An artist's impression of some of the SKA's 15-metre dishes underneath the Milky Way. Image: SPDO/TDP/DRAO/Swinburne Astronomy Productions.

The location of the Square Kilometre Array (SKA) - a giant collection of radio dishes, arrays and antennae that will combine to form the largest telescope ever built - has surprisingly been awarded to both countries competing to host it, splitting the SKA not only over two countries but two continents.

"The SKA will be one of the top global science projects of the twenty-first century," says Dr Richard Schilizzi, Director of the SKA's Programme Development Office at the University of Manchester. It will revolutionise radio astronomy, with twenty percent of the telescopes to be found within a square kilometre in the Karoo region of South Africa. Other telescopes spreading into eight other African nations as well as South Africa's rival to host the SKA, Australia, will combine with that central square kilometre to form one giant telescope that will achieve an angular resolution of 0.1 arcseconds.

The science and technology of the SKA will be formidable:

The announcement that both South Africa and Australia, who were competing against each other to host the SKA, is a surprising one borne out of the wish to maximise investments already made in both countries, say the SKA Organisation, a multi-national consortium of countries including the UK. What makes their decision slightly controversial is that the organisation's own Site Advisory Committee had ruled that while both bids were excellent, South Africa had the edge overall after considering criteria such as levels of radio interference and long term sustainability of a radio quiet zone, the physical characteristics of the site, long distance data network connectivity, operating and infrastructure costs as well as the political and working environment. However, taking into account that South Africa and Australia, with whom South Africa had been competing, have invested large sums already by building two precursor telescopes - MeerKAT (the Karoo Radio Telescope) in South Africa and ASKAP (the Australian SKA Pathfinder) the advisory committee decided that being inclusive was the best way forward. While the split decision will incur extra cost for the 2.5 billion dollar radio telescope, it is hoped that it will increase the scientific returns, particularly during the project's first phase.

South Africa's Minister for Science and technology, Naledi Pandor, expressed some surprise at the decision given that the advisory committee had recommended South African bid as the best one on the table.

"[This] is an unexpected decision given the search for a single site," she said in a statement. "We had hoped the unambiguous recommendation of the SSAC would be accepted as the most sound scientific outcome. However, in order to be inclusive the SKA organisation has agreed to consider constructing one of the three SKA receiver components in Australia. We accept the compromise in the interest of science and as acknowledgement of the sterling work done by our scientists and the excellent SKA project team."

Contrasting views came from the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Sydney. "This is a fantastic outcome for Australia and for international science," says CSIRO's Chief executive, Dr Megan Clark.

Wherever the SKA was to be built, British scientists, as part of the SKA Organisation, were always going to have a hand in the science. "The decision for a dual site maximises use of investments already made in both locations," says Britain's Minister for Universities and Science, David Willets. "It also ensures that all the great experience already gained can be put to best use designing and delivering the next phase of the project, in which UK scientists will play a key role."

Phase I will begin construction in 2019, consisting of a mix of 15 metre radio dishes initially built in South Africa and combined with MeerKAT, followed up by more dishes built and combined with ASKAP in Western Australia's remote Murchison Radio Observatory 600 kilometres north-east of Perth. Mid-frequency arrays will be constructed in South Africa, while low frequency arrays will be assembled purely in Australia. As a result, each country will contribute different science: Australia (and its partner, New Zealand) will specialise in big picture large scale surveys, while the South African contribution, shared by its partners Botswana, Ghana, Kenya, Madagascar, Mauritius, Mozambique, Namibia and Zambia, will focus on targeted observations.

Phase II will follow several years after completion of Phase I, taking what has been learned from the initial phase and applying it to the South African array to increase the sensitivity. However, funding has not yet been guaranteed for phase II, design studies are yet to be implemented and it remains to be seen how the decision to split the SKA will affect the long-term planning of the telescope.

To learn more about the SKA, visit the project's website at www.skatelescope.org.