BOLTON, JOHN GATENBY

(b. Sheffield, England, 25 June 1922; d. Buderim, Australia, 6 July 1993),

radio astronomy, “radio stars,” Caltech, Owens Valley Radio Observatory, Parkes Radio Telescope, radio source identifications, quasars.

Bolton was one of the early founders of radio astronomy. He was responsible for the discovery and identification of many of the earliest “radio stars,” carried out important early surveys of discrete sources, established the radio astronomy program at the California Institute of Technology (Caltech) and the Owens Valley Radio Observatory, and was the first director of the Parkes Radio Telescope. Later in his career, he developed new techniques that led to the location and identification of more than one thousand quasars. For his pioneering research in radio astronomy Bolton received many honors, including the Bruce Medal of the Astronomical Society of the Pacific, the Edgeworth David Medal of the Royal Society of New South Wales, the Encyclopaedia Britannica Gold Medal and Prize for Science, the American Astronomical Society’s Henry Norris Russell Lectureship, and the Gold Medal of the Royal Astronomical Society. He was a Fellow of the Royal Society, a Commander of the Order of the British Empire, a Fellow of the American Academy of Arts and Sciences, a foreign associate of the U.S. National Academy of Sciences, an Honorary Fellow of the Indian Academy of Sciences, and a Fellow of the Australian Academy of Science.

Early Years. John Gatenby Bolton was born in Sheffield, England, on 25 June 1922, to John and Ethel Bolton, both of whom were schoolteachers. After graduating from King Edward VII Grammar School, he entered Trinity College, Cambridge, and a few days after completing his final exams in May 1942 he enlisted in the Royal Navy. After a brief introduction to electronics, he began designing and testing airborne radar units. In 1944 he joined the aircraft carrier HMS Unicorn as a radar officer. At the end of the war he left the ship in Sydney, Australia, and on the basis of his radar background secured a research post with the Commonwealth Scientific and Industrial Research Organization’s (CSIRO) Division of Radiophysics, where he was assigned to the radio astronomy group.

The Radio Source Surveys. Radio astronomy was in its infancy at this time. Following the pioneering efforts of Karl Jansky and Grote Reber in the United States during the 1930s and early 1940s, radio astronomy blossomed in the late 1940s and early 1950s, largely as a consequence of developments associated with radar during the war. In the late 1940s, Britain and Australia emerged as the two leading nations in this new branch of astronomy, with much of the Australian development taking place through the CSIRO’s Division of Radiophysics. Bolton went to work at the Division’s Dover Heights field station, which was located at a former World War II radar station, 5 kilometers to the south of the entrance of Sydney Harbor. It was sited on top of a 79-meter coastal cliff, which offered special advantages for radio astronomy research.

Bolton teamed up with Bruce Slee, and in November 1946 they began studying radio emission from the Sun. In 1947 Bolton, Slee, and Gordon Stanley investigated the enigmatic radio star in the constellation of Cygnus, which had just been reported by British radio astronomers. By March 1948 Bolton’s team had not only confirmed the existence of the Cygnus A radio source but had also discovered five others, including Taurus A, Centaurus A, and Virgo A. The equipment used for these searches was primitive by twenty-first century standards and comprised simple Yagi antennas operating at frequencies of 60, 100, and 200 megahertz that were used to determine the first radio source spectra. These Yagi antennas, similar to modern TV antennas, were positioned on the roof of a World War II concrete blockhouse at Dover Heights, close to the cliff edge.

The search was now on to solve the mystery of the radio stars, and the first thing to do was obtain their precise positions so that photographs of these regions could be examined to see if there were any optical counterparts. Unfortunately, the positions of the sources obtained in Sydney were imprecise, as they relied solely on the rise-time of the sources as they appeared above the eastern horizon. This technique became known as sea interferometry, but what was needed was a site that also allowed the radio astronomers to track the setting times of these sources over the western horizon. However, the only relatively nearby locations that permitted this were in New Zealand, 2,000 kilometers to the east of Sydney.

