Australian Dictionary of Biography

Clabon Walter (Cla) Allen (1904-1987), astronomer, was born on 28 December 1904 at Subiaco, Perth, third child of James Bernard Allen (d.1912), a South Australian-born lecturer in physics at Perth Technical School, and his wife Alice Hooper, née Aitken, a trained nurse who was born in New Zealand. Cla was educated at the High School, Perth, and the University of Western Australia (B.Sc., 1926; M.Sc., 1929; D.Sc., 1936). In 1926 he was appointed to a research fellowship at the newly established Commonwealth Solar Observatory at Mount Stromlo, Federal (Australian) Capital Territory, becoming an assistant there in 1928.

Allen’s first considerable undertaking, a photometric study of the solar spectrum, established at once both his own reputation and that of the observatory. Besides providing a much better picture of the temperature structure and element abundances of the sun, it led to the development of the `curve-of-growth’ technique of analysing stellar spectra, which remained the standard method for many years. Observing the 1940 eclipse of the sun in South Africa, he obtained important results on the solar corona, among them measurements of its electron density which were to prove invaluable to radio astronomers.

During World War II Allen was asked to find a way of predicting intermittent interruptions to radio communications, known as `fadeouts’, which were understood to be related to disturbances on the sun. He did so in a remarkably short time and with conspicuous success. This work led him to foreshadow the identification of the solar wind—energetic particles emitted from featureless areas of the solar surface and constrained to move in streams by forces in the solar atmosphere.

After the war Allen worked closely with the solar group at the radiophysics laboratory of the Council for Scientific and Industrial Research, Sydney. The team was conducting its epoch-making studies of the radio emission from the sun. For several years he was the only optical astronomer in the world to take an active part in a radio astronomy program. He was particularly friendly with Joseph Pawsey, the leader of the group, who lent the Mount Stromlo observatory a 200-MHz receiver which Allen used to monitor solar `noise’ and to survey the radio emission from the southern part of the Galaxy. His final contributions from the observatory were two papers written with (Sir) Richard Woolley, the definitive accounts of the structure and physical nature of the solar corona and the solar chromosphere as they seemed at that time.

In 1951 Allen accepted an invitation by (Sir) Harrie Massey to become Perren professor of astronomy at University College, London, and director of the University of London Observatory at Mill Hill. Within a few years he had built up his observatory into one of the best astronomical departments in England. In 1955 he published the first edition of Astrophysical Quantities, a compilation of numerical data of astrophysical interest. Universally known as `AQ’, it is the most quoted book on the subject. A fellow (1936) of the Royal Astronomical Society, he held a number of positions in the society and other professional bodies. He retired in 1972 and returned to Canberra.

Twenty-five volumes of Allen’s diary, started in 1922 as a means of improving his poor English expression, are held by the National Library of Australia. Concerned less with scientific matters than with social life and customs in early Canberra, its style is inimitable—only Cla could have written: (8 September 1929) `I had a look into Pepys’ diary this afternoon but thought it not as interesting as my own’. In 1977 he published Hiking from Early Canberra. He emerges from his writings as a man of good sense and integrity, with a talent for friendship. A staunch supporter of St Andrew’s Presbyterian Church, Forrest, he sang in the choir, and in his younger years walked 10 miles (16 km) from Mount Stromlo to the Sunday service, then 10 miles back.

Allen was one of the finest Australian scientists of his day. He had a deep, almost intuitive understanding of physics and a talent for finding significant and rewarding problems. Survived by his wife Rose McKenzie, née Smellie, whom he had married on 25 May 1937 at the Baptist Tabernacle, Gisborne, New Zealand, and by their five sons, he died on 11 December 1987 at his Red Hill home and was cremated with Uniting Church forms.