Siding Spring Observatory, astronomical observatory located on Siding Spring Mountain, near Coonabarabran, at an altitude of nearly 4,000 ft (1,220 m) in the Warrumbungle Mts. of New South Wales, Australia. It began as a field station for Mt. Stromlo Observatory and is operated by the Australian National Univ. The principal instrument is a 153-in. (389-cm) reflecting telescope, which was jointly financed by the Australian and British governments. Other equipment includes 40-in. (102-cm) and 26-in. (66-cm) reflectors, a 48-in. (122-cm) Schmidt camera telescope similar to that at Palomar Observatory, and a 24-in. (61-cm) rotating telescope used for measuring the polarization of starlight.