Between June and September 1948 Bolton and Stanley observed the radio stars Cygnus A, Taurus A, Centaurus A, and Virgo A from 300-meter high coastal cliffs at Leigh and Piha to the northeast and west of Auckland, while Slee continued parallel observations from Dover Heights. This strategy was a resounding success, for precise positions were obtained for all four sources and when photographs of the relevant sections of sky were examined, the Sydney radio astronomers were able to associate the Taurus A radio source with the Crab Nebula (the remains of a supernova that was widely observed in 1054 CE), Centaurus A with a galaxy crossed by a distinctive dark dust lane, and Virgo A with a galaxy known to contain a peculiar jet. These identifications were published in Nature and the Australian Journal of Scientific Research and created a major impact, for they showed that these sources were in no sense radio stars but were associated with the remnants of galactic supernova, as well as with distant galaxies. The realization that these so-called radio galaxies were the most energetic objects known in the universe attracted the attention of astronomers around the world and ushered in the modern era of radio astronomy.

In 1949 a nine-element Yagi antenna was set up on the roof of the blockhouse, and was used to discover fourteen new sources, including the powerful radio galaxies Hydra A, Hercules A, Fornax A, and Pictor A. Early in 1952 Bolton, Stanley, and Slee completed a new twelve-element Yagi array, and this was used to detect a total of 122 sources. This was the most complete radio survey carried out worldwide at that time, and the apparent excess of weak sources in their catalog opened a long-standing debate about the cosmological implications of radio source population statistics.

Bolton, Stanley, and Slee wanted to construct a much larger radio telescope at Dover Heights, but with many competing innovative projects from Division of Radio-physics colleagues and limited funding from the government, their bid was unsuccessful. Their ingenious response was to build a new radio telescope themselves— as a lunchtime project. Over a three-month period in 1951 they used shovels and a wheelbarrow to excavate a dish-shaped depression in the sand 150 yards north of the blockhouse. After constructing a 72-foot diameter dish and testing out the system, they expanded this to 80 feet, and when this was furnished with an antenna mast and dipole it fed radio signals from directly overhead through to equipment in a mobile laboratory. At the time, this was one of the largest radio telescopes in the world, but the disadvantage was that it was fixed, so it could not move and point to selected areas of sky. Instead, different areas of sky passed through the beam of this novel radio telescope as Earth rotated, but it was possible to expand the survey area slightly by tilting the mast that supported the dipole antenna. Fortunately, at the latitude of Sydney, the plane of Earth’s galaxy passes almost directly overhead, so for the first time, the Dover Heights radio astronomers were able to investigate the radio emission from this vital central part of Earth’s galaxy. They were excited to discover a strong new radio source located at the very center

of this galaxy, and named this Sagittarius A. 'this is the distinctive source with celestial coordinates of 328 degrees (longitude) and -01 degree (latitude) shown in Figure 1. Several years later, the International Astronomical Union adopted the position of Sagittarius A as the official center for a new international system of galactic coordinates (equivalent to latitude and longitude here on Earth).

In 1953, when it appeared that the Radiophysics Laboratory could not fulfill his ambitious plans to build an even larger radio telescope at Dover Heights, Bolton temporarily left radio astronomy to work with the laboratory’s cloud physics group. Until his departure for Caltech in 1955, he pursued a variety of cloud-seeding experiments designed to bring rain to Australian farmers.

During the seven years he spent at Radiophysics, Bolton was involved in forefront research that led to discoveries that would change the nature of astronomical research. Through this work he became well known and highly respected in the international astronomical community, even though his education and experience were in physics and electronics.

The Caltech Interlude. Although the first pioneering observations in radio astronomy had been made in the United States, by the 1950s the United States had fallen far behind Australia and the United Kingdom in this important, new, and rapidly developing field. With the support of the Radiophysics chief, Taffy Bowen, Bolton went to Caltech to exploit the opportunity of complementing radio observations with those made with the large optical telescopes at the Mount Wilson and Palomar observatories. Funding was readily acquired from the U.S. Office of Naval Research for a new radio observatory, with strong support from Caltech and private donors.

