The radio astronomy observatory of the University of Cambridge. The main instrument is an Earth rotation synthesis interferometer, which consists of eight 13-metre 43-foot dishes on an east-west baseline 5 kilometres 3 miles long. This is called the Ryle Telescope after Sir Martin Ryle who founded the observatory in 1946 and was its first director. He was joint winner of the Nobel Prize for Physics in 1974 for the development of the principle of Earth rotation synthesis. In addition, there is a low-frequency deep-survey telescope of Yagi antennas operating at 151 MHz and using the same principle. The observatory has specialized in cataloguing radio sources, producing the Third, Fourth, Fifth, Sixth and Seventh Cambridge catalogues abbreviated to 3C, 4C etc. at different frequencies. These have led to the discovery of many quasars and radio galaxies. The first pulsars were detected at the MRAO in 1967. A development of the 1990s has been the construction of an optical interferometer COAST.