In 1908, an explosion occurred over central Siberia, releasing a blast of between 10-20 megatons at an altitude of ~10km, flatenning 2000sq.km of forest and causing distinctive 'glowing' sunsets around the globe. The cause of the explosion remains the subject of debate, with explanations for the occurrence ranging from Alien activity, to the distinctly more feasible asteroid or comet blast theory.
Tunguska - D.M.G. - Produced and edited by Daniel McGurty 2011
http://www.nature.com/scientificamerican/journal/v298/n6/images/scientificamerican0608-80-I3.jpg
