Apollo: The astronauts’ light flashes — a puzzle that was solved
The crews of Apollo 12, 14 and 17 reported light flashes and streaks seen in darkness during their medical debriefings. NASA determined that the perception arose inside the eye itself — cosmic rays striking the retina.
Background
What the crews reported
In the medical debriefings after their flights, several Apollo crews described light flashes or "streaks of lights" seen in darkness — usually while trying to sleep.
Apollo 12 (1969): Charles "Pete" Conrad, Richard "Dick" Gordon and Alan Bean each describe the experience independently. The NASA medical team considers whether it matches what Buzz Aldrin reported after Apollo 11, and whether cosmic rays reaching the retina might be the cause.
Apollo 14 (1971) and Apollo 17 (1972): crew and debriefers work systematically through the characteristics of the phenomenon. On Apollo 17 two of the three crew members report it — in lunar orbit and on the lunar surface.
The resolution
NASA concluded that the perceptions were internal to the astronauts' vision rather than caused by external light sources. They are produced by high-energy cosmic rays passing through the eye and striking the retina. What was then novel and unexplained is today a well-documented biological effect.
Why this event is here
Five audio records across two PURSUE tranches deal with this phenomenon. It appears in the UAP holdings because it was unexplained at the time — not because it remained so. That is precisely its value: it shows how an anomalous observation by several credible witnesses ultimately resolves into physiology.