Big Dish

A radio telescope in a big bowl is about ready to get to work. Construction was finished in July, and scientists have spent the last couple of months checking it out.
The telescope is known as FAST. It was built in a natural bowl-shaped depression in south-central China. It’s 500 meters wide — almost a third of a mile. That makes it the second-largest single-dish radio telescope in the world.
FAST is patterned after the Arecibo Telescope in Puerto Rico, which is also built in a natural basin. The terrain makes it easier to support the telescope, which forms a wide, shallow dish. It also provides some shielding from radio interference here on Earth.
That design means the telescope can’t move to follow astronomical objects as Earth spins on its axis. Instead, a tracking system above the dish moves, allowing the telescope to keep an eye on an object for up to a few hours. That design comes with a trade-off, though — astronomers can’t use more than 300 meters of the radio dish at a time.
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