Angelo Secchi

Angelo Secchi

Infobox Scientist
name = Angelo Secchi
box_width =

image_width =150px
caption = Angelo Secchi
birth_date = 29 June 1818
birth_place = Reggio Emilia
death_date = 26 February 1878
death_place =
residence = Rome
citizenship =
nationality = Italian
ethnicity =
field = astronomy
work_institutions = Observatory of the Roman College
known_for =
prizes = "Légion d'honneur", France
religion = Roman Catholic
footnotes =

Father Pietro Angelo Secchi SJ (29 June 1818 – 26 February 1878] was an Italian astronomer. 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.


He 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 had to leave Rome. Father Secchi spent the next two years in Britain 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.

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. Under his direction, the crumbling Observatory was relocated to a new facility on top of the Church of St. Ignatius (the chapel of the the College). Father Secchi served as Director until his death.

His position was challenged In 1870, when the remnant of the Papal States around Rome was taken over by the Kingdom of Italy. The College was declared property of the Italian government. When the government moved to take over the Observatory as well, Father Secchi protested vigorously, and threatened to leave the Observatory for one of several positions offered to him 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.

Astronomical works

Father Secchi made contributions to many areas of astronomy.

* He revised 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 a detailed map of Mars.

* 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 Stellar classification#Harvard system, he still stands as discoverer of the principle of stellar classification, which is a fundamental element of astrophysics.

Other scientific and technical work

Father Secchi was active in oceanography, meteorology, and physics, as well as astronomy.

He invented the Secchi disk, which is used to measure water transparency in oceans and lakes.

He studied the climate of Rome and invented a "Meteorograph" for the convenient recording of several categories of weather data. He also studied the aurora borealis and the effects of lightning, and investigated the cause of hail.

He organized the systematic monitoring of the Earth's magnetic field, and in 1858 established a Magnetic Observatory in Rome.

Father Secchi also performed related technical works for the Papal government.

In 1854-1855, he supervised an exact survey of the Via Appia in Rome. This survey was later used in the topographic mapping of Italy.

He supervised construction of lighthouses for the ports of the Papal States. In 1858, he traveled to France and Germany to procure the necessary projection lenses.


Secchi Crater on the Moon and Secchi Crater on Mars are named after him.

The two STEREO (Solar TErrestrial RElations Observatory) spacecraft each carry an instrument package called SECCHI (Sun Earth Connection Coronal and Heliospheric Investigation).

Works (incomplete)

*cite book
title = Misura Della Base Trigonometriea Eseguita Sulla Via Appia (Measurement of the Trigonometric Base Performed On the Via Appia)
date = 1858
location = Rome

*cite book
title = Il Quadro Fisico del Sistema Solare Secondo le Piu Recenti Osservazioni (The Physical Framework of the Solar System According to the Most Recent Observations)
date = 1859
location = Rome

*cite book
title = Sui Recenti Progressi della Meteorologia (On The Recent Advances In Meteorology)
date = 1861
location = Rome

*cite book
title = Sulla Unitá delle Forze Fisiche (On the Unity of Physical Forces)
date = 1864
location = Rome

*cite book
title = Le Soleil: Exposé des Principales Découvertes Modernes (The Sun: Presentation of the Major Modern Discoveries)
date = 1870
location = Paris

*cite book
title = Le Stelle (The Stars)
date = 1877
location = Milan

*cite book
title = Lezioni Elementari di Fisica Terrestre (Elementary Lessons In Terrestrial Physics)
date = 1879
location = Turin And Rome


*cite web
title = Angelo Secchi
work = Catholic Encyclopedia
publisher = New Advent
url =
accessdate = 10-1-2008

*cite web
last = MacDonnell
first = Fr. Joseph F, S.J.
title = Angelo Secchi, S.J.: the Father of Astrophysics
work = Jesuit Scientists and the Jesuit Tradition
publisher = Fairfield University
url =
accessdate = 10-1-2008

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