Artist concept of the Space Very Long Baseline Interferometry

Five radio telescopes in Australia and sixth in South Africa were synchronously operated for the first time as single radio telescope as wide as half the world from April 20 through May 3, l982.

The project to operate the telescopes in unison as single instrument to observe astronomical radio sources, called "very long baseline interferometry" (VLBI), was jointly directed by the Australian Commonwealth Scientific and Industrial Research Organization (CSIRO) division of radiophysics and NASA's Jet Propulsion Laboratory, Pasadena, California.

The resolving capability of both optical and radio telescopes is governed by the size of the aperture; the larger the aperture, the smaller the observable detail. Through computer processing, several radio telescopes thousands of miles apart are pointed at the same object and produce the same angular resolution as would single radio telescope several thousand miles in diameter. Thus the most distant and powerful sources known in the universe -- quasars and radio galaxies known to be as far away as 20 thousand million light years -- can be observed in great detail with networks of radio telescopes.

The VLBI technique is also useful for geodesy. By measuring the difference in the time of arrival of quasar signals at two antennas, the relative locations of the two


While the VLBI technique is commonly used in the northern hemisphere for astronomy and geodesy, the Australian experiment is the first time that VLBI has been used for detailed mapping of radio sky sources and high accuracy geodesy in the southern hemisphere. The precisely measured locations of the radiotelescopes will make it possible to monitor crustal motion in Australia.

A more advanced VLBI system is expected to be in full operation in Australia by l988.

VLBI data collected on videotape at each site will be combined and computer-processed at JPL to determine accurate antenna positions and to produce images of the observed sources.

The high resolution capabilities of the telescope system were used to investigate structure in the nucleus of the nearest giant radio galaxy, Centaurus A. Sagitarius A, in the center of the Milky Way, was also observed. In all, about 30 quasars and galaxies were studied in the two weeks of arraying of the telescopes.

Principal investigators of the experiment are Dr. Robert A. Preston of JPL and Dr. David L. Jauncey of the CSIRO.

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