The first winter solstice observed at the meridian line of Santa Maria degli Angeli in Rome

TL;DR

This paper presents the first detailed analysis of the 1701 winter solstice observation at Santa Maria degli Angeli, highlighting its historical significance and comparing its data with modern ephemerides.

Contribution

It provides the first presentation and discussion of Francesco Bianchini's 1701 winter solstice data and assesses its accuracy against current astronomical models.

Findings

Bianchini's measurements are consistent with modern ephemerides.

The meridian line was effectively used to measure Earth's obliquity in 1701.

The historical instrument remains in good condition and relevant for modern studies.

Abstract

The page written by the astronomer Francesco Bianchini (1662-1729) and containing the data of the 1701 winter solstice observed at Santa Maria degli Angeli is presented for the first time in figure 2 and widely discussed along this paper. The great meridian line in the Basilica of Santa Maria degli Angeli in Rome was built in 1701/1702 with the scope to measure the Obliquity of the Earth's orbit in the following eight centuries, upon the will of pope Clement XI. During the winter solstice of 1701 the first measurements of the obliquity have been realized by Francesco Bianchini, the astronomer who designed the meridian line, upgrading the similar instrument realized by Giandomenico Cassini in San Petronio, Bononia. In this paper the accuracy of the data observed by Francesco Bianchini is discussed and compared with up-to-date ephemerides. The modern situation of this historical instrument is also presented.