Miller Goss (NRAO)

Impact of CSIR/CSIRO Solar Noise Research -1945 to 1951- on the Development of Radio Astronomy Techniques

Abstract

In Australia solar radio astronomy began at CSIR, Division of Radiophysics, in October 1945. The initial participants were Pawsey, Payne-Scott and McCready. Initially most of the activities of Pawsey’s group at RPL (Radiophysics Laboratory) were in “solar nose” research. “Cosmic noise” research was started by Bolton and colleagues in mid 1947. (The name “radio astronomy” was invented in 1948 by both Pawsey and Ryle.) The early solar noise research lead to the first inteferometry in radio astronomy on Australia Day 1946 by Ruby Payne-Scott at Dover Heights; the course of radio astronomy development was influenced in a major fashion by the appearance in late January 1946 of the second largest sunspots in modern history. The technique used was the sea-cliff interferometer, a Lloyd’s mirror. The “cosmic nose” sea-cliff interferometry followed in the footsteps of the solar observations. The first Michelson interferometer built at the RPL was designed by Pawsey, Alec Little and Ruby Payne-Scott. The Potts Hill Reservoir swept-lobe interferometer for fast imaging of solar burst was used from May 1949 to August 1950 at 97 MHz. Bernie Mills used this same instrument for his first “vertical interferometer” observations of the “radio star” Cygnus A. Mills and Thomas published a position that was within a few arc min of the final adopted position. Their results were much superior to the sea-cliff observations of Bolton, Stanley and Slee. The first earth rotational synthesis was carried out by Christiansen and colleagues using the Potts Hill grating array at 20 cm in 1952-to 1954; the Fourier transforms were done by hand.
Other contributions to radio astronomy technology were the two swept-frequency solar instruments developed by Paul Wild and colleagues at Penrith and later at Dapto. The ability to detect both the time and frequency domain lead to the brilliant classification of solar bursts in a 6 month period in 1949 (Type I, Type II and Type III); the frequency drift rate of the relativistic Type III burst of 20 MHz/s was a major challenge.
Contributions to a theoretical understanding of radio emission processes (free-free, plasma emission and later synchrotron emission) as applied to solar radio emission had a major impact on the understanding of the processes for galactic sources (HII regions and SNR) and for an explanation of the galactic non-thermal background. The contributions to extragalactic research are obvious.
As an aside, I will show a few images made by a Life photographer in 1952 of the azimuth sea cliff interferometer at Dover Heights. This innovative instrument was designed by John Bolton and lead to the re-discovery of Puppis A as well as the large ( 10 deg) radio source associated with Centaurus A.