Un interféromètre de type Christiansen fonctionne depuis Février 1958 à la Station de Nançay sur la longueur d'onde 3.2 cm. Cet appareil comprend 8 miroirs paraboliques de diamètre 1.10 m régulièrement disposés sur une poutre de 11.5 m à monture méridienne; le préamplificateur est monté également sur la poutre.

The observations of the sun at centimeter wavelengths made at Pulkovo in 1956–58 have shown: (1) There are regions of appreciable size over the majority of sunspots that have “enhanced” radio emission at centimeter wavelengths [1]. The nature of this emission shows that it belongs to the slowly varying component. In fact, as long as a group of sunspots persists, the flux of such an active region preserves its almost constant value. (2) The emission is partly circular, the polarized flux changing in magnitude but inappreciably. The sign of polarization rotation remains constant [2], which appears to be positive proof that a rather intense and stable magnetic field exists in these regions. (3) The extent of the regions is about that of the spot nuclei [3]. (4) Their brightness temperature amounts to several million degrees. (5) The height at which enhanced radio emission is produced is of the order 1.07 ± 0.02R⊙ [4].

In 1957 July the two-dimensional intensity distribution of radio emission over the solar disk was determined at 3.2- and 10-cm wavelengths. The observations were carried out on the radio telescope 31 m in diameter at the Crimean Radio Astronomical Station of the Physical Institute of the Academy of Sciences of the U.S.S.R. The radio telescope was an immovable parabolic reflector with the axis set in the meridian plane on 22-degrees declination [1]. Scanning the pattern of the radio telescope in the declination range ±32 minutes of arc to obtain the intensity distribution was done by setting the feed and preamplifier on a movable carriage reciprocating near the focal plane. In combination with the sun's daily movement it provided the two-dimensional solar distribution along a zigzag line. These sections gave the radio picture.

During 1957 we studied the solar radio radiation at a wavelength intermediate between the centimeter region with its slowly varying bright spots and the meter-wavelength region with its noise storms. At this intermediate wavelength (88 cm) the slowly varying bright-spot and the noise-storm producing regions merge into two aspects of the same persistent, bright, solar radio regions.

L'observation quotidienne du soleil à l'aide de l'interférometre à 32 antennes de Nançay [1] se poursuit sans interruption depuis le mois de Juin 1956. Bien que la période de maximum d'activité solaire dans laquelle nous nous trouvons ne soit pas très favorable à l'étude des propriétés du soleil calme, nous avons déjà obtenu un certain nombre d'enregistrements (3 ou 4 par mois en moyenne) absolument dépourvus des fluctuations toujours présentes dans le cas d'une émission non thermique liée à un centre d'activité, et de sursauts brefs de type I caractéristiques des orages de bruit.

La composante lentement variable du rayonnement radioélectrique solaire provient de régions d'étendue finie de l'atmosphère du soleil, dans lesquelles la température et la densité électronique sont normalement élevées. Ces régions appelées “centres d'activité radioélectrique” (C.A.R.) ne sont pas connues directement par les observations. En effet, les mesures journalières effectuées avec un radiotélescope fournissent une valeur du rayonnement solaire sur une longueur d'onde qui est la somme du rayonnement de base d'origine thermique de l'atmosphère normale et de l'émission d'un nombre indéterminé de C.A.R. sur cette longueur d'onde.

The K-coronameter developed at the High Altitude Observatory [1] to study the electron corona outside of eclipse has been in routine use since 1956 September. Up to the present date, usable observations have been obtained on some fifty-five days, and the accumulated information on the corona out to one solar radius from the limb has permitted the development of models of the electron corona above the quiet disk, the polar regions, and the active regions. The last of these, since it departs from the spherically symmetric model, should be of interest to radio astronomers.

The significance of 10-cm radio observations for studying the physical conditions in the lower corona of the solar atmosphere and for providing an index of solar activity comparable with the Zürich sunspot number is now well established. This radio emission from the solar disk has been observed daily at the Laboratories of the National Research Council of Canada in Ottawa since 1947, and the results interpreted in terms of a daily level of flux (near 17h U.T.) and of bursts of noise that may appear during the day.

Attempts to construct large parabolic reflectors for microwaves have met with the following difficulty. For normal operation of radio telescopes, the form of the reflecting surface must not deviate from the theoretical by more than 0.1λ; therefore, the larger its size the higher the requirements for relative accuracy (i.e., the ratio of the largest permissible deviation to the cross-section of the reflector). So far, a relative accuracy better than 10–4 has not been attained in any of the existing radio telescopes, and there are no grounds for supposing that it can be increased considerably.

Since the deviation from the theoretical form of the surface should not be more than 0.1λ, then for a relative accuracy of 10–4, the diameter of the reflector D cannot be much larger than 1000λ, and the beamwidth cannot be less than 3 minutes of arc (the beam angle is equal to about λ/D at half-power width).

The observations of the sun by the large Pulkovo radio telescope [1] began in 1956 December. In accordance with the antenna dimensions, a fan-beam diagram about one minute of arc in width and one degree in height was expected (at λ = 3.2 cm).

