Alex Rollins, age 13, of E1 Paso, Texas, for his question:
HOW DOES A RADIO TELESCOPE WORK?
A radio telescope is an instrument that collects and measures faint radio waves given off by objects in space. Radio telescopes collect radio waves just as optical telescopes collect light.
Most radio telescopes have parabolic or bowl shaped reflectors to collect the waves from space. These reflectors are made from wires or sheet metal. Motors in the telescope can turn the reflector toward any source of radio waves in the sky. The reflector then focuses these waves on a small radio antenna, which changes them into electric signals.
A radio receiver takes the signals from the antenna and tunes in only the signals that the astronomer wishes to observe. The receiver simplifies or strengthens the signals and then records them.
The signals may be recorded as wavy lines on paper or on a tape that can be analyzed by an electronic computer. The computer combines the signals from the receiver and uses them to draw a picture of the source of the radio wave.
Two or more radio telescopes can be connected to produce a sharper radio picture of an object than a single telescope can. Astronomers use the term "radio interferometer" for telescopes connected in this way. The longer the base line or distance between the telescopes, the better the interferometer can focus on an object.
Astronomers can make a very long base line interferometer, sometimes using telescopes located in different continents. Both telescopes observe the same object and record the radio signals from it on computer tape. A computer later plays the tapes from each telescope and compares the signals. In this way, astronomers can produce pictures of radio sources that are 1,000 times as sharp as images produced by light telescopes.
The world's largest radio telescope, with a reflector 1,000 feet in diameter, stands near Arecibo, Puerto Rico.
Many radio telescopes can also send powerful radio waves to the moon and to the planets nearest the earth.
After radio waves have been sent to the moon or to a planet, the telescope then picks up the radio echoes coming back. Astronomers call this technique radar astronomy because it operates on the same principal as radar.
By studying the radio echoes, astronomers can measure the distance to the moon or a planet. They also can use the echoes to make a map of the moon or planet that shows details as small as 300 yards.
American engineer Karl Jansky accidentally discovered radio waves from space in 1931. In 1939, an American amateur radio operator named Grote Reber built the first radio telescope.
After World War II ended, astronomers in Australia, England and The Netherlands experimented extensively with radio astronomy.
British astronomer Sir Bernard Lovell built the first giant radio telescope in 1957. The reflector of this telescope, at the Jodrell Bank Observatory in Manchester, England, has a diameter of 250 feet.