The 6 GHz transitions of the 2π3/2, J = 5/2 excited state of OH are present in emission in the direction of several OH-emission regions (Rickard et al. 1975; Knowles et al. 1976), and in absorption in compact thermal sources (Gardner and Whiteoak 1975). This has suggested that transitions in the next highest state near 13 GHz (J = 7/2) might also be widely observable. A single detection has already been reported in W3OH by Turner et al. (1970). In this paper we report the observation of narrow-band emission in several other sources.

A departure from an isothermal mass distribution in a rich cluster is expected if the genesis involves a coherent recollapse phase. The character of this departure is calculated and looked for in the data available for the Comma Cluster. No significant deviation from an isothermal mass distribution is found for r < 360’.

Hodge 11 (= SL 868) is a red, globular-like cluster (V ≅ 12.1, B—V = 0.62), situated on the east side of the LMC about 5 kpc projected distance from its centre (Gascoigne 1966). It was included in a programme to study the chemical evolution of the LMC by determining ages and metal abundances for a number of its clusters. Figure 1 shows a preliminary colour-magnitude diagram, found from four AAT plates calibrated with the AAT two-channel photometer. The choice of the radius, 1′.37 (23 pc), within which the stars were measured, was guided by the surface photometry of the cluster described later (Figure 3). But while it makes the number of “clean” stars inside the radius rather small, those outside it are too unlikely to be cluster members. As yet the calibration extends only to V = 19.6, and the nature of the cluster cannot be determined unambiguously. But Figure 1 already shows an unusual feature, in the very blue colour of the group of stars at V ≅ 19, B—V = 0.60, which on the usual interpretation would point to a metal abundance possibly lower than any yet encountered.

At the centre of the Parkes 64—m radio telescope a region of diameter 17 m has recently been resurfaced to improve its efficiency at high frequencies. The first measurements using this section have been made at 22 GHz, in observations of both continuum sources and water tfapour masers. For these observations the receiver front-end used a mixer cooled in liquid nitrogen, followed by a 5 GHz cryogenic parametric amplifier as a second stage. The option of switching against an offset horn was available and the total system noise temperature was ∽ 750 K.

The causes of various traits of the polar motion are still unknown or uncertain. For exploring these the Chandler nutation has the advantage of being readily observable and it should be independent of external torques. This nutation shows a prograde motion of the earth’s axes of rotation and of excitation about each other. For simplicity the positions of the poles of rotation P and excitation ψ (Munk & MacDonald, 1960) are given in terms of dimensionless excitation functions which apply in principle whether they come from distributions of mass, relative motions or torques. Let O be the pole of zero excitation and R be the angular distance between P and ψ.

One of the unusual features of the lenticular galaxy NGC 5128 is the presence of HI absorption (Roberts 1970; Whiteoak and Gardner 1971) and H2CO absorption (Gardner and Whiteoak 1976) against the radio source located near the nucleus. Using the Parkes 64-m radio telescope we have made HI and H2CO observations with improved resolution, and have also detected OH absorption in this galaxy. For the OH and H2CO observations, the equipment and observing procedure have already been described (e.g. Whiteoak and Gardner 1973; Gardner and Whiteoak 1976); for the HI observations they will be described in a forthcoming paper (Whiteoak and Gardner, to be submitted to Aust. J. Phys.).

A time scale may be defined as a system for dating events. A clock is a device for interpolating between observations of the time scale. From antiquity, time scales have been based on the earth’s rotation; even today, the atomic-based time scale Universal Coordinated Time (UTC) is adjusted annually, or when necessary, to keep it in time with the rotating earth. However, the continual search for greater accuracy in time keeping has led to the adoption of time scales based on other phenomena, so that there are now four classes of time scales in use, as summarised in Table I.

Over the past ten years, there has been considerable interest in the infrared continua of quasars, however few published colours exist in the literature. The only major compilation of infrared data out to 2.2 μ is that of Oke et al. (1970). The intrinsic faintness of the sources prevented the acquisition of significant high quality data. This situation is not expected to remain static for very long. The recent introduction of new high sensitivity InSb detectors has made it possible for a large number of sources to be measured, and published data is expected to increase significantly over the next few years.

It has been recently suggested (Crawford 1979) that there is an interaction between a photon and curved space-time that can be observed as a redshift of the photon frequency. Since the amount of the redshift is a function of the curvature it may be used to discriminate between gravitational theories. This is easily done using the parametrized post-Newtonian (PPN) limit fully described in the review article by Will (1972).

In November 1975 workers at the Herzberg Institute for Astrophysics in Canada (Avery et al. 1976) discovered cyanodiacetylene in Sgr B2. This molecule is the heaviest yet detected in interstellar space, having a molecular weight of 75 amu, and is the longest linear molecule known.

Rich clusters of galaxies are a common feature of the large-scale structure of the Universe. Those studied so far, show striking regularities with

1. (a) a smooth radial gradient of number density.

2. (b) ’isothermal’ distributions, which according to Bahcall (1975) have a scatter of only ±15% in the size of their characteristic core radii.

3. (c) their limiting structural diameters are ~50 Mpc (cf. Abell, 1975), if they are identified with superclusters.

4. (d) the magnitude of the velocity dispersion about their centres is generally 600-1000 km s-1, and the velocities are cpnsistent with a gaussian distribution (Yahil and Vidal, 1976; also Faber and Dressier, 1976).

5. (e) The extreme velocities are generally within ±3000 km s-1, and for Coma are ∼2400 km s-1 (Tifft and Gregory, 1976).

6. (f) elliptical galaxies tend to predominate near the centre, spirals in the surrounding loose groups.

When the separation between two stars becomes sufficiently small, tidal forces may cause one or both stars to disrupt. Roche (1850) studied the problem of the stability of a liquid in synchronous, circular orbit with a point mass, and predicted an instability of the liquid star for separations ≤ 2.5 r S⅓ where R is the initial radius of the liquid star, and S is the ratio of the mass of the point to the mass of the liquid star. Darwin generalized the problem to allow for two liquid stars in circular orbit. The whole of the classical research has been systematically analysed by Chandrasekhar (1969) using the tensor virial method. An error in Chandrasekhar’s analysis was corrected by Tassoul (1975).