Radio-astronomical observations of the annular eclipse of 1958 April 19 (η = re/r⊙ = 0.939, ϕ = 18°14′34″.08, λ = −7h18m 01s.86) were especially interesting since this year was, apparently, the year of maximum solar activity. Some preliminary results of the observations carried out by a joint expedition of the Soviet and Chinese Academies of Sciences, equipped with seven radio telescopes, are described in this report.

Observations of the spectrum of solar radio bursts at meter wavelengths have indicated the desirability of measuring positions on the sun's disk not only as a function of time but also as a function of frequency. With this objective in view, we are now using a swept-frequency interferometer to determine the east-west disk coordinate of the transient solar sources at time intervals of ½ second and freqency intervals of about 5 Mc/s within the frequency range 40 to 70 Mc/s. The accuracy to which the centroid of the source is located is about ±1 minute of arc. In its initial form [1], the interferometer contained two aerials separated by a distance of 1 km. As a result of preliminary tests, two major additions have been made: (1) a second interferometer of much smaller spacing (¼ km) has been added to resolve the usual ambiguities associated with two-aerial interferometry, and (2) an automatic system of lobe-switching and phase-calibration has been incorporated to facilitate the reduction of the complex data recorded.

L'interféromètre à 32 antennes de Nançay [1, 2], a permis de caractériser un nouveau type d'émission sur 169 Mc/s accompagnant certaines éruptions chromosphériques. Cette émission s'identifie sûrement avec la deuxième partie des grands sursauts ou “phase d'orage” signalée par R. Payne-Scott [3] et H. W. Dodson [4], mais certains caractères la différencient cependant nettement des orages de bruit.

The sun has been observed daily at the University of Michigan during the last year with three sweep-frequency receivers covering the 100 to 580 Mc/s band three times a second. The output is displayed as an intensity-modulated line on a precision cathode-ray tube that is photographed on a 35-mm film moving about one centimeter per minute, thereby producing a frequency-time record with solar intensities recorded as variations in photographic density. The combination of the film characteristic and the logarithmic response of the IF amplifier permits the recording of a wide range of intensities in greater detail than before. A number of typical radio events associated with solar flares have been obtained; a typical sequence is a short group of intense type III bursts (fast drifts) followed within minutes by a type II burst (slow drifts) lasting 10 to 30 minutes, and followed by a type I noise storm, with or without a continuum increase, continuing for hours or days. The type I event is usually confined to frequencies below about 200 Mc/s, whereas the type III and type II (bursts) have been recorded up to 580 Mc/s.

The outstanding bursts of radio emission from the sun, which are termed spectral type II or “slow-drift” bursts, are a rare phenomenon. Even at sunspot maximum the average rate of occurrence is only about one burst every 50 hours, so that a long series of observations is needed to define the characteristics of the bursts. The present study uses the records made over the past 5½ years with the 40 to 240 Mc/s Dapto radio spectrograph. During this period, 65 bursts of this type were recorded.

During 1956-57, 15 type II radio bursts have been recorded on the Dapto radio spectrograph during times of observation with the Sydney Hα flare patrol camera. We believe that we have established identifications of the optical disturbances responsible for 13 of these bursts, and alternative identifications for the remaining two. As Table I shows, some of these were prominences ejected at the limb. Some were disappearing filaments that ejected matter and were accompanied by the development of two parallel lines of flares, one on either side of the position of the former filament. Others were flares, almost all being particularly bright and showing some evidence of dark-hydrogen activity.

The occurrence of increased radio noise at the onset of short-wave fadeouts (SWF's) was noted by Appleton [1], who attributed the enhancements to solar emission. Payne-Scott [2], observing at about 19 Mc/s, measured burst intensities and times of occurrence to compare these high-frequency phenomena with radio events in the VHF range from 50 to 100 Mc/s.

Apparatus for measuring changes in the received intensity of 18–Mc/s cosmic noise has been in operation at the Sampson Station of the Observatory of Rensselaer Polytechnic Institute since 1957 February. It is similar in principle to the equipment of the High Altitude Observatory on which is based the contribution of the Warwicks [1] to this Symposium.

The sweep-frequency equipment at the Harvard Radio Astronomy Station, Fort Davis, Texas, has now been running continuously since 1956 September, recording solar radio activity in the frequency range from 100 to 580 Mc/s. The following contribution describes preliminary investigations of the correlation of the radio data with solar corpuscular emissions. This work was initiated to examine the well-known suggestions that the origins of the type II and type III radio bursts are associated with the ejection of auroral particles and cosmic rays respectively.

It has been well established that a strong association exists between flares and type III bursts: Loughhead, Roberts, and McCabe [1] showed that 60 to 70 per cent of type III bursts occurred during the lifetimes of flares or microflares of apparent area exceeding about 20 × 10–6 solar hemispheres. On the other hand, only about 22 per cent of all such flares are associated with bursts. This low figure indicates that there are differences of degree or type between various flares, but the large area range involved shows that flare size alone is not the determining factor.