(Government Astronomer : Retired)



The following article was written by the late Dr. Harley Weston Wood DSc FRAS (31st July 1911 − 26 June 1984), who was only just retired as the 7th Government Astronomer of New South Wales in 1974. Australian born from the country town of Gulgong N.S.W., near Mudgee, he started work as a school teacher, but changed to an astronomical career when he was appointed as Assistant Astronomer at Sydney Observatory after the death of James Nangle in 1941. He began work during the Second World War years in 1943, where he began activities in doing time observations in Sydney for the war effort and in training of service men in the art of sea navigation or movements under the cover of night. This resulted in the publication Elementary Astronomy for Service Use (See these pages within Southern Astronomical Delights.) His work continued the long project of the Astrographic Catalogue, which was started in the 1880s under Henry Chamberlain Russell. The work for this was greatly expanded after 1944, when Melbourne Observatory was closed by the Victorian Government. Here Sydney Observatory continued the Melbourne Observatory parts of the sky for the star catalogue. Dr. Wood was also very active in the fight to save Sydney Observatory as a functioning observatory until the place was changed into an historical site and astronomical museum during 1982. The Observatory is now managed by the Powerhouse Museum (Museum of Applied Arts and Sciences) under the Curator of Astronomy, Dr Nick Lomb.

Dr. Wood became the first President of the Astronomical Society of Australia (ASA) in 1966 through to 1968, and is properly remembered with the public ASA Harley Wood Lecture beginning in 1987, which started just two years after his death at the age of 71 years, and now also the annual Harley Wood Winter School.

Dr. Wood was a great populariser of astronomy in Sydney for both the community and among amateur astronomers. I first meet Dr. Wood as a visitor to Sydney Observatory at the age of eight or nine years old, and he was among the first to guide me in the right direction and my further interest in astronomy.

Additional information and a portrait of him can be found at the the Sydney Observatory Website at; Harley Wood Public Lecture on Monday 2 July.

An obituary of him appears in ; QJRAS, 26, 2, p.219-223, (1985)

I have attached this particular article to the Australian historical section of Southern Astronomical Delights, as it reflects the optimism of Australian astronomy in the 1970s, where the country interest into modern day astronomy was in an ascendancy, especially with the creation of the large world-class optical telescope of the Anglo-Australian observatory at Siding Spring near Coonabarabran. This was the time when our knowledge of the southern Milky Way and Magellanic Clouds were thoroughly being investigated for there importance.

This article has personal interest to me, as it was one of the first I had read about astronomy from the Australian point of view. At the time I didnt know much about astronomy at all, and this inspired me to learn more about it. I even heard the late Dr. Wood present this very same lecture to the British Astronomical Association (N.S.W. Branch) in late 1974. I have obtained this from a hand-out given at that meeting. I know of no other published version, and would be interested in finding its original source. It is historical enough to warrant publication, and gives insight to the development of national astronomy from the individual States in Australia to wholly the domain of the Federal Commonwealth of Australia. Enjoy!

Andrew James : 01st October 2007

[1924 to 1974]

Government Astronomer (Retired)

The fact that I have recently retired gives me an excuse for talking about the course taken by astronomy while I have been interested in it and about the work done at Sydney Observatory in my time.

Astronomy has gone through a great change, indeed a transformation, since my first contact with it. My interest began at school in the early 1920s, which justifies the 50 year period in the title. At that time a school friend and I built small telescopes, with which we got a great deal of star-gazing Pleasure, and read every bit of astronomical literature on which we could lay our hands. At that time it was not recognised that most of the nebulous patches which appear in the sky are really great systems of stars. Catalogues of them have been compiled for about 140 years and over 13,000 objects included but there was still difference of opinion as to whether or not they could be systems of stars. It was true that their spectra corresponded to integrated star light and novae appearing in, them seemed to indicate a distance compatible with their consisting of stars. However, supernovae had also been. observed and as these had not yet been recognised their interpretation as ordinary novae gave the distances as much closer. Then in the early 1920s, just the period when my interest was being stimulated, the Andromeda Galaxy was resolved into stars by Edwin Hubble who interpreted the distance as being about a million light years. This at once resolved the problem and enormously enlarged our concept of the universe.

