Janssen, Pierre Jules César(redirected from Janssen, Pierre Jules Cesar)
Janssen, Pierre Jules César(pyĕr zhül sāzär` zhäNsĕn`), 1824–1907, French astronomer. In 1857–58, in Peru, he worked on the determination of the magnetic equator; in the Azores (1867) he examined magnetic and topographical conditions; and in Japan (1874) and in Algeria (1882) he observed the transit of Venus. Janssen accompanied various solar eclipse expeditions, notably that to Guntur, India, in 1868, where he devised a new method of studying the solar prominences spectroscopically and discovered, almost simultaneously with J. N. Lockyer, the chemical constitution of the prominences. He was active in the establishment of the astrophysical observatory of Meudon in Paris and in 1876 became its director. There he gathered an important series of solar photographs included in his Atlas de photographies solaires (1904). He later became director of the observatory on Mont Blanc.
Janssen, Pierre Jules César
Born Feb. 22, 1824, in Paris; died Dec. 23, 1907, in Meudon. French astronomer. Member of the Paris Academy of Sciences (1873) and of the Royal Society of London (1875). One of the founders of the spectral analysis of celestial bodies.
In 1868 and independently of J. N. Lockyer, Janssen invented the spectral method of observing solar prominences on the limb of the sun’s disk during periods when the sun was not in eclpse.