First observations of speed of light tracks by a fluorescence detector looking down on the atmosphere. (22nd May 2018) - Abdellaoui, G.; Abe, S.; Jr., J.H. Adams; Ahriche, A.; Allard, D.; Allen, L.; Alonso, G.; Anchordoqui, L.; Anzalone, A.; Arai, Y.; Asano, K.; Attallah, R.; et al.