Since the Second World War astronomy has lived through its golden age, undergoing a complete transformation. Before the war, astronomy meant optical astronomy and observations were confined to the use of the narrow range of visible spectrum capable of penetrating the Earth's atmosphere – about 1 octave in all. Since that time new advances have made it possible to observe at radio, infrared, ultra-violet, X-ray and gamma-ray wavelengths covering a spectrum of some 56 octaves. An exciting consequence of the new era has been the discovery of new classes of galaxies with extraordinarily high energy and luminosity, pushing back the limits of the observable universe beyond all expectations.
What started this great revolution? It may be fairly said that it all began in 1948 in Sydney, Australia, when a three-man team led by a 26-year-old Yorkshireman named John Bolton discovered that three distant objects, known from optical observations, were extremely powerful emitters of radio waves. One, which Bolton called 'Taurus A', was located in our own galaxy; the Crab Nebula. The other two ('Virgo A' and 'Centaurus A') were external galaxies. This discovery marked the beginning of the new era in which the universe could be explored by means of its high-energy galaxies. The pursuit of this subject became the main theme of Bolton's scientific life.
Not only was Bolton one of the great pioneers of radio astronomy, but to those who knew him personally, a friend of truly remarkable individuality. With his unlimited courage and penetrating intuition, and physically indefatigable when in intense pursuit of whatever he was after, John Bolton was a phenomenon that had to be experienced to be believed. So different was he from other scientists of his eminence that it was almost as if he did not belong with them.
John Gatenby Bolton was born in Sheffield on 5 June 1922. After going through his local grammar school, he won a scholarship to Trinity College, Cambridge. He graduated in 1942 and joined the Royal Navy as a Radar Officer, but was soon recruited into radar research at the then secret Telecommunications Research Establishment (TRE). Among other famous figures in radio astronomy who also served time at TRE were Hey, Hanbury Brown, Bowen, Ryle and Lovell. In 1944 Bolton did get to sea in the aircraft carrier Unicorn in the Pacific where he even became involved in dangerous flight testing and survived a forced landing in a naval fighter.
After the war Bolton settled in Sydney and joined the Council for Scientific and Industrial Research (CSIR) – later to be renamed the Commonwealth Scientific and Industrial Research Organization (CSIRO) – whose Radiophysics Laboratory was directed by E.G. (Taffy) Bowen, formerly a radar pioneer in Watson Watt's team. The Laboratory was in the process of changing over from its secret wartime radar work to peacetime programmes. Among the latter was the investigation of radio emission from the Sun that had been discovered during the war. The group led by J.L. (Joe) Pawsey included names that would later become well known among the international astronomical community: Mills, Christiansen, Piddington, Kerr, Bracewell, Wild  and numerous others.
To most of these scientists Pawsey was the much-loved father figure of Australian radio astronomy. Not so for Bolton however, one of whose first experiences was being ordered back to the lab by Pawsey when the latter unexpectedly visited the site and found the aerials not pointed at the Sun, because Bolton was looking for other radio sources.
Bolton was reassigned to assist a colleague, Gordon Stanley, to build equipment to go on an eclipse expedition to Brazil in the following year. All equipment in those days was home-made and very primitive by modern standards. It was a matter of great good fortune for astronomy that the expedition was called off and Bolton was 'released' to do what he pleased with the equipment they had built, and to avail of Stanley's services as well. They lost no time in moving the equipment out to the cliff-top site called Dover Heights, and so began a period of epoch-making observations.
Although Bolton intended to work primarily on non-solar radio sources, for his first observation at Dover Heights and his maiden publication in August 1947, he took part in a pioneering solar discovery. He and two colleagues (at another field station) took observations at three well separated frequencies (60, 100 and 200 MHz) of the first identified solar outburst of Type II (as later designated by Wild). Bolton and co-authors correctly attributed the delays in arrival time with decreasing frequencies to the passage of a physical agency upwards through different levels of the corona. They estimated a velocity of almost 1000 km/s, close to that of auroral particles, and noted that an aurora was in fact observed in some parts of Australia a little more than a day after the outburst.
Dover Heights had been a RAAF radar station, part of the wartime defences of Sydney. It is located at the top of a sheer cliff overlooking the Pacific, just to the south of the entrance to Sydney Harbour. In the previous two years Pawsey and his colleagues had used the site to make pioneering observations of the Sun. As the Sun rose above the Pacific horizon, radio emission from sunspots reached the cliff-top aerial along two paths, one direct and the other reflected by the sea's surface. From the interference pattern so generated it was possible to locate the source of the emission (in one dimension) to an accuracy of a few minutes of arc . This 'cliff interferometer' (as Pawsey called it) was the radio analogue of Lloyd's mirror in optics.
