Landmark Australia and Oceania
Siding Spring Observatory
Siding Spring Observatory is a place on a mountain in Australia where big telescopes look at the stars. The sky there is very dark at night!
Siding Spring Observatory sits on Mount Woorut in New South Wales, Australia, next to Warrumbungle National Park. The Australian National University chose the site in 1962 for its dark, cloudless skies. Today it is home to many telescopes, including the Anglo-Australian Telescope, the largest optical telescope in Australia.
Siding Spring Observatory, on Mount Woorut near Coonabarabran, is run by the Australian National University's Research School of Astronomy and Astrophysics, which calls it Australia's leading facility for optical and infrared astronomy. Chosen in 1962, it was officially opened in 1965. Its best-known instrument, the 3.9 m Anglo-Australian Telescope, opened in 1974.
Photo: Diceman Stephen West, CC BY-SA 3.0, via Wikimedia Commons
Discover the observatory
Siding Spring Observatory is on top of a mountain in Australia.
At night the sky there is very dark, so telescopes can see faint stars.
Siding Spring Observatory stands on Mount Woorut, 1,165 meters above sea level, about 25 kilometers west of the town of Coonabarabran in New South Wales. It borders Warrumbungle National Park.
The Australian National University (ANU), which runs it, says it is the largest optical observatory in Australia.
The ANU places the observatory on Mount Woorut at 1,165 m, about 25 km west of Coonabarabran (the RSAA says 28 km, the ANU Archives around 30 km), on the eastern edge of the National Heritage-listed Warrumbungle National Park; its Research School of Astronomy and Astrophysics gives 1,164 m. The university's land covers about 151 hectares, from the summit precinct down steep slopes to the north and south.
The ANU calls it Australia's foremost optical and infrared observatory. The site is on the Country of the Gamilaraay/Kamilaroi language group, who have lived in the area for at least 20,000 years.
- Where
- Mount Woorut, near Coonabarabran, New South Wales, Australia
- Height above sea level
- 1,165 m
- Officially opened
- 5 April 1965
- Run by
- Australian National University
Away from the city lights
Long ago, astronomers watched the stars from a mountain near a city.
The city grew, and its lights made the night sky brighter. So they looked for a darker place!
Astronomers had long watched the sky from Mount Stromlo Observatory, near Canberra. By the 1960s, light from the growing city had become a problem for the observatory there.
Astronomers tested several sites, and in 1962 the university chose Siding Spring for its dark, cloud-free skies. The first telescope took its first pictures in 1964, and the observatory was officially opened on 5 April 1965.
By the 1960s light pollution from Canberra was a problem for Mount Stromlo Observatory. In 1960 the director, Bart Bok, won government support to test possible sites, and Mount Bingar near Griffith and Siding Spring near Coonabarabran showed the most promise. Bok favored Mount Bingar, but most of his team favored Siding Spring, and on 12 May 1962 the ANU's vice-chancellor, Leonard Huxley, chose it.
The first telescope, a 40-inch Boller & Chivens instrument, took its first images on 12 February 1964. One ANU page says the university opened the observatory in 1964; the ANU Archives give the official opening as 5 April 1965.
A telescope from two countries
One of the best-known telescopes here was built by two countries working together.
It sits inside a big white dome!
One of the best-known telescopes at Siding Spring is the Anglo-Australian Telescope. Australia and the United Kingdom worked on it together. It opened in 1974 and has a mirror 3.9 meters across, which makes it the largest optical telescope in Australia.
The United Kingdom left the partnership in 2010. Since 2018, the ANU has run it.
The Anglo-Australian Telescope was a joint venture of the Australian and British governments; the organization formed in 1974 to run it, the AAO, was a bi-national facility. The ANU Archives say debates, arguments and delays meant it opened only in 1974 (by Prince Charles) and came into regular use in June 1975. The archive calls it a 3.8 m telescope; the ANU's telescope page and the AAO give a 3.9 m mirror.
It is equatorially mounted. The UK withdrew in 2010, and in July 2018 the observatory duties passed to the ANU.
Hundreds of stars at once
A robot on the big telescope moves optical fibers into place.
That way the telescope can study hundreds of stars and galaxies at the same time!
The Anglo-Australian Telescope has a robotic spectrograph that can study hundreds of galaxies and stars at the same time.
The telescope has carried out several important surveys of the southern sky. It also helps in the search for planets around other stars.
Its 2dF robot, built by the AAO, moves optical fibers into place so the telescope can capture 400 spectra at once.
The AAO says its early use of optical fibers made multi-fiber spectroscopy highly productive in the 1980s; it then built 2dF, a fiber-positioning robot that captures 400 spectra at once, and the surveys that followed gave astronomers some of their richest data.
Other telescopes include a 2.3 m telescope from the 1980s used by students, the Uppsala Telescope moved here in 1982, and the ANU's SkyMapper, which began a digital survey of the southern sky in 2014. The ANU Archives count 10 operational telescopes run by Australian, British, Polish, American and Korean researchers.
- Anglo-Australian Telescope mirror
- 3.9 m across
- Telescope opened
- 1974
- 2dF robot
- 400 spectra at once
- SkyMapper survey began
- 2014
A dome on the mountain
In this photo, a big white dome sits on a round white building.
