GUIYANG, July 23 (Xinhua) -- Technicians began assembling the world's largest radio telescope, whose dish is the size of 30 football grounds, deep in the mountains of southwest China's Guizhou Province on Thursday.

In the afternoon, technicians began to assemble the telescope's reflector, which is 500 meters in diameter and made up of 4,450 panels. Each panel is an equilateral triangle with a side length of 11 meters.

Once completed, the single-aperture spherical telescope called "FAST" will be the world's largest, overtaking Puerto Rico's Arecibo Observatory, which is 300 meters in diameter.

Nan Rendong, chief scientist of the FAST project with the National Astronomical Observatories, Chinese Academy of Sciences, told Xinhua that the bigger the dish is, the more capable the telescope is and the weaker messages it will receive.

"A radio telescope is like a sensitive ear, listening to tell meaningful radio messages from white noise in the universe. It is like identifying the sound of cicadas in a thunderstorm," he said.

With a perimeter of about 1.6 km, it will take about 40 minutes to walk around the telescope.

The giant dish is built upon a naturally-formed bowl-like valley in the southern part of Guizhou.

"There are three hills about 500 meters away from one another, creating a valley that is perfect to support the telescope," said Sun Caihong, chief engineer of FAST's construction, explaining the reason why this site was chosen.

The Karst formation in the local landscape is good for draining rainwater underground and protecting the reflector, Sun said.

The surrounding area has "radio silence" as there are no towns and cities within a sphere of five km and only one county center within a sphere of 25 km, he said.

The huge dish is actually hung over the ground supported by thousands of steel pillars and cables. There will be maintenance passages under it.

To overlook the whole reflector, visitors have to climb up to the top of one of the hills. A hill-top observation platform is under construction and will be open to the public, Sun said.

Not only will it be huge, the new telescope is also very sensitive.

The dish can shift to receive radio from different angles, said Zheng Yuanpeng, chief engineer of the telescope's panel project.

"Panels can change their positions through connected wires and parallel robots. We can control their position with an accuracy of 1 mm," Zheng said.

The new telescope is expected to greatly enhance Chinese scientists' capacity to observe outer space.

Wu Xiangping, director-general of Chinese Astronomical Society, said that for years Chinese scientists have worked on "second hand" data collected by others and failed to achieve breakthrough.

"Having a more sensitive telescope, we can receive weaker and more distant radio messages. It will help us to search for intelligent life outside of the galaxy and explore the origins of the universe," Wu said.

The construction of the telescope began in March 2011 and is set to finish next year.