detector over numerous sessions while on Mir. During those sessions, when they detected a LF, they pressed a button on a joystick. After each session, they recorded down their comments about the experience. Particle tracks that hit the eye during the time when the astronauts indicated that they detected a LF would have had to pass through silicon layers, which were built to detect protons and nuclei and distinguish between them. The findings show that "a continuous line" and "a line with gaps" was seen a majority of the time. With less frequency, a "shapeless spot", a "spot with a bright nucleus" and "concentric circles" were also reported. 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. With regards to the probable cause of the LF, the researchers concluded that nuclei are likely to be the main cause. They based this conclusion off of the finding that in comparison to an "All time" period, an "In LF time window" period saw the nucleus rate increase to about six to seven times larger, while the proton rate only increased by twice the amount when comparing the two time periods. Hence, the researchers ruled out the Cherenkov effect as a probable cause of the LF observed in space, at least in this case. Ground experiments in the 1970s Experiments conducted in the 1970s also studied the phenomenon. These experiments revealed that although several explanations for why the LF were observed by astronauts have been proposed, there may be other causes as well. Charman et al. (1971) asked whether the LF were the result of single cosmic-ray nuclei entering the eye and directly exciting the eyes of the astronauts, as opposed to the result of Cherenkov radiation within the retina. The researchers had observers view a neutron beam, composed of either 3 or 14 MeV monoenergetic neutrons, in several orientations, relative to their heads. 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. Observers viewed the neutron beam after being completely dark-adapted. 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