Bolton, with his colleagues Stanley and Slee, adopted the same technique (which he renamed the 'sea interferometer') to search for radio sources. At this time there was evidence of only one discrete source in the sky other than the Sun. While surveying the radio galaxy, J.S. Hey and colleagues in England noticed that a region in the constellation of Cygnus showed fluctuations. They concluded that such a variable source must be of small angular size. Eventually it turned out that the fluctuations were not intrinsic to the source but due to scintillations caused by the Earth's atmosphere, a phenomenon that also required the source to be of small angular size. As Pawsey later put it, 'Hey came to the right conclusion for the wrong reason, which is the mark of a good physicist'. Anyway, the evidence was there, and so Bolton and Stanley began their search in the Cygnus region.
After a period of negative results it happened! There before their eyes on the recording chart was a beautiful set of fringes enabling them to locate the source and set an upper limit to its angular size of eight minutes of arc. Gordon Stanley has written of how Bolton and he reacted:
The most memorable moment of our association occurred when we first saw interference fringes from Cygnus A. In a world now accustomed to inexplicable results from radio observations, it is difficult to comprehend the emotional impact of an observation which took us from partially explicable solar system and galactic radio emission phenomena, into the realms of phenomena with inexplicably high energy outputs, no matter where they were located. Neither of us ever approached such an emotional high again in our work.
It took several years for the optical identification of Cygnus A and then it was found that this extremely strong source corresponded to a very dim distant galaxy. This made everyone instantly realise that the accessible radio universe would be far larger than the visible one.
Then followed the discovery of the three sources mentioned at the beginning. Determining their positions well enough to make the identifications was no simple matter. It involved shipping the equipment to New Zealand and towing it with an army truck to more than one location with a cliff of adequate height and appropriate orientation. Months of hard work later, there was enough justification to write to three famous optical astronomers, all of whom had an interest in the Crab Nebula – Jan Oort, Bengt Strömgren and Rudolf Minkowski. The letters provoked enthusiastic responses and led to co-operation and lifelong friendships. To quote Bolton: 'The identification of the Crab Nebula was a turning point in my own career and for non-solar radio astronomy. Both gained respectability as far as the "conventional" astronomers were concerned.'
The other two sources were identified with what were initially thought to be nebulae in our own galaxy (surely they couldn't be extragalactic!): Virgo A with M87 and Centaurus A with NGC 5128. Within a year both were recognized as extragalactic; they were elliptical galaxies. This then was the start of the radio study of the universe. And despite a crowded and illustrious career ahead of John Bolton, this, surely, was his finest hour. The remarkable thing about Bolton's early identifications was his success despite the crudeness (by modern standards) of the available data. He had uncanny intuition and a propensity for being right.
By 1949 Bolton had been joined by Kevin Westfold, a radio astronomy theorist, and the two of them turned their attention to making a whole-sky survey of galactic background radiation at 100 MHz. Meanwhile Stanley and Slee continued searching for sources with increased sensitivity. Within a year they had brought the number of sources detected at Dover Heights to 22.
At this time radio astronomy at the Radiophysics Laboratory was being carried out under Pawsey's general direction by some seven or eight groups of which Bolton's was one. The Sun, the Moon, the galaxy and the cosmos were all being investigated and every group was making a significant impact on the international scene, though the Dover Heights source identifications were the jewel in the crown. It is fair to say that at this stage Australia led the world in radio astronomy. Recognition of Australia's position was manifest by the decision of the International Union of Radio Science (URSI) to hold its 1952 general assembly in Sydney – the first time an international conference of any kind had ever been held in the Southern Hemisphere. At this conference Bolton really found his feet. He suddenly found that scientists with illustrious names treated him as an international celebrity. And how he loved it!
