Editing Apollo 17 (section)

==== Light-flash phenomenon and other experiments ====
{{main|Cosmic ray visual phenomena}}

Beginning with Apollo 11, crew members observed light flashes that penetrated their closed eyelids. These flashes, described by the astronauts as "streaks" or "specks" of light, were usually observed while the spacecraft was darkened during a sleep period. These flashes, while not observed on the lunar surface, would average about two per minute and were observed by the crew members during the trip out to the Moon, back to Earth, and in lunar orbit.<ref name="lightflash"/>

The Apollo 17 crew repeated an experiment, also conducted on Apollo 16, with the objective of linking these light flashes with [[cosmic ray]]s. Evans wore a device over his eyes that recorded the time, strength, and path of high-energy atomic particles that penetrated the device, while the other two wore blindfolds to keep out light. Investigators concluded that the available evidence supports the hypothesis that these flashes occur when charged particles travel through the [[retina]] in the eye.<ref name=lightflash>{{cite book |last1=Osborne |first1=W. Zachary |last2=Pinsky |first2=Lawrence S. |last3=Bailey |first3=J. Vernon |editor-last1=Johnston |editor-first1=Richard S. |editor-last2=Dietlein |editor-first2=Lawrence F. |editor-last3=Berry |editor-first3=Charles A. |others=Foreword by [[Christopher C. Kraft Jr.]] |title=Biomedical Results of Apollo |url=http://lsda.jsc.nasa.gov/books/apollo/cover.htm |access-date=August 26, 2011 |year=1975 |publisher=NASA |location=Washington, D.C. |id=NASA SP-368 |chapter=Apollo Light Flash Investigations |chapter-url=http://lsda.jsc.nasa.gov/books/apollo/S4CH2.htm |url-status=dead |archive-url=https://web.archive.org/web/20110917234433/http://lsda.jsc.nasa.gov/books/apollo/cover.htm |archive-date=September 17, 2011 }}</ref>

Apollo 17 carried a sodium-iodide crystal identical to the ones in the gamma-ray spectrometer flown on Apollo 15 and 16. Data from this, once it was examined on Earth, was to be used to help form a baseline, allowing for subtraction of rays from the CM or from [[cosmic radiation]] to gain better data from the earlier results.{{sfn|Apollo 17 Preliminary Science Report|pp=20-1–20-2}} In addition, the S-band transponders in the CSM and LM were pointed at the Moon to gain data on its gravitational field. Results from the [[Lunar Orbiter]] probes had revealed that lunar gravity varies slightly due to the presence of [[Mass concentration (astronomy)|mass concentrations]], or "mascons". Data from the missions, and from the lunar subsatellites [[Apollo 15#Particles and Fields Subsatellite|left by Apollo 15]] and [[Apollo 16#Particles and Fields Subsatellite|16]], were used to map such variations in lunar gravity.{{sfn|Apollo 17 Preliminary Science Report|pp=14-1—14-2}}<ref name ="band:">{{cite web|publisher=[[Lunar and Planetary Institute]]|work=Apollo 17 Mission|title=Science Experiments – S-Band Transponder|date=2019|access-date=February 12, 2022|url=https://www.lpi.usra.edu/lunar/missions/apollo/apollo_17/experiments/s_band/|archive-date=August 5, 2020|archive-url=https://web.archive.org/web/20200805010805/https://www.lpi.usra.edu/lunar/missions/apollo/apollo_17/experiments/s_band/|url-status=live}}</ref>