The LAGO detection network consists of dozens of water Cherenkov detectors (WCD) deployed in Latin America.
In this section you will learn about the basis of the detection of high-energy astroparticles, not only WCD but also the measurement of the atmospheric Cherenkov and the air fluorescence, and instruments onboard balloons and satellites.
While the speed of light in vacuum (c) is constant, this speed is reduced in material, to 0.75c in water, for example. This means that particles can go through a material at a speed larger than the speed of light in that material (but always smaller than c).
When a particle goes through a medium at such a speed, it produces a cone of light just like a plane produces a supersonic bang upon crossing the speed of sound, or a boat (or a duck) produces a "V" behind him because it moves faster than the waves propagate.
This light was discovered by a Russian physicist named Cherenkov in 1934 and is responsible for the typical blue glow of water in nuclear reactors. It is used frequently in particle detectors, as a high-energy particle going through a water volume will produce this characteristic light.