Jules Janssen
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Pierre Jules César Janssen (22 February 1824 – 23 December 1907), usually known as Jules Janssen, was a French
astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either ...
who, along with English scientist Joseph Norman Lockyer, is credited with discovering the gaseous nature of the solar
chromosphere A chromosphere ("sphere of color") is the second layer of a star's atmosphere, located above the photosphere and below the solar transition region and corona. The term usually refers to the Sun's chromosphere, but not exclusively. In the ...
, and with some justification the element
helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic ta ...
.


Life, work, and interests

Janssen was born in Paris into a cultivated family. His father, Antoine César Janssen (born in Paris, 1780 – 1860) was a well known
clarinet The clarinet is a musical instrument in the woodwind family. The instrument has a nearly cylindrical bore and a flared bell, and uses a single reed to produce sound. Clarinets comprise a family of instruments of differing sizes and pitch ...
tist from Dutch/Belgian descent (his father emigrated from
Walloon Brabant Walloon Brabant (french: Brabant wallon ; nl, Waals-Brabant ; wa, Roman Payis) is a province located in Belgium's French-speaking region of Wallonia. It borders on (clockwise from the North) the province of Flemish Brabant (Flemish Region) and ...
to Paris). His mother Pauline Marie Le Moyne (1789 – 1871) was a daughter of the architect Paul Guillaume Le Moyne. Pierre Janssen studied
mathematics Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented in modern mathematics ...
and
physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which ...
at the faculty of sciences. He taught at the
Lycée Charlemagne The Lycée Charlemagne is located in the Marais quarter of the 4th arrondissement of Paris, the capital city of France. Constructed many centuries before it became a lycée, the building originally served as the home of the Order of the J ...
in 1853, and in the school of
architecture Architecture is the art and technique of designing and building, as distinguished from the skills associated with construction. It is both the process and the product of sketching, conceiving, planning, designing, and constructing buildings ...
1865 – 1871, but his energies were mainly devoted to various scientific missions entrusted to him. Thus in 1857 he went to Peru in order to determine the magnetic
equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can also ...
; in 1861–1862 and 1864, he studied telluric absorption in the solar spectrum in Italy and Switzerland; in 1867 he carried out optical and magnetic experiments at the Azores; he successfully observed both
transits of Venus frameless, upright=0.5 A transit of Venus across the Sun takes place when the planet Venus passes directly between the Sun and a superior planet, becoming visible against (and hence obscuring a small portion of) the solar disk. During a tran ...
, that of 1874 in Japan, that of 1882 at
Oran Oran ( ar, وَهران, Wahrān) is a major coastal city located in the north-west of Algeria. It is considered the second most important city of Algeria after the capital Algiers, due to its population and commercial, industrial, and cultural ...
in Algeria; and he took part in a long series of solar eclipse-expeditions, e.g. to Trani (1867),
Guntur Guntur () is a city and the administrative headquarters of Guntur district in the States and union territories of India, Indian state of Andhra Pradesh. Guntur is spread across 168.49 km square and is the third-largest city in the state. ...
(1868),
Algiers Algiers ( ; ar, الجزائر, al-Jazāʾir; ber, Dzayer, script=Latn; french: Alger, ) is the capital and largest city of Algeria. The city's population at the 2008 Census was 2,988,145Census 14 April 2008: Office National des Statistiques d ...
(1870), Siam (1875), the Caroline Islands (1883), and to Alcosebre in Spain (1905). To see the eclipse of 1870, he escaped from the Siege of Paris in a balloon. Unfortunately the eclipse was obscured from him by cloud. In the year 1874, Janssen invented the Revolver of Janssen or Photographic Revolver, instrument that originated the
chronophotography Chronophotography is a photographic technique from the Victorian era which captures a number of phases of movements. The best known chronophotography works were mostly intended for the scientific study of locomotion, to discover practical inform ...
. Later this invention was of great use for researchers like Etienne Jules Marey to carry out exhibitions and inventions.


