Talk given at the International Cosmic Ray Workshop "Tien-Shan 2006", held from 25 to 27 August 2006 near Almaty, Kazakhstan; 8 pages, 4 figuresThe Pierre Auger Observatory aims to determine the nature and origin of the ultra-high energy cosmic rays (UHECR). The Auger hybrid detector combines fluorescence observations of extended air showers, initiated in the atmosphere by these most energetic particles, with measures of the shower front at the ground level by its large array of Cherenkov water tanks. This allows to improve considerably the precision on reconstructed primary cosmic ray parameters, and to make important cross-calibrations between two techniques at these energies, unreachable with accelerator experiments. The Southern Auger s...