12.2.2. Parkes Survey

The most extensive survey of the Southern Hemisphere radio sources has been made with the 210-foot radio-telescope near Parkes, Australia. This survey was initially made at 408 MHz (75 cm), except for the region 20° > < 27°, which was surveyed at 635 MHz (50 cm). Each source detected in the 50- or 75-cm finding survey was re-observed at 20 and 11 cm to obtain more accurate positions and flux densities at these wavelengths. The Parkes survey essentially replaces an earlier survey made at 86 MHz using a Mills Cross-type antenna with a resolution of about 48 minutes of are. Unlike the Cambridge 2C survey, made about the same time and at nearly the same wavelength, the Mills Cross survey was mostly limited - not by inadequate resolution to separate nearby sources, but by low sensitivity. Nevertheless, later work has shown that this survey was surprisingly accurate for its time, at least for the sources not near the limit of detection.