The use of Cherenkov light in the detection of high-energy cosmic rays and neutrinos: The Pierre Auger and IceCube Observatories

For centuries, visible light has been used to unveil the Universe. Technological advances in recent decades have extended our vision by allowing the detection of photons across a wide spectrum, from radio waves to gamma-rays. Above O(similar to 1 TeV), however, electromagnetic radiation may not penetrate the gases and dust between their sources and us. Two windows into the highest-energy phenomenon in the Universe are cosmic rays and neutrinos. So far, fluxes of charged particles above EeV and neutrinos above TeV have been measured. Here, we review the role of Cherenkov light in the detection of these two cosmic messengers by focusing on the Pierre Auger Observatory and the IceCube Neutrino Observatory, and illustrate the continued importance of light in revealing the Universe.