New radiotelescope array gives astronomers a sharper electronic ear on the universe
To the naked eye the night sky is a familiar place. When the eye is replaced by a sensitive radio antenna, however, the sky becomes strange and unfamiliar.
"Gone from the night sky are all the familiar stars and constellations. The moon and planets are almost invisible, or even silhouetted against the brightly shining radio sky. In place of all the stars we have known for centuries there are sprinkled a host of brilliant new radio stars and new constellations, sharing the perpetual night of radio astronomy with the blazing band of the Milky Way, far more brilliant than it appears in ordinary light," explains Frank D. Drake of Cornell University.
Since 1932, when American radio engineer Karl Jansky discovered a background his coming from the center of our galaxy, astronomers have been exploring this new aspect of the heavens around us. They have discovered that the radio telescope has provided them with an invaluable window into the dynamic and violent processes that lie behind the apparent, celestial calm seen with visible light.
Until now the radio-wave pictures of the other planets, neighboring stars, dust clouds floating in space, and distant galaxies have been considerably less distinct than the images captured by the world's biggest and best optical telescopes.
With the dedication of a large new radiotelescope, prosaically christened the Very Large Array (VLA), in New Mexico last Friday, the situation has changed. Now radio astronomers can map the heavens with a degree of detail equal to or better than is the case optically, and they hope to use this new capability to solve a number of outstanding astronomical mysteries.
Rather than one giant and unwieldy parabolic dish, the VLA consists of 27 smaller dish antennas. Each is 82 feet in diameter and weighs 210 tons. These are mounted on cars that run on a set of 'Y' shaped railroad tracks. Each branch of the 'Y' is about 13 miles long. The tracks are laid out in a desolate , grama-grass covered basin in New Mexico.
Through a technical trick called "aperture synthesis" this collection of smaller antennas can mimick the performance of a single dish 21 miles in diameter. Each of the 27 antennas is pointed at the desired place in the sky. Then a computer is used to combine all these signals into the equivalent of what would be received by a single, larger antenna.
In addition, the VLA can be used a little like a "macro-zoom" telephoto lens on a camera, explains Robert Havlen, assistant director of the National Radio Astronomical Observatory (NRAO). To look at relatively close, diffuse sources such as a nebula, the antennas are trundled into a compact arrangement. To look at extremely distant sources, like enigmatic quasars, the antennas are stationed as far apart as possible.
According to the National Science Foundation, which funded the new telescope, it cost $78 million. This compares with a 1972 estimate of $75 million. So, taking inflation into account, it was constructed well within budget.
Radio astronomers are enthusiastic. Requests are running four to six times higher than can be scheduled.
In fact, the VLA was in use on a half- time basis during the latter days of its construction. Already it has made some significant scientific observations, Dr. Havlen says. These observations give some insight into how this new instrument will be used.
Since April the VLA has been following the course of a supernova, a tremendous stellar explosion, detected in April 1979. The telescope is taking a "snapshot a month" to give the first detailed view of a star in the process of self-destruction.
The new telescope has also mapped the aftermath of the birth of a star.And it has spent some time looking at neighboring planets.It has mapped part of the surface of Venus, looked at the gigantic radiation belts around Jupiter, and established that the surface temperature of Titan, Saturn's planet-sized moon, is a hundred degrees cooler than some other measurements had suggested.
The completion of the VLA signals the coming of age of radio astronomy.