy better than 0.5 mm. Therefore the transit's times are systematically in delay with respect to the ephemerides. It is emphasized the opportunity of considering the Clementine Gnomon as introductory in modern astrometry besides its key role in the history of astronomy. Seeing effects on the solar image are studied using video. The need of a definitive solution in restoring the original pinhole is also shown.