Karl Jansky first discovered radio waves in 1931. In the late 1930ís an American engineer named Grote Reber built the first-bowl shaped radio telescope and operated it in his backyard. His radio telescope collected and measured radio waves given off by objects in space.
Scientists discovered that the Sun and the center of the Milky Way galaxy were strong sources of radio waves. Radio Telescopes also detected strong radio waves coming from black or dark places in space. These were discovered to be exploded stars and a rare type of distant galaxy.
How Radio Telescopes Work
Radio telescopes can produce images of objects in space that would have been missed by an optical telescope. Optical telescopes need to have some kind of light to see an object, but radio telescopes donít need light to "see." Radio telescopes helped discover pulsars (collapsed stars that send out regular pulses of radio waves) and quasars (extremely distant star-like objects that produce an enormous amount of radiation).
Many radio telescopes use a bowl-shaped reflector called a dish to collect radio waves from space. The reflector focuses the waves onto an antenna that changes them into electric signals. A radio receiver amplifies these signals and records their strength at different frequencies and from different directions. The information is analyzed by a computer to draw a picture of the source of the radio waves or to analyze the chemicals found in the source.
Large radio telescopes are also used as giant radar systems to map the surfaces of the Moon and planets. Scientists send radio waves into space to bounce them off of moons, planets, or other objects. Receivers record the radio echoes that bounce back to Earth. Astronomers call this technique "radar mapping."
Radar mapping works the same way as an ultrasound with a baby. The machine will bounce sound waves off the baby inside the mother, and when it bounces back, it will form a picture. The sound is a vibration and when the machine picks up the vibration bouncing back, it is catching the echo. It is also like a fish detector. The fish detector sends out a sound wave. The fish detector collects the sound wave when it comes back. The computer in the fish detector can tell you how far the fish are, depending on how long it took the sound wave to travel back to the boat.
Unless otherwise noted, all images courtesy of NASA. Permission for use at http://www.nasa.gov/gallery/photo/guideline.html.
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