(b. Modena, Italy, 21 March 1838; d. Spilamberto, Modena province, Italy, 24 March 1905)
After obtaining his degree in engineering at the archiginnasio of Modena, Tacchini studied astronomy at the observatory of Padua under Giovanni Santini and Virgilio Trettenero. In 1859, following his appointment as deputy director of the observatory of Modena, he established connections with Secchi and Schiaparelli in order to study problems related to the new astrophysics. In 1861 he maintained an active scientific correspondence with Secchi.
Appointed adjunct astronomer at the Palermo observatory in 1863, Tacchini began observations and research on solar physics using the spectroscope. The daily observations of the phenomena on the surface of the sun convinced him of the need for a well-planned national program in order to follow its various phases. He called this effort the study of “solar meteorology,” at a time when scientists were just becoming aware that the phenomena of terrestrial meteorology depend upon solar phenomena. The exceptional maximum of the eleven-year sunspot cycle that occurred in 1870, accompanied by the appearance on earth of numerous polar auroras, intensified his observations of the sun at Rome and Palermo.
Secchi and Tacchini decided to found a society to coordinate the work of various Italian observatories and, using standard criteria, to observe solar activity and to promote research on solar physics. Since the spectroscope was virtually the only instrument used for this purpose, the society, founded in 1871, was called the Society of Italian Spectroscopists: its Memorie, the first periodical on astrophysics, is still being published by the Italian Astronomical Society, which replaced it in 1920.
A skilled administrator, Tacchini prepared and directed many astronomical expeditions. For the transit of Venus in 1874, Tacchini accompanied his colleagues Alessandro Dorna and Antonio Abetti to Muddapur in Bengal. The principal aim of this expedition was to make extremely accurate observations of the contacts of the disk of Venus with the limb of the sun by using the spectroscope. He traveled to various parts of the world to observe seven total solar eclipses, concentrating his observations especially on the corona and the prominences.
During the eclipse of 1883, which he observed in the Caroline Islands, Tacchini noted white prominences, in contrast with the vivid red ones of hydrogen. Photographic techniques later made it clear that these prominences, which were more extensive than those of hydrogen, are produced by calcium.
In 1879 Tacchini succeeded Secchi as director of the observatory at the Collegio Romano and as director of the Central Meteorological Office, from which he established a vast network of meteorological stations throughout Italy. Fully aware of the advantages of a clear and calm sky, he and Riccò promoted the construction of an observatory on Mt. Etna, at 9,650 feet, for astrophysical and geophysical research. Also with Riccò he enlisted the collaboration of the observatory in Catania for the international project of preparing a chart and a photographic catalog of the sky.
Tacchini was a foreign member of the Royal Astronomical Society and of the Royal Society, and was awarded the Rumford gold medal and the Janssen Prize.
I. Original Works. Most of Tacchini’s numerous publications are in the Memorie della Società degli spettroscopisti italiani, in the Atti dell’ Accademia dei Lincei, and in the publications of the Central Meteorological Office. They include II passaggio di Venere sul sole dell’ 8 e 9 dicembre 1874 osservato a Muddapur del Bengala (Palermo, 1875); and “Eclissi totali di sole del dicembre 1870, del maggio 1882, dell’agosto 1886 e 1887,” in Relazioni e note (Rome, 1888). His correspondence with Secchi is preserved in Italy.
II. Secondary Literature. See G. Abetti, “Celebrazione del primo centenario della nascità di Pietro Tacchini”, in Coelum, 9 (1939), 81: E. Millosevich, “Necrologia di P. Tacchini”, in Astronomische Nachrichten, 168 , no. 4009(1905); and A. Riccò, “Necrologia di P. Tacchini,” in Memorie della Società degli spettroscopisti italiani, 34 (1905), 85.