"On their trips to and from the Moon, Apollo astronauts saw small white flashes of light while in the dark — even with their eyes closed. They usually saw no more than a couple each minute, although at least one astronaut saw so many he had trouble sleeping. What caused these flashes?
The answer is cosmic rays. Because of their high speeds, thousands of these cosmic rays were passing through the bodies of the Apollo astronauts every second. Most went straight through because atoms are mostly empty space. Some cosmic rays, however, hit atoms in the astronauts’ bodies. The ones hitting atoms in the astronauts’ eyeballs released a small amount of energy in the form of small flashes." (source: NASA.gov)
Cosmic Ray I-III - Edition 15, each - Hahnemuhle photorag 308 g - 37,5cm x 50cm