Abstract
The career and scientific contribution to the development of radio astronomy by Bernard Yarnton Mills (1920–2011) is the focus of this chapter. Mills’s major achievements are described, including the invention of the Mills Cross radio telescope and his investigations into the nature of the discrete radio sources and their significance in cosmology.
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Notes
- 1.
The swept-lobe interferometer was a Michelson interferometer (see Appendix A) with a response pattern that could be moved back and forth over the sun at a rate of 25 times a second. With the sea-cliff interferometer, the motion of the response pattern was limited to the slow rate governed by the rotation of the earth (scan duration of the sun about 2 min of time).
- 2.
The sea-cliff interferometer (see Appendix A) had first been used by McCready, Pawsey and Payne-Scott (1947) to investigate the source of solar radio emission. This was in fact the first use of interferometry in radio astronomy. Bolton and his team at Dover Heights went on to use the sea-cliff interferometer for the pioneering work in investigating the cosmic radio sources, and this resulted in the first three optical identifications of discrete radio sources, two extragalactic and one the Crab Nebula, the remnant of the supernova of 1054 (Bolton, Stanley, & Slee, 1949).
- 3.
Unsourced quotations are from Bernie Mills's autobiographical notes, held by the University of Sydney Archives.
- 4.
The first identifications of radio sources with optical objects required an accuracy of about 1 arcmin.
- 5.
For a full discussion of the identification of Cygnus A, see Sullivan, W. T. 2009. Cosmic noise: a history of early radio astronomy, Cambridge, Cambridge University Press pg 335.
- 6.
A technique to move the response pattern of the interferometer back and forth over a limited region of the sky; with this scheme, the long-term instrumental instabilities could be partly eliminated.
- 7.
In 1946, Robert Dicke of Princeton University developed an eponymous switching system for the detection of weak radio astronomy sources at microwave frequencies.
- 8.
The increased bandwidth leads to an increased sensitivity.
- 9.
The extended sources were observed to be larger than 1° on the sky, while the compact sources were smaller than 1°.
- 10.
The radio link was used to transmit (1) the signals back to the central receiver and (2) the control signals from the home station to the distant aerial.
- 11.
The reduction in side-lobe level was due to the filled geometry of both arms of the cross.
- 12.
See Appendix A.
- 13.
The mathematical operation to apply to the observational data in order to produce an image of the radio sky
- 14.
Fred Hoyle (1915–2001), prominent UK astrophysicist and cosmologist, primarily known for the theory of stellar nucleosynthesis. One of the founders of the Steady State theory of the universe along with Hermann Bondi and Thomas Gold. The Steady State theory is an alternative to the Big Bang model of the evolution of the universe. In the Steady State theory, the density of matter in the expanding universe remains unchanged due to a continuous creation of matter. The modern Big Bang theory is one in which the universe has a finite age and has evolved over time through cooling, expansion, and the formation of structures through gravitational collapse. The Big Bang is the accepted model of the universe in the twenty-first century.
- 15.
For a uniform distribution of sources in the universe as predicted in a Steady State universe, the slope was predicted to be −1.5; for an evolving universe (Big Bang), the slope was predicted to be somewhat more negative due to the changing properties of the sources over the lifetime of the universe (higher density of radio sources when the universe was younger).
- 16.
As an interesting aside, Bowen would later recreate the event of driving in the first peg at the Parkes site at another location some distance to the south of the telescope, effectively editing Mills and Christiansen out of his own history (see Fig. 3.18). In 1971, Frank Kerr told W.T. Sullivan about the staged event: “… Taffy Bowen went up to the site… with McCready and he got McCready to take a picture of him driving the post in. And that picture has been published in various propaganda journals”. In addition, Paul Jelbart, a nearby neighbour who lived on an adjacent property at Parkes, witnessed the recreation in September 1961, only a month before the official opening. The site of the recreation is some 200 m south of the 64 m telescope (John Sarkissian, private communication).
- 17.
Radio sources with previously determined accurate positions on the sky, usually associated with known radio galaxies or quasars. Often these sources had well determined flux densities.
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Frater, R.H., Goss, W.M., Wendt, H.W. (2017). Bernie Mills: Cross-Type Telescopes and Discrete Radio Sources. In: Four Pillars of Radio Astronomy: Mills, Christiansen, Wild, Bracewell. Astronomers' Universe. Springer, Cham. https://doi.org/10.1007/978-3-319-65599-4_3
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