The galaxies populate the whole of the space, which is accessible to observation from the Earth, that is to a distance of several thousand million light~years. Many millions are observable by the largest telescopes. The distances of the nearer ones can be found by means of their stellar contents. The galaxies occur sometimes in clusters about 3,000 of which have been catalogued. Investigations of these give the greatest fairly reliable distances. Measurement of Doppler shifts of the spectral lines of the galaxies leads to the important result that the velocities away from us of distant galaxies are approximately proportional to their distances, the velocity being about 30 kilometres per second greater for each additional million light-years.

A natural conclusion from recognition of most of the nebulae as great systems of stars was that the Milky Way belongs to the same class. Since we are situated within the Milky Way it was a difficult task to untangle its structure and even its size. The size came to be fairly reliably recognised from a study of globular clusters of stars made by H. Shapley. These clusters of stars are tightly packed groups containing up to several hundred thousand stars.

The distances of these clusters could be found by recognising their stars and from this deriving means of determining the distances of others. They were found to lie in a system which seemed to be coextensive with the Milky Way with the centre of the system in the direction of the constellation Sagittarius. At first this gave a diameter of 200,000 light years for the Milky Way. But the role of absorbing material in the galaxies had not then been realised and when it came to be so it was recognised that this material made distant objects appear fainter and [2] therefore more distant. The revision of the size leads to a diameter about 100,000 light years in the plane of the Milky Way, which is disc-shaped and much thinner perpendicular to its plane.

A flattened system such as even the naked eye reveals the Milky Way to be, must be in rotation and naturally it was thought that the Milky Way must have a spiral structure similar to that observed in galaxies. Some traces of this structure were revealed by studies by W. Morgan of bright blue stars which had been found to inhabit the spiral arms of galaxies.

In this period a new and powerful tool for astronomical research was being developed. In 1932 Jansky of the Bell Telephone Laboratories detected radio waves from the densest part of the Milky Way and in 1940 Grote Rober, a radio engineer working as an amateur, made a map of the sky at a frequency of 460 megahertz. Then, arising from a suggestion by a Dutch astronomer, a spectral line of 21cm. wavelength from neutral hydrogen in interstellar space was discovered. The importance of a discovery of a line lies largely in the fact that Doppler shifts of the wavelength of the line yield radial velocities of the material in which the line arises and the intensity of the line is related to the amount of the material. By analysis of the results of observations on this spectral line over wide areas of the sky, it was possible to derive a model which gave the velocity of the material at different distances from the centre of the Galaxy. Using this model the inverse process became possible. That is, by observing the velocity indicated by the line it was possible to determine the position in the Milky Way of the material where the line was being emitted. Then these bodies of hydrogen gas were plotted it was found that they lie along arms which look not unlike the arms seen in distant galaxies, consistent too with that derived from the hot blue stars.

The detailed study of the galaxies began to occupy an important place in the work of many astronomers. Besides the stars seen individually in the nearer galaxies indicators of somewhat greater distances were found by recognising gaseous nebulae and clusters of stars. The spiral galaxies may have different forms and there are others which show no structure of arms and have an elliptical or circular outline in the sky. These elliptical galaxies contain less interstellar material from which new stars form in galaxies like the Milky Way and consequently there are few newly formed hot blue stars such as occur in the nebulae of the arms of the Milky Way. Many of these galaxies contain a high concentration of material towards their centres. These nuclei way give 10-13 times as much light as the Sun and may vary with the period of the order of a month. The great activity of the centres is revealed by their spectra, which corresponds to that of glowing gas.

In 1962 the radio astronomers detected radiation coming apparently from highly concentrated sources. When some of these were identified they were found to be blue star-like objects and their spectra revealed large red shifts which were interpreted to mean that the objects are receding from us very quickly. If these are interpreted in the same way as the velocities of the galaxies these quasi-stellar objects, or quasars, must lie at great distances and be immensely bright, some of them scores or even hundreds of times brighter than whole galaxies of usual type. Then, the optical astronomers made an examination of some blue stellar objects which had been known to exist away from the plane of the Milky Way and some of these showed red shifts of a similar character to the quasars discovered by the radio astronomers, the chief difference being lack of radio emission. A characteristic of the radio sources is the ejection of matter and it is very frequently found that there are major areas of the radiation on each side of the centre.