A project undertaken by Bolton that should find a place in any account of his career is the 72-foot hole-in-the-ground antenna built in 1951 for a survey of the region near the galactic centre, which at the latitude of Sydney passes directly overhead. The excavation was done mostly by Bolton and Slee. Westfold also helped to dig, and Gordon Stanley trucked loads of ash from a powerhouse each week to stabilise the sand out of which the hole was formed. The reflecting surface was made from steel strips formerly used for binding packing cases, and performed adequately at the operating frequency of 160 MHz. It was interesting however that the 'site' for the hole was chosen not to be visible from the official working area of the Dover Heights station. All of the digging etc. had to be carried out in one's own time (lunch, after hours, etc.) and in secrecy. Somewhere along the way Bowen was made aware of this exercise and, predictably, supported it. To be fair to Pawsey, after a first demonstration of the potential of this dish in early 1952, he too enthusiastically supported its upgrading to 80 ft. in diameter and to 400 MHz in frequency. Observations with this improved version, made with Dick McGee, led to Bolton's suggestion in 1958 that Sagittarius A was the nucleus of our Galaxy. Three years later the IAU ratified the view, making the position of the (radio ) source the zero of longitude in the new system of galactic coordinates.
By 1953 the glorious days of Dover Heights were drawing to a close. The Lloyd's mirror technique could no longer compete with two or multi-element interferometers. So Bolton found himself at the crossroads – what next?
Dover Heights is today a public park – the 80-foot hole is a level playing field. One of John's last public appearances was at the unveiling of a memorial tablet there in November 1989 to commemorate the 40th anniversary of the publication of the first paper on identifications. One of us (JPW) was unable to be present. Instead I sent a message, which was read out, saying that I had a lifelong habit of associating special times with popular songs of the day, and that I had always associated the great days of Dover Heights with that well-known, haunting melody that introduces Pinnochio; perhaps with the detection of Cygnus A in mind:
Like a bolt out of the blue
Fate steps in and sees you through
When you wish upon a star
As dreamers do.
At this time the work of the Radiophysics Laboratory comprised two major programmes: radio astronomy and cloud physics, the latter prompted by the desire to make artificial rain. Pawsey directed the first and Bowen himself directed the second. It seems that Bowen was not satisfied with the rate of progress in cloud physics. He would dearly love a John Bolton to stir the group up. And it came about that around August 1953, Bowen struck a deal with Bolton. If Bolton would join the cloud physics group for two years or so, Bowen would use all his influence (see below) to obtain for Bolton the plum directorship of radio astronomy at the California Institute of Technology which was about to enter the field .
So for eighteen months Bolton worked in cloud physics, His main contribution was to investigate the effects of air temperature and pressure on the decay of silver iodide (the favoured cloud-seeding agent). This he did by injecting silver iodide into a cloud chamber and counting the number of ice crystals generated. The results were published in November 1954. He then turned his attention to the development of silver iodide burners for rainmaking trials in Queensland and Tasmania.
In January 1955 he left the group to start up radio astronomy at Caltech, which operated the foremost optical telescopes in the world.
Since the early (pre-war) pioneering days of Karl Jansky, the father of radio astronomy, and Grote Reber, radio astronomy in the USA had been taking a back seat compared to the activity in Australia and England. We have already mentioned TRE in England where Bolton worked for a while and where radar was developed. The corresponding centre in the US, set up much later, was the MIT Radiation Laboratories headed by Lee DuBridge. Here, work on microwave devices and measurements was carried out by a battery of distinguished physicists – Bethe, Dicke, Pound, Purcell and Van Vleck, among hundreds of others. Taffy Bowen was one of the key players in the drama of radar in the Second World War and was personally responsible for carrying an early sample of a 'magnetron' invented at Birmingham University across the Atlantic to the Radiation Laboratories. We mention this visit and Bowen's subsequent stay for some years at the Radiation Labs as it has a bearing on the Bolton story. The links of friendship Bowen forged then were crucial in obtaining generous financial support from foundations in the US for the Parkes 210-foot telescope to be built many years later. In return, Bowen arranged for Bolton to spend time at the California Institute of Technology where Lee DuBridge was now President.
As has been said, Bolton went to Caltech in January 1955 and in the six years before be returned to Australia in 1961, created the Owens Valley Radio Observatory which was quickly recognised as a world centre and which provided a much needed boost to radio astronomy in the USA. Bolton's crew in this exercise came from all over the world – England, Australia, New Zealand, India, Canada and Norway. The graduate students were American and included Barry Clark, Ken Kellerman, Al Moffet and Bob Wilson. One of us (VR) was the Indian and was hired to maintain the radio equipment that Gordon Stanley had already built. In Bolton's own account of the Owens Valley period he dwells on the education he received, from the very first day, from Minkowski on the need for and importance of accurate radio positions as the only way to make identifications that would lead to progress.
