Schmitt's Persistent Light Flashes, Apollo 17 Lunar Orbit
NASA-UAP-D6, Apollo 17 Technical Crew Debriefing, 1973
Excerpt from the January 4, 1973 Apollo 17 Technical Crew Debriefing in which Lunar Module Pilot Harrison Schmitt describes persistent light flashes observed during dark-adapted flight, including one instance he attributed to the lunar surface.
Brief
Harrison Schmitt reported light flashes occurring nearly continuously throughout dark-adapted portions of the Apollo 17 mission. One flash, in particular, he believed originated on the lunar surface rather than within his visual system. During the ALFMED experiment — when the crew wore blindfolds — no visible flashes were perceived; yet Schmitt observed them again before sleep that same night, suggesting their recurrence was independent of the experimental protocol.
Metadata
- Agency
- NASA
- Release
- 5/8/26
- Incident
- 1973
- Type
- PDF • .pdf
- Length
- 2 pages
- Classification
- UNCLASSIFIED
- Programs
- Apollo 17, ALFMED
- Tags
- light flashes, lunar surface, dark adaptation, cosmic ray interaction, ALFMED, Apollo 17, 1973, deep space biology
Key points
- Schmitt reported light flashes occurring 'just about continuously' during dark-adapted periods of the entire flight.
- One flash was specifically interpreted by Schmitt as originating on the lunar surface rather than being an internal visual artifact.
- During the ALFMED blindfold period, Schmitt perceived no visible flashes, distinguishing masked from unmasked states.
- Flashes resumed before sleep later that same night, confirming the phenomenon persisted beyond the structured experiment window.
Most interesting
- Light flashes reported by Apollo astronauts are generally attributed to high-energy cosmic ray particles traversing the retina or visual cortex — a biological interaction, not an external light source.
- The ALFMED (Apollo Light Flash Moving Emulsion Detector) was a dedicated NASA experiment designed to record and correlate these flash events with particle tracks.
- Schmitt was the first professional geologist to walk on the Moon and the only scientist-astronaut to conduct a lunar surface EVA.
- The cessation of perceived flashes during the blindfold phase — and their return afterward — raises unresolved questions about whether masking suppressed awareness or whether the two observation windows sampled different flux conditions.
- Apollo 17 was the last crewed lunar landing mission; its debriefing data remains a primary record for human-perceived anomalous light phenomena in deep space.