Discovery of helium

In 1868 Janssen discovered how to observe solar prominences without an
eclipse An eclipse is an astronomical event that occurs when an astronomical object or spacecraft is temporarily obscured, by passing into the shadow of another body or by having another body pass between it and the viewer. This alignment of three c ...
. While observing the solar eclipse of 18 August 1868, at
Guntur Guntur () is a city and the administrative headquarters of Guntur district in the States and union territories of India, Indian state of Andhra Pradesh. Guntur is spread across 168.49 km square and is the third-largest city in the state. ...
,
Madras State Madras State was a state of India during the mid-20th century. At the time of its formation in 1950, it included the whole of present-day Tamil Nadu (except Kanyakumari district), Coastal Andhra, Rayalaseema, the Malabar region of North and ...
(now in
Andhra Pradesh Andhra Pradesh (, abbr. AP) is a state in the south-eastern coastal region of India. It is the seventh-largest state by area covering an area of and tenth-most populous state with 49,386,799 inhabitants. It is bordered by Telangana to the ...
), British India, he noticed bright lines in the spectrum of the chromosphere, showing that the chromosphere is gaseous. Present in the
spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors ...
of the Sun, though not immediately noticed or commented upon, was a bright yellow line later measured to have a
wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tr ...
of 587.49 nm. This was the first observation of this particular spectral line, and one possible source for it was an element not yet discovered on the earth. From the brightness of the spectral lines, Janssen realized that the chromospheric spectrum could be observed even without an eclipse, and he proceeded to do so. On 20 October, Joseph Norman Lockyer in England set up a new, relatively powerful spectroscope. He also observed the emission spectrum of the chromosphere, including the same yellow line. Within a few years, he worked with a chemist and they concluded that it could be caused by an unknown element, after unsuccessfully testing to see if it were some new type of hydrogen. This was the first time a chemical element was discovered on an extraterrestrial body before being found on the earth. Lockyer and the English chemist
Edward Frankland Sir Edward Frankland, (18 January 18259 August 1899) was an English chemist. He was one of the originators of organometallic chemistry and introduced the concept of combining power or valence. An expert in water quality and analysis, he was ...
named the element after the Greek word for the Sun, ἥλιος (''helios'').


Observatories

At the great Indian eclipse of 1868 that occurred in
Guntur Guntur () is a city and the administrative headquarters of Guntur district in the States and union territories of India, Indian state of Andhra Pradesh. Guntur is spread across 168.49 km square and is the third-largest city in the state. ...
, Janssen also demonstrated the gaseous nature of the red prominences, and devised a method of observing them under ordinary daylight conditions. One main purpose of his spectroscopic inquiries was to answer the question whether the Sun contains
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
or not. An indispensable preliminary was the virtual elimination of oxygen-absorption in the
Earth's atmosphere The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing fo ...
, and his bold project of establishing an observatory on the top of
Mont Blanc Mont Blanc (french: Mont Blanc ; it, Monte Bianco , both meaning "white mountain") is the highest mountain in the Alps and Western Europe, rising above sea level. It is the second-most prominent mountain in Europe, after Mount Elbrus, and ...
was prompted by a perception of the advantages to be gained by reducing the thickness of air through which observations have to be made. This observatory, the foundations of which were fixed in the hard ice that appeared to cover the summit to a depth of over ten metres, was built in September 1893, and Janssen, in spite of his sixty-nine years, made the ascent and spent four days taking observations. In 1875, Janssen was appointed director of the new astrophysical observatory established by the French government at
Meudon Meudon () is a municipality in the southwestern suburbs of Paris, France. It is in the département of Hauts-de-Seine. It is located from the center of Paris. The city is known for many historic monuments and some extraordinary trees. One of t ...
, and set on foot there in 1876 the remarkable series of solar photographs collected in his great ''Atlas de photographies solaires'' (1904). The first volume of the ''Annales de l'observatoire de Meudon'' was published by him in 1896. (see also
Meudon Great Refractor Meudon Great Refractor (also known as the ''Grande Lunette'') is a double telescope with lenses (83 cm + 62 cm), in Meudon, France. It is a twin refracting telescope built in 1891, with one visual and one photographic, on a single square ...
) Janssen was the President of the Société Astronomique de France (SAF), the French astronomical society, from 1895 to 1897.de la Société astronomique de France''
1911, vol. 25, pp. 581–586


International Meridian Conference

In 1884 he took part in the
International Meridian Conference The International Meridian Conference was a conference held in October 1884 in Washington, D.C., in the United States, to determine a prime meridian for international use. The conference was held at the request of U.S. President Chester A. ...
.


