Milagro (the Spanish word for miracle) was a ground-based water Cherenkov radiation telescope situated in the Jemez Mountains near Los Alamos, New Mexico at the Fenton Hill Observatory site.
It operated in the TeV region of the spectrum at an altitude of 2530 m. Like conventional telescopes, Milagro was sensitive to light but the similarities ended there.
This cascade of particles are traveling near the speed of light and generate Cherenkov radiation as they pass through the atmosphere and the water in the Milagro experiment.
The photons of Cherenkov radiation are detected by an array of detectors or photomultiplier tubes which send a signal to a recorder.
[2] In November 2008 Milagro published the surprising result of observing cosmic ray anisotropy.