The Discovery and Identification by Karl Guthe Jansky of Electromagnetic Radiation of Extraterrestrial Origin in the Radio Spectrum

December, 1957, marks the 25th anniversary of the completion of Karl Guthe Jansky's field studies which proved that electromagnetic waves in the radio spectrum of extraterrestrial origin were reaching the earth. April, 1958 will mark the 25th anniversary of the date on which this basic discovery was disclosed in full to the scientific world. This paper describes, briefly the steps which led to Jansky's basic discovery, some of the important results of later studies in radio astronomy, and the relationship between pure and applied science illustrated by the basic discovery and subsequent work in this field.