Pierre Janssen
Pierre Jules Cesar Janssen ( born February 22, 1824 in Paris, † December 23, 1907 in Meudon ) was a French astronomer.
Janssen found 1868 a way to observe the solar corona without eclipse. In the same year he discovered an unknown element in the solar spectrum, the helium. Both succeeded at the same time - regardless of Janssen - the English astronomer Norman Lockyer.
Curriculum vitae
1853 Janssen gave lessons in the school of Charlemagne. In 1857 he traveled to Peru to determine the magnetic equator. In 1859 he accompanied the naturalist Alfred Grandidier on its world tour, but had to cancel due to illness this after six months. From 1861 to 1862, and 1864, he studied the " telluric " lines in the solar spectrum and showed that they result from absorption of water vapor in the atmosphere (Latin tellus " earth "). From 1865 to 1871 Janssen taught in a school of architecture. In 1867 he led optical and magnetic experiments in the Azores.
In 1868, Janssen showed the gaseous nature of the red solar corona and developed a method to observe this process and outside the time of a solar eclipse. One such method was the same year as Norman Lockyer; a year later this succeeded William Huggins and Karl Friedrich Zöllner.
On August 18, 1868 in India was observed a total solar eclipse. It was observed by French astronomers, including Janssen, as well as British. At the same time observed from Norman Lockyer, of London, the sun. When evaluating both discovered almost simultaneously, but independently, a hitherto unknown element with a wavelength of 587.49 nanometers made up by a bright yellow line in the spectrum of the chromosphere of the Sun noticeable. Lockyer ( and Edward Frankland ) proposed the name of this new element before: helium. As Janssen made known his discovery, he wanted no one to believe there had never found a new element in the universe, before it could be discovered on Earth first.
1870 Janssen left the besieged Paris in a balloon because he wanted to watch a solar eclipse in Oran, Algeria. 1873 Janssen was elected to the Académie des sciences; the Accademia dei Lincei in Rome, he was a member since June 1872. In 1874 he traveled to observe the transit of Venus to Japan.
To document the transit of Venus, Janssen developed a " photographic revolver ". With this powered by a clockwork apparatus he was able to record 48 shots in time intervals of one second on an annular plate. Through this " photographic revolver " the French physiology Étienne- Jules Marey was to construct his " Chronological photographic gun " encouraged with the moving objects in space - such as birds in free flight - could be recorded photographically series.
1875 Janssenzum director of the new astrophysical institution in Meudon (→ Paris Observatory ) was appointed. In 1876 he succeeded in excellent sun photographs, which he published in 1904 in the Atlas de photographies solaires. 1882 Janssen observed the transit of Venus in Oran. In 1887 he turned to solar observations at the Pic du Midi de Bigorre in the Pyrenees. In September 1893, he climbed the Mont Blanc and stayed for four days at the summit to watch the sun. The aim was to find out whether the sun oxygen. In addition, an observatory, near the Observatory of Joseph Vallot, also built on the Mont Blanc. 1896 Janssen gave out the first part of the Annales de l' Observatoire de Meudon.
Pierre Jules César Janssen died on December 23, 1907 at his workplace Meudon.
Honors
The Mars crater Janssen as well as a moon crater Janssen were named in honor Janssens.
The Jules Janssen Award and the Janssen Medal ( French Academy of Sciences), are named after Pierre Jules César Janssen.