The second live class from China's space station was held on Wednesday afternoon, delivered by Shenzhou-13 crew members Zhai Zhigang, Wang Yaping and Ye Guangfu to students on Earth.
The class began at 3:40 p.m. (Beijing Time) and was attended by students from three classrooms across China. The main classroom was located in the China Science and Technology Museum, while others were respectively set up in Lhasa in southwest China's Tibet Autonomous Region and Urumqi in northwest China's Xinjiang Uygur Autonomous Region.
Wang, assisted by the other two crew members, conducted several scientific experiments, such as the crystallization of supersaturated solution, a liquid bridge demonstration, water-oil separation and throwing objects under the zero-gravity condition, amazing numerous students on Earth.
The 45-minute lecture also featured an introduction to the space science facilities and a real-time Q&A session with the students via video call, according to the China Manned Space Agency.
In the first experiment of the class, Wang used a bag of supersaturated sodium acetate solution to demonstrate its crystallization in micro-gravity.
After Wang squeezed the solution from the bag, it became a transparent fluid ball floating in front of the camera. Wang used a small stick covered with crystal nuclei to touch the fluid ball and it quickly became crystallized.
"It looks like an ice ball, but as I touch it, I can feel that it's warm," Wang told the class.
The space teacher explained that the solubility of sodium acetate in water of higher relative temperature is very high, and it very easily forms a supersaturated solution. Just a small trace of crystal nuclei causes the sodium acetate to crystallize, releasing a lot of heat.
Another micro-gravity experiment showed how to separate oil from water in space. Wang prepared a small bottle of oil and water, which were separated at the begining, while the students on the ground also had such bottles, allowing them to follow the procedure.
The teacher and students all shook bottles to mix oil and water into a fluid mixture. The students found their mixture gradually separated into oil and water again, but the fluid in space remained as a mixture.
When Wang asked for a method of separating water and oil in space, a student from Beijing suggested swinging the bottle in a circle. Wang's teammate Ye Guangfu tried the method and succeeded in separating the two.
Wang said that centrifugation, the simple principle behind the experiment, can play an important role in science experiments. She said that the space station is equipped with a centrifuge, which the crew can use to separate and prepare medical samples such as blood and urine.
Wang and Ye then jointly introduced two laboratory cabinets aboard the Tiangong space station. They first showed how they used the high-quality microgravity experiment cabinet, which can offset the influence of air disturbances and platform vibration with air spray and magnetic levitation techniques.
"With this cabinet, we can conduct more precise experiments to enhance the measurement accuracy," Ye said.
They then showed students the containerless experiment cabinet, in which samples can float in the middle to avoid possible contamination and shape changes caused by the contact with the container surface.
"You see, we are quite busy working here," Ye said while echoing a student's curiosity about their work rhythm in space.
According to Ye, the trio have carried out diverse studies in fields such as medicine, physics, material science and life science in space. They have also conducted space application experiments related to some advanced detection technologies and traditional Chinese medicine.
"We can closely communicate with scientists on the ground, and the experiment data can be transmitted to them in real time," Ye said.
"After the Wentian and Mengtian laboratory modules are sent into space, the astronauts will carry out more scientific experiments in broader fields," he said, and both Chinese and foreign scientists will then have the opportunity to carry out research aboard China's space station, which will serve as a space experiment platform for the world.
When answering a question from a student from Xinjiang, Wang said that the scientists have planned to send fruit flies to the space station, as they are often applied in the study of biology.
The soon-to-be-launched Wentian module will be equipped with experiment cabinets for research on animals, plants and microorganisms. "The space station will embrace not only experiments conducted by scientists, but also fanciful ideas from you," Wang told the students.
Other interesting questions raised by the students included "What time do the astronauts in orbit follow?" and "Does water boil in space?"
When a student from Beijing said that he wanted to become a scientist and asked if he would have the opportunity to conduct experiments aboard the space station in the future, Ye praised his great ambition and encouraged him to study hard, exercise well and pursue his dream bravely.
"What's the difference between looking at the moon from Earth and from the space station?" Tenzin Chodron, a 14-year-old student from Tibet, asked from her classroom in Lhasa.
Born into a herding family in the Tashiding village of Xigaze City, she is always fascinated by the bright moon at night. "I hope I can board the space station one day to see what the Qinghai-Tibet Plateau looks like from space."
"Children in rural areas do not often have the opportunity to attend a live science lecture and talk to astronauts. This popular-science class can ignite their aspirations in science and space," said Phuntsok Paljor, a sci-tech instructor at the Lhasa Eighth High School.
At the end of the class, the trio expressed their expectations for the students on Earth. "We hope you will continue to gain scientific knowledge and explore the mysteries of science. The future space station is waiting for you guys," Wang said.
The three astronauts went into space onboard the Shenzhou-13 spaceship and entered the country's space station on Oct. 16, embarking on the country's longest-ever crewed mission for space station construction.
On Dec. 9, 2021, the trio delivered the first live lecture from China's space station, showing the students their living and working areas at the Tianhe core module and several scientific experiments under the zero-gravity condition.
