The Moon has a far side, not a dark one

China now has two history-making robots sending back images from an area of the Moon where humankind has never been before. This side of the Moon is distant and mysterious, but, despite pop culture references to the contrary, it isn’t always dark. In fact, after touching down on the lunar surface, the probe sent back a snapshot of its new home that shows a rocky, cratered, and distinctly lit landscape.

China’s probe â€" which includes a lander and a rover â€" landed at 10:26 AM Thursday, Beijing time, as part of China’s Chang’e-4 mission to scout out the side of the Moon we can’t see from Earth. Since it takes the Moon roughly the same amount of time to spin around its axis as it does to orbit the Earth, we only see one half of the Moon: its near side. China’s landing on the Moon’s far side was a world first, in part because of the technical difficulties posed by that distance. It’s really difficult to get radio signals from Earth to robots on the far side â€" or vice versa â€" when the entire bulk of the Moon is planted in between.

China bridged the signal gap by sending up a satellite called Queqiao, which communicates with the probe and relays information, including photos, back to Earth. There’s light in the photos because there’s light on the far side of the Moon: in fact, there is no permanently dark side of the Moon. “Half the moon is always lit by the Sun â€" just like the Earth,” Frederick Walter, a professor of physics and astronomy at Stony Brook University, says in an email to The Verge.

Our planet experiences daylight and night because Earth spins on its axis as it orbits the Sun. The side pointing toward the Sun is bright, the side pointing away is a night. Over the course of 24 hours, the slow spin of the world cycles through both. (Things get weird at the poles, but even they experience both light and darkness.) The Moon goes through a similar cycle, but on a slower schedule: a full lunar day is roughly 29 Earth days long. Walter calculates that when the Chang’e-4 probe touched down on the Moon’s far side, it was roughly 9 AM local lunar time.
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