Figure 1: The proposed Southern African Large Telescope will be based on a southern hemisphere equivalent of the Hobby-Eberly Telescope at McDonald Observatory, Texas. (Courtesy: HET Board)
Abstract. The announcement by the South African government
of its decision to support the construction of a large telescope for optical/infrared
astronomy has given new impetus to the development of basic science on the
African continent. The Southern African Large Telescope (SALT) will be a
southern hemisphere equivalent of the Hobby-Eberly Telescope recently
completed at McDonald Observatory, Texas. This 9m-class telescope is of
revolutionary design and highly cost-effective. SALT will be a major
scientific and technological project with international partners. This new
telescope plus the existing facilities at the South African Astronomical
Observatory should be seen as a focus for the development of basic science
on the African continent. It will enable African scientists to be
internationally competitive in astronomy well into the 21st century.
Sommaire. L'annonce par le gouvernement d'Afrique du Sud de
subventionner la construction d'un grand télescope pour l'astronomie
optique et infrarouge a donné un nouvel élan au développement de la
recherche fondamentale sur le continent Africain. Le "Southern African Large
Telescope" (SALT) sera l'équivalent, dans l'hémisphère Sud, du
Télescope Hobby-Eberly récemment achevé à l'Observatoire McDonald au
Texas. Ce télescope de la classe des 9 m est d'une conception
révolutionnaire et peu onéreux. Avec le concours de ses partenaires
internationaux, SALT sera un projet d'une importance scientifique et
technologique majeure. Ce nouveau télescope ajouté aux infrastructures
existantes à l'Observatoire Astronomique d'Afrique du Sud devrait
focaliser le développement de la recherche fondamentale sur le continent
Africain. Il permettra aux scientifiques Africains d'être
internationalement tout à fait compétitifs dans l'astronomie du 21e
siècle.
Astronomy has played an important role in the lives of humans since the dawn of civilization. It can, with some justification, be called the first of the sciences. Initially a knowledge of the heavens and the celestial cycle was crucial for survival: to know when to plant, when to hunt, when to reap. Later, astronomy became increasingly important to travellers and explorers, which is why astronomy started in South Africa. The Royal Observatory at the Cape of Good Hope was established in the 1820s, with the directive to map the southern skies and to provide the crucial time service required for maritime navigation.
The work of the Observatory for the first 150 years was primarily to prepare star catalogues with precise star positions and to provide accurate time signals. The Observatory also provided the first geodetic survey of South Africa. In addition, as a result of a photograph of a comet taken at the Observatory in 1882, worldwide photographic surveys of the heavens were initiated. Latterly, the Observatory concentrated more on establishing standards of stellar brightness in the southern hemisphere, which are still used today as the most precise stellar photometric standards anywhere.
In 1972 the South African Astronomical Observatory (SAAO) was formed by a merger of existing observatories within South Africa. The problems caused by increasing light pollution in the cities were solved by re-locating the major telescopes in South Africa to a hill near Sutherland in the Northern Cape. This site benefits from the clear, dark skies of the Karoo and is located well away from major population centres. There are four main telescopes situated there (of diameter 1.9m, 1.0m, 0.75m and 0.5m). The SAAO is the National Facility for optical/infrared astronomy in South Africa. Most of the telescope time (80%) is available to researchers from South African universities and institutions - the other 20% of the telescope time is available to `international' researchers, to encourage scientific collaboration and technological exchange.
In the 1970s a radical shift in the scientific direction of the Observatory took place. The scientific programme changed towards understanding the physics of the planets, stars, galaxies and the Universe itself. To the present day this work continues, as the prime function of the Observatory is to further fundamental research in astronomy and astrophysics at a national and international level through the provision and use of a world-class astronomical facility.
In 1996 the South African Government published its White Paper on Science & Technology. This far-reaching policy statement as well as stressing the importance of a National System of Innovation specifically included basic research as a critical element
``Scientists engaging in basic research contribute to the intellectual vibrancy of society as part of a strong R&D base needed .... for participating in and sometimes leading, a global scientific community."
