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Over the past several years, discussions have been occurring in several countries about the next logical step in radio astronomy following the construction of the large millimetre array ALMA. An initiative has emerged to develop a telescope to provide two orders of magnitude increase in sensitivity over existing facilities at metre to centimetre wavelengths. To achieve this goal will require a telescope with one square kilometre of collecting area - one hundred times more collecting area than the Very Large Array (VLA).

Credit: Canadian glactic plane survey

The Square Kilometre Array (SKA) will probe the gaseous component of the early Universe, thereby addressing fundamental questions in research on the origin and evolution of the Universe. The SKA will complement planned facilities at other wavelengths, such as ALMA and James Webb Space Telescope (JWST). HI, CO and continuum radiation would be observed from the interstellar medium of most of the galaxies the JWST will discover in the infrared at large redshifts.

Extensive discussion of the science drivers and of the evolving technical possibilities has led to a concept for the Square Kilometre Array and a set of design goals. The SKA will be an interferometric array of individual antenna stations, synthesizing an aperture with diameter of up to several 1000 kilometers. A number of configurations are under consideration to distribute the 1 million square metres of collecting area. These include 30 stations each with the collecting area equivalent to a 200 metres diameter telescope, and 150 stations each with the collecting area of a 90 m telescope ( more about design and location proposals ).

Approximately 50% of the collecting area is to be contained within a centrally-condensed inner array of 5km diameter to provide ultrahigh brightness sensitivity at arc-second scale resolution for studies of the faint spectral line signatures of structures in the early Universe. Another 25 % of the collecting area will be located within a diameter of 150 km, and the remainder out to 3000 km or more. This high angular resolution capability will allow imaging of faint emission from the interstellar medium of distant galaxies, as well as the surface of stars, and the active nuclei of galaxies.

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