Secchi, Angelo (1818-1878)

Father Pietro Angelo Secchi was an Italian astronomer, director of the Observatory at the Pontifical Gregorian University (then called the Roman College) for 28 years. He was a pioneer in astronomical spectroscopy, and was one of the first scientists to state authoritatively that the Sun is a star.

Father Pietro Angelo Secchi was born in Reggio Emilia, a city in northern Italy, where he studied at the Jesuit gymnasium. At the age of 16, he entered the Jesuit Order in Rome. He continued his studies at the Roman College, and demonstrated great scientific ability. In 1839, he was appointed tutor of mathematics and physics at the College. In 1841, he became Professor of Physics at the Jesuit College in Loreto. In 1844, he began theological studies in Rome, and was ordained a priest on 12 September 1847. In 1848, due to the Roman Revolution, the Jesuits had to leave Rome. Fr. Secchi spent the next two years in the United Kingdom at Stonyhurst College, and the United States, where he taught for a time at Georgetown University in Washington, DC. He also took his doctoral examination in theology there.

He returned to Rome in 1850. On the recommendation of his late colleague Francesco de Vico, he became head of the Observatory of the College at age 32. In 1853, under his direction, the crumbling Observatory was relocated to a new facility on top of the Sant'Ignazio Church (the chapel of the College). Secchi served as Director until his death.

His position was challenged after 1870, when the remnant of the Papal States around Rome was taken over by the Kingdom of Italy. In 1873, the College was declared property of the Italian government. When the government moved to take over the Observatory as well, Secchi protested vigorously, and threatened to leave the Observatory for one of several positions offered to him by foreign observatories. He was offered important scientific positions and political dignities by the government, but refused to pledge allegiance to the Kingdom in place of the Pope. The royal government did not dare to interfere with him, and he continued as Director. He died in 1878 at age 59, in Rome.

A commemorating medal was issued in 1978 - at the centenary of Secchi's death - for the 13th Philatelic and Numismatic convention in Reggio Emilia. The obverse of the 31.6 mm diameter and 12 gram weight bronze medal shows half-right facing portrait of Father Secchi, with his name, birth and death years in legend. The medalist was Luigi Teruggi, whose name can be discovered below the shoulder.

Rome 1 reverseRome 1 obverse

The reverse shows the interior of the Scpecola, with the telescope and the opened slit of the dome. Legendr around is: XIII. CONVEGNIO FILATELICO NUMISMATICO "CITTA' DEL TRICOLORE", refers to the event. Below the name and coats of arms of the city of Reggio Emilia is visible along with the date of issue 30th September 1978.

Secchi was especially interested in the Sun, which he observed continually throughout his career. He observed and made drawings of solar eruptions and sunspots, and compiled records of sunspot activity. In 1860 and 1870, he organized expeditions to observe solar eclipses. He proved that the solar corona and coronal prominences observed during a solar eclipse were part of the Sun, and not artifacts of the eclipse. He discovered solar spicules.

Secchi made contributions to many areas of astronomy. He revised Friedrich Georg Wilhelm von Struve's catalog of double stars, compiling data for over 10,000 binaries. He discovered three comets, including Comet Secchi (C/1853 E1). He produced an exact map of the lunar crater Copernicus. He drew some of the first color illustrations of Mars and was the first to describe "channels" (canali in Italian) on the planetary surface.

As an tribute to him the primary set of imaging instruments on the STEREO satellites is named to the Sun-Earth Connection Coronal and Heliospheric Investigation, i. e. SECCHI.

Secchi's four classes of stellar spectra, from a colored lithograph in a book published around 1870. This shows how someone looking through a spectrograph on a large telescope would see the spectrum from the brightest stars. The spectra would be much fainter for most stars, making for difficult observing. The principal spectral lines are identified underneath by letters that Fraunhofer assigned.