Paranal Observatory. Road leading up the Cerro Paranal mountain in Chile, towards the Very Large Telescope (VLT) at upper left. The VLT comprises four 8.2-metre mirror telescopes (Antu, Kueyen, Melipal and Yepun). The images from each are combined by interferometry, giving an image equal to that obtained by one 16 metre diameter mirror. This makes the VLT one of the most powerful telescopes in the world. The mirrors are flexible and are constantly adjusted by computers to compensate for errors. The VLT is operated by the European Southern Observatory. It is at an altitude of 2600 metres in the Atacama Desert, one of the driest places on Earth. This provides the VLT with excellent viewing conditions.