China's lunar lander Chang'e-4 and rover Yutu-2 are still working on the Moon's far side after their landing in January. As the Sun rose in Moon on Friday after the two-week-long lunar night, the two devices also woke up simultaneously to resume work.
It's the eighth lunar day for the "lady" lander and the "rabbit" rover on the Moon. A full day on the Moon is roughly as long as a month on the Earth, as the two globes go around the Sun in different manners.
The Chang'e-4 and the Yutu-2 are both solar-powered, meaning there has to be sunlight for them to work. So during the 14-day long lunar night, the two devices have to go to "sleep mode" like a PC to save power.
Dark side and bright side
During the Moon's rotation around the Earth, the "dark side" or far side of the Moon stays invisible to us.
The rotation of the Moon around the Earth, with Chang'e-4 and Yutu-2 on the Moon's far side. The Moon in the picture is enlarged for clarity. /CGTN Picture
So it's impossible for us to see the two space vehicles in a telescope.
The Moon, which lies in between the lander and us, also blocks telecommunication signals. To get around it, the Chinese space program launched a satellite named "Queqiao" to form a data link.
The Queqiao relay satellite, its orbit and how it connects the Earth with the far side of the Moon /CGTN Picture
But for the Sun, it's another story. For half of the time during the Moon's rotation around the Earth, the far side can be illuminated by the Sun. So the Chang'e-4 and Yutu-2 can receive sunlight to charge their batteries.
How the Sun can illuminate the Moon's far side when it's not visible from the Earth /CGTN Picture
That's why you can see reports on CGTN Digital about the "sleeping" and "waking up" of the lander and rover every two weeks. And the cycle will go on till the end of the mission.
Any more questions about China's space mission? Email your questions to gong.zhe@cgtn.com and we at CGTN Digital will try to find the answer for you.