The Chatterton Astronomy Department aims to apply interferometers with very high resolving power to optical astronomy. The programme of the stellar intensity interferometer at Narrabri Observatory was completed in 1972 and since then the work has been directed towards building a more sensitive instrument with higher resolving power. As a first step a much larger intensity interferometer was designed but was not built because it was large, expensive and not as sensitive as desired. Efforts are now being made to design a more sensitive and cheaper instrument. A version of Michelson’s stellar interferometer is being built using modern techniques. It is hoped that it will reach stars of magnitude +8 and will work reliably in the presence of atmospheric scintillation. It is expected to cost considerably less than an intensity interferometer of comparable performance. The pilot model of this new instrument is almost complete and should be ready for test in 1984.

A brief account is given of the early development of a new sources. Following the chance discovery that it was unaffected by scintillation it was proposed to apply the same principle to measuring visible stars. This proposal met with vigorous opposition from physicists when it was realised that it implied that the time of arrival of photons in two mutually coherent beams of light must be correlated. Two laboratory experiments were done to demonstrate that this correlation does in fact take place. Then, after a pilot model had measured the angular size of Sirius, a full scale stellar intensity interferometer was built and installed at Narrabri in Australia. In a programme lasting 12 years it measured the angular diameters of 32 single stars in the spectral range O to F and established the first wholly empirical temperature scale for stars in that range. For the last 10 years the work has been continued by the construction of the larger and more sensitive Sydney University Stellar Interferometer called SUSI.