The general term Cherenkov detector is among those used to indicate an instrument or set of instruments to detect photons or particles through the Cherenkov radiation they produce. (The term IACT for imaging atmospheric Chernkov telescope) is generally synonymous, but implying imaging ability, and specifically using the atmosphere to generate the Cherenkov radiation.) Such detectors used for astronomical purposes may be specifically termed a Cherenkov telescope and are used as a means of observing the results of gamma-ray photons (i.e., a Cherenkov gamma-ray telescope) and/or cosmic-ray particles hitting the Earth's atmosphere. High energy photons produce particles (e.g., by pair production), which travel fast enough to trigger the radiation. This can happen repeatedly through a downward cone-shaped volume of the atmosphere, each time more photons and particles produced at lower energies, termed