A path leads up through the grass, under a cloudy sky.
This photo, taken in February 2009, shows the dome of the Anglo-Australian Telescope. A rounded white roof with a railed walkway sits on a tall white round wall, on top of a brick base, with a path and trees in front.
Visitors can see the telescope from a free public viewing gallery, which is closed at night, and there is a hands-on astronomy exhibition.
The photograph (Stephen West, Commons user Diceman, own work, February 2009) shows the Anglo-Australian Telescope's dome: a ribbed white dome with a railed walkway, a tall cylindrical wall with a few vents, a dark brick base, a curving path with a handrail and a lower building to the right.
The RSAA says the AAT has a free public viewing gallery, closed at night and in severe weather. The ANU notes that bushfires have threatened the observatory several times; in January 2013 some buildings were lost, but none of the telescopes was damaged.
Amazing facts
-
Astronomers moved their telescopes far from the city to get away from its bright lights!
The ANU built Siding Spring because light from the growing city of Canberra had become a problem at Mount Stromlo Observatory.
The ANU Archives say Canberra's growth produced enough light pollution by the 1960s to challenge Mount Stromlo Observatory, which led to the search for a second site.
-
A robot helps the big telescope look at hundreds of stars at once!
The 2dF robot on the Anglo-Australian Telescope places optical fibers so the telescope can capture 400 spectra at once.
The AAO describes 2dF as a fiber-positioning robot that captures 400 spectra at once, an unprecedented development whose surveys gave astronomers some of their richest data.
-
Visitors can watch the big telescope from a special room!
The Anglo-Australian Telescope has a free public viewing gallery; it is closed to the public at night.
The RSAA says the AAT has a free public viewing gallery that overlooks Warrumbungle National Park; it is closed to the public at night and in severe weather.
Words to know
- observatory
- a place with telescopes for studying the sky
- telescope
- a tool that collects light to make faraway things look clearer
- light pollution
- too much light from towns and cities that makes the night sky bright
- dome
- a rounded roof
- spectrograph
- an instrument that splits light into its colors so scientists can study it
- astronomer
- a scientist who studies stars, planets and space
Discovery challenge
-
Which country is Siding Spring Observatory in?
In which country is Siding Spring Observatory?
Siding Spring Observatory, on Mount Woorut in New South Wales, is in which country?
- Australia
- Chile
- Canada
Show the answer
Australia
Australia!
Australia.
Australia, near Coonabarabran.
-
Why did astronomers pick this place?
Why did the ANU choose Siding Spring for its observatory?
What did the ANU look for when it chose Siding Spring in 1962?
- Dark, cloud-free skies
- A big city nearby
- A sandy beach
Show the answer
Dark, cloud-free skies
Dark skies with no clouds!
Its dark, cloud-free skies.
Dark, cloud-free skies, away from city lights.
-
Which two countries built the big telescope together?
Which two countries worked together on the Anglo-Australian Telescope?
The Anglo-Australian Telescope was a joint venture of which two governments?
- Australia and the United Kingdom
- Australia and Japan
- Australia and Brazil
Show the answer
Australia and the United Kingdom
Australia and the United Kingdom!
Australia and the United Kingdom.
Australia and the United Kingdom; the UK withdrew in 2010.
-
In which year did the big telescope open?
In which year did the Anglo-Australian Telescope open?
In which year was the Anglo-Australian Telescope opened?
- 1974
- 1962
- 2014
Show the answer
1974
In 1974!
In 1974.
1974; it came into regular use in June 1975.
-
How many spectra can the 2dF robot capture at once?
How many spectra can the 2dF robot capture at the same time?
How many spectra at once can the AAO's 2dF fiber-positioning robot capture?
- 400
- 4
- 40
Show the answer
400
400!
400 spectra.
400 spectra at once.
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For parents & teachers
What children will learn
- Explain what light pollution is and why astronomers avoid it.
- Describe what an optical telescope collects.
- Explain how countries can share a big science project.
Recommended ages: 4 to 17 · About 15 minutes
Talk about it
- Why do you think observatories are often built on mountains?
- How many stars can you see from your home at night? Would you see more far from town?
- Why might two countries build a telescope together?
Try at home or in class
- On a clear night, count the stars you can see inside a cardboard tube, first near a street light and then away from it.
- Find Coonabarabran and Warrumbungle National Park on a map of New South Wales.
Key vocabulary: observatory, telescope, light pollution, dome, spectrograph, astronomer
Where these facts come from
- Wikidata , Wikimedia Foundation (CC0 1.0)
- Siding Spring Observatory , Australian National University
- Siding Spring Observatory , ANU Research School of Astronomy & Astrophysics
- Anglo-Australian Telescope , ANU Research School of Astronomy & Astrophysics
- A New Observatory: The Establishment of Siding Spring , ANU Archives
- Building Highlight: Siding Spring Observatory , ANU Archives
- About us , Australian Astronomical Optics (Macquarie University)
- File:Anglo-Australian Telescope dome.JPG , Wikimedia Commons
- Wikimedia Commons , Wikimedia Foundation (Per file (public domain, CC0, CC BY or CC BY-SA); see each media record)
Checked, not yet human-reviewed. Last updated November 1, 2026. Spotted a mistake? Tell us.