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. In 1868 he introduced the spectroscopic technique to observe solar prominences. He also invented innovative methods in imagery and photography. This paper focuses on the period from the foundation of Meudon Observatory, associated with 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 by Janssen to the top of the mountain. As most documents are written in French, this fantastic and unbelievable adventure at the end of the nineteenth century, deserves to be told in English, and it reveals the long-term vision of Janssen's astronomy. It involved specialized instruments, located in well-chosen places where atmospheric interference was minimized. High altitude observations, from Mont Blanc (or from balloons, also experienced by Janssen), prefigure space astronomy which developed