Cosmic ray visual phenomena
[2] Researchers believe that the LF perceived specifically by astronauts in space are due to cosmic rays (high-energy charged particles from beyond the Earth's atmosphere[3]), though the exact mechanism is unknown.
[9] The main shapes seen are "spots" (or "dots"), "stars" (or "supernovas"), "streaks" (or "stripes"), "blobs" (or "clouds") and "comets".
[9] For example, Jerry Linenger reported that during a solar storm, they were directional and that they interfered with sleep since closing his eyes would not help.
[9] On the Apollo 15 mission all three astronauts recorded the same LF, which James Irwin described as "a brilliant streak across the retina".
[12] On Lunar missions, once their eyes became adapted to the dark, Apollo astronauts reported seeing this phenomenon once every 2.9 minutes on average.
These results in combination with considerations for geometry and Monte Carlo estimations led researchers to conclude that the visual phenomena were indeed caused by cosmic rays.
[14][15] The SilEye-Alteino and Anomalous Long Term Effects in Astronauts' Central Nervous System (ALTEA) projects have investigated the phenomenon aboard the International Space Station, using helmets similar in nature to those in the ALFMED experiment.
[13]: 518 The data collected also suggested to the researchers that one's sensitivity to the LF tends to decrease during the first couple of weeks of a mission.
Hence, the researchers ruled out the Cherenkov effect as a probable cause of the LF observed in space, at least in this case.
The composition of these beams ensured that particles generated in the eye were below 500 MeV, which was considered the Cherenkov threshold, thereby allowing the researchers to separate one cause of the LF from the other.
[7] The 3 MeV neutron beam produced no reporting of LF whether it was exposed to the observers through the front exposure of one eye or through the back of the head.
All but one observer reported seeing fainter but a higher number of "points" or short lines in the center of visual field.
They also suggested that because the number of LF observed decreased significantly when the beam entered the back of the head, the LF were likely not caused by the visual cortex being directly stimulated as this decrease suggested that the beam was weakened as it passed through the skull and brain before reaching the retina.
The most probable explanation proposed was that the LF were a result of the receptors on the retina being directly stimulated and "turned on" by a particle in the beam.
In another experiment, Tobias et al. (1971) exposed two people to a beam composed of neutrons ranging from 20 to 640 MeV after they were fully dark-adapted.
The observer described them as being similar to "luminous balls seen in fireworks, with initial tails fuzzy and heads like tiny stars".
The other observer who was given one exposure lasting three seconds long, reported seeing 25 to 50 "bright discrete light, he described as stars, blue-white in color, coming towards him".
Considering the experiments conducted, at least in some cases the LF observed appear to be caused by activation of neurons along the visual pathway, resulting in phosphenes.
