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Time to power up the largest radio telescope in the world. China’s Five-hundred-metre Aperture Spherical Telescope, or FAST, began spying on outer space on 25 September.

FAST will measure radio waves in space, allowing us to study the rotation of galaxies, monitor the behaviour of pulsars and keep an eye out for signals sent by aliens.

It is situated in a remote, mountainous area of Guizhou Province in south-western China, which will help protect it from radio-wave interference, like signals sent by cell phones and Wi-Fi. Construction began in 2011, spurring the relocation of a small village. The telescope will go through a testing and debugging phase before full operation begins, according to the Chinese Academy of Sciences.

The telescope, named for the size of its dish – 500 metres across – is about 200 metres wider than its closest rival, the Arecibo Observatory in Puerto Rico, built in the early 1960s.

That means that it will be able to see dimmer objects than the Arecibo telescope can detect, says at the Lunar and Planetary Laboratory at the University of Arizona in Tucson.

“Being bigger means it collects more light,” Nolan says. “So if you’re looking at a faint signal, it’ll be brighter in the bigger telescope.”

Squishable dish

The curved bowl of a radio telescope directs the light it catches into a detection device, usually suspended above the dish. A parabola-shaped disc focuses light into a single point, but can cause distortion as the telescope targets different parts of the sky. Smaller telescopes can move their dishes to observe different regions of space, but FAST is too big to steer.

To avoid that problem, FAST’s mirrored panels and its receiver are designed to move in conjunction, allowing scientists to create a parabola-shaped bowl pointed at whatever part of the sky is under observation.

“They’re going to have that be a flexible mirror that they can deform to point at the right place,” Nolan says. “Instead of turning it, they’re just going to squash it to be the right shape.”

The construction of the telescope shows that observatories like Arecibo aren’t a relic of the past, says at the Arecibo Observatory.

“That they put the money into building FAST is a vote of confidence that telescopes of the Arecibo pattern, these large single-dish telescopes, do have a future,” he says.

“As far as we’re concerned, imitation is the greatest form of flattery,” says , also at the Arecibo Observatory. “It’s very nice to have another sibling very much like ourselves.”