The extent to which the studies of galaxies have become important in astronomy is revealed by the fact that not long ago there was a conference on such a restricted subject as the nuclei of galaxies. These provide many mysteries but one of the conclusions of this conference was that the limits of conventional physics seemed not yet to be surpassed.

The radio astronomer now plays an important part in the investigation of the galaxies, of the Milky Way and of the Sun. I dare say that if the literature were combed it might have been possible to find someone speculating before the period being covered by this talk that there would be radiation at wave-lengths now commonly observed by the radio astronomers. However, it is quite certain that no one at the beginning of the period could even have dreamt of the extent to which this branch of the science has grown and the degree to which it aids astronomical investigation.[3]

An understanding of the evolution of stars is something that has grown greatly in the past 50 years. The general picture is that! a star begins as a mass of gas in an extended volume of space and as the gas contracts under gravitation and perhaps magnetic forces it grows warmer and when the gas becomes opaque it heats up until processes of atomic fusion supply enough energy to make it stable. A general idea of the structure of a star was founded at the beginning of the period but it was only when the source of energy was revealed that the evolution of the stars could be on a firm basis. The stable state reached by a star depends on the mass of gas which has been collected together to form it. If it is a moderate sized amount of gas like the Sun or smaller then it reaches a state like the Sun or cooler and can go on shining for thousands of millions of years. However, if the amount of gas is very much greater the star will become a very blue hot star giving off an enormously greater amount of energy. A star like Rigel might give 50,000 times as much light as the Sun. Such giant performers use up their energy at a disproportionate rate and cannot last for the long ages that smaller stars can do. So, they must go through an unstable period and reach a new. stable state in which they shine much less brightly. White dwarf stars like the companion of Sirius had been known for a long time before there was any explanation of them. A white dwarf star has contracted to a state which in its density is of the order of a tonne per cubic centimetre but, if the star after its unstable stage has a mass above 1.4 times that of the Sun, it may contract still further to a neutron star with the density 108 times that of a white dwarf. It has to be realised that a star which is contracted to such an extent may be only 10 kilometres in diameter and could have yielded more gravitational energy than the energy available in atomic processes and much of this energy would have been in the form of radiation. Quite a long time ago gravitational contraction was suggested as a possible source of stellar energy but it was realised to be entirely insufficient for a star like the Sun. Now it is emphasised that gravitation has a large share in the energy bank of the Universe and plays a basic role in high energy astrophysics. In the neutron stars the component electrons and protons would be so crushed together as to form neutrons. Neutron stars were predicted in the 1930s. Then in 1967 pulsars were discovered by radio astronomers at Cambridge. These are stars which vary in brightness with a period which is a fraction of a second. The contraction which has occurred for the star to reach the neutron star stage must increase the angular [4] rotation and the magnetic energy a great deal. The best explanation of the pulsars is that they are rapidly spinning neutron stars being derived after the unstable stage when the star has been a supernova. The magnetic field is of the order of l012 gauss and the period lengthens by 15 microseconds per year and so the rate of energy loss agrees fairly well with the amount of energy that would be needed to maintain the emission of the Crab Nebula.

With a greater mass the star could not be sustained even as a neutron star and in further collapse it would reach the stage where the gravitational field would be so great that no energy could leave the star. For a body of material as massive as the Sun such a state would occur if all of the mass were within a diameter of perhaps six kilometres. Such black holes have been the subject of a good deal of theoretical discussion but clearly enough they are hard to observe since they emit nothing but, on the other hand, their gravitational field can still be felt and several astronomers have made, perhaps not very well substantiated, claims to have observed black holes.

