History of planetary science. The Pic du Midi Planetary Observation Project : 1941–1971

When, in 1941, Bernard Lyot attempted to observe planet Mars at Pic du Midi, he experienced unusual viewing conditions. He realized that this circumstance was not at all exceptional for the Pic but representative of a remarkable property of the high altitude site. He decided to design, and put into operation at the top of the mountain a refractor, 60 cm in diameter, specially conceived for high angular resolution. uch a capability, Henry Camichel, Jean Focas and Audouin Dollfus initiated a deep and long-term research project based upon planetary surface exploration, with high telescopic magnification. analysis, photographic work, double image micrometry, photometric and polarimetric sensing were the most frequently used techniques and they were combined. Full exploitation of all these approaches required 30 years of continuous work, essentially coordinated by Observatoire de Paris at Meudon. oject was completed almost at the time when spacecraft missions within the Solar System began to replace telescopic work for planetary physics. s time, the Pic du Midi work have released new basic physical properties about planets and satellites. Knowledge was acquired and fundamental problems settled, which are reviewed.