The AAT can be used in many configurations, each requiring a different instrument or detector to collect and analyse the light. Most astronomers use charge coupled devices (CCDs) to collect data. These highly sensitive solid state devices convert feeble light into digital signals which are then collected and stored on computers for further analysis, rather like an electronic photograph. However, traditional photography is also still used for special projects.
The most commonly used instruments on the AAT are its spectrographs, which split the light from distant objects into its constituent colours. Parts of the resulting spectrum can then be studied in detail to measure important properties such as the temperature, chemical composition, velocity or distance of an object, revealing vital facts about distant stars, galaxies and nebulae that photographs cannot show.
Other specialised instruments collect 'light' energy from the infrared (IR) region of the spectrum and are thus sensitive to the temperature of objects too cool to emit visible light. Using the most recent technical advances, the AAO has taken a lead in designing and building IR instruments, the latest of which, IRIS, provides both images and spectra of the sky. New IR instruments are currently under consideration. Infrared images are especially useful for studying the earliest stages of star formation, normally hidden at visible wavelengths by dust clouds.
Over the past decade the AAO has pioneered the use of optical fibres in astronomy and currently leads the world in this work. The latest of these instruments, the Two-Degree Field facility (or 2dF) uses flexible optical fibres, to collect the light from up to 400 faint stars or galaxies from a two degree field of view. This light is directed to a spectrograph, where the 400 individual spectra are detected by a CCD for analysis. Two degrees of sky is about four Moon diameters across, and is a four-fold increase in area of the AAT prime focus, which was already considered to be wide field for a 4-m telescope. This instrument dramatically improves the efficiency of the telescope, which has traditionally observed one object at a time, allowing astronomers to carry out previously impractical observing projects.
THE AAT: FACTS & FIGURES
|Base of Dome||1134m||Length||15m|
|Top of Dome||1184m||Wgt of central tube/mirrors||116 tonnes|
|Wgt with horseshoe mounting||260 tonnes|
|Working diameter||3.893m||OTHER MIRRORS|
|Thickness at outer edge||0.63m||Total number||8|
|Weight||16.19 tonnes||Maximum in use at any time||4|
|Cervit blank cast||May 1969||Diameters||0.376-1.47m|
|Figuring of surface completed||June 1973||Weight of largest||860kg|
|Diameter of central hole||1.067m|
|Coated annually||2.5g of aluminium||BUILDING|
|Height (to base of dome)||26m|
|Diameter||37m||Depth of excavation||0.3m|
|Weight||560 tonnes||No. of floors or part floors||9|
|Roatation time||5 min|
|Rotates at 32 bogeys||DIRECTORS|
|Driven by||4 3.5kW DC motors||Dr E J Wampler||Sep 1974 - Mar 1976|
|Dr D C Morton||Jul 1976 - Mar 1986|
|OBSERVING||Dr R D Cannon||Oct 1986 - Sep 1996|
|Av. clear night time||65%||Dr B J Boyle||Oct 1996 - Jul 2003
|Typical scheduling: Observing||341 nights||Prof M M Colless
||Jan 2004 -
|Instrument tests etc||20 nights|
|Aluminising primary mirror||4 nights|
|Astronomers using the AAT||250 per year|