This photo of the dark side of
our moon was taken by NASA’s
Lunar Reconnaissance Orbiter.
(Click to enlarge)
I don’t quite understand the specifics of the explanation below, but the illusion of a spiral is created by how the camera took these photographs. The site Life’s Little Mysteries explains:
"Imagine a series of very narrow pie slices collected 12 times each day, one after another… It takes roughly 360 slices to fill in the whole pie. Each day the sun direction is progressing around the moon, thus the direction that the sun is striking the surface changes. So the shadow directions slowly progress around the moon, thus leading to the illusion."
– New Photo of Moon’s North Pole Reveals Spiral Illusion, Space.com>>
– Life’s Little Mysteries>>
– Lunar Reconnaissance Orbiter (LRO)>>