a IRE TRANSACTIONS ON ANTENNAS AND PROPAGATION January

Radio Astronomy and Radio Science

LLOYD V. BERKNER, PRESIDENT, IRF:

HILE radio astronomy has added a new dimen- sion to the sciences of astronomy and astro- physics, its rigid instrumental requirements have

plowed the hinterland of ra- dio science. IT'hen widespread space communications arrive in the next few years, the in- strumental methods of space radio relay will be the direct derivatives of radio astron- omy. For the extremes of sen- sitivity, stability, integration capabilities and noise sup-

, pression have been basic re- ' quirements of radio astronomy for two decades. Likewise, an-

L. 17. BEREVER tenna and feed characteristics in radio astronomy represent

the limits of progress in radio optics a t any time. T o achieve these goals, instrumental development has been supported by the most advanced theoretical develop- ment of radiometers and antennas carried out in the physics sciences. And, in turn, these developments have provided to all radio science and technology a wellspring of fundamental knowledge that is applicable in almost every advanced endeavor in radio technology.

. In the field of astrophysics, the contributions of radio astronomy have been explosive. Its observational data point the finger directly to the processes of star formation and destruction, toward the basic processes of galactic evolution, and toward phenomena at the observational limits of the universe. Involving neutral hydrogen and ionized matter in magnetic fields in space, the hyper- fine 21-cm radiation and the polarized radiations in regions of nebulosity provide scientific opportunities that could only be exploited in the radio spectrum. Radio astronomy has shown us the center of our galaxy insur- prising detail, when before i t was hidden from view by

the intervening concentrations of dust in the plane of the 3.1 i 1 k y Way.

While optical astronomy deals primarily with stars and their aggregations into galaxies and galactic groups, together with some spectacular dust clouds of minor im- port, radio astronomy deals with the other half of the u n i v e r s e t h e masses of neutral hydrogen in various phases of concentration and condensation in the galactic areas and into new stars. I t views the movement of this material into and out of the galactic center. I t follows with special interest the disintegration products of the supernovae with their enrichment of the interstellar gas with heavy elements, explosions whose gases expand under strong magnetic control giving rise to marked wave polarization. Radio astronomy views special extra- galactic phenomena which points the optical telescope to extraordinary events among the millions of galaxies. In this, its capability sometimes transcends the limits of optical observations. I t may yet completely resolve the nearer galaxies such as the Andromeda into the special phenomena that, taken together, may characterize a typical galaxy more precisely. But, above all, radio astronomy has given a new insight to solar processes, especially the important active regions that give rise to chromospheric eruptions and solar cosmic rays. I t views the Sun as a typical astrophysical subject. Together with special observations, radio astronomy is revolutionizing our comprehension of solar and terrestrial relations.

T o achieve these successes, instrumental development has pushed outward the limits of radio science step by step. Since the historic observations of Jansky and Reber, of Southworth and Hey, of Purcell, Ewen, van der Hulst and Pawsey, sensitivities have climbed from power fluxes of to 10+4, 10-zj, lo-% and even watts/cm*/cps, and the end is not in sight. The low-noise input has given way to the parametric amplifier and to the maser with its input characteristics approaching noise levels at absolute zero of temperature. Methods of

1981 Berkner: Radio A4stronomy and Radio Science 3

input switching of a wide variety provide stability levels that promise measurement of antenna temperature dif- ferences of lop3 degrees. The old limit of 62 per cent feed efficiency seems about to tumble with improved Fresnel coverage to perhaps 85 per cent or better with cor- responding improvement of mainlobe-to-sidelobe ratio. Antennas are working to repeatable precisions of seconds of arc for reasonable scan distances, bringing them to- ward the precision of optical instruments. Precise meas- urements of polarization a t high sensitivity and stability have been brought within reach in the microwave ranges. Absolute measurements of radiation flux are setting new standards for precision in the microwave regions and with optimum horns promise to standardize sky sources to a repeatable few per cent so that variable sources can he studied. NYth high stability, integration methods provide useful measurements up to 50 d b below noise, so that only 40 kw gives useful echoes from the

Sun, nearly 1.5 X los km away, and integration is feasible over long intervals.

These and many other instrumental advances have been stimulated bl- the never-ending demands of radio astronomy toward new capabilities, toward new experi- mental opportunities. B u t their realization has advanced radio science as a whole to new capabilities. Radio as- tronomy has "put-on-the-shelf" a whole variety of ad- vanced radio techniques which have been quickly ex- ploited in radar, space technology, and advanced com- munications. I t represents, perhaps, the prime example of the cross stimulus of a science and a technology in pro- ducing enormous advance to both. And we must not for- get that this new dimension to astronomy was born from the curiosity and perspicacit>- of a radio scientist whose instruments and techniques brought him into contact with this new and now not so mysterious radiation that permeates the universe.