Antoine Henri Becquerel (1852-1908) was a French physicist and the discoverer of radioactivity. After Wilhelm Conrad R?ntgen's discovery of x-rays, Becquerel noted an unknown energy that was emitted from uranium salts. He left a rock and a well-wrapped photographic plate in his desk drawer and found later that the plate, though unexposed to light, had developed patterns which would ordinarily indicate exposure. Announced in 1896, he had accidentally discovered a new "penetrating ray" that came to be called radioactivity. Soon after, his student Marie Sklodowska-Curie, and her husband Pierre Curie showed that thorium also emitted what were then called Becquerel rays. In 1900 Becquerel isolated electrons in radiation, and in 1902 he presented the first evidence of radioactive transformation. In 1903, he shared the Nobel Prize in Physics with Pierre and Marie Curie "in recognition of the extraordinary services he has rendered by his discovery of spontaneous radioactivity". He authored detailed studies of the physical properties of cobalt, nickel, and ozone, studied how crystals absorb light, and researched the polarization of light. He developed serious and recurring burns on his skin frrom handling radioactive stones which may have been a contributing factor in his "sudden death" in 1908 at the age of 55. The SI unit for radioactivity, the becquerel (Bq), is named after him. There is a crater called Becquerel on the Moon and also a crater called Becquerel on Mars.