By use of an apodized occulting dish before the objective lens of a coronagraph the instrumentally scattered light can be reduced to about 10-9 B⊙. Observation of the streamers of the solar corona from 1.8 to 5.25 R⊙ outside of eclipse from a balloon at 30 km altitude are described. A solar streamer complex present at the west limb on 5 March 1964 was apparently the origin of the particles causing the recurrent geomagnetic storms of late 1963 and early 1964.

A Lyot coronagraph with a saw-toothed external occulter was flown in an Aerobee rocket on June 28, 1963. Twenty-three white-light photographs, with exposure times from 1 to 56. seconds were secured at altitudes from 131 km to 204 km. The corona was recorded from 3.5 to 10 solar radii from the Sun's center. The coronal brightness function followed distributions determined during total solar eclipses; however, the brightness level was two to three times greater, suggesting that a significant quantity of light originates from small-angle forward-scattering by material between the earth and the sun, which is not illuminated during a total eclipse. One coronal streamer was recorded to about ten radii, before disappearing into the corona. Trails of slow-moving particles in space are conspicuous in most of the photographs.

Some possible strong astronomical emission lines in the infrared region are discussed. The line at 12.8 microns, which results from a transition between the fine structure components of the ground state of the ion Ne+, is thought to be emitted from galactic H II regions and also possibly from extended stellar envelopes. The line at 28 microns is emitted in the J = 2 to J = 0 rotational transition in the (para) hydrogen molecule, and could be emitted from interstellar H I regions and from collapsing protostars. Estimates of the expected intensities of these astronomical emission lines are given.

Observations from space vehicles of low frequency radio waves are discussed in relation to the observations made at higher frequencies from ground based observatories. It is shown that at frequencies below about 5 MHz the radiation is primarily extragalactic in origin, and that the observed values of sky brightness are consistent with the extrapolated values.

An absorption effect observed at frequencies below 2 MHz appears to be isotropic and suggests that the Sun is at the centre of an H II region with emission measure 5 pc. cm-6. It is shown that if this region is contained in the Galaxy it will have a significant effect on the synchrotron radiation from the plane and on the rotation measure of polarisation of discrete sources.

Observations of long-wavelength (λ > 30 m) radio radiation in space are reported and analyzed in the framework of the terrestrial environnement.

Measurements at low altitudes (~ 300 km) at the frequencies of 4.0 and 7.0 MHz have revealed the existence of very high radio noise levels during the night and on certain occasions during the day. These strong signals were at least 50 db higher than the expected cosmic background and are attributed to man-made and atmospheric radio noise.

Measurements at high altitudes (3000–11000 km) at the frequencies of 2.2 and 0.7 MHz have produced a flux value at 2.2 MHz in agreement with the expected cosmic radio background, but the flux value obtained at 0.7 MHz is approximately 15 db higher than the anticipated flux from cosmic sources. Harmonic gyroradiation from the artificial and the outer Van Allen belts might be the cause of the high radio flux observed at 0.7 MHz.

Since September 29, 1962, a sweep-frequency receiver covering the range 0.5 to 12 MHz has been operating in a 1000 km height, 80.5° inclination orbit about the earth for about 5 hours a day on the average. Only a very small portion of the data has yet been analyzed, and from this the spectrum of the galactic radio emission between 1.5 and 5 MHz has been determined fairly reliably, but it has not been possible from these data to extend this up to 10 MHz with any accuracy. Although there is no provision for absolute gain calibration of the receiver in flight, the data are so consistent as to give confidence to the pre-flight calibration. The greatest uncertainty hinges on the effects of the ionization on the antenna impedances. To evaluate these, galactic noise measurements have been made under a variety of local electron densities and different magnetic field strengths : these values have then been extrapolated to zero electron density and the free space values obtained by this extrapolation procedure are taken as a measure of the galactic emission. At 2.3 MHz the brightest region of the galaxy is centred on the south galactic pole and has a temperature of about 1.8 × 107 °K. The lowest temperature, about 5.0 × 106 °K, at 2.3 MHz was found for the region centred on R. A. 9 hr., dec + 75°. At this same frequency the brightness temperature versus frequency curve has a elope of — 1.7; at 1.5 MHz the slope is — 1.3 and at 5.0 MHz the slope is — 2.2.

