FAST is the world's largest single-dish radio telescope. It sits in a natural karst depression in Guizhou, China, with a reflector 1,640 feet (500 meters) across.
Its nickname is Tianyan, the Eye of Heaven.
In September 2016 it caught its first signal.
An ordinary dish is rigid. This one is made of perforated aluminum panels on a steel-cable mesh hung from the rim.
The shape changes.
4,500 metal panels move in real time and form a parabola.
From the spherical reflector, the system shapes a working patch 984 feet (300 meters) across. Only that patch listens at one moment.
A lightweight cabin with the receiving antenna hangs 459 feet (140 meters) above the reflector. Cables and servo motors move it, and a parallel robot provides half-closed-loop precision control.
Before FAST, telescope construction faced an engineering limit near 328 feet (100 meters). It broke that limit and showed a new way to build large radio telescopes.
How long is 1,640 feet?
About five and a half American football fields, end to end.
The dish does not sit still.
It reshapes itself while it listens.
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