Some results after 10 years of site testing at Concordia, Antarctica

At an altitude of 3250m and at a latitude of $75^\circ$S, the Italo-French Concordia station was open to winter-over teams in 2005. It is one of the high points of the Antarctic polar plateau. These extreme remote sites are expected to provide exceptional conditions for astronomical observations, specially in the infra-red ranges, given the very cold winter temperatures, averaging well below -60C. Being very flat as highest points of that very broad polar plateau, they are also not subject to the famous katabatic winds that can be devastating on the Antarctic coast, and in fact their mean wind speed along the year are the weakest known on Earth, less than 3 m/s. Besides the resulting absence of danger that such winds would present for large size optical instruments, this situation offers another benefit, which is an excellent free atmosphere seeing above a very thin but turbulent surface layer. This paper emphasizes these seeing peculiarities, but not only. It is presented as simply following a significant fraction of my slide presentation during the meeting.