Radio and radar astronomy and the exploration of the universe

The role of radio and radar astronomy in space exploration is discussed and compared with present and future techniques that use electromagnetic waves of all lengths, gravity waves, atomic particles, etc. A brief description of the universe is then given with the aid of a series of scale drawings, and the possible ranges of the different techniques are considered. The place of space probes and manned space travel in space exploration is also mentioned. It is pointed out that radio astronomy is not only the most promising technique presently available for observing the most distant parts of our universe but it may be the only one.