The two people on the top floor of the Weiming Institute's Observation Building were not the only ones who saw the aurora that night.
Across Beijing and its outskirts, many people looked up and saw the red glow filling half the northern sky.
By Weiming Lake at Peking University, Gu Ming and Sarah, out for a walk on their second day as newlyweds, also stopped. The northern glow reflected on the lake as they watched the aurora and exchanged a smile.
In a corridor at the Haidian District Maternal and Child Health Hospital, a young man who had just become a father kept taking pictures through the window.
In a Dongcheng alley, an elderly couple watched for ages, reluctant to go back inside.
At the construction site east of the Weiming Institute, all the workers stopped what they were doing and looked up at the red sky.
On the roof of the Observation Building, Li Dong waited until the red glow in the north gradually faded before returning to his chair and picking up his laptop.
This time, Li Dong had collected a complete set of linked observations from four points of the same mass of plasma ejected from the corona.
With this data as a reference, he could pin down the ion-electron energy relaxation rate, the hardest quantity to calculate accurately in the Proton-Boron-11 Fusion Battery.
The next step for the Fusion Battery was now to wait for Xue Qikun's apparatus for observing nonequilibrium plasma dynamics to be completed.
That wait lasted two months.
By late November, all the fencing around the vacant lot east of the Weiming Institute had been removed, and the workers were leaving one after another with the last few loads of tools.
A circular main hall more than forty meters in diameter