page_title: Angelo Secchi
section_title: Astronomical works
hierarchical_section_title: Angelo Secchi / Astronomical works
caption_attribution_description: Roma, Pincio: Mira dell'Osservatorio astronomico del Collegio Romano per la determinazione del meridiano di Roma (posta in situ nel 1860) e busto dell'astronomo Angelo Secchi (1878). Il busto, di Giuseppe Prinzi è situato presso la Casina Valadier.
context_page_description: Angelo Secchi S.J. was an Italian Catholic priest, astronomer by the Italian region of Emilia. He was director of the observatory at the Pontifical Gregorian University 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.
context_section_description: 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.
  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.
  However, his main area of interest was astronomical spectroscopy.  He invented the heliospectrograph, star spectrograph, and telespectroscope. He showed that certain absorption lines in the spectrum of the Sun were caused by absorption in the Earth's atmosphere.
  Starting in 1863, he began collecting the spectra of stars, accumulating some 4,000 stellar spectrograms. Through analysis of this data, he discovered that the stars come in a limited number of distinct types and subtypes, which could be distinguished by their different spectral patterns. From this concept, he developed the first system of stellar classification: the five Secchi classes. While his system was superseded by the Harvard system, he still stands as discoverer of the principle of stellar classification, which is a fundamental element of astrophysics.  His recognition of molecular bands of carbon radicals in the spectra of some stars made him the discoverer of carbon stars, which made one of his spectral classes.
caption: bust by Giuseppe Prinzi at Pincio, Rome
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