1912: Victor Hess discovers cosmic rays

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In August 1912, Austrian physicist Victor Hess made a historic balloon flight that opened a new window on matter in the universe. As he ascended to 5300 metres, he measured the rate of ionization in the atmosphere and found that it increased to some three times that at sea level. He concluded that penetrating radiation was entering the atmosphere from above. He had discovered cosmic rays.

Learn about cosmic rays: http://cern.ch/go/m6gm