Tianyan (天眼, lit. “Heavenly Eye” or “The Eye of Heaven”), is a radio telescope located in the Dawodang depression (大窝凼洼地), a natural basin in Pingtang County, Guizhou Province, southwest China. It consists of a fixed 500 m (1,600 ft) dish constructed in a natural depression in the landscape. It is the world’s largest filled aperture (single dish) radio telescope, and the second largest radio telescope (after the Russian RATAN-600, which has a sparsely filled aperture).
Chinese scientists are now at work debugging the telescope’s software and instruments and doing some trial observations. That’s according to Zheng Xiaonian, deputy head of the National Astronomical Observation (NAO) under the Chinese Academy of Sciences, which built the telescope.
Project officials said the new telescope will be used for many astronomical pursuits, including an exploration of the very early universe, but a primary focus will be a hunt for signals from possible, distant extraterrestrial civilizations. In other words, FAST will be used in part to listen for radio waves from aliens on other worlds. Peng Bo, NAO’s director, said.
FAST beats the Arecibo telescope in Puerto Rico into second place, with its 305-metre diameter dish. But the two giant telescopes are similar. Each uses natural geological depressions in the landscape known as “karst”, giant sinkholes created by nature, that fit the rough outline of the telescope dish. Both are static structures in the sense that the dish only looks straight up, staring at the zenith. They therefore depend on the rotation of the Earth for different parts of the sky to come into view over the course of the day. To follow an object for a few hours at a time, the detector, which is suspended above the centre of the dish, can be shifted. This is much akin to moving one’s head in front of a mirror left to right in order to scan what lies behind.
But while the Arecibo detector cage hangs in a fixed position, the FAST telescope uses an ingenious mechanism based on cables and pulleys that allows it to position the entire detector cage anywhere across the face of the dish. Another major difference is that Arecibo’s dish is of a fixed, spherical shape whereas FAST uses an advanced system of cables and actuators that deform the spherical mirror, much like a rubber sheet, to create a parabolic shape. This allows a two to three times larger part of the sky to be accessed than is possible with Arecibo.
FAST is optimised to detect signals coming from neutral hydrogen, the most abundant element in the universe. This is found in diffuse clouds in the interstellar medium that fills the space between the stars in galaxies. This is the raw material from which stars form. FAST will be able to make a complete census down to much lower levels of the hydrogen content of the local universe than has been possible so far. How much hydrogen is found, where and in what kind of agglomerations, will have direct consequences for how scientists think the universe evolved from its earliest phase and how galaxies formed and have continued to grow with time.