Jules Janssen, the Birth of Solar Physics, the Foundation of Meudon Observatory, and the Mont Blanc Adventure (1875-1895)

Abstract

Jules Janssen is a well known astronomer. He introduced in 1868 the spectroscopic technique to observe permanently solar prominences. He also invented innovative methods in imagery and photography. This paper focuses on the period going from the foundation of Meudon Observatory, associated to the birth of astrophysics and solar physics in France, to the Mont Blanc saga, with the creation of the observatory and the three scientific ascents of Janssen to the top of the mountain. As most documents are written in French, this fantastic and unbelievable adventure for the end of the XIX th century, deserves to be related in English, and reveals the long term vision of Janssen's astronomy. It involved specialized instruments, located in well chosen places where atmospheric troubles are minimized. High altitude observations, at Mont Blanc (or from balloons also experienced by Janssen), prefigure space astronomy which will develop much later. Hence, Janssen appears as a precursor of modern astronomy, well ahead of his time.

130 years of spectroheliograms at Paris-Meudon observatories (1893–2023)

“…Jules Janssen (1824Janssen ( -1907 founded Meudon observatory in 1875 and introduced physical astronomy in France. 1 It took two decades to organize the new institution 2 and build powerful instruments (such as the 16 m double refractor, the largest of Europe); meanwhile, Janssen started photographic observations of the solar photosphere and developed high spatial resolution photography 3 revealing thin details such as granules and small sunspots called pores, with a small optimized refractor built by Adam Prazmowski (1821-1885). Images were recorded on 30 × 30 cm² glass plates.…”