Bolton, who was joined by Stanley, located a suitable site for Caltech’s planned new radio observatory in the

remote Owens Valley, about 200 miles north of the Caltech Pasadena headquarters, and they began the construction of a two-element interferometer. At this time, radio telescopes fell into two main categories: those operating at meter wavelengths, which used wire arrays, often in the form of interferometers; and those working at the shorter decimeter and centimeter wavelengths, which used single parabolic dishes. Bolton, Stanley, and Caltech’s chief engineer, Bruce Rule, designed the first radio interferometer operating at decimeter wavelengths by using a pair of large 90-foot (27.4-meter) parabolic dishes mounted on wheels and capable of being positioned at stations along a 1,600-foot (487.7-meter) railway track. While the interferometer was under construction at Owens Valley, Bolton, Stanley, and Harris (1958) used a 24-foot antenna on Mount Palomar to do hydrogen-line studies at 21 centimeters. This was followed by the observation of an occultation of Taurus A by the solar corona using a 25 Megahertz array, which they built at Owens Valley. In this study, they were able to establish the existence of scattering by the solar corona out to much greater distances than had hitherto been determined by other workers operating at higher frequencies.

The Owens Valley interferometer quickly became one of the premier radio telescopes in the world and was used initially to determine radio source coordinates with unprecedented accuracy. In collaboration with astronomers from Caltech and the Mount Wilson and Palomar observatories, the program of the Owens Valley Radio Observatory led to the identification of radio galaxies at ever-increasing redshifts and ultimately to the discovery of quasars. Other programs were aimed at determining the two-dimensional brightness distribution of radio galaxies, radio source spectra and polarization, the study of planetary atmospheres and surfaces including Jupiter’s unique radiation belts, interstellar hydrogen clouds, and the first high-frequency galactic plane survey. Most of the work was published by his students and postdoctoral fellows, but Bolton provided the inspiration, and much of the hard labor of observing, reducing the data, designing and building the radio telescopes, and preparing the papers for publication.

Director of the Parkes Radio Telescope. In 1961 Bolton returned to Australia to supervise the completion of the new 210-foot (64-meter) radio telescope near Parkes, New South Wales, and to become the first director of the radio telescope, which was the largest in the Southern Hemisphere. One of the first observing programs at Parkes was the initiation of a Southern Hemisphere sky survey. Under Bolton’s leadership more than two thousand radio sources were detected, and accurate positions and flux densities were measured at three wavelengths, 11, 20, and 75 centimeters. Bolton and a series of colleagues and students went on to refine the survey, and they made more sensitive observations at additional wavelengths in order to determine the spectra of the various radio sources and establish more accurate positions. Later they extended the survey itself to 11 centimeters, and more than eight thousand sources were cataloged in fourteen publications over a period of nearly a decade of painstaking work.

By the late 1960s Bolton’s research was almost entirely involved in optical work in collaboration with a series of students and postdoctoral associates such as Margaret Clarke, Jennifer Ekers, Jasper Wall, Jet Merkelijn, and Ann Savage. Optical identifications were made for nearly one thousand sources and were reported in a series of more than forty research papers published between 1965 and 1982. During this period, Bolton returned frequently to Caltech to inspect the original Palomar Sky Survey plates and to observe at the Palomar and Lick observatories. He also took part in the planning and commissioning of the new 3.9-meter Anglo Australian Telescope (AAT) at Siding Spring and became the first chairman of its time allocation committee. He urged the use of an altazimuth mount for the AAT , but optical astronomers were not yet ready to depart from the traditional equatorial mount. Based on his experience at Parkes and Caltech, Bolton argued for a strong, relatively large observatory staff on the mountaintop to support the complex operations of a modern observatory, but again he ran into opposition from the “traditionalist” astronomers at Australia’s Mount Stromlo Observatory.

Bolton designed and built a blink machine capable of simultaneously examining pairs of plates from the 48-inch UK Schmidt Telescope in two colors. It differed from conventional blink machines of the 1970s in that the plates were viewed with TV cameras, which could present the images side by side or coincidentally with the signal from one reversed. Bolton’s machine was a great success not only for research, but for teaching as well, because several people could view the monitor with up to a hundred times magnification. Everyone who saw the prototype wanted one, and over time he built three machines. Later modifications included interfacing with a computer. The optical identifications provided a grid of accurately known positions in the southern radio sky, which was used to better calibrate the pointing of the Parkes Radio Telescope.

