Chronology of Background Radiation Fields
| 1912 | Victor Hess discovers that the ionization of air increases with altitude indicating the existence of cosmic radiation, |
| 1956 | Herbert Friedman detects evidence for extrasolar X-rays. |
| 1962 | Riccardo Giacconi, Herbert Gursky, F. Paolini, and Bruno Rossi formally discover the X-ray background. |