The Lake County Astronomical Society

Astronomy Bio...Giovanni Donati

Jay Bitterman

Giovanni Battista Donati was born on December 16, 1826 in Pisa, Italy. He obtained his university education at the University of Pisa. In 1852 he began his career, as a student, in astronomy at the observatory of Florence. In 1854 he became assistant to G. B. Amici.

From 1854 to1864 Donati discovered six comets. On June 2, 1858, the first and most dramatic comet was named after him. It was extraordinarily beautiful and had, in addition to its major tail, two extra narrow tails. On July 18, 1860, he observed the total solar eclipse at Torreblanca, Spain. Also, in 1860 Donati used his talents and his time in the development of stellar spectroscopy. He set out to compare the Sun's spectrum with those of other stars, and then used this technique to examine the properties and composition of comets. He observed that when a comet was still at a distance from the Sun, its spectrum was identical to that of the Sun. As the comet approached the Sun, it's magnitude (brightness) increased and its spectrum changed. Donati deduced that when the comet was still far from the Sun, the light that it emanated was simply reflected sunlight. When the comet got closer to the Sun it became so heated that it emitted its own spectrum and revealed the comet's composition. Donati's memoir "Intorno Alle Sine Degli Spettri Stellar" was published in 1862. He suggested the feasibility of a physical classification of the stars.

On August 5, 1864, he discovered the gaseous composition of comets by utilizing prismatic analysis from the light of one then visible. The spectroscopic observation of the 1864 comet rendered a spectrum having three lines named alpha, beta, and gamma. Secci also observed the three lines in the 1866 comet. In 1868 Huggins showed that these lines were due to the presence of carbon.

In 1864 he succeeded Amici to the directorship of the observatory of Florence. One of his major responsibilities as director of the observatory was to supervise the work at Arcetri that was not far from Florence where a new observatory was being set up. It was formally established a year before Donati's death.

On December 22, 1870, he again observed an eclipse using a spectroscope of his own design that incorporated five prisms. Later he constructed an even more complex spectroscope having no fewer than 25 prisms. He also published papers giving an estimate of the distance between the Earth to the Sun and his findings on the structure of the Sun itself.

Donati also had a great interest in atmospheric phenomena and events in higher zones, such as the aurora borealis. On February 4, 1872, while investigating the great aurora, he began to refer to such phenomena as a distinct branch of science, referring to it as "cosmical meteorology"; but he did not pursue the subject. His pioneering research efforts were in the use of spectroscopy to elucidate the nature of comets.

On September 20, 1873, while attending the International Meteorological Congress in Vienna, he fell ill of cholera, and died a few hours after returning to Arcetri.

Historic material furnished with permission from Chris Wetherill. Visit his web site at: