Abstract

We have carried out a campaign to monitor seeing at a 5640m altitude on the summit of Co. Chajnantor at Atacama, for the 6.5m telescope TAO project planned by the University of Tokyo. The seeing conditions were measured at 0.5?m using a DIMM (Differential Image Motion Monitor) during 8 nights in November 2006 and April 2007. In April, the measurement was done on a 2m-tower to suppress effect of ground-layer turbulence. The best night showed median seeing of 0.?38, while the total median seeing is 0.?69. This is comparable or even better than most of the major observatories. Together with the high transparency in infrared wavelength owing to the extremely high altitude of 5640m and its accessibility, the summit of Co. Chajnantor is one of the best site for infrared astronomy on the Earth.