"I saw the lights of cities on Earth and lightning ripping through the night sky. From our orbit I saw the darkness and emptiness of space and I wondered where the boundary is between the sky and the stars," he said. "I will never forget those scenes."

[责任编辑：郑成琼 ]

"Once a pilot is admitted to the astronaut team, they must immerse themselves in more than 30 subjects, including physics, astronautics and astronomy. Normally, university courses in each of these subjects last four years, but our astronauts have just one year to complete their studies and they must pass exams about every topic," said Li Xinke, Party chief at the Astronaut Center of China.

Liu Wang, who took part in the 2012 Shenzhou IX/Tiangong I mission, said it was awe-inspiring and unforgettable to observe the Earth and the universe from space.