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The highest frequency at which a radiotelescope can be used depends on the surface accuracy. The rms error of the surface should be less then l/16th of the shortest wavelength. This should be not only under static conditions but also when the telescope is being driven, under the influence of wind and temperature changes. With this in mind we can trace back the development of the paraboloidal dish since the time when Grote Reber constructed his antenna in Wheaton, Illinois.

The existence of ‘haloes’ in clusters of galaxies was deduced by Ryle and Windram (1968) for the Perseus cluster and by Willson (1970) for the Coma cluster at 408 MHz by comparing total flux measured by a single dish with the sum of fluxes of radio sources found in the field. A direct measurement of the extended source Coma C was made by Jaffe et al. (1976) at 610 MHz. the failure to detect the halo of Coma at higher frequencies is attributed by all authors to a steep spectrum of this extended component.

The accuracy of the absolute value of solar flux depends on the temperature calibration techniques and the knowledge of the gain of the aerial used for the measurements. Recent advances in low-noise receivers, microwave components, and amplifier stability have reduced considerably the errors due to temperature calibration techniques. At present the knowledge of the gain of the aerial used for calibrations (usually a pyramidal horn) presents the largest source of doubt of an absolute calibration. Investigations of this problem suggest that a ‘standard gain horn’ should be employed at all observatories in absolute solar calibrations.

The pulsed radio sources1,2 emit energy almost simultaneously over a wide frequency band3. Pulses from the source at 19h 19m 37s, + 21°47′02″ (epoch 1950) have been received with the Australian 210 ft telescope at frequencies of 85, 150, 630, 1,410 and 2,700 MHz. This report covers measurements of the spectrum of the pulses, the characteristics of the intensity variations at different frequencies, and observations of the structure and polarization of the pulses. A previous communication4 discussed measurements of the period of the pulses and of the dispersion between 85 and 1,410 MHz.

A large project of studying various transitions and isotopic species of CO in M82 has been carried out with the 30-m IRAM radio telescope. A l!6x1!0 area was mapped in 12CO(2→1) with 13″ resolution (Loiseau et al., 1988a). The purpose of these observations was to obtain high signal-to-noise, high resolution data for comparison with the 12CO(1→0) observations of Nakai et al. (1987). A 13CO(2→1) observation covered the central 1!0x0!7 region (Loiseau et al., 1988b) and allowed to establish the velocity field of CO in the inner nuclear region. The position angle of the rotation axis of 13CO is aligned with the optical rotation and at some 30° relative to the 12CO velocity field. The 13CO map also shows the existence of clumped emission in the central region.

The outstanding feature of the last triennium was most certainly the abrupt generalisation of the use of array detectors, particularly CCDs (charge coupled devices). The latter pervade all subdivisions of instrumental astronomy. The gains achieved by their high quantum efficiency, their stability, their capability of delivering immediately recordable signals which can be processed by appropriate computational means, have been the cause of spectacular progress regarding the photometric precision of weak signal measurements.

Publisher Summary This chapter discusses the basic concepts related to antenna calibration. Direct antenna calibrations of radio telescopes—such as the measurement of the polar pattern on a turntable—are usually not possible. Present-day radio telescopes are too large for these methods, which are generally employed in the testing of antennas for radio communication purposes. To achieve meaningful calibration by scaling, both a far-field measurement of the polar pattern of the model and near-field probing of the aperture field in the model and of the full antenna need to be combined. Consequently, very specialized and intricate measurements must be made before a successful antenna calibration is available. The criteria for the selection of calibration sources are described in the chapter, and lists of calibrators, both for positional and for flux scale calibration, are given. With a view of the discrepancies between observatories at frequencies of 408 MHz and below, discussion of present-day accuracy of the flux scale is undertaken. The techniques of calibration are described, as used in the tests of the 100-m fully steerable, paraboloidal radio telescope at Effelsberg. A description of the aims of a complete pointing theory is also presented.

Global configuration of magnetic field in several spiral galaxies were determined by analysing characteristic variation of Faraday rotation within the galaxy disks. The majority has an open spiral, bisymmetric field configuration, while some (10–20%) have a ring field.

Total-power and polarization observations of NGC 253 at 10.7 GHz have been performed with the 100-m MPIfR radio telescope. The observed arm/interarm polarization contrasts are discussed in the context of possible field configurations in spiral arms.

Total-power and polarization observations of NGC 253 at 10.7 GHz have been performed with the 100-m MPIfR radio telescope. The observed arm/interarm polarization contrasts are discussed in the context of possible field configurations in spiral arms.

A NEW series of observations of the galactic radio emission has been conducted at the frequencies of 20, 30 and 85 Mc/s. These low-resolution observations made with scaled aerials were intended to investigate the spectral index of the galactic radio emission in the frequency region 10–100 Mc/s.

High-resolution surveys of the galactic radio emission show detailed structure both near the galactic plane and at high galactic latitudes. Some of this structure is describable as ‘spurs’ while the rest comprises isolated features. We describe here measurements of the spectral index of the background radiation with a resolution of 3°.5. These measurements are aimed at a detailed understanding of the high-latitude synchrotron emission.

