T HE WORLD'S FIRST radiotelescope designed specifically for astronomical observations was built in 1937, a few years after Karl Jansky's pioneering discovery of radio waves from the Milky Way. The radiotelescope was conceived by Grote Reber who built the instrument practically unaided in his own back yard at Wheatstone, Illinois. It consisted (figure 1) of a 31-ft parabolic reflector which focused the radio waves arriving from a small region of the sky onto a focal dipole. The signals were then amplified and detected in a high-frequency receiver and the output registered on a pen recorder. Reber's radio telescope (preserved at the National Radio Astronomy Observatory, Green Bank, W. Va.) stands as the prototype of the giant instruments that exist today.