Radiation Hunter

Physicist Victor Hess prepares to ascend in a hot air balloon in April 1912 to measure a mysterious form of radiation later known as cosmic rays. Hess discovered that the rays are more intense at high altitudes than at the surface, indicating they come from beyond Earth. His 1912 flight took place during a total solar eclipse. The intensity of the rays did not diminish during the eclipse, eliminating the Sun as their source. Today, astronomers know the rays come from exploding stars, the cores of galaxies, and other distant sources, although the source of some cosmic rays is still unknown. [AIP]