Peter Mezger and the Development of Radio Astronomy in the US and Germany, and the Discovery of Radio Recombination Lines

Abstract

Some aspects of the development of radio astronomy are traced, beginning with several important developments that occurred 50 years ago in 1944. The seminal paper of Van de Hulst in that year discussed the detectability not only of the 21 cm line of neutral hydrogen but also the recombination lines in the radio spectrum. However, because of a computation or transcription error, he over-estimated the effect of pressure broadening. After Kardashev reinvestigated the problem in 1959, two groups in Russia led by Dravskikh and Sorochenko, and one in the US led by Mezger, discovered these lines at about the same time. The recombination line program was the first success of the 140-ft telescope, which was the first major instrument of the fledgling National Radio Astronomy Observatory. This telescope proved much harder to build than anticipated for a variety of technical and managerial reasons. Mezger fully exploited its capabilities to measure recombination lines and map compact HII regions.