The circular feature prominently visible is what remains of the Culgoora Radioheliograph (designed and built by Paul Wild). This was a 96-element, 3 km diameter radio synthesis telescope for solar radio observations at a frequency of 80 MHz. Each telescope had a diameter of 15 m, with a wire mesh surface. With this instrument solar activity, for example the appearance and development of sunspots, was investigated from 1967 to 1986.