Robert-Aglaé Cauchoix, Paris, 1825

Glass, metal;
Aperture ø 16,9 cm;
Focal length f=238 cm

INAF – Rome Astronomical Observatory, [n.i. M0011/2494]

This telescope originally belonged to the Collegio Romano Astronomical Observatory and is a very important instrument in the history of stellar and solar astrophysics. Acquired in 1824, its initial mounting, a quite sophisticated one, was altazimutal. When Angelo Secchi (1818-1878) renewed the Observatory, he installed the telescope on its current equatorial mounting. It was mainly used for solar observations. In the second half of 19 th century, the investigation on the physical and chemical properties of the Sun was one of the main research lines of the infant astrophysics. Secchi gave major contributions to the physical understanding of phenomena such as spots, prominences and flares taking place in the solar photosphere and chromosphere The observations were registered either with the usual drawing technique, or the innovative technique represented by photography.By adding an objective prism to this instrument or to the large Merz refractor, Secchi collected a great deal of observations on which he based his first star spectral classification, on which lies stellar astrophysics. In 1886, owing to its exceptional optical quality, the objective was mounted on a new tube and provided with a more modern equatorial mounting built by Giuseppe Cavignato (masterful technician at the Padua Observatory) following the instructions of Pietro Tacchini (1838-1905), Director of the Collegio Romano Observatory after Secchi. In 1913 Giorgio Abetti (1882-1982) used the telescope with an objective prism and photographed the spectra of various stars used by Secchi for his classification, also studying the optical characteristics of the instruments utilized by the Jesuit astronomer. The telescope was later moved to the newly founded Monte Mario Observatory; the last research work it was involved in was the transit of Mercury on the solar disc of May 1970; however, the instrument was still used as a teaching aid until the ‘80s of the 20th century. Recently the objective has been put back in its original brass tube (see above) built in 1825. [a.a., m.f., f.p.]

Bibl.: Calisi in Chinnici (ed.) 2009, p. 199; Abetti 1920, p. 15.