FAST: China's Telescope Finally Operational

The largest full dish radio telescope in the world is ready to probe the mysteries of the universe...
19 February 2020


A nighttime view of the Milky Way from Earth.


China is one of the largest countries in the world in terms of raw square footage. It covers more than 3.705 million square miles, which is why it's been the perfect place to build Earth's largest 'filled-aperture' radio telescope. FAST, which stands for "Five-hundred-metre Aperture Spherical Telescope", is finally operational after nine years of construction.

What are astronomers hoping to find with FAST? Why are radio 'scopes' necessary to understand our universe, and why must they be built in the middle of nowhere?


Scientists might know it as FAST, but those that live near this massive construct have nicknamed it Tianyan, which means Eye of the Sky or Eye of Heaven. Constructed in the Dawodang depression in Pingtang County, the radio telescope stretches 500 metres in diameter, or more than 1,600 feet. 

Filled-aperture telescopes like FAST are those that have a massive dish, but can't move or be aimed. They're amazing tools for collecting deep-space data but are entirely unable to gather information from near the horizon.

The telescope project started in 2011, and it received its first signals in 2016. Once it reached that point, astronomers subjected it to three years of testing, commissioning and calibration. Then on Jan 11th, 2020, it was finally declared fully operational. Its dish is made up of 4,500 individual panels, controlled by 2,200 winches that can tilt each panel individually to aim the otherwise stationary telescope at different parts of the sky. 

How Do Radio Telescopes Work?

When you hear the word telescope, you might picture one that allows you to peer into the depths of space using visible light. While this type of telescope takes pretty pictures, it's limited as to how far it can see. 

Before we had those powerful optical versions, radio telescopes were our go-to tools for observing the void around us. The technology dates back to 1933, when an engineer accidentally discovered a radio wave emanating from space, creating radio astronomy. 

Radio telescopes work by collecting radio signals from space and sending them to the receiver. The receiver converts them into electrical signals, which are fed into a detector. This turns the signal into an image, which can then be analysed by a computer. 

You won't want to check out a radio telescope receiver, though. They're kept at below-freezing temperatures because the equipment is so sensitive it could potentially pick up the noise created by atoms moving around. Even if it's this noise is far too quiet for a person hear without assistance, it's often enough to interfere with the readings of a radio telescope.

Radio telescopes paint a picture of the sky. Instead of using visible wavelengths of light like their optical counterparts, they build each piece of the puzzle from the radio signals they receive. 

Where To Build Them

While they might vary in dish size, and are built all around the globe, every single radio telescope has one thing in common — they're constructed as far away from civilisation as humanly possible. That's due to our reliance on electronic devices, many of which produce radio frequency (RF) interference. The frequency generated by a simple item we take for granted, like a cellphone or a microwave, can make it impossible for the telescope to paint a complete picture of the sky.

For example, the Parkes radio telescope in New South Wales, Australia, was affected by RF interference for decades. Eventually it was discovered that the microwave astronomers were using to heat their lunches was the culprit. 

Modern electronics are designed to minimise the amount of RF interference they produce, but if one microwave can plague astronomers with its phantom signals, imagine how hard it would be to get a clear picture in the middle of a city. To be able to take photos of the remote edge of the universe, radio telescopes have to be located as far away from civilisation as possible. 

Understanding Our Universe

Why are radio telescopes so important? They let us see things we'd never be able to observe otherwise because they don't emit light on the visible spectrum. Radio telescopes let us paint a picture of the universe by studying the radio waves that are naturally generated by stars, galaxies, black holes and other celestial bodies. Additionally, if we send out radio waves from Earth we can capture these as they reflect off something in the cosmos and return. 

One recent milestone — a picture of a black hole — wouldn't have been possible without radio telescopes. The Event Horizon Telescope, as it was called, was actually a massive collaborative effort of multiple telescopes spread out around the globe. Scientists effectively turned the entire planet into one enormous radio telescope, and they were able to accomplish something that had previously been impossible.

A lot more is going on in the universe than we can see with our eyes, and radio telescopes fill in the gaps we might not be able to catch with optical telescopes. It's like watching a movie without the dialogue or music tracks. You can still figure out what's going on, but you don't have all of the pieces of the puzzle so it's more difficult to understand where they fit.

Looking Toward the Future

FAST in China is the biggest of many filled-aperture radio telescopes around the globe, and the fact that it's finally operational is cause for celebration. It will help us paint a more comprehensive picture of the universe around us, one radio wave at a time. If you ever visit, though, make sure you leave your cellphone at home.


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