Angelo Secchi (Italian pronunciation: [ˈandʒelo ˈsekki]; 28 June 1818 – 26 February 1878) was an Italian Catholic priest and astronomer from the Italian region of Emilia. He was 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.
Secchi was born in Reggio Emilia, 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 were ordered to leave Rome. Secchi spent the next two years in the United Kingdom at Stonyhurst College, where he met Alfred Weld, the Jesuit astronomer in charge of the Stonyhurst Observatory, who may have inspired him to take up the science. He moved on to the United States, where he taught for a time at Georgetown University in Washington, D.C. He also took his doctoral examination in theology there.
During his stay in America, he met Commander Matthew Fontaine Maury, the first director of the United States Naval Observatory in Washington. He studied with Maury and corresponded with him for many years.
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.
Secchi was elected to the American Philosophical Society in 1860.
His director 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.
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.
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.
The first star recognized as a Be star was Gamma Cassiopeiae, which Secchi observed in 1866; the first star ever observed with emission lines.
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.