A development of recent years is space science. The first satellite was launched in October, 1957 and since then space research has grown in stature. The first manned satellite occurred in 1961 and the first landing on the Moon in 1969. Interplanetary space in the vicinity of the Earth has been explored and space probes have journeyed to Mars, Venus, Jupiter and Mercury. The surface structure of all these bodies is better known as a result of this and the magnetic fields and the particle radiation in interplanetary space has been explored. Analysis of the paths of the satellites around the Earth has given new clues to details about its shape and observations of the satellites have found application in geodetic survey and navigation. The orbiting astronomical observatories now observe radiations from the stars and from space at wavelengths which cannot penetrate the Earths atmosphere and new and significant data are being gathered from a wide range of objects.

Turning to the work of Sydney Observatory which works in positional astronomy a large part of the activity of the Observatory during my time has been associated with the production of astrographic catalogues. At first we were doing a good deal of work with the transit instrument to determine positions of stars to serve as reference positions for reduction of measures made on the photographic plates. In the astrographic catalogue project the whole of the sky was divided among different observatories and the Observatory at Sydney had a share as big as any observatory in a very crowded area which included a long stretch of the heavily populated part of the Milky Way. The whole of this work has been completed and we also did a large section of the work of the Melbourne Catalogue. Melbourne Observatory was closed as a State Institution in 1944 and in 1948 the International Astronomical Union asked Sydney Observatory to take over the work. We did this and somewhat the greater part of the work was published from Sydney. Altogether the positions of towards a million star images on photographic plates were published in these Catalogues. In more recent times we have been engaged in other cataloguing projects by photography. In 1955-56 we photographed a large section of the southern sky in collaboration with Yale University Observatory. This photograph has been made the basis of some valuable catalogues published in recent times. We also acquired a modern photographic lens and made the camera for it with the object of re-photographing the zone in which our astrographic work was carried on and possibly also the zone we took over from Melbourne. Actually the photography has been carried on beyond these zones. The value of the work is that with the positions of these stars determined at such widely different epoch it will be possible to find proper motions for a great many of the stars.

For move than 20 years Sydney Observatory has been engaged in the determination of positions of minor planets most of which have orbits between those of Mars and Jupiter. In recent years this has been directed more particularly to the observations of those minor planets whose investigation can make a contribution to fundamental astronomy. Other work which may be mentioned is on double stars the investigation of which gives data for determining the masses of stars and of the motions of stars which may serve as a basis for establishing distance scale and for the investigation of the clusters of stars. In recent years the Observatory ha obtained a new measuring machine which will assist in the catalogue work. This machine [5] gives a digital readout of the measurements which can be produced in a machine readable form for processing by a computer. The Observatory has also obtained a rubidium frequency standard which serves as a basis of a clock for the timekeeping of the Observatory.

In Australia we can look forward to a good future in astronomical science. In recent years a new Observatory has been founded at a good site on Siding Spring Mountain near Coonabarabran. In the Southern Hemisphere investigation of the Milky Way and Magellanic Clouds must be significant. The Clouds lie at a distance of about one tenth that of the Great Galaxy in Andromeda and so studies in them from southern observatories can be made which would require telescopes many times larger to make similar observations on the Andromeda Galaxy. A telescope of 3.8-metre aperture built by a collaboration of the Australian and British Governments is nearing completion. Then, we should look forward to new developments in radio-astronomy. There is the hope that it will be possible to build a new radio-telescope capable of observing at wavelengths of a few millimetres. The significance of this is that radiation at these wavelengths enables investigation to be made of the molecules which occur in space and which are being revealed for the first time by these techniques. In recent years the astronomers of the University of Sydney have had an ingenious interferometer at near Narrabri to measure the diameter of many more stars than had previously been done. The same astronomers have plans for the building of a larger interferometer which would make accessible to observation many more stars and provide new date for determining accurate masses and distances of binary stars. Positional astronomy in the Southern Hemisphere is in need of great development because it should be brought into line with its state in Northern Hemisphere and at Sydney Observatory we are hoping that a positional Observatory can be established in a country Site with good apparatus and excellent conditions which could enable an important contribution to be made to this field.

NOTE: Text written as [*NN] is the page number in the original document.

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