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The traditional approach to the extragalactic distance scale rests on a pyramid of primary, secondary and tertiary indicators of increasing range and decreasing accuracy. Thismulti-step procedure, fraught with the danger of cumulative errors, has led in recent years to two main, widely diverging scales: the ‘long’ scale (Sandage and Tammann 1974, 1975, 1976) implying a Hubble constant and the ‘short’ scale (de Vaucouleurs 1978, 1979; de Vaucouleurs and Bollinger 1979; de Vaucouleurs and Peters 1981; de Vaucouleurs et al. 1981) leading to H0 ≃ 100. Several authors have already shown that the long scale rests on very precarious foundations (Capaccioli and Fasano 1980, de Vaucouleurs 1981, Hanes 1980); counter arguments have been offered in its defence and to criticize the short scale (Tammann, Sandage and Yahil 1979, Sandage and Tammann 1982). For want of a conclusive test a consensus was still lacking.
This review is concerned mainly with the solar modulation of galactic cosmic rays and the progress that has been made since the Tenth International Conference on Cosmic Rays (Calgary, June 1967), My aim is to set out some of the advances in the basic theories; to indicate why certain disagreements between convection-diffusion theory and observations (noted in Webber’s invited review at Calgary) are to be expected; and to indicate some of the currently emerging areas of interest.
We give an account of the life and work of William James, including his many contributions to astronomy in Australia mainly through his skill in designing, figuring and testing aspheric surfaces.
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.
The problem of the surface migration of solar magnetic fields is discussed. It is shown that, unless some form of reconnection takes place below the surface, magnetic tension should effectively prevent such migration and the possibility of U-loop formation and transport is considered. As a first step, the buoyancy of a magnetic ‘U-loop’ within an isothermal atmosphere is considered. It is shown that such a configuration may form by the reconnection of the arms of an Ω-loop associated with an active region, and is likely to be buoyant initially and rise through the region. However, as it rises, the net buoyancy decreases and, provided that the temperature within the loop is even marginally less than that outside, it will reach a sub-surface configuration in which the net buoyancy is zero. The significance of this result for solar magnetic fields is then assessed.
Until comparatively recently solar activity was discussed in terms of independent centres around the Sun’s surface. These centres, which form a constantly but slowly changing pattern, were thought to be linked only beneath the photosphere by tangled magnetic fields, themselves dominated by the mechanical energy of mass motions at photospheric and lower levels. Recent discoveries now indicate that active centres interact with one another above photospheric level and especially through linkages within the corona. The linkages appear to be of at least two distinctive kinds: magneto-hydrodynamic shock waves capable of travelling vast distances through the corona at ∼103 km/s and triggering eruptions at distant centres; and magnetic field lines which loop high and wide in the corona and convey energy in the form of fast particles. These two kinds of interaction will be considered in turn.
The Parkes 64-m antenna has been used to map ammonia emission in the (J,K = 1,1) and (J,K = 2,2) transitions toward molecular cloud complex NGC 6334. This complex contains a number of OH and H2O masers, HII regions and IR sources, and is a rich source of molecular line emission.
Distributions of observed and derived quantities are presented with a linear resolution of ∼ 1 pc. Velocity anomalies are present near the two OH masers NGC 6334A and B, and the source of ammonia emission located near the northernmost H2O maser is one of the most intense sources of NH3 emission in the Galaxy.
The binary X-ray source GX 1 + 4 was observed during a balloon flight in 1986, November. The source was in a relatively high intensity state. Time analysis of the data shows that the pulsation period was 111.8 ± 1.0 s indicating that one or more episodes of spin-down occurred between 1980 and 1986. Folded pulse profiles are very broad with an indication of a notch at the peak. Evidence has been found for a correlation between hard X-ray intensity and phase of the proposed 304 day orbital period. The time averaged intensity since 1980 is an order of magnitude lower than during the 1970’s. A survey of the post 1980 data shows that several reversals of the period derivative have occurred. Spin-up at the rates typical of the 1970’s has been followed by a dramatic spin-down episode with dP/dt>2.4 × 10−7 s/s.
The role of astronomy in the cultural exchanges between India and China through several centuries is taken as an example of astronomy shaping human life. Then the tradition of astronomy in the development of scientific thought is examined. The contribution of astronomy in shaping the post-Renaissance society is briefly introduced. It is concluded that the recent developments of ideas in cosmology throw light on the intrinsic nature and limitations of the scientist as a human being.
Bursts of gamma rays lasting from a fraction of a second to several seconds have been observed by spacecraft since 1967 (Klebesadel et at. 1973). Events with fluxes in excess of 10−4 erg cm−2 s−1 are seen at the rate of several per year for gamma ray detectors with an energy threshold of ˜50 keV. The sources of these bursts remain unidentified and the mechanism(s) responsible for the production of the gamma rays remain(s) in the realm of conjecture. (For a review see Ramaty and Lingenfelter 1982).
Spectrometers give information on the chemical composition and physical properties of celestial objects. The Earth’s atmosphere restricts the observable spectra to windows in the absorption. Most of these windows are less than one octave wide. To increase the amount of information gained, it is necessary to increase the resolution of the spectrometers. With the advent of balloons, rockets and spacecraft, it is possible to make observations free from atmospheric absorption and it is possible to gain more information by increasing the bandwidth of spectrometers. This paper describes an infra-red Fourier transform spectrometer. The interferometer has a bandwidth of over one decade, from 500 to 5,000 cm-1, with a maximum resolution of 10 cm-1. The resolution can be electronically controlled. There are no absorbing or refracting parts in the interferometer and the resolution is limited by mechanical considerations.
The Parkes interferometer consists of the 210-ft para-boloidal reflector of the ANRAO, and a 60-ft paraboloidal reflector mounted on rail tracks. These extend from 400 ft to 1400 ft from the 210-ft paraboloid and run both north-south and east-west. The baseline may be continuously varied during observation; receivers operating simultaneously at 468 and 1402 MHz enable the determination of complete visibility functions over the range 200λ to 2000λ.
The history and achievements of interferometric angular diameter measurements have been reviewed recently by Hanbury Brown (1974) and only a brief outline will be given here. As the title is intended to imply, the present discussion will be limited to interferometry involving baselines in excess of telescope aperture diameters.
Following the ‘prompt’ radio outburst seen soon after the neutrino emission in SN 1987A (Turtle et al. 1987), we initiated a program to monitor the supernova at the Tidbinbilla Deep Space Communications Complex at 8.4 GHz in a search for radio emission from the expanding remnant. No radio emission has been detected to date (DOY 151, May 30 1988).
A knowledge of the on-ice seeing is a key requirement for planning future Antarctic observatories. In this paper we discuss the likely negative impact on seeing produced by the development of the deep winter surface temperature inversion (Ekman layer). The Automated Astronomical Site Testing Observatory (AASTO) will deploy, as one of its complement of site-testing instruments, an automated differential image motion monitor (DIMM) telescope designed to generate seeing data throughout the Antarctic winter. Here we describe the multi-aperture concept which has been developed for this mission, and touch upon some of the critical technological considerations associated with the low power budget and with the requirement of autonomous operation at very low temperature (–90°C).