In July 1979 Bolton suffered a severe heart attack. Although he was no longer capable of long nighttime hours at the telescope, he spent the next eighteen months with his associates finishing the analysis of data already in hand, archiving thirteen years of data from the Parkes 11-centimeter catalog, and bringing the catalog up to date in computer-readable form. He and Letty, his wife of thirty-three years, then retired to Buderim on the Queensland coast in 1981, and enjoyed the next decade surfing in the warm Pacific Ocean and playing golf. He died at his home on 6 July 1993.

John Bolton was known to have strong opinions, and had little tolerance for people and ideas that did not coincide with his own. Nor did he have any patience for bureaucracy or authority. But he was generous with his students and young colleagues, often refusing to be included as a coauthor for works that he had initiated and directed. Many of his students and postdoctoral associates went on to productive careers in radio astronomy: one (Robert Woodrow Wilson) was a future Nobel Prize winner, and six others later became directors of observatories or research institutes. He was survived by Letty and her two children from a previous marriage, Brian and Peter (whom he had adopted).

BIBLIOGRAPHY

WORKS BY BOLTON

“Discrete Sources of Galactic Radio Noise.” Nature 162 (1948): 141–142.

With G. J. Stanley and O. B. Slee. “Positions of Three Discrete Sources of Galactic Radio Frequency Radiation.” Nature 164 (1949): 101–102.

With K. C. Westfold. “Structure of the Galaxy and the Sense of Rotation of Spiral Nebulae.” Nature 165 (1950): 487–488.

With G. J. Stanley and O. B. Slee. “Galactic Radiation at Radio Frequencies VIII.” Australian Journal of Physics 7 (1954): 110–129.

With N. A. Qureshi. “The Effects of Air Temperature and Pressure on the Decay of Silver Iodide.” Bulletin of the American Meteorological Society 35 (1954): 395–399.

With G. J. Stanley and B. G. Clark. “A Solar Occultation of the Crab Nebula at a Wavelength of 12 Meters.” Publications of the Astronomical Society of the Pacific 70 (1958): 594–597.

With G. J. Stanley and D. Harris. “A 21-Cm Survey for Galactic Longitudes 294° to 328°, Latitudes +/-8°.” Publications of the Astronomical Society of the Pacific 70 (1958): 544–555.

With V. Radhakrishnan. “21-Cm Absorption Studies of Galactic Radio Sources.” Astronomical Journal 65 (1960): 498.

With R. W. Wilson. “A Survey of Galactic Radiation at 960 Mc/s.” Publications of the Astronomical Society of the Pacific 72 (1960): 331–341.

With others. “The Parkes 2700-MHZ Survey: Part Fourteen; Catalogue and New Optical Identifications.” Australian Journal of Physics 46 (1979): 1–14. “Radio Astronomy at Dover Heights.” Astronomical Society ofAustralia, Proceedings 4 (1982): 349–358.

“The Fortieth Anniversary of Extragalactic Radio Astronomy: Radiophysics in Exile.” Astronomical Society of Australia, Proceedings 8 (1990): 381–383.

OTHER SOURCES

Goddard, Dorothy E., Raymond F. Haynes, and R. P. Robertson, eds.“Pioneering a New Astronomy: Papers Presented at the John G. Bolton Memorial Symposium, Dec. 1993.” Special issue, Australian Journal of Physics 47, no. 5 (1994): 495–680.

Kellermann, K. I. “John Bolton.” Physics Today 47 (1994): 73–74.

———. “John Gatenby Bolton (1922–1993).” Publications of the Astronomical Society of the Pacific 108 (1996): 729–737. Murdin, Paul. “John Gatenby Bolton.” In Encyclopedia ofAstronomy and Astrophysics, edited by Paul Murdin. Philadelphia: Institute of Physics Publishing; London and New York: Nature Publishing Group, 2001.

Wild, J. P. “John Bolton (1922–1993).” Quarterly Journal of theRoyal Astronomical Society 35 (1994): 225–226.

Wild, J. P., and V. Radhakrishnan. “John Gatenby Bolton.” Biographical Memoirs of Fellows of the Royal Societ y 41 (1995): 72–86.

———. “John Gatenby Bolton, 1922–1993.” Historical Records of Australian Science 10 (1996): 381–391.

Wayne Orchiston Kenneth I. Kellermann