A CONVERSATION BETWEEN SKY AND GROUND Taken by Yingwei Chen on August 28, 2016 @ china

On August 16th, 2016 (BJ Time), China has successfully launched the worlds 1st quantum satellite in the northwestern Gobi Desert, Jiuquan. The satellite, Quantum Experiments at Space Scale (QUESS), named as Micius after one ancient Chinese philosopher and scientist at 5th BC, is orbiting the Earth at a period of about 90 minutes at an altitude of 500 kilometers. On the early morning of August 27th, an alignment test between the satellite and ground-based telescope (GBT) at the Xinglong Observation Station has been carried out. The Xinglong Observation Station is affiliated with National Astronomical Observatories, CAS, China, and one of the five stations used for communicating with the satellite. Because the satellite is moving quite fast, in order to make the perfect alignment and effective communication, the position of the satellite will be forecasted with the station before the satellite passing through the sky area where the GBT is located. As soon as the satellite enters the observable zone, GBT will send up a laser beam (shown in the red color) to the satellite. Once the red laser beam is received by the satellite, a second laser beam (in the green color) will be sent down to the ground almost simultaneously, and GBT will captures the beam and feed it into an optical fiber if successful communication is established. The whole send-and receive process is within 3 seconds. It turned out the whole experiment had been successful as demonstrated in the picture. In the picture, the red light has a wavelength of 671 nm and the green light has a wavelength of 532 nm.