The huge parabolic antennas used in some radio telescopes, as well as other forms of high-gain antenna systems, can work for transmitting in the same way as they function for receiving. The large power gain developed in the interception of a faint signal from space also can increase the effective transmitted power of a signal greatly. By sending out short pulses of radio energy, generated by a transmitter in the laboratory, and then listening for possible echoes, astronomers can make accurate determinations of the distances to other objects in the Solar System. The use of radio telescopes for distance determination, motion analysis, and surface mapping of extraterrestrial objects is called radar astronomy.
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