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Published online by Cambridge University Press: 14 August 2015
Since their discovery in 1946, the discrete sources of radio-frequency radiation have provided some of the most difficult problems in radio astronomy. For their effective study, one requires a very highly sensitive radio telescope sufficiently precise for accurate position determination and with sufficient resolution to observe separately the detectable radio sources. These requirements led to the development of the Sydney 3.5-m Cross-type radio telescope, which is a pencil-beam instrument with a beamwidth of about 50 minutes of arc and a sensitivity such that under ideal conditions a source of intensity about 1/10,000 that of the strongest known source, Cassiopeia A, is just detectable.