Albert Einstein (1879-1955), physicist, at the Yerkes Observatory, Chicago, USA in 1921.
(c) Science Photo Library /Historisk Bildbyrå
Einstein (right of centre) was born in Germany but became a US citizen after emigrating there in 1933. The Yerkes Observatory houses a 40-inch refracting telescope, the largest ever used. Einstein's mass-energy equation resulted from his 1905 paper on Special Relativity. This paper, with his 1915 General Theory of Relativity, replaced the Newtonian world view, rewriting our concepts of gravity, space and time. In the year this photograph was taken he won the Nobel Prize in Physics for his work on the photoelectric effect.