Death, honors, and legacy

Janssen died at Meudon on 23 December 1907 and was buried at
Père Lachaise Cemetery Père Lachaise Cemetery (french: Cimetière du Père-Lachaise ; formerly , "East Cemetery") is the largest cemetery in Paris, France (). With more than 3.5 million visitors annually, it is the most visited necropolis in the world. Notable figure ...
in Paris, with the name "J. Janssen" inscribed on his tomb. During his life he was made a Knight of the
Legion of Honor The National Order of the Legion of Honour (french: Ordre national de la Légion d'honneur), formerly the Royal Order of the Legion of Honour ('), is the highest French order of merit, both military and civil. Established in 1802 by Napoleon ...
and a Foreign Member of the
Royal Society of London The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. The society fulfils a number of roles: promoting science and its benefits, r ...
.
Crater Crater may refer to: Landforms * Impact crater, a depression caused by two celestial bodies impacting each other, such as a meteorite hitting a planet * Explosion crater, a hole formed in the ground produced by an explosion near or below the surf ...
s on both
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...
and the
Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
are named in his honor. The public square in front of
Meudon Observatory The Paris Observatory (french: Observatoire de Paris ), a research institution of the Paris Sciences et Lettres University, is the foremost astronomical observatory of France, and one of the largest astronomical centers in the world. Its histor ...
is named ''Place Jules Janssen'' after him. Two major prizes carry his name: the
Prix Jules Janssen The Prix Jules Janssen is the highest award of the Société astronomique de France (SAF), the French astronomical society. This annual prize is given to a professional French astronomer or to an astronomer of another nationality in recognition ...
of the French Astronomical Society, and the Janssen Medal of the
French Academy of Sciences The French Academy of Sciences (French: ''Académie des sciences'') is a learned society, founded in 1666 by Louis XIV at the suggestion of Jean-Baptiste Colbert, to encourage and protect the spirit of French scientific research. It was at ...
. Janssen named minor planet
225 Henrietta 225 Henrietta is a very large outer main-belt asteroid. It was discovered by Austrian astronomer Johann Palisa on April 19, 1882, in Vienna and named after Henrietta, wife of astronomer Pierre J. C. Janssen. The asteroid is orbiting at a distance ...
discovered by
Johann Palisa Johann Palisa (6 December 1848 – 2 May 1925) was an Austrian astronomer, born in Troppau, Austrian Silesia, now Czech Republic. He was a prolific discoverer of asteroids, discovering 122 in all, from 136 Austria in 1874 to 1073 Gel ...
, after his wife, Henrietta.


Notes and references


Further reading

*
Obituary
from ''Popular Astronomy'', 1908, vol. 16, pp. 72–74
Obituary
from ''Astronomische Nachrichten'', 1908, vol. 177, p. 63 (in French)
Obituary
from ''The Astrophysical Journal'', 1908, vol. 28, pp. 89–99 (in French)
Janssen statue
description and black-and-white picture from ''The Observatory'', 1922, vol. 45, pp. 175–176

from the High Altitude Observatory at Boulder, Colorado * * * * {{DEFAULTSORT:Janssen, Pierre Jules Cesar 1824 births 1907 deaths Burials at Père Lachaise Cemetery Discoverers of chemical elements 19th-century French astronomers Members of the French Academy of Sciences Foreign Members of the Royal Society Foreign associates of the National Academy of Sciences Chevaliers of the Légion d'honneur Honorary Fellows of the Royal Society of Edinburgh Scientists from Paris Helium Spectroscopists Recipients of the Lalande Prize