Siding Spring Observatory, Astronomical observatory on Mount Woorat, Warrumbungle National Park, Australia

Siding Spring Observatory is a research facility on Mount Woorat in the Warrumbungle National Park at 1,165 metres above sea level, about 60 telescopes strong, not all operational. Its best-known instrument is the 3.9-metre Anglo-Australian Telescope, and the site holds more than A$100 million of research equipment. The 2.3-metre ANU telescope sits in a simple cuboid dome that co-rotates with the tube.

Mount Stromlo Observatory, established by the Commonwealth Government in 1924, was overwhelmed by Canberra's light pollution by the 1950s, and Bart Bok initiated the search for a new site. The ANU chose Siding Spring in 1962 for its dark, cloud-free skies, and by the mid-1960s had built three telescopes plus a road, housing, power and water. The 3.9-metre Anglo-Australian Telescope followed in 1969, and in 1984 Prime Minister Bob Hawke opened the ANU's 2.3-metre telescope.

The observatory's name comes from Siding Spring Mountain, also called Mount Woorat, in Warrumbungle National Park. The site is one of several observatory codes of the Minor Planet Center: 413 for the main observatory, 260 for the UK Schmidt's digitized sky survey, E10 for the Faulkes Telescope South and E12 for the Siding Spring Survey hunting near-Earth objects.

The observatory stands at 1,165 m on Mount Woorat inside Warrumbungle National Park, reached by road from Coonabarabran. The site is a working research facility, so check access arrangements before travelling; nights are cold and the weather can change quickly at this altitude.

The Uppsala Schmidt Telescope, built in 1957 in Sweden, moved to Mount Stromlo and then to Siding Spring in 1982; it now runs the Siding Spring Survey searching for near-Earth asteroids. In 2008 the 2-metre Faulkes Telescope South there measured asteroid 2008 HJ's rotation at 42.7 seconds, the shortest then known.