In a developing country like South Africa it is inappropriate to try to develop competence in fundamental science across all fronts. In the first instance, research thrusts must be aligned to support strategic needs, be these economic, social, environmental or military. Fundamental research of a more open-ended curiosity-driven nature also has its place in the culture of any nation. However, to achieve maximum impact the Government needs to make clear choices with respect to focus areas from the point of view of funding. A very strong case can be made that astronomy should be such an area of focus for South Africa.
Many of these arguments apply to other countries in Africa. If such countries are to develop to become global economic players then science and technology has to be an important component of the development of society. To quote the White Paper again
``Scientific endeavour is not purely utilitarian in its objectives and has important associated cultural and social values .... not to offer ``flagship" sciences (such as physics and astronomy) would be to take a negative view of our future - the view that we are a second class nation, chained forever to the treadmill of feeding and clothing ourselves."
| Year | Activity | Budget ($ million) |
| 98/99 | Concept development and site assessment | 1.5 |
| 99/00 | Initial procurement and ground breaking | 4.0 |
| 00/01 | Component development and installation | 6.0 |
| 01/02 | Integration of mirror and tracker system | 5.0 |
| 02/03 | First light and commissioning | 2.5 |
| 03/04 | Completion and science operations | 1.0 |
| 20.0 |
Table 1: SALT Construction Schedule and Funding Profile
For 50 years the largest optical/infrared telescope in Southern Africa has been the 1.9m Radcliffe reflector, now at SAAO's observing site outside Sutherland in the Northern Cape. It is proposed that a new Southern African Large Telescope (SALT) for optical/infrared astronomy be constructed and sited there as well. This has been agreed by national and international committees as the most urgent requirement for the development of astronomy in Southern Africa. Such a telescope would enable South Africa to remain internationally competitive in astronomy well into the 21st century and furthermore provide a focus for the development of basic space science on the African continent.
Originally SALT was planned as a 4m-class telescope (similar to the ESO New Technology Telescope or more recently the WIYN telescope at Kitt Peak). However, a new concept in telescope design is proving to be much more attractive to South African astronomers. The plan is to construct a southern hemisphere equivalent of the Hobby-Eberly Telescope recently completed at McDonald Observatory, Texas.
The Hobby-Eberly Telescope (Figure 1) is a radical departure in design of optical/infrared telescope. The design is based on a tilted-Arecibo concept, with the telescope fixed at 35° to the zenith but capable of full 360° azimuth rotation. During an observation the telescope remains stationary and a tracker beam at the top end enables an object to be followed for 12° across the sky. This telescope can effectively observe an object in an annulus 12° wide in a zone centred on 35° from the zenith. Scientific requirements in the southern hemisphere to enable the whole of the Small Magellanic Cloud to be accessible from the latitude of Sutherland will require this angle of tilt to be increased to 37°.
The primary mirror, measuring 11 metres across, will be constructed from 91 hexagonal segments, each 1 metre in diameter. Because the telescope is stationary during an observation the pupil moves across the primary mirror (Figure 2). The maximum area that is imaged on to the detector corresponds to a 9.2-m mirror - at the edge of the travel of the tracker the pupil is still equivalent to a 7-m telescope. The large amount of spherical aberration is removed over a 4 arcmin field by a spherical aberration corrector. The light is fed by fibre optics to spectrographs of various resolutions in a thermally controlled basement - though it is also possible to mount a light-weight instrument at the prime focus.
The telescope has been designed essentially as a spectroscopic survey instrument with a spectroscopic capability over the wavelength range 0.35 to 2.0µm. It will be most competitive scientifically when used on astronomical targets uniformly distributed on the sky or clustered on a scale of a few arcmins. Because the telescope will be queue scheduled it is particularly effective in time variability studies on time scales of a day or longer.