The Caltech interferometer was unique and a forerunner of later instruments in having as elements large dishes operating at a frequency as high (at that time) as 1 GHz. It had the sensitivity and baseline to resolve a substantial fraction of the sources observed. Among the sources not resolved at the longest baseline was 3C295, which was identified by Bolton with an object for which Minkowski with the Palomar 200-inch telescope got a redshift of 0.46, roughly three times the highest then known and a record which was to stand for fifteen years. There were many interesting discoveries made by members of Bolton's group during his years at Caltech, but his own interest in building the Owens Valley Observatory was, as he has stated himself, 'to extend the observable scale of the universe to look-back times as great as the oldest stars in our own system'. It was a unique and unforgettable experience to see Bolton go about this exercise in as cool and low-key a manner as someone building a cattle shed or repairing a washing machine. He gave people tasks about which they may not have had a clue to start with. He never taught you how to do anything, as if that would have been a presumption. But his example and even more his expectation made people rise to heights that they would never have dreamt possible.
The Caltech chapter of Bolton's story would be incomplete without a mention of 3C48. Quite simply, 3C48 was the first identification of a quasar , which was made public without a redshift in a paper presented at the Christmas 1960 meeting of the American Astronomical Society with the authors T.A. Matthews, J.G. Bolton, J.L. Greenstein, G. Munch and A.R. Sandage, the chronological order in which they were involved. Matthews, who was the Canadian in the group, obtained a position for the radio source that beautifully fitted a 16th magnitude star. Spectra werc obtained by Münch and Sandage and measured by Greenstein. After considerable tuition from Ira S. (not Taffy) Bowen, director of the Palomar Observatory, Bolton arrived at a possible fit for the lines at a redshift around 0.37, but a four-angstrom discrepancy was unacceptable to the spectroscopists and stopped matters dead for about three years. It was hence poetic justice that, as will be recounted shortly, Bolton played a vital part in the dramatic story of 3C273, hailed by most as the first true identification of a quasar, and that its very high redshift caused the high redshift of 3C48 to become accepted.
Most of this section on Caltech is written as seen through the eyes of one of us (VR) who was on the spot from early 1959 when the action began at Owens Valley. However JPW can make a small contribution. On a visit to Caltech in 1957 I spent a day at Mount Wilson Observatory and watched Babcock measure solar magnetic fields by observing the split of spectral lines by the Zeeman effect. Next day I made the long drive to Owens Valley with John Bolton. I said 'I wonder if it would be possible to measure galactic magnetic fields by observing the Zeeman splitting of the hydrogen line'. We talked about it, exchanging ideas in an exhilarating conversation throughout the drive. Next day I wrote the Bolton and Wild paper that incorporated the ideas of both of us. This paper started a prolonged search in a number of observatories and was eventually successful.
It is somewhat enigmatic that while Bolton was at Caltech, he and Pawsey maintained an extensive and regular correspondence on which way to go in radio astronomy. It was as though Bolton felt isolated and needed someone experienced to talk to; and he turned to his former director in spite of their earlier uneasy relationship.
To the surprise and disappointment of everyone at Caltech, Bolton announced abruptly in late 1960 that he was returning to Australia to supervise the steelwork that had commenced on the 210-foot telescope that Bowen had been planning for years. This he did, not from the ground but from up on the structure. He also surveyed and reset every one of the more than one thousand panels over an acre of surface. The telescope was commissioned in late 1961 and Bolton took charge as Director of the Australian National Radio Astronomy Observatory (ANRAO) to begin a third and equally spectacular phase of his career. Parkes attracted astronomers from all over the world including several who had worked with Bolton in California. Major contributions were made in almost every branch of radio astronomy of which there were now a large number. Bolton's lifelong interest in the discovery, classification and identification of radio sources found his greatest reward in these years. The Parkes Catalogue, in the making of which Bolton was the leading light, lists more than 8,000 sources including several hundred quasars. He published more than 60 papers in this field.
More than anyone else, Bolton brought radio and optical astronomy together, through constant interaction with the best optical astronomers of his time, through the use of optical telescopes himself for identification purposes, and through efforts to set up major facilities like the Anglo-Australian Telescope and the UK Schmidt Telescope. He was among the earliest to recognise the unity of astronomy across all wavelengths.
