The naked-eye cluster, Messier 7, is situated in the constellation of Scorpius, south of the great Sagittarius star clouds, and close to the galactic centre.

Clusters containing cepheids, and especially clusters containing more than one cepheid, provide information on the advanced evolutionary stages of massive stars, and on the factors which influence the period-frequency relations and lifetimes of cepheids. NGC 1866, in the LMC, is already well known in this respect. NGC 2010 was found by Hodge to contain two cepheids. Two more variables have been found in this cluster which, from their magnitudes and colours, are almost certainly cepheids, though we do not yet have periods for them. We noticed also that two known cepheids, HV 2868 and HV 2870, are associated with NGC 2136.

Over a period of one year from March 1967, the 24-inch rotatable telescope at Siding Spring Observatory was used to make polarization measurements for about 1400 stars, most of which were within 400 pc of the Sun. It was found that the E vectors of the polarization formed quite definite patterns on the sky which could only be produced if the magnetic field has a helical structure. Results of model-making showed that the magnetic lines of force form tightly wound right-handed helices of pitch angle 7°. They lie on the surface of tubes which have elliptical cross-sections of axial-ratio 3 with semi-major axes parallel to the galactic plane.

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.

During 1968 we have found at Parkes several types of emission in the lines of the 18 cm quadruplet of the ground-state OH molecule. This note describes a strong source of 1612 MHz emission near galactic longitude 331°.

OH emission was originally detected in the vicinity of HII regions, and a search of a large number of HII regions showed that about a third had associated OH emission. This type of emission is usually strongest at 1665 MHz, and is also seen at 1667 MHz and weakly on one of the satellite lines.

Observations of galactic HII regions in the longitude range 280° to 300° have recently been made at the OH-line frequencies 1612.231, 1665.402 and 1667.358 MHz using the Parkes radio telescope. Strong emission was observed at 1612 and 1665 MHz from a source near the regions of Hα emission RCW 48 and RCW 49 (Rodgers, Campbell and Whiteoak).

Time variations in both the NGC 6334 and Orion OH sources have been reported by the Berkeley group. The variations in NGC 6334 have been partially confirmed by the group at the Lincoln Laboratory, who show that the variations are confined to the southern source, NGC 6334B. These latter authors find variable components at —6.6 and —7.9 km/s at 1665 MHz and at —8.9 km/s at 1667 MHz. Both features at 1665 MHz appear to vary, both up and down, with time; during 1966 October the characteristic rise time was nine days or less. The Berkeley results show that the linear polarization was constant during a two-week period in 1965 October. The Lincoln Laboratory results from 1966 October to 1967 June show that both the degree and sense of circular polarization remain constant as the three features vary with time.

The lack of any direct measurements on the spin temperature of the neutral hydrogen in the Galaxy has led to considerable controversy in the past. Estimates of the temperature have depended strongly on whether they are based on emission or absorption studies. The widely accepted value of 125°K based on emission studies dates back to Schmidt. He adopted this figure on the premise that the maximum observed brightness temperatures in the galactic plane were in directions of high optical depth. The brightness temperature was then equated with the spin temperature on the assumption that the temperature did not fluctuate very much in a large region around the Sun.

In a current programme at the Molonglo Radio Observatory using the high-resolution pencil beam of the instrument (∼3′ arc) an attempt is being made to extend the measured spectra of known planetary nebulae down to 408 MHz. Of 23 such planetaries already investigated, 14 have been detected. The main results will be given elsewhere; here it is proposed to discuss in detail only the well-known planetary nebula IC 418.

The Orion Nebula is the best known and most often observed of the bright emission nebulae. However, the radio continuum spectrum of the nebula has been the subject of some misconception, particularly at low frequencies. A rediscussion is worthwhile as the spectrum has been used to derive an electron temperature for the nebula which is at variance with other determinations and carries important implications. Also some of the difficulties of measurement and problems of interpretation are relevant to similar investigations of other emission nebulae.

Electron temperatures of compact gaseous nebulae such as planetaries may be derived from radio-frequency data combined with isophotic contours accurately corrected for resolution effects, from the continuum jump at the Balmer limit and other features of the nebular continuum, and from forbidden line ratios.

The physical properties and spatial distribution of 12 pulsars discovered with the Molonglo radio telescope have been discussed by Mills. Several more pulsars have been detected and details will be published when the measurements are complete. Parameters of a recently discovered pulsar, MP 0628, are given in Table I. All the Molonglo pulsars have been found by visual examination of chart records. The use of pulse lengthening circuits to improve the visibility of pulsars on slow charts, and the continuation of the observations over several hundred hours with the greatest available sensitivity have been factors contributing significantly to the success of the Molonglo pulsar search.

The radioheliograph at Culgoora has recently been used to investigate the interesting changes which take place in the amplitudes of the pulses from PSR 0950+08, 1133+16 and 1919+21. The experiments had two main objectives: (i) to investigate the temporal changes in the spectrum near 80 MHz; (ii) to search for periodicities in the pulse amplitudes with periods extending up to one or two minutes.

Observations at a number of frequencies indicate that for at least two pulsars the average pulse shape has a slow but quite definite frequency dependence. Figure 1 shows average pulse shapes for CP 1919, CP 0950 and CP 1133. With the exception of those at 408 MHz these results were obtained at Parkes. The 408 MHz pulse shapes were obtained at Jodrell Bank by Lyne and Rickett. Circumstances of the observations are listed in Table I. Linearly polarized feeds were used at all frequencies.

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.

Gold has suggested that pulsars are rotating neutron stars with strong magnetic fields. We have studied the simplest such model, one having an external dipole field aligned with the rotation axis.

In a study of radio sources in the southern sky, observations have been made of 190 sources noted as ‘extended’, ‘possibly extended’ or ‘confused’ in the Parkes and other catalogues.

Radio contours are presented for Fornax A (NGC 1316), Virgo A (NGC 4486) and the central component of Centaurus A (NGC 5128). These three objects are intrinsically strong radio emitters identified with bright galaxies. The work forms part of a survey of all bright galaxies with the Molonglo cross down to a corrected total magnitude of 11m.0 with an extension down to photographic magnitude 12m.5 in an limited region of the sky.

Since the Molonglo cross-type radio telescope was completed in 1967 July, a considerable proportion of the observing time has been taken with calibrating the pointing of the north-south arm. In a current programme the aim is to obtain accurate positions for sources contained in the flux density catalogue recently prepared by Wyllie. This will provide a uniform set of several hundred positions and flux density calibrators covering the +20° to −90° declination range observable at the Molonglo Observatory.

The over-estimation of the flux density of radio sources near the lower limit of a survey has often been considered in the past. The use of digital recording and analysis techniques now enables a quantitative approach to the problem. Monte Carlo techniques may be used to determine the error distribution, including any systematic bias.