The receiver in the satellite UK-2 is briefly described. Interference-free data received where the satellite is near the apogee of its orbit is of interest for astronomical and ionospheric work, and typical samples of such data are shown, the salient features being pointed out. Among the tatter are the ionospheric noise bands, and the propagation of waves in the i-mode. The method of determination of the orientation of the satellite at any given time is described, and the consequent conclusions about the polarisation of the signals are stated.

A critical review is given of the theory and experimental observations of antenna impedance behaviour in a plasma, as related to radio astronomy. The emphasis is on electrically small antennas. Three simplified cases of plasma are considered, namely, cold plasma without magnetic field, cold plasma with magnetic field and warm plasma without magnetic field. Newly reduced experimental results are reported for the case of cold plasma without magnetic field, showing detailed agreement with theory in the neighbourhood of a cutoff in the propagation of the extraordinary magnetoionic wave.

The admittance of a wire dipole of overall length 20 m was measured at a height of approximately 125 km in the night-time ionosphere. Measurements were obtained at 60 kHz and at a frequency swept over the range 1.4 MHz to 1.8 MHz so as to include the gyro frequency. The results are interpreted in terms of a theory due to Kaiser, and fair agreement is obtained. The electron density and collision frequency in the plasma surrounding the aerial are estimated.

A radio antenna within the ionosphere can receive extraterrestrial radiation incident only within a limited cone of directions. A brief review is presented of the theoretical calculations, using various models, of the size and shape of the cone, and the magnitude of the received signal, both from a uniformly bright sky and from a single point source. The approximations of ray theory are discussed and the effects of the curvature of the earth and the inclusion of the terrestial magnetic field are mentioned.

Solar radio noise in the frequency range 1.5 to 10 MHz appears sporadically in the Alouette sweep-frequency recordings above the galactic noise level. The type III bursts can be readily identified, but other spectral types are much more difficult to identify from only the satellite records. Using a plausible model for the coronal electron densities, the Type III frequency drift curves have been interpreted as corresponding to a source velocity in the range 0.1 to 0.15 times the velocity of light. Preliminary estimates have also been made of the coronal temperatures from some of the burst durations.

Other solar noise events of longer duration have not been classified other than as enhanced solar noise at this stage. These enhancements frequently show an intensity structure, extending down to the 1.5 MHz lower frequency limit of the equipment. These events are discussed briefly.

A study program was initiated at the Goddard Space Flight Center in 1962 to survey the astronomical observations most readily and profitably performed by an orbiting radio observatory, to analyze the antenna configurations most appropriate for such a mission and to develop the radiometers and other supporting instrumentation required for a radio astronomy satellite. This study has culminated in the conceptual design of a spacecraft intended solely for radio astronomical observations at wavelengths beyond the ionospheric cut-off. By utilizing long (250 m) antenna elements with a terminating resistance placed an odd number of quarter-wavelengths from the end, a V-antenna can be formed having a beamwidth less than 30° and an 18 db front-to-back ratio over a band of frequencies near 5 MHz. Proper combinations of four such long elements in a double-V or X configuration, furthermore can be made to yield some gain over a, dipole for observations as low as 0.3 MHz. A step-frequency, Ryle-Vonberg radiometer which employs an all solid-state-component comparison noise source has been developed to perform over a 70 db dynamic range with a relative accuracy of ± 0.5 db. A simple, precise instrument to measure both the resistive and reactive components of antenna impedance has also been developed for satellite use. Observations with this system from a gravity-gradient stabilized spacecraft in a 6000 km orbit would afford significant contributions to galactic studies, solar physics, and planetary astronomy by extending radio observations to frequencies in the range 0 3 to 10 MHz.