The Anglo-Australian Telescope
Commissioned in 1974 (read a brief history), the Anglo-Australian Telescope (AAT) was one of the last large telescopes to be constructed using the traditional equatorial mounting, in which one of its rotation axes is parallel to the Earth’s axis. Its excellent optics, exceptional mechanical stability and precision computer-control make it one of the finest telescopes in the world. Also important to the AAT's success has been its suite of state-of-the-art instrumentation, which is constantly being upgraded and improved.
Until the 1970s, most of the world’s largest telescopes had been built in the northern hemisphere. To help redress the balance, the AAT was constructed in Australia so that astronomers could explore in detail some of the most exciting regions of the sky, including the centre of our own Milky Way Galaxy and its nearest neighbour galaxies (particularly the Magellanic Clouds). Some of the finest globular clusters and nearest radio galaxies are also best seen from the southern hemisphere.
The Anglo-Australian Telescope was originally a joint venture of the Australian and UK Governments, but the telescope is now 100% Australian owned. It is operated by the Australian Astronomical Observatory, which was known as the Anglo-Australian Observatory until July 2010. The AAO is now a division of the Commonwealth Department of Industry, Innovation, Climate Change, Science, Research and Tertiary Education.
The Anglo-Australian Telescope has a mirror 3.9 m in diameter, which makes it the largest optical (visible light) telescope in Australia. The AAO also operates the smaller UK Schmidt Telescope, which has a 1.2 m diameter correcting lens and a 1.8 m diameter mirror, and is optimised for large-scale population census surveys of the sky.
What is the AAT used for?
The AAT is used to study individual stars and galaxies, as well as performing large-scale surveys and searches. Some recent projects include:
· The Anglo-Australian Planet Search, a long term, high-precision search that has found more than 40 planets around neighbouring stars;
· WiggleZ (‘wiggles’), a program to help determine the nature of Dark Energy (an unknown entity that is making the Universe expand at an ever-increasing rate) by measuring the clustering patters of distant galaxies;
· GAMA (Galaxy Mass and Assembly), a survey of galaxies and galaxy clusters to investigate the formation and evolution of galaxies;
· GALAH (Galactic Archaeology with HERMES), a new project to understand the chemical evolution of our own Galaxy by surveying a million stars.
Some achievements of the AAT
The AAT has:
· Detected clouds near the surface of the planet Venus through its very dense atmosphere;
· observed the spectacular explosion of the Supernova 1987A, the brightest supernova since the invention of the telescope four centuries earlier. This supernova gave astronomers unprecedented insight into the death of a star.
· discovered extremely small, “ultra-compact” dwarf galaxies;
· made the first detection of an isolated brown dwarf star in our Galaxy;
· measured the ratios of visible and invisible mass in the Universe;
· discovered streams of stars in our Galaxy that are the remnants of dwarf galaxies that have been absorbed into our own.
Using the AAT
The AAT has a mirror 3.9 m in diameter, the largest in Australia. Following its inauguration in 1974, the telescope began regular observations in 1975. While it is no longer one of the world’s largest, excellent instrumentation has kept it doing leading research, and it remains one of the most productive telescopes of its class.
Today, professional astronomers don’t look through telescopes: they have developed instruments that are far better at recording and analysing light than eyes are. The telescope itself is just a set of mirrors for collecting starlight and funnelling it to a location where it can be recorded either as an image or as a rainbow-like spectrum, which reveals detailed information about the star.
Photographers today have moved from film-based cameras to digital ones, but the same change took place decades ago in astronomy. Images that were once recorded with photographic plates are now captured by more sensitive electronic detectors called charge-coupled devices (CCDs). The AAT is now used mainly for spectroscopy (see below), but its current imaging instrument, IRIS2, works in the infrared, using a detector of 1024 x 1024 pixels. While that is small by the standards of commercial digital cameras, it is much more sensitive than normal camera detectors.
Analysing the light from stars and galaxies is called spectroscopy, and involves spreading the light out into its component wavelengths, just as sunlight going through a prism is spread into its component spectrum colours from violet to red. Once again, the spectra of target objects are recorded by sensitive electronic cameras.
