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What is radio astronomy?
Astronomers explore the universe by passively detecting electromagnetic radiation emitted by celestial objects. Radio astronomers concentrate on the relatively long wavelength (or low frequency) radio waves that penetrate the atmosphere with little impediment or distortion. These radio signals have frequencies between about 30 Megahertz and 40 Gigahertz, or equivalently, wavelengths from 10 metres down to 7 millimetres.
+ More ( NRAO website).

Is radio astronomy an important scientific field?
Radio astronomy has been crucial in uncovering phenomena such as quasars, pulsars, superluminal motion and the cosmic microwave background, and has led to three of the six Nobel prizes awarded for work in astrophysics, as well as one for the technique of radio interferometry ( Penzia & Wilson, Taylor & Hulse, Ryle & Hewish).

Are there a lot of radio telescopes around the world?
There are radio telescopes in 25 countries around the world.

Some of the largest single dish telescopes are :
• Arecibo (300 m) situated in Puerto Rico,
• Effelsberg (Germany, 100 m),
• Parkes (Australia 64 m),
• Robert C. Byrd Green Bank (USA 100 m),

Some of the major multi element radio telescopes are :
• The Very Large Array (VLA), situated close to Socorro, New Mexico(USA) where 27 antennas can be separated up to a distance of about 36 km. Each antenna is 25 m in diameter.
• The Australia Telescope Compact Array (ATCA) close to Narrabri in Australia, in which 6 antennas are separated up to 6 km. Each antenna is 22m diameter.
• The Westerbork Synthesis Radio Telescope (WSRT), located in the Netherlands, consists of 14 dish-shaped antennas. Each antenna has a diameter of 25m.
• The Giant Metrewave Radio Telscope (GMRT) close to Pune in Indiaconsist of 30 dishes of 45 meters each separated by distances up to 25 km.
• Under construction, the LOw Frequency ARray (LOFAR) and will consist of 25.000 small antennas built in the Netherlands, on one big central location (320ha) and almost one hundred outrigger stations, each
of 1 or 2 ha.

Why do radio astronomers need a new radio telescope?
History has shown that for any scientific discipline to remain active and productive, the power of its instrumentation must grow exponentially with time. Without this growth the discipline tends to stagnate and new discoveries are not made. Most of the currently used radio telescopes were built ten to thirty years ago. For radio astronomy to progress a new telescope with one hundred times the collecting surface of existing telescopes will be needed in about ten years time.

What is the difference between SKA and today's radio telescopes?
Covering frequencies of 0.1–25 GHz, it will make a revolutionary break with today’s radio telescopes.
It will:
• have a collecting area of almost one million square metres, giving it 50 times the sensitivity of today’s best radio interferometer;
• be the first aperture synthesis telescope with multiple independent fields of view (up to 100 at one time);
• integrate computing hardware and software on a massive scale, in a way that best captures the benefits of these exponentially developing technologies.

Why one square kilometre?
Increasing a telescope's collecting area increases its sensitivity. Thanks to higher sensitivity, weaker signals emitted by more distant or fainter celestial objects, can be received. One of the aims of the SKA is to receive signals from the early Universe (the most distant objects that can be observed). These signals are very faint and hence require a very sensitive telescope so they can be detected. This means the SKA needs to be very large.

Will other telescopes still be useful once SKA is constructed?
The Square Kilometre Array will complement other planned instruments in the optical, infrared and millimetre wavebands. It will study the hydrogen gas content and magnetic fields of the same galaxies observed in dust and molecules by ALMA (the Atacama Large Millimeter Array) and in stars by the JWST (James Webb Space Telescope).

For example, combining centimetre wavelength observations from the SKA with those at millimetre-wavelengths from ALMA will give distances to starburst galaxies—even those optically obscured—at any redshift.

What can be studied thanks to SKA?
The SKA’s superior resolving power and image quality will be crucial to studying the formation and evolution of stars, galaxies and quasars, untroubled by dust. It will allow astronomers to see, for the first time, even normal galaxies at distances where cosmological effects dominate.

Thanks to SKA, astronomers will study the Dark Ages and the dawn of galaxies, the earliest pre galactic structures and the evolution of large scale structure of the Universe. The SKA will observe the evolution of galaxies and the stars forming within them, exploring the roles of mergers, Dark Matter and magnetic fields in these processes. Using its highest frequencies the SKA will be able to measure redshifted molecular lines in the interstellar medium of early galaxies. The SKA will be able to measure galaxy rotation curves, giving unique information about the total Dark Matter present in those galaxies.

By timing many millisecond pulsars to sub-microsecond accuracy, the SKA will be able to detect the long-period gravitational radiation emitted by ultramassive black hole binaries throughout the Universe.
Through astrometric observations of parent stars the SKA will compile a census of Jovian planets in the solar neighbourhood and put statistical constraints on their orbital separations and masses.
The SKA will be able to conduct the Search for Extraterrestrial Intelligence (SETI) with a sensitivity up to 100 times greater than is now possible, targeting many stars simultaneously.

When will the SKA telescope be built ?

The timeline is

1991	Concept
1994	International Working Group formed
1997	Start of design and prototyping
2000	Signing of first Memorandum of Agreement
2006	Reference design selected Sites short-listed
2007	Start of US Technology Development Program (TDP)
2008	External review of preliminary specifications Start of Preparatory Phase of the SKA (PrepSKA)
2008-11	System design
2009	External engineering review of design
2011	Site selection completed
2012	SKA Pathfinder telescopes completed Start of Phase 1 construction
2014	Early science with Phase 1
2015	Production readiness review
2016	Phase 1 completed (15-20% SKA)
2020	Phase 2 completed (full array for low- and mid-band frequencies) Start of Phase 3 system design (high-band)
2022	Start of Phase 3 construction

Where will the SKA telescope be built ?
See SKA location or Site white papers for more details.

What will the SKA telescope look like?
See SKA design or design white papers for more information.

How much will it cost?
A number of possible technology options are under consideration, which are estimated to cost €300 M for Phase 1 and €1,200 M for Phase 2; thus, the target cost to build an array capable of operating at frequencies from ~70 MHz to 10 GHz is €1,500 M.. The Phase 1 and Phase 2 costs include 100 M€ and 500 M€ respectively for infrastructure, software, labour, management costs, and delivery; the remaining two-thirds in both cases is for hardware components. The third phase of the SKA Program, an extension to at least 25 GHz, is less well-defined, and the technical outlines and costs of its implementation are yet to be established.

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