Workers install a feedback source cabin for the single-aperture spherical telescope "FAST" in Pingtang County, southwest China's Guizhou Province, June 21, 2016. The 500-meter aperture spherical telescope (FAST), to be completed within 2016, is expected to be the world's largest, overtaking Puerto Rico's Arecibo Observatory, which is 300 meters in diameter. (Xinhua/Liu Xu) 

Photo taken on June 21, 2016 shows the single-aperture spherical telescope "FAST" in Pingtang County, southwest China's Guizhou Province. The 500-meter aperture spherical telescope (FAST), to be completed within 2016, is expected to be the world's largest, overtaking Puerto Rico's Arecibo Observatory, which is 300 meters in diameter. (Xinhua/Liu Xu) 

Photo taken on June 21, 2016 shows the single-aperture spherical telescope "FAST" in Pingtang County, southwest China's Guizhou Province. The 500-meter aperture spherical telescope (FAST), to be completed within 2016, is expected to be the world's largest, overtaking Puerto Rico's Arecibo Observatory, which is 300 meters in diameter. (Xinhua/Liu Xu) 

Workers install a feedback source cabin for the single-aperture spherical telescope "FAST" in Pingtang County, southwest China's Guizhou Province, June 21, 2016. The 500-meter aperture spherical telescope (FAST), to be completed within 2016, is expected to be the world's largest, overtaking Puerto Rico's Arecibo Observatory, which is 300 meters in diameter. (Xinhua/Liu Xu) 

Photo taken on June 21, 2016 shows the single-aperture spherical telescope "FAST" and a viewing platform in Pingtang County, southwest China's Guizhou Province. The 500-meter aperture spherical telescope (FAST), to be completed within 2016, is expected to be the world's largest, overtaking Puerto Rico's Arecibo Observatory, which is 300 meters in diameter. (Xinhua/Liu Xu)