What astronomers do
Astronomers work in teams. Most astronomers using the AAT are from Australia and the UK, but scientists from all over the world can be members of the observing teams. A team applies to use the Anglo-Australian Telescope by writing an observing proposal and submitting it to a committee, the Australian Time Assignment Committee. The committee looks at the proposed projects, and the nature of the observing time needed (e.g, if the project can be done when then Moon is bright) and then allocates time to them. Not all proposals can be accepted: usually about twice as much time is asked for than is available. A schedule is then drawn up. Astronomers then usually travel to the telescope to take up their time allocation, although recently there has been a move towards remote observing. This involves astronomers visiting the AAO’s Sydney office, where there is a remote observing laboratory that is networked to the telescope.
Telescopes are giant light buckets. Measuring and analysing the light, however, is done with specialised instruments attached to the telescope. No two of the world’s large telescopes are exactly alike, so instruments are generally built to go on one particular telescope. (A smaller number of ‘travelling’ instruments have been built for use on many different telescopes.) The AAO is a world leader in building advanced instrumentation for its own and other major telescopes.
In particular, the AAO helped pioneer the use of fibre optics in astronomy in the early 1980s, and has become one of the world’s leading institutions in this field. By using flexible optical fibres, the light from many individual objects¾stars, galaxies, or even individual parts of galaxies¾can be directed into a spectrograph and analysed simultaneously. This ‘multi-object spectroscopy’ technique greatly improves the speed and efficiency of data gathering, making possible very large-scale survey projects.
In the 1990s the AAO built a ground-breaking instrument for the AAT, the two-degree field or ‘2dF’ system. It used a robotic arm to place optical fibres onto a large field plate, allowing astronomers to collect light from objects (usually galaxies) spread over a large (two degree) field of view – a piece of sky about 16 times the size of the full Moon. Light from up to 400 objects could be gathered simultaneously. In one night, astronomers could collect and analyse the light from thousands of stars or galaxies, a task that would have taken years in the past.
In 2006, 2dF was upgraded with a powerful new spectrograph called AAOmega. In mid-2013, this was joined by another specialised instrument called HERMES (High Efficiency and Resolution Multi-Element Spectrograph). Together, they make the AAT the world’s best instrument for wide-field spectroscopic surveys.
The UK Schmidt Telescope is also used for multi-object spectroscopy with fibre optics, but is currently being upgraded with robotic ‘Starbugs’ technology. This is an AAO innovation that allows up to 300 fibres to be moved simultaneously in the focus of the telescope by means of miniature autonomous robots. It dispenses with the 2dF-style robotic arm and its ‘one-at-a-time’ fibre positioning process.
For further information, including manuals, observing guides and technical specifications, try the Instruments page.
The Anglo-Australian Telescope: facts and figures
|Base of dome||1134m||Length||15m|
|Top of dome||1184m||Mass of central tube and mirrors||116 tonnes|
|Mass including horseshoe mounting||260 tonnes|
|Working diameter||3.893m||Other mirrors|
|Thickness at outer edge||0.63m||Total||6|
|Mass||16.19 tonnes||Maximum in use at any time||5|
|Cervit blank cast||May 1969||Diameters||0.376 – 1.47m|
|Figuring of surface completed||June 1973||Weight of largest mirror||860kg|
|Diameter of central hole||1.057m|
|Coated annually with 2.5g of aluminium||
|Height to base of dome||26m|
|Diameter||37m||Depth of excavation||0.3m|
|Mass||560 tonnes||Number of floors||9|
|Rotation time||9 minutes|
|Rotates on 32 bogeys||
|Driven by four 3.5 KW motors||Dr E J Wampler||1974-1976|
|Dr D C Morton||1976-1987|
|Dr R D Cannon||1987-1996|
|Average clear nights||65%||Dr B J Boyle||1996-2003|
|“Director’s time (special projects)||36 nights/yr||Dr M M Colless||2003-2012|
|Service time||30 nights/yr||Prof WJ Couch||2013-|
|Astronomers using AAT||300/yr|
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