Book of the solar disk drawings

“31 agosto 1859”
["31 august 1859"]
[Angelo Secchi]
Pencil drawing, 290 x 305 mm
Historical archives of INAF-Rome Astronomical Observatory, Monte Porzio Catone (Rome)

On 1 September 1859, the British astronomer Richard Carrington noted a sudden, very intense and brief flare, inside an extensive and complex spot region observed on the solar disk. Following the details of this observation, Carrington noted the coincidence between the singular solar phenomenon reported and some extraordinary events that occurred at the same time on the ground (intense geomagnetic storms, unusual auroras, anomalies in the telegraph systems) strengthening the hypothesis of the existence of Sun-Earth interactions.
The phenomena described above, now known as the “Carrington Event” of 1859, were also observed and studied by Angelo Secchi. During the solar observations carried out in white light with the Cauchoix refractor telescope from August 25 to September 6, 1859 (Figure 1), Secchi recorded the characteristics of the many structures that appeared during that time on the solar disk and studied in detail The spot group n. 219 of his register, which had originated the flare observed by Carrington and other scientists of the time.
The figure reproduced here shows some examples of the sketches produced during these observations. They present the solar disk with a diameter of about 245 mm with the position of the equator and the solar poles, the spots, the facolae and the observed pores, and various annotations. These indicate the time of observation, the conditions of the terrestrial atmosphere, the calculations made for the estimation of the heliographic position of the different regions seen and some of their characteristics, for instance, the particular brilliance, the new appearance, the rapid evolution. In the drawing concerning the observations of 28 August 1859 (Figure 2), Secchi shows the complex nature and twisted shape of the spot group N. 219 also with details resolved using a lens that allowed larger enlargements than those obtained for full-disk observations. Moreover, in some communications of the period, he reports about a spectacular Aurora Borealis seen in Rome on the night of 29 August 1859, some disturbances recorded by the magnetometers used for the measurement of the Earth’s magnetic field, and malfunctioning of the telegraph network. In his writings, he hypothesizes the existence of relations between the Sun and the planets of the solar system, introducing the term “solar meteorology” to describe the phenomena related to the activity of the Sun.

Ilaria Ermolli, INAF-Osservatorio Astronomico di Roma
Marco Ferrucci, INAF-Osservatorio Astronomico di Roma