Adaptive optics: a breakthrough in astronomy

Until the 1970s, atmospheric seeing was considered as an absolute limitation for angular resolution of ground-based optical telescopes, exactly at the time of the conception of the new generation of giant optical telescopes, as the VLT and the Keck. Emerging in the context of the cold war with many constraints due to the research being classified, but with the new possibilities of digital control, astronomical adaptive optics was shown to be feasible in 1989 and gradually convinced an initially skeptical astronomical community of its potential. Twenty years later, it is a mandatory ingredient for the planning of Extremely Large Telescopes on the surface of the Earth, and has allowed many discoveries concerning galactic and extragalactic objects. Some directions for new developments are discussed.