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Construction of the Southern African Large Telescope (SALT), which is planned to become the largest single telescope in the Southern Hemisphere, has moved closer with commitments to joint funding from overseas partners in Poland, the United States and Germany.

The South African government announced its commitment to provide half the funding for the telescope a year ago (see Nature 393, 403; 1998). With 84 per cent of the expected cost of $16.4 million (without instrumentation) now committed, construction of the telescope will commence later this year. The telescope is expected to take five years to complete.

The largest overseas contributor so far is the Polish Ministry of Science, which has said it will provide $2.5 million for the construction, with an extra $0.5 million from a consortium of Polish universities and research institutions. A further $1.2 million for construction costs and $1 million for running costs over the first ten years has been promised by Rutgers University in the United States.

The third overseas partner is the University of Göttingen in Germany, which has committed $1.3 million towards the telescope's construction. Prospective partners that have not yet committed funds include Carnegie Mellon University, Iowa State University and the University of Wisconsin in the United States, and the astronomical community in New Zealand.

SALT will be have an effective diameter of 9.2 metres. Like its twin in the Northern Hemisphere, the Hobby-Eberly Telescope, recently built in Texas, SALT will be able to collect and analyse the light from many celestial objects at a time over a field of view of approximately 5 arcminutes.

Conventional telescopes need to move to track objects in the sky as the Earth rotates, butALT will remain stationary, with a 5.5-tonne ‘tracker assembly’ at the top of the telescope moving instead. This design limits observations to the time it takes a celestial object to move through 12 degrees, which translates to between 50 minutes and 2.5 hours, depending on how close to the Equator the telescope is located, but it seldom takes more than an hour to make a particular observation.