Radar was developed (c.1935–40) independently in several countries as a military instrument for detecting aircraft and ships. One of the earliest practical radar systems was devised (1934–35) by Sir Robert Watson-Watt, a Scots physicist. Although the technology evolved rapidly during World War II, radar improved immensely following the war, the principal advances being higher power outputs, greater receiver sensitivity, and improved timing and signal-processing circuits. In 1946 radar beams from the earth were reflected back from the moon. Radar contact was established with Venus in 1958 and with the sun in 1959, thereby opening a new field of astronomy—radar astronomy.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.