For 45 years, the 1,000-foot-wide (305-meter) dish near Arecibo, Puerto Rico, has ranked as the world's largest single-aperture radio telescope. But Arecibo's long reign is about to come to an end.On December 26th, Chinese scientists and dignitaries gathered near Dawodang in Guizhou Province for the groundbreaking of an even larger radio giant. Known as FAST (for Five-hundred-meter Aperture Spherical Telescope), the structure will be assembled over a deep, natural depression in this sparsely populated — and thus radio-quiet — region.
A Chinese news report notes that the $100-million project has been in development since 1994. When completed in 2014, FAST's array of 4,600 panels will have roughly 2½ times Arecibo's collecting area.
Unlike Arecibo, the location of the receiver, which is suspended above the dish, can be moved to target sources anywhere within 40° of the zenith (with 8-arcsecond pointing precision, notes the project's Chinese-language home page).More importantly, FAST's will be able to alter large portions the reflector's figure from its natural spherical shape to a paraboloid with an effective aperture of roughly 1,000 feet (300 meters). This should allow FAST to resolve sources only 3 arcseconds across — and while that's nothing special compared to multiple-antenna arrays such as the VLA or ALMA, it's unprecedented for a single radio receiver.
Once operational, FAST will be operated by China's National Astronomical Observatories, under the auspices of the Chinese Academy of Sciences. According to Nan Rendong, the project's lead scientist, the giant dish will survey pulsars, very distant galaxies, and other cosmic sources at frequencies from 70 megahertz to 3 gigahertz.
FAST's huge aperture is likely to inaugurate the study of distant, discrete sources beyond the capabilities of current instruments. As Nan notes, "Its unique contributions to science may not yet be predictable at present."
Speaking of ALMA, short for the Atacama Large Millimeter/submillimeter Array, in mid-December this multinational project took delivery of its first 40-foot (12-meter) antenna. Eventually this dish and 49 more just like it will be linked form an interferometric array that functions as a single telescope. Another sixteen 7- and 12-meter dishes will comprise a second array. They'll all be sited in the very dry Andean desert on Cerro Chajnantor in northern Chile, at an altitude of 16,500 feet (5,060 meters).