Radio telescopes: single-dish and interferometers

By 1970 radio astronomy had emerged as a major tool for exploring galactic and extragalactic phenomena. The telescope antennae had grown in size and precision of surface from the early primitive World War II radar dishes. Greater size meant greater resolution and sensitivity; radio sources, including galaxies, could be mapped in finer detail and at larger distances. At the same time, the technology of radio receivers was undergoing rapid development; the intrinsic electronic noise of receivers, the background static, was (and still is) being continuously reduced so that any particular dish could detect fainter signals in a shorter observing time.

Notable among the very large steerable single-dish telescopes that had come on line at this point were the 250-foot telescope at Jodrell Bank near Manchester, UK (operated by the University of Manchester), the 300-foot telescope at Green Bank, West Virginia (the National Radio Astronomy Observatory or NRAO), and, by 1972, the 100-m radio telescope in Effelsberg, Germany (operated by the Max Planck Institute for Radio Astronomy, MPIfR, in Bonn, see Fig. 4.1).

The construction of larger and larger single-dish radio telescopes has engineering limitations and, fortunately, is not the only means of increasing resolution. Radio interferometers, the use of an array of antennae covering a much larger area, could, by combining signals, effectively act as one telescope with an enormously increased aperture.