Cosmic Ray Light Shows: Astronauts See Retinal Flashes from Apollo to the ISS

Astronaut Don Pettit described seeing “luminous dancing fairies” in the ISS, a retinal flash caused by galactic cosmic rays that pierce the craft and the eye. Apollo crews reported similar flashes, and the ALTEA detectors on the ISS linked heavy-ion particles to these events, explained by direct ionization or Cherenkov radiation. Although brief and seemingly harmless, these particles pose long-term brain and eye health risks for deep-space missions, influencing radiation-mitigation strategies for Artemis and future journeys to the Moon and Mars.