Fly's Eye

The Fly's Eye was a cosmic-ray observatory operating in western Utah in the 1980s and early 1990s. It consisted of 67 1.6-m telescopes, each dividing a portion of the sky into 13 or so pixels, designed to watch the entire sky and record air showers from cosmic rays. It began operation in 1981 and from 1986 to 1993, it include a twin of the complete original configuration that was located 3.4 km from the original, the two termed Fly's Eye 1 (FE1) and Fly's Eye 2 (FE2). This provided a stereo view, producing additional data useful for analysis. Among its detections was the 1991 Oh-My-God Particle, which had orders-of-magnitude more energy than any previously detected cosmic ray particle, and as of 2023 is still the most energetic ever detected. Subsequent follow-on cosmic ray observatory projects include the High Resolution Fly's Eye (HiRes) and the Telescope Array Project (TA).