The Pierre Auger Observatory is the largest telescope on Earth, covering a surface area of 3.000 km2. It is located in western Argentina near the city of Malargüe at an altitude of about 1.400 m.
Scientists are using Auger to measure the direction and energy of the most energetic cosmic rays that are continuously hitting the Earth. Some of these particles have energies that exceed those that can be produced by the most advanced man-made accelerators (such as the LHC at CERN, for instance) by several orders of magnitude. The cosmic acceleration mechanisms that lead to such extreme energies have not yet been clarified.