While optical telescopes -- instruments that collect and focus light to magnify objects -- had brought planets and stars closer to astronomers for centuries, in 1931 telescopes took on a whole new dimension that began to reveal the invisible universe as well.
American engineer Karl G. Jansky of the Bell Telephone Laboratories discovered radio waves from space and started the new field of radio astronomy. The first radio telescopes that were built consisted of large parabola-shaped dishes connected to recording and display equipment. The equipment could receive and analyze radio waves in a process that was similar to the way an optical telescope gathers and transforms light. But with radio telescopes, astronomers could tune in to stars and galaxies far out in the universe that gave faint or even no visible light, and they no longer had to worry about the interference of cosmic dust or the gloom of rainy days.
In addition to receiving radio waves, radio telescopes could send waves to bounce off objects in space. By listening to the resulting echo, astronomers could accurately measure the distance between Earth and space objects and could map physical details on objects in space as small as 300 yards across.
Since their invention, radio telescopes have allowed astronomers to map galaxies, discover quasars and pulsars (galaxies and objects that emit radio waves), and observe numerous complex organic molecules in the space between stars. Since 1960, they have often been used in the search for intelligent life outside our solar system.