Because of a conscious decision not to build a general-purpose telescope but rather a telescope with specialised spectroscopic capabilities the whole design is extremely cost-effective. The estimated cost of constructing a southern hemisphere Hobby-Eberly Telescope is US $20 million, comparable to the cost of a general-purpose 4m-class telescope.
Astronomy is a science that takes the Universe for its laboratory and in which physical laws and theories are applied, tested and refined at temperatures, pressures and scales otherwise unobtainable. Modern astronomy (including astrophysics and cosmology) is currently one of the most rapidly advancing branches of physical science. The end of the twentieth century is seeing major developments in astronomical research throughout the world.
The SALT will be the most powerful single telescope for optical/infrared astronomy in the southern hemisphere. Its prime scientific capability is astronomical spectroscopy, the study of the light emitted or absorbed by celestial objects. The optical/infrared spectral region lies at the heart of modern observational astronomy. It is particularly rich in physical diagnostics which have developed from the accumulation of over a century of observation, associated laboratory experiments and theoretical work. Much of our understanding of the Universe (stars, galaxies, chemical composition, motions, expansion of Universe) comes from spectroscopic analysis of celestial objects.
Because of its enormous primary mirror - effectively a 9.2m telescope - and state-of-the-art electronic detectors, the SALT will be able to observe very faint astronomical objects. Key research projects where SALT is expected to make seminal contributions include:-
There is a wide variety of science that SALT can tackle - for example, programmes involving the chemical composition and evolution of the Milky Way and nearby galaxies, redshifts of high-z quasar candidates from imaging surveys, evolution of the gas in galaxies through quasar absorption lines, kinematics of gas, stars and planetary nebulae in distant galaxies, optical characterisation of X-ray objects discovered by AXAF, follow-up of objects from the Sloan Digital Sky Survey, to name but a few.
On 1 June 1998 the Minister of Arts, Culture, Science and Technology announced during his budget speech in parliament that South Africa would fund 50% of the construction cost of SALT. This decision was taken at the highest level by the South African Cabinet. In approving the construction of SALT Cabinet specifically noted the following advantages:
The remaining 50% of the construction cost of SALT will be contributed by international partners. A number of countries and individual institutions have expressed an interest in collaboration with South Africa in a large telescope. In particular the Hobby-Eberly Telescope Board has agreed to make available the detailed plans and drawings of the HET telescope in return for telescope time. The universities of Carnegie Mellon and Rutgers in the USA and Göttingen in Germany are interested in participating in the SALT project. Carnegie Mellon has already prepared a promotional video for the purposes of raising $6 million from potential donors. Countries that have expressed an interest in participating in SALT include Poland, New Zealand and Nigeria.
A feasibility study has shown that South African industry has the capability to construct over 50% of the telescope. Figure 3 shows a stage in the construction of the Hobby-Eberly Telescope. Any funding contributed by South Africa will be to the benefit of South African industry. In addition there will be technological spin-off to South African industry from joint ventures with industry internationally. The construction time scale and funding profile for SALT are given in Table 1.
The SAAO with its outstation at Sutherland is the major observatory for optical/infrared astronomy on the African continent. This facility should be available to other African countries in order to encourage the development of basic space science. It should be seen as the focus of astronomical development on the continent. Already scientists and engineers have come from Namibia, Malawi, Zambia, Zimbabwe, Nigeria and Egypt to train at SAAO. Basic space science on the African continent would be encouraged by the provision of observation time at this premier research facility.
SALT should be seen as the driver of this initiative, as part of the Deputy President of South Africa, Mr Thabo Mbeki's, African Renaissance. We need to strengthen the astronomical community in South Africa especially by developing research groups at the Historically Black Universities. The SAAO itself should be seen as an international facility within Africa. To encourage links with other countries in Africa and promote the development of astronomy groups within physics departments at universities, South Africa will need to help in providing training as well as access to the research facility. Training for MSc/PhD degrees could be provided at existing departments at some South African universities. Research projects could be carried out jointly with astronomers at the National Facilities in South Africa and at the universities. The major question is how these initiatives can be funded.
