How the Arcetri Astronomical Observatory became Astrophysical

From Firenze University Press Journal: Il Colle di Galileo

Simone Bianchi, INAF-Osservatorio Astrofisico di Arcetri

The Arcetri Observatory boasts two inaugurations: the first in 1869, when the provisional positioning of the Amici telescope was unveiled to the public, and the second in 1872, upon completion of the main building.1 In spite of the fact that Giovanni Battista Donati (1821–1873), Arcetri’s founder, is included among the pioneers in the application of spectroscopy to research in astronomy — and therefore in astrophysics — the Observatory began as an astronomical one focusing on studies in classical, positional, astronomy.2Only half a century later did the Observatory become astrophysical. The impulse was given by the transfer of the Physics Institute to Arcetri and the construction of the Solar Tower. While the roles played in these events by Antonio Garbasso (1871–1933) and Giorgio Abetti (1882–1982) have been well researched,3 our aim here is to foreground the less known contribution of Antonio Abetti (1846–1928), who was director of the Observatory.

Antonio aimed to channel efforts at Arcetri toward avant-garde scientific research while at the same time promoting the career of his son Giorgio.

An American in Arcetri

Nominated director of the Arcetri Observatory at the end of 1893, Antonio Abetti had al-ready gained long experience in the field of positional astronomy at the Observatory of Padua under the guidance of Giuseppe Lorenzoni (1843–1914). Although he did not directly study astrophysics, he certainly had familiarity with the field from his contact with Lorenzoni, one of the first Italian spectroscopists. Indeed, Abetti himself made spectroscopic observations of the transit of Venus across the Sun in India in 1874. Throughout 1894, Abetti was often in Padua to receive advice from Lorenzoni on measures to take at Arcetri and to coordinate refurbish-ing operations on the astronomical equipment at the workshop of the Paduan Observatory.

In the spring of 1894, Abetti and Lorenzoni greeted the enterprising American astrophysicist George Ellery Hale (1868–1938) in Padua. Hale greatly admired the Memorie della Società degli Spettroscopisti Italiani, the world’s first astrophysics journal. In Italy, he met members of the Società to promote the project of his own The Astrophysical Journal, a publication which would release its first issues the following year (Chinnici 1997). On April 29, Hale came to the Arcetri Observatory, together with Pietro Tacchini (1838–1905), president of the Societàand editor of the Memorie. During their visit, Abetti showed them the Observatory’s minor tel-escope, a Fraunhofer refractor with an 11 cm aperture, which Donati had installed in a small dome in front of the Observatory.

The three men discussed the possibility of using it — together with a spectroheliograph, a photographic instrument invented by Hale a few years before — to obtain monochromatic images of the Sun. Abetti was therefore quite open to the idea of initiating studies in astrophysics at Arcetri; he indeed approached Tacchini to help him find funding for equipment and personnel. But the project did not get off the ground.Although the Fraunhofer telescope was not used for astrophysics, it did serve to pique the interest of the young Giorgio Abetti once it was restored and set in the East dome above the Observatory building. At the time, Giorgio was still a high school student; he wrote to Loren-zoni about using a micrometer for that telescope. Indeed his father Antonio confided to his colleague in Padua his wish to see his son undertake a career in the most modern scientific fields and to participate in the “dizzying race in electricity, photography and spectroscopy” (Bianchi & Gasperini 2017).

After taking his degree in physics in Padua in 1904, Giorgio first went to Germany and then to the U.S. in 1908–1909. Of particular importance was his visit to the Mount Wilson Observatory in California, of which Hale was director. Here Giorgio witnessed a tower telescope, a vertical instrument with a long focal length used together with the spectroheliograph to observe the Sun. It was during this visit that Giorgio conceived the project of constructing a solar tower in Italy as well (this is how he referred to Hale’s “tower telescope”). Given his enthusiasm for international collaboration, Hale took the project to heart, returning to Arcetri in summer 1909. Together with Antonio Abetti, he identified a possible position for the tower, namely the area in front of the Observatory, on the top of the hill in place of the old small dome.

DOI: https://doi.org/10.36253/cdg-13085

Read Full Text: https://oajournals.fupress.net/index.php/cdg/article/view/13085