The Anglo-Australian Telescope

AAT Overview (24MB Quicktime movie)

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 Department of Industry, Innovation and Science.

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.

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.

The AAT is used to study individual stars and galaxies, as well as performing large-scale surveys and searches.  Some recent projects include:

• 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.
• DEVILS The Deep Extragalactic VIsible Legacy Survey (DEVILS) is a spectroscopic campaign at the Anglo-Australian Telescope aimed at bridging the near and distant Universe by producing the highest completeness survey of galaxies and groups at intermediate redshifts (0.3<z<1.0). Our sample will consist of ~58k galaxies to Ymag<21.2, over ~6 sq. deg. to >95% completeness in three well studies deep extragalactic fields (COSMOS, ECDFS and XMM-LSS).
• OzDES A survey to measure the redshifts of tens of thousands of galaxies and obtain spectra of supernovae and other transients. The galaxy redshifts were used to make the most detailed measurement of the Universe's expansion history, leading to a better understanding of the physics behind the acceleration of the Universe.
• SAMI A spatially-resolved spectroscopic survey of ~3000 galaxies, the largest ever to date, to explore the kinematics and internal astrophysical processes of galaxies to understand galaxy formation.
• 2dFLens A spectroscopic survey of 100,000 galaxies to test gravitational physics by comparing the velocities of galaxy lenses with the shape distortions of background galaxies caused by weak gravitational lensing, and to perform photometric redshift calibration of the input imaging surveys.

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.

Imaging

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.

Spectroscopy 

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.