PROCEEDINGS OF THE IRE

Report on URSI Commission V-Radio Astronomy *F. T. HADDOCKt, MEMBER, IRE

OBJECTIVEST HE objectives of URSI Commission V are the in-

ternational exchange of scientific data, theory,and programs of investigations, and the coordina-

tion of observational programs involving internationalcooperative effort. Of particular interest are the contin-uous monitoring of solar radio emission at several fre-quencies, the coordination of Ursigrams, the setting upof a basic solar index from radio observations, the selec-tion of particular radio sources for a standard sequenceof radio intensities, and the coordination of effort invarious countries toward the protection of certain fre-quency bands for observational radio astronomy. It alsoinitiates, coordinates, or arranges symposia on subjectsof interest to radio astronomers.

TECHNICAL PROGRAMThe Twelfth General Assembly of URSI in Boulder,

Colo. was attended by radio astronomers from over adozen nations. Commission V's sessions were very heav-ily attended by both active participants and interestedobservers. The technical sessions consisted of the follow-ing: techniques of reception, large antennas (joint ses-sion with Commission VI), solar radio research, radiosources, radio propagation (scintillation, absorption,and refraction through the earth's atmosphere), radioemission from the galaxy, radio studies of the planetarysystem (radar echo observations of the moon, emissionfrom the moon, the planets and comets). In additionthere were joint sessions with Commissions III and IVon whistlers, and with Commission VII on masers.The chairman of each technical session opened with

a resume of progress in the general field of his sessionsince the Eleventh General Assembly held in 1954.

Techniques of ReceptionMore than a dozen separate radio telescopes were de-

scribed. These included the 10-cm solar instrument inOttawa, the 169-mc interferometer in France, the aper-ture-synthesis system in Cambridge, the helix inter-ferometer in Washington D.C., the 21-cm ChristiansenCross in Sydney, the precision interferometer in Tokyo,two sensitive traveling-wave tube radiometers in theU.S., the radio polarimeter for solar bursts at Cornell,and the 96-element Yagi array operating on 13 metersat Stanford.

* Original manuscript received by the IRE, April 17, 1958.t Past Chairman, U.S.A. Commission V; University of Michigan,

Ann Arbor, Mich.

Large Antennas

Large steerable, paraboloidal reflectors 25 meters indiameter and larger were described. These are locatedin Bonn, Germany; Dwingeloo, Netherlands; PulkovaObservatory, U.S.S.R.; and Manchester, England.Other types described are at Ohio State University,Stanford University, and St. Michel Observatory inFrance. Plans were reported for large instruments thatshould be in operation within the next year or two.These included the 140-foot steerable paraboloid forGreenbank, W. Va.; the 230-foot paraboloid for Sydney,Australia; the pair of 90-foot paraboloids on N-S andE-W tracks for use as variable-spacing interferometersfor Bishop, Calif.; the 85-foot precision reflectors forAnn Arbor and for Greenbank; the 84-foot reflector nowinstalled at the Navy Research Laboratory in Washing-ton; the plans for a 600 by 400-foot cylindrical parabo-loid at Urbana, Ill.; the 25 by 700-meter cylindrical paraboloid reflectors for an interferometer in Russia.The discussions and reports that followed included

the problem of confusion of radio sources within the an-tenna beam, the tolerances of reflectors, the advantagesof flat arrays steered by phase shifting, design problemsin paraboloidal reflectors, arguments for high resolutionand high antenna gain, the possible use of other reflect-ing surfaces, the focal ratio of paraboloids, informationtechniques applied to bandwidth, coherency of signal,etc., aperture blocking by the antenna feed, and im-portance of slide lobe levels, etc.

Solar Radio ResearchResults on the occultation of the radio source, Taurus

A (Crab Nebula), by the solar corona during the monthof June in the last five years were announced by scien-tists from Cambridge, Moscow, and Paris. Reports weremade on observations of the emission from the quiet sunat a wavelength of 8.6 mm during eclipse, on measure-ments of the sun at 21 cm with a 0.066-degree antennapencil beam, and on a number of observations at variouswavelengths from 6 mm to many meters. Observationswere reported from numerous groups on the nature ofsolar radiation from both the quiet and the active sun.Polarization of solar bursts, the dynamic spectra of solarbursts, the effects of Faraday dispersion in the solarcorona and Faraday rotation in the earth's ionosphere,and the escape of the extraordinary mode of propaga-tion from the sun were described. Correlation of geo-magnetic activity, solar flares, and cosmic rays werealso reported. Evidence of solar radio emission fromrelativistic electrons was presented.

