The Great Melbourne Telescope [GMT] was built by Thomas Grubb of Dublin in 1868 and erected at Melbourne Observatory in 1869. It was a reflecting telescope with a speculum (metal) mirror of 48 inches (1.2 metres) diameter. At the time it was the second largest telescope in the world and the largest in the southern hemisphere.
The design and construction was overseen by a committee of eminent British astronomers, which approved Thomas Grubb’s revolutionary design. Although incorporating many of Grubb’s earlier innovations, the telescope was on a larger scale than anything he had previously attempted. Grubb’s firm went on to make many of the major telescopes around the world in the second half of the 19th century.
The telescope was operated at Melbourne Observatory by a Great Melbourne Telescope Observer: Albert Le Sueur (1869-70), E. Farie MacGeorge (1870-72), Joseph Turner (1873-83), and Pietro Baracchi (1883-92); thereafter it was used rarely.
The astronomers had to painstakingly observe faint nebulae and distant galaxies, then produce pencil sketches of their observations. Repeated observations over many nights were needed to gain an accurate drawing.
The telescope was working near the limits of available technology. There were underlying difficulties with tarnishing of its mirrors, flexure in the primary mirror, and vibration due to wind.
The telescope was not well suited to the emerging astronomical techniques of photography and spectroscopy. It took some excellent photographs of the moon, and some early photos of nebulae, which required exposures of up to 40 minutes. But smaller refracting telescopes were better suited at the time to photographic work.
When Melbourne Observatory closed in 1944, the telescope was sold to the Commonwealth Observatory at Mount Stromlo, Canberra. At Mount Stromlo the telescope was given a new 50-inch glass mirror made by Grubb-Parsons, and became an integral part of Mt Stromlo’s work from 1961 into the 1970s.
In the 1990s the telescope was rebuilt with two large-scale digital cameras for the MACHO project, a search for evidence of dark matter. Our first ever glimpse of MAssive Compact Halo Objects was through the GMT. Then in January 2003 a bushfire swept across Mt Stromlo, its firestorm destroying the majority of the telescopes and buildings.