The huge telescopes in the Namibian desert
Cosmic gamma rays collide with the Earth day and night, but the elusive sparks of Cherenkov light they give off can only be observed on moonless nights far away from human habitation. This large telescope forms part of the HESS experiment, and is waiting for the sunset on the Namibian plains to start recording data. It is when the four telescopes simultaneously record the same spark that the cosmic gamma ray direction can be accurately determined.