Ryle , Sir Martin

(1918–1984) British radio astronomer

Ryle, the son of a physician, was born at Brighton and studied at Oxford University. He spent the war with the Telecommunications Research Establishment in Dorset working on radar. After the war he received a fellowship to the Cavendish Laboratory of Cambridge University and in 1948 was appointed lecturer in physics. In 1959 he became the first Cambridge professor of radio astronomy, having been made in 1957 the director of the Mullard Radio Astronomy Observatory in Cambridge. Ryle was appointed Astronomer Royal in 1972 and in 1974 was awarded, jointly with Antony Hewish, the Nobel Prize for physics. He was knighted in 1966.

It was mainly due to Ryle and his colleagues that Cambridge, after the war, became one of the leading centers in the world for astronomical research. He realized that one of the first jobs to be done was simply to map the radio sky. He therefore began in 1950 the important series of Cambridge surveys. The first survey used the principle of interferometry and discovered some 50 radio sources. The second survey in 1955 listed nearly 2000 sources, many of which turned out to be spurious. The crucial survey was the third one, the results of which were published in 1959 in the Third Cambridge Catalogue (3C). This listed the positions and strengths of 500 sources and has since become the definitive catalog used by all radio astronomers. The use of more sensitive receivers in 1965 enabled the 4C survey to detect sources five times fainter than those in the 3C and covered the whole of the northern sky; 5000 sources were cataloged. Finally, with the opening of two highly sensitive radio telescopes in 1965 and 1971, important areas of the sky are being surveyed in depth: a full survey would take over 2000 years.

The two new telescopes, the One Mile telescope and then the Five Kilometer telescope, operate by a technique developed by Ryle and called ‘aperture synthesis’. A number of radio dishes are used to give a very large effective aperture, much larger than the aperture of a single dish, and hence produce very considerable resolution of detail in a radio map of an area of the sky. The dishes are mounted along a line, some fixed in position, some movable, and are used in pairs, at different distances apart, to form interferometers.

These telescopes and other equipment were used by Ryle and his colleagues to investigate pulsars, which were discovered at Cambridge by Antony Hewish and Jocelyn Bell, quasars, radio galaxies, and other radio sources. Ryle quickly appreciated that the distribution of radio sources throughout the universe had cosmological implications and that the number of sources found tended to support the evolutionary big-bang theory rather than the steady-state theory.