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PROCEEDINGS OF THE IRE

Radio SourcesVarious characteristics of radio sources, both galactic

and extragalactic, were described in nearly two dozenreports. Measurements of the size of radio sources in-volved interferometer spacings of thousands of wave-lengths. This resulted in the measurement of diametersin seconds of arc, and radio effective brightness tempera-tures of millions of degrees. Detailed "isophotal" mapsof the intensity of radio emission over extragalacticnebulas at wavelengths of 21 cm, 120 cm, 370 cm, and187 cm were reported by various groups. The relativespectra of 30 radio sources using the brightest radiosource as a reference were reported by the Cambridgegroup. Results indicated a slight difference in the spec-trum index for galactic sources and extragalacticsources. Reports from Jodrell Bank and from the De-partment of Terrestrial Magnetism in Washington onthe spectra of sources at wavelengths below 30 mc weregiven. In this region the absorption of radio source emis-sion by interstellar electrons plays an important role.Several reports of "isophotal" maps of the radio con-tinuum emission from the Milky Way were described.Measurements by the French of the radio source HydraA, which was thought to be intrinsically variable, indi-cate that no variations greater than the experimentalaccuracy of about 5 per cent were recorded. The inten-sity of the four major radio sources at a wavelength of21 cm was reported by the Dutch to accuracy of about15 per cent. The Cambridge radio source survey statis-tics at 160 mc were discussed. This new survey was com-pared to the old survey at 80 mc and results are thesame; they both show an increase in the number densityof sources with source faintness. This paper provokeddiscussion on the confusion of sources within the radiobeam. It was stated that in order to avoid confusion onecould only consider one source for every ten to twentybeam widths of sky area surveyed as being reliable. Thiscriterion gives 100 sources per steradian with the Cam-bridge equipment and 400 sources per steradian with theSydney equipment. The criterion was arrived at inSydney from detailed analog statistical tests. A discus-sion of the radio emission from Coma Cluster of extra-galactic nebulas then followed. Reports were made onthe cosmological implications of the results of the Cam-bridge survey. The measurement of the linear polariza-tion component in the emission from the Crab Nebulamade at a wavelength of 3 cm with the NRL 50-foot re-flector was reported. This evidence supports the assump-tion of radio emission from the Crab Nebula by the syn-chrotron radiation mechanism. The Russians and theFrench discussed the occultation of the Crab Nebula bythe moon. They differed on the "center" of the radioemission. The Dutch also described similar occultationmeasurements of the Crab Nebula.

Radio PropagationReports on the scintillation of the major radio sources

at a number of wavelengths were presented, and the

origin of the scintillation associated with spread-F oc-currence and with irregularities in the F layer was dis-cussed. Altogether there were six reports over a widerange of frequencies on the scintillation of radio stars.Reports were also given on the atmospheric refractionand absorption at millimeter and centimeter wave-lengths. The attentuation of 4-mm waves by the at-mosphere and by clouds were reported. Fair weathercumulus clouds produce attenuations as large as 4 db.Various methods of computing the height responsible forradio star scintillations were critically analyzed, and itwas concluded that the defects in each method precludeusable height determinations at present. A theory forproducing ionospheric irregularities by the infall of in-terstellar particles was presented and was criticized.

Radio Waves from the GalaxyThis session included four reports on the galactic

background radiation from the radio continuum atwavelengths from 15 meters to 22 cm, hydrogen-linestudies of the structure of our galaxy and absorption ina region of radio sources, extragalactic 21-cm observa-tions, and a search for the OH-line emission. A reportfrom Sydney on a comparison of Mills crosses operatingat 19 mc and 85 mc shows clearly the absorption effectsof ionized hydrogen clouds lying in the galactic plane.The Dutch announced an outstanding finding that onespiral arm near the center of our galaxy, as seen in ab-sorption in front of a radio source, is moving at the ex-ceptional velocity of 50 km/sec from the center. TheHarvard group reported observations of expanding neu-tral hydrogen regions with galactic clusters around theOrion and the Lacerta associations. Radio red shiftmeasurements on extragalactic clusters of galaxies werealso described by the Harvard group. A report was madeon the comparison of the position of 200 sources inMills' catalog with objects on the 48-inch PalomarSchmidt plates. Various optical objects were associatedin position with radio sources: clusters of galaxies, ion-ized hydrogen regions, ordinary galaxies, double and pe-culiar galaxies, pairs and triplets of faint galaxies. It wassuggested that a number of radio sources could be as-sociated with ghost galaxies which are gaseous galaxiesnow devoid of stars because of collision between twogalaxies, the gas being left behind. An unsuccessful ef-fort to detect the 1667-mc spectral line from the OHradical was reported.

