DURING the second half of the 20th century astronomy has undergone a revolution with the advent of observations using radio, infra-red, ultra-violet, X-ray and gamma-ray emissions from celestial bodies - all to supplement the conventional optical observations. As a consequence, new classes of galaxies have been discovered with extraordinarily high energy and luminosity, making possible the study of the universe to the very fringe of its observable limits.
What started this great revolution? In my opinion it all began in 1948 when a 26-year-old Yorkshireman named John Bolton with two colleagues discovered that three distant objects, known from optical observations, were extremely powerful emittors 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.
Bolton graduated from Cambridge University in 1942 and then joined the Royal Navy as a radar officer. His ship, the aircraft carrier Unicorn, took him to the Pacific and Australia. After the war he settled in Sydney, married a Sydney girl and joined the Radiophysics Laboratory of the Council for Scientific and Industrial Research (CSIR). The laboratory was directed by Dr E. G. ('Taffy') Bowen and Bolton joined Dr J. L. (Joe) Pawsey's group which was investigating the newly discovered radio waves from the Sun. Bolton was observing (with the primitive and makeshift equipment of those days) from an ex-RAAF radar station located near a cliff edge at Dover Heights, south of the entrance to Sydney harbour. As the sun rose above the Pacific horizon the cliff-top aerials received signals from the sun along two paths: one direct, the other reflected from the sea. The signals interfered with one another and produced a fringe pattern that permitted accurate location of the source.
Bolton's great discoveries came when, on his own initiative, he began to search the sky for radio sources. Only one had so far been discovered, by JS Hey, in England, and that by indirect means. Bolton and his colleagues located this source in the constellation of Cygnus by means of a beautiful set of interference fringes. He then turned to other parts of the sky and these led to the discovery of other sources and the first optical identifications previously referred to.
In 1955 Bolton joined the California Institute of Technology where he initiated a programme of radio astronomy. He built up a fine radio observatory at Owens Valley with two large 'dish' antennae that could operate as an interferometer. Bolton became a dominant force in US astronomy, producing not only important results but also a splendid crop of students who have become leaders around the world.
In 1961 he returned to Australia where Taffy Bown had organised the building of the 210ft Parkes radio telescope. Bolton commissioned the telescope and became director of this, the Australian National Radio Astronomy Observatory. The Parkes telescope under Bolton's direction played a vital part in the dramatic discovery of the first quasar (star-like object) to be identified with an extra-galactic object - a very distant, extremely luminous one. Thus began the search for quasars representing the most distant known objects in the universe. Bolton's foremost project was the optical identification of radio sources; this he pursued relentlessly at Parkes, whose catalogue exceeds 8,000 sources including several hundred quasars.
Under Bolton's direction, the Parkes telescope played an essential role in Nasa's Apollo missions to the moon. How many people know that those first steps of Neil Armstrong were brought to our television sets via the Parkes telescope?
Bolton was a man of great determination once he set his mind on a goal. He did not mind ruffling a few feathers in achieving it, especially those of administrators. It was a matter of total dedication. But he was very fair and left behind a group of disciples devoted to his memory.
I have spent many happy hours in Bolton's company - playing cricket for the Radiophysics XI in Sydney, playing table tennis at Owens Valley and playing billiards in the dome of the 200in telescope at Mount Palomar. The strong competitive spirit was always there. It was a pleasure to compete with him, but I preferred having him on my side as on the cricket field. There his concentration while batting was reminiscent of Herbert Sutcliffe's.
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