Solar Observations by Angelo Secchi. I. Digitization of Original Documents and Analysis of Group Numbers over the Period of 1853–1878

Abstract

Abstract Angelo Secchi, an Italian Jesuit and prominent scientist of the 19th century, and one of the founders of modern astrophysics, observed the Sun regularly at the Collegio Romano in Rome, Italy, for more than 25 yr. Results from his observations are reported in articles published in the scientific journals of the time, as well as in drawings and personal notebooks that are stored in the historical archive of the Istituto Nazionale di Astrofisica Osservatorio Astronomico di Roma. The latter material, which reports solar observations performed from 1853–1878, includes original documents from Secchi and from a few of his close collaborators. The above unique material has recently been digitized for preservation purposes and for allowing the scientific exploitation of data not easily accessible so far. A total of more than 5400 digital images have been produced. Here we present the archival material and the new digital data derived from it. We also present results obtained from our primary analysis of the new digital data. In particular, we produced new measurements of the group number from 1853–1878, which will be available for future recalibration of the group number series.