Frenchspectroscopist. In 1862 he discovered and named the telluric lines in the Sun's spectrum which originate in the Earth's atmosphere, and realized that similar lines in the spectra of planets would reveal the composition of their atmospheres. In 1868, independently of J. N. Lockyer, he observed the spectra of solar prominences at a total eclipse, and went on to invent the spectrohelioscope. He found a new line in the solar spectrum, which Lockyer attributed to a new element later named helium. In a celebrated adventure in 1870, during the Franco-Prussian War, Janssen escaped by balloon from a besieged Paris and flew to the Atlantic coast to observe a solar eclipse.
Subjects: Astronomy and Astrophysics.