Atmospheric focusing is a phenomenon occurring when a large shock wave is produced in the atmosphere, as in a nuclear explosion or large extraterrestrial object impact. The shock wave is refracted horizontally by density variations in the atmosphere so that it can have impacts in localized areas much further away than the theoretical extent of its blast effect. In large bombs, some effects may thus be found hundreds of kilometers from the blast site (such as in the case of the Tsar Bomba test, where damage was caused up to approximately 1,000 km away).