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Apollo Light Flash Investigations (AP009)
Principal Investigator
Research Area:
Ocular physiological phenomena
Radiation biology
Species Studied
Scientific Name: Homo sapiens Species: Human

The observation of visual phenomena, described generally as "light flashes", was reported by one Apollo 11 crewmember during routine post-mission debriefings. This was somewhat surprising, since the observations had not been reported during previous Mercury, Gemini, or early Apollo flights. The crews of Apollo 12 and 13 were briefed on the phenomena. In flight, all crewmembers reported the ability to "see" the flashes with relative ease when the spacecraft was dark with their eyes open or shut. Subsequently, researchers set out to determine the nature of the phenomena and whether it posed a threat to astronauts.

The scientific community advanced several theories to explain the light flash phenomenon. The phenomenon was thought to have been attributed to penetration of the eye by cosmic ray particles with retinal stimulation occurring by one of two mechanisms. One explanation postulated that Cerenkov radiation was responsible for the light observed. A second explanation was that the bulk of the reported light flashes were caused by cosmic ray particles producing phosphenes due to direct interaction of ionizing radiation with nervous tissue in the retina. The experiments that followed on Apollo 14, 15, 16, and 17 were designed to determine which mechanism was more likely to be the primary cause of light flash sensations.

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Anonymous. Special technical services for investigation of light flash phenomena, final report. 1973; March 1. NASA Contractor Report, NASA-CR-128866. [NTRS]

Chapman PK, Pinsky LS, and Benson RE. Observations of cosmic-ray induced phosphenes on Apollo 14. In: Warman EA, editor. Proceedings of the National Symposium on Natural and Manmade Radiation in Space; 1971 March 1-5; Las Vegas, Nevada.

Liwshitz M. The origin of light flashes observed by Apollo astronauts. NASA Contractor Report, NASA-CR-123173; September 30, 1971.

McNulty PJ, Pease VP, Bond VP. Role of Cerenkov Radiation in the eye Flashes Observed by Apollo Astronauts. Life Sciences and Space Research XIV, Akademie-Verlag, Berlin, 1976.

Osborne WZ, Pinsky LS, Bailey JV. Apollo light flash investigations. In: Johnson RS, Dietlein LF, Berry CA, eds. Biomedical Results of Apollo. Washington, DC: NASA Headquarters; 1975:355-365. NASA SP-368. [NTRS]

Pinsky LS, Osborne WZ, Bailey JV, Benson RE, Thompson LF. Light flash observed by astronauts on Apollo 11 through Apollo 17. Science 1974. March 8; 183(4128):957-9. []

Cosmic radiation
Dark adaptation
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Data Information
Data Availability
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Light flash count: cloud
Light flash count: mixture
Light flash count: star
Light flash count: streak
Light flash count: total
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Mission/Study Information
Mission Launch/Start Date Landing/End Date Duration
Apollo 14 01/31/1971 02/09/1971 9 days
Apollo 15 07/26/1971 08/07/1971 12 days
Apollo 16 04/16/1972 04/27/1972 11 days
Apollo 17 12/07/1972 12/19/1972 12 days

Additional Information
Managing NASA Center
Johnson Space Center (JSC)
Responsible NASA Representative
Johnson Space Center LSDA Office
Project Manager: Pamela A. Bieri
Institutional Support
National Aeronautics and Space Administration (NASA)