Scanning the sun with a highly directional array

A survey is given of the very highly directive equipment and methods which have been devised to obtain details of the distribution of radio emission over the solar disk. A new instrument is described; it operates on a wavelength of 21 cm and gives, for the first time, radio pictures of the sun. This radio heliograph combines principles of the multielement interferometer and the Mills Cross. It consists of 64 parabolic antennas, 19 feet in diameter, arranged along two lines, each 1240 feet in length, in form of a cross. Multiple pencil beams about 3' arc wide are produced by the system; by means of these, the sun is scanned television-wise. The radio heliograph is being used to produce daily pictures of the sun.