Contributions of overseas observatories

Before sketching the activities in radio astronomy elsewhere in the world, let me start with a brief historical survey. Radio astronomy had its beginnings in the United States, with the pioneer work of Jansky in the early 1930’s, followed by Grote Reber in the late thirties and early forties. Jansky, in the course of radio atmospheric studies at the Bell Laboratories, showed that at meter wavelengths the dominating source of noise is not terrestrial but celestial, with the radio intensity at 15‐m wavelength varying as a function of position in the sky. The most intense radiation came from the Milky Way in the direction of Sagittarius, which was known to be the direction of the center of our galaxy. Reber, who worked in h:s own back yard at Wheaton. Illinois, produced the first maps of sky brightness, at the somewhat shorter wavelength of 1.5 m and later at 70 cm. Taken together, these pioneer observations of Jansky and Reber raised puzzles which were inexplicable by existing theories and indeed are not yet settled, for the sky brightness was several orders of magnitude greater than expected. American physicists for the most part remained oblivious to this particular large‐scale puzzle of nature, and it remained for physicists and astronomers abroad to make most of the advances during the decade which followed World War II. Four groups have been outstanding: the Radiophysics Laboratory of CSIRO in Sydney, Australia; the English radiophysics groups at the Cavendish Laboratory and the University of Manchester; and the astronomers of the Observatory of Leiden, Holland.