As hinted earlier, Bolton and the Parkes dish were essential elements in the drama of the identification of the source 3C273 as a quasar. Cyril Hazard, who at Jodrell Bank had pioneered the lunar occultation technique of determining accurate positions for radio sources, happened to be in Australia in Hanbury Brown's group at the University of Sydney. He was invited by Bolton to take part in observations at Parkes of occultations of the radio source RC273, several of which had been predicted for 1962. It was typical of Bolton to figure out that the most critical of these occultations would require an extension of the existing zenith angle coverage of the telescope, and that this could be achieved by grinding off a considerable amount of metal from the bearing housings. We were not there to witness it but, knowing John, we can picture him with the grinder, hand-rolled cigarette hanging from his lip, knee braced against a girder and grinding away in a shower of sparks. In any event the observation was spectacularly successful and, as a final touch to the drama, Bolton and Hazard each carried a record and travelled on different planes to Sydney. Maarten Schmidt of the Mount Wilson and Palomar Observatories in Pasadena established a redshift as 0.158, considered astoundingly large for an object that looked like a star.
This was the breakthrough and it led Greenstein and Matthews to believe the 'redshift' of 0.37 obtained earlier for 3C48 and to publish it in a paper following those on 3C273 .
The Parkes telescope also played an important part in several of NASA's Apollo missions. Not many may know that Neil Armstrong's first steps on the Moon, seen all over the world, live on television, came via Parkes. Another and unplanned occasion was when a sudden emergency on another of the Apollo missions required Parkes to come on line in a matter of hours. It so happened (that one of us (VR) was to have observed that night, and quickly had to clear the focus cabin of the pile of equipment that had taken all day to assemble. In a situation of such urgency, kicking someone off the dish required no effort but, to quote the London Times, 'Bolton, typically, left nothing to chance. With the Australian sun beating down, he stood, stop watch in hand, rehearsing teams of his perspiring staff in hand-cranking the axis gearing of the 1000-ton dish at rates correct to follow the spacecraft should mains power fail',
Several changes took place at the Radiophysics Division in the period 1971-72. Bowen retired as the Chief of the Division and his place was taken by Paul Wild. John Bolton retired as Director of ANRAO but continued at Parkes as Astronomer at Large until 1981 when after a heart attack he decided to retire and moved to a coastal resort in the warmer climate of Queensland.
Bolton's contribution to astronomy was not only through his own work but also through his influence on others. Many of his numerous students went on to do great things. To mention a few: Ken Kellerman was the moving spirit behind the Very Long Baseline Array with antennas spread out over thousands of miles across the USA; he also served as a Director of the Max Planck Institute for Radio Astronomy in Bonn. Barry Clark was the system designer of the most complex radio astronomy instrument in the world – the Very Large Array in New Mexico; Ron Ekers became the first Director of the VLA and later returned to his homeland to direct the Australia Telescope; Jasper Wall became Head of the Royal Greenwich Observatory; Marc Price became Director of the ANRAO at Parkes; Al Moffat became Director of the Owens Valley Observatory; and Bob Wilson won the Nobel Prize as co-discoverer of the 3º cosmic background.
No-one who came in contact with Bolton would have failed to notice that determination was his main characteristic. This came through in sports even more quickly than it did in other areas. Whether at cricket, table tennis, snooker or golf, once he had decided that he would win, it did his opponent little good being a much better player in other circumstances. Bolton's power of concentration was phenomenal and his resolve unshakeable.
Most people who have known Bolton paint him as harshly intolerant of mediocrity and poor judgment. This may be true, but only if it interfered directly with his plans or actions, when most of us would react in the same way. Bolton was a fearless individual who could be ruthless. He was especially harsh on administrative staff who unnecessarily and bureaucratically interfered with his operations. On one occasion an irritating directive from CSIRO Head Office found its way on to a Parkes notice board. Within a day there appeared, written in large letters diagonally across the notice 'Head Office has no jurisdiction at this observatory, JGB'. But Bolton was a fair and friendly person, rather shy deep down, a person of great integrity and strength of character.
Letty, his wife for 43 years, cheerful, vivacious, outgoing, hospitable, was the perfect partner for John. The two of them kept open house for their staff, and John would have the same standards of perfection in barbecuing steaks and providing fine wines for his guests as he did for his astronomy. John was the devoted father of Letty's two sons by her former husband, killed in the war. John maintained his Yorkshire accent to the end, while Letty's uninhibited broad Australian accent took California by storm.
During John's retirement his health deteriorated with heart trouble and pneumonia but his mind remained as sharp as ever and he saw many visitors. After a final attack of pneumonia he died at home on 6 July 1993.
A one-day John G. Bolton Memorial Symposium was held at Parkes on 10 December 1998. On this occasion the assembled company, including Letty, gathered round a commemorative sundial and stood in silence for a minute. In the ground, beneath the sundial, lay the ashes of a very special man.
This memoir was originally published in Historical Records of Australian Science, vol.10, no.4, 1996. It was written by:
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