Cynthia Utley, age 16, of Willingboro, N.J., for her question:

WHEN WAS RADIO ASTRONOMY DEVELOPED?

Radio astronomy is a branch of astronomy in which celestial objects and astrophysical phenomena are studied by examining their emission of electromagnetic radiation in the radio portion of the spectrum. Development of radio astronomy started in the 1930s.

Unsuccessful attempts to detect celestial radio emissions were made during the latter part of the 19th century. Nothing positive came from these first efforts.

Then in 1932, an American radio engineer named Karl Jansky became the first to detect radio noise from the region near the center of the Milky Way. It came about when Jansky was working at the Bell Telephone Laboratories. Jansky detected the noise during an experiment to locate distant sources of terrestrial radio interference.

The distribution of this galactic radio emission was mapped by an American engineer named Grote Reber. Reber used a 31 foot paraboloid that he built in his backyard in Wheaton, I11.

In 1993 Reber also discovered the long sought after radio emission from the sun. It was later realized, however, that solar radio emission had been detected a few years earlier, when strong solar bursts had interfered with the operation of British, American and German radar systems designed to detect aircraft.

As a result of the great improvements made during World War II in radio antennas and sensitive receivers, radio astronomers flourished in the 1950s. Radio scientists adapted their wartime radar techniques to the construction of a variety of radio telescopes in Australia, Great Britain, the Netherlands, the United States and the U.S.S.R., and the interest of professional astronomers was soon aroused by a series of remarkable discoveries.

Discrete sources of radio emission were catalogued in increasing numbers, and beginning in the 1950s many radio sources were identified with distant visible galaxies.

Quasi stellar radio sources called quasars were discovered in 1963.

Cosmic radio emission, so far as is known, comes entirely from natural processes, although from time to time radio telescopes are also used to search (so far unsuccessfully) for possible sources of radio emission from extraterrestrial intelligence.

Because of the random motion of electrons, all bodies emit thermal, or heat, radiation characteristics of their temperature. Careful measurements of the intensity and spectrum of emissions are used to calculate the temperature of distant celestial bodies, such as the planets in the earth's solar system, as well as of hot clouds of ionized gas located throughout the galaxy.

Radio astronomy measurements, however, often are concerned with the much more intense non thermal emission arising from charged particles such as electrons and positrons moving through weak galactic and intergalactic magnetic fields.

When the particle energy is so high that its velocity is close to the speed of light, the radio emission from these "ultra relativistic" particles is referred to as synchrotron radiation,

a term borrowed from the high energy physics laboratory, where this type of radiation was first discovered.