Radio Planetary SystemSeveral reports were made of detailed studies of moon

radar echoes. NRL contributed a study of echoes atwavelengths from a few meters to 10 cm. A significantfinding was that the echoes from the moon have a sharpclean leading edge which indicates that the echo comesfrom an unusually small central area of the moon. Thismakes it possible to measure precisely the distance tothe moon. The moon appears to be an extremelysmooth reflector of radio waves. The practical use of

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Haddock: Report on URSI Commission V

voice transmission via the moon was reported by thesame group as being accomplished in 1954 with a 100-watt transmitter and a 3-kc bandwidth receiver. A taperecording of a speech transmission echoed by the moonwas demonstrated to the audience. Reproduction wasimpressive. Measurements made at NRL at the wave-length of 10 cm display a leading edge measurable toabout 2 gsec. The result of two days' observation indi-cated a systematic error between the observed and thecalculated lunar distance of 9 km when based on theArmy Map Service value for the earth's equatorial radi-us. This discrepancy is eliminated when based on theEphemeris value for earth's equatorial radius. By directmeasurement of the distance to the moon it is possibleto determine the equatorial radius of the earth withintwenty feet. The Jodrell Bank report on the moon alsoindicated that the lunar echo originated from an area inthe central region of the lunar disk. Stanford Universityreported that at 106 mc, using two cross-polarized re-ceivers, both polarizations frequently faded simulta-neously and disappeared completely for twenty minutesat a time, indicating the presence of some unknown ef-fect. This unknown effect was also observed by theCanadians at a frequency of 488 mc. These "double-fade" observations cast doubt on the calculation of theinterplanetary electron densities based on the Faradaytechnique. The NRL group reported the measurementof thermal radio emission from Venus, Mars, and Jupi-ter. The Ewen-Knight group reported the detection ofthermal radiation from Saturn and the detection ofradio emission from planetary nebulae. They use atraveling-wave tube receiver at a wavelength of 4 cmwhich is able to record antenna temperature changes ofthe order of 0.01°K with an integration time of 5 min-utes. The National Bureau of Standards reported thedetailed analysis of nonthermal radiation from Jupiterbased on a model of the Jovian ionosphere. They con-clude that the nonthermal radio source resides on asolid rotating body with a period of rotation slightlyfaster than that observed optically on the atmosphere ofJupiter. There is an apparent relationship between non-thermal Jupiter radio emission and solar activity. Thegreater the solar activity, the less often the detection of

radio bursts from Jupiter. There were a number of re-ports of the radio bursts from Jupiter at frequencies inthe range from 15 to 30 mc. Ohio State University re-ported the detection of Jupiter bursts at a frequency ashigh as 45 mc. Yale University reported the possible de-tection of Jupiter-like bursts from Saturn. A series of re-ports followed on detection of radio emission from thebright Comet 1956h. The Belgians reported detection at600 mc, the Germans at 1420 mc, and Ohio State Uni-versity possibly at 20 mc.A large number of observers failed to detect the comet

at various frequencies from 19 mc to 10,000 mc.

REPORT ON THE BUSINESS SESSIONNumerous points of business were taken up during

this session. In particular, the following resolutions wererecommended to the Twelfth General Assembly, andwere later passed upon. The following Subcommissionsof Commission V were continued and their membershipwas brought up to date: Subcommission on the BasicSolar Index, under the chairmanship of S. Chapman andSubcommission on Standards, under the chairmanshipof C. L. Seeger. A new Subcommission on FrequencyAllocation was established, under the chairmanship ofF. T. Haddock, which is charged with preparing recom-mendations to be submitted to the International Tele-communications Union meeting in 1959.

Commission V recommended that URSI assent tothe request of the International Astronomical Union tosponsor a joint symposium on radio astronomy in Paris,prior to the General Assembly of the IAU in August,1958.Commission V also suggested the following persons to

serve on the joint URSI-IAU Organizing Committee:J. L. Pawsey (President, Committee 40, IAU) Chair-man; A. C. B. Lovell (President of Commission V);R. N. Bracewell, Editor; J. F. Denisse, Local Arrange-ments; R. L. Minkowski; H. C. van de Hulst; V. V.Vitkevitch; F. T. Haddock, Secretary; Fred Hoyle.A detailed report of Commission V activities at the

Twelfth General Assembly has been compiled. Personsinterested can write the author of this report for the fewremaining copies.

C~(A5

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