Radio astronomy came into being in the late 1940s when astronomers realized that radio waves from outer space could be used, as light waves were used, to measure the physical characteristics of objects in space and their relative distances from the earth.
Radio astronomy has been concerned with the study of the strength, direction, and variation in radio emissions from the sun, moon, and stars. The principal tool has been the radio telescope, which uses a large, concave metal reflector and a directive radio-receiving antenna. In 1951, NRL produced the largest accurately figured radio telescope, a 50-foot, machined-aluminum, steerable paraboloid installed atop NRL's Building 43. NRL accomplishments using this telescope included:
- the first detection and measurement of interstellar ionized atomic hydrogen clouds as discrete radio sources (1953);
- the first detection of the absorption of emission of radio stars by interstellar hydrogen gas (1956);
- the first detection of radio emissions from Mars, Venus, Jupiter, and Saturn (1956 to 1958);
- the first successful measurement of surface temperatures of Venus, Mars, and Jupiter; and
- the first measurement of the spectrum of continuous radio emission from the Crab Nebula.