KNOWLEDGE of the intensity–frequency relation of extraterrestrial radio emission has been obtained from scaled aerial experiments at frequencies higher than 20 Mc/s (refs. 1 and 2) and from ground-based or satellite-borne radiometers operating below 10 Mc/s (refs. 3, 4 and 5). The low-frequency observations, whether ground-based or satellite-borne, are affected by the ionosphere. The consequence of these ionospheric effects has resulted in difficulties being experienced when reconciling the observations in frequency regions below 10 Mc/s with those above 20 Mc/s.

Pulsars display a complicated pattern of amplitude variations. The scale of variations range from months through hours to sub-milliseconds. The purpose of this note is to present polarization data for CP 1919 and intensity distribution data for PSR 0833—45 which are relevant to pulse-to-pulse variations and the variation over periods of hours respectively.

FOUR further pulsars have been discovered at the Molonglo radio observatory during a pulsar search at 408 MHz. One of the four pulsars, MP 0254, a high galactic latitude pulsar, was discovered in November 1968, but failed to appear on any of some twenty subsequent transits. In a recent observing session this pulsar was observed twice, allowing measurement of the dispersion and pulse width. Two of the pulsars (MP 1706 and MP 1911) were among many suspected pulsars noted during a close re-examination of the search records made since October 1968 using the two beam technique which led to the discovery of eighteen pulsars1–4. Recent observations have confirmed the existence of MP 1706 and MP 1911, and have enabled their properties to be measured. The fourth pulsar, MP 1154, was discovered during a search for high dispersion pulsars along the galactic plane using a two channel dispersion remover which was described in connexion with the discovery of MP 1240 (ref. 3).

THE pulsar CP 1919 (ref. 1) was observed at Parkes2 in March 1968 at a number of radio frequencies. On occasions the frequencies 85, 150, 150.9, 630 and 1,410 MHz were used simultaneously, with the 210 foot telescope tracking the source for some 4 h. The data have now been examined for statistical occurrence properties and a quantitative description of the source can be given. The statistics of pulse occurrence are of general interest because theories of emission (and pulse propagation) require these data. And anyway an observatory embarking on a programme of searching for such objects must know the statistical properties of pulse occurrence to aid in determining an observational programme.

WE recently described1 the discovery of seven pulsars found in a search at the Molonglo Radio Observatory using the 408 MHz radio telescope. A conclusion reached on the basis of this search was that pulsars are galactic objects associated with the disk or the spiral arms, but with a somewhat anomalous distribution. A zone of avoidance along the inner regions of the galactic plane was suggested, based on the argument that dispersion in the thin layer of an ionized medium closely confined to the galactic plane results in the loss of the distant pulsars. This communication describes the discovery of further pulsars which follow the same general pattern of galactic distribution.

Uniform distribution of radiated power is a necessary requirement in many aerial applications. Radio beacons and television transmitting aerials are examples of such a requirement. Aerials made from slotted circular waveguides have found application in engineering practice. We have computed the azimuth distribution of radiation from waveguides with eight and twelve, transverse slots. Combined with existing literature, the design of aerials with extremely high azimuth uniformity is possible.

A survey at 85 MHz is presented of the sky south of declination 0 = _20�,and of the northern galactic spur region to 0 = +20�. The survey was made withthe 210 ft telescope at Parkes, New South Wales. At this frequency the observedbeamwidth was 3.5� by 3� 8� to half-power points. The radiation characteristics ofthe survey aerial and of scaled aerial models were studied to enable corrections to bemade for radiation received by the aerial from regions outside the main beam.Absolute beam temperatures derived from the observed aerial temperatures had anr.m.s. accuracy of better than 7%.

A survey of the sky between S + 25� and S - 25� at 85 and 150 MHz is described, made with aerial beams 3.8� X 3.5� and 2.2� X 2.2�. Absolute measurements of aerial temperature are tabulated for points spaced 2�. A computer program is described which has enabled these results to be reduced to brightness temperatures, which are tabulated for the same points.

PULSAR surveys carried out at the Molonglo Radio Observatory during February and March, 1969, have resulted in the discovery of three new pulsars. They have been designated MP 0450, MP 1642 and MP 1818. The last two were found in areas of the sky which had not previously been searched for pulsars using the Molonglo radio telescope. The position of MP 0450, however, had been searched twice before during the pulsar survey programme, but the pulsar was not detected presumably because of long term variations of its pulse amplitude.

Measurements of sky intensity have been made at the frequencies 14�1, 20, 30,48�5, and 85 MHz with scaled aerials of low resolution directed towards declination S = - 34�. The measurements were carefully calibrated in terms of thermal resistors. Ionospheric effects were eliminated by planning of observations.

In the framework of the diffusive shock acceleration of relativistic electrons in extragalactic jets, we show that it is possible to derive the speed of the jet. For this purpose, we transform continuity relations through an oblique shock front into the reference frame of the observer. We apply these calculations to knot A of the M87 jet. Measuring the deviation of the fluid through the shock front from high-resolution radio maps and the deviation of the magnetic field from optical polarization maps (Fraix-Burnet et al., 1989), we derive speeds of about 0.01 c (Fraix-Burnet and Biermann, in preparation). The compression ratio is most probably 4 and the magnetic field is nearly parallel to the shock front both upstream and downstream.