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The early history of the Cavendish Laboratory is best known for ground-breaking work in the study of atomic structure, but the birth of long-distance radio communication also stimulated research on the properties of the upper atmosphere which enabled such propagation to occur. Begun by E.V. Appleton, who was later awarded the Nobel Prize in 1947 for his discovery of the ionosphere, radiophysics at the Cavendish was continued until 1939 by J.A. Ratcliffe and it was he who initiated radioastronomy in 1945. What triggered Ratcliffe's interest was an occasion in February 1942 when radar stations along the south coast were blinded by radio interference, initially thought to be jamming by enemy action, but later found to be radiation emitted by the sun when a large sunspot was present on the disk. Anxious to regenerate radiophysics at the end of the war, Ratcliffe attracted M. Ryle, a wartime colleague, back to the Cavendish and suggested that investigation of this new solar phenomenon might be an interesting project.
By 1946 Ryle had set up a primitive radio telescope and discovered that the sun was a continuous emitter of radio waves, in addition to the more intense outbursts associated with sunspots. More importantly, however, he demonstrated the existence of other celestial radio emitters, then called radio stars, and radioastronomy in Cambridge had begun. I joined Ryle's group in 1948 and this essay outlines the course of my personal research, leading to the discovery of pulsars in 1967, which has been ranked as one of the major astronomical breakthroughs of the past fifty years.
One of the most exciting aspects of modern science has been our growing understanding of the structure of the Universe and how it has evolved since the beginning of time. Scientific books do not usually rank amongst the best-sellers, but the outstanding success of Stephen Hawking's famous book A Brief History of Time shows how this subject has captured the popular imagination. To a large extent our present picture has come about through discoveries in radioastronomy in which Cambridge has played a leading role. In this chapter I shall sketch a few highlights of the Cambridge work.
The beginnings of radioastronomy in England were stimulated by the wartime discovery of radio waves emitted by the Sun. In the dark days of February 1942, shortly after the German warships Scharnhorst and Gneisenau had made their dash to base through the English Channel, anti-aircraft radar stations experienced severe jamming signals. At first assumed to be enemy activity, it was later found by J. S. Hey, engaged in operational research, that the signals came from the Sun's direction and were associated with an active sunspot, also seen by optical astronomers at the Royal Observatory, Greenwich. Systematic investigation of this unexpected type of solar radiation was an obvious choice for a university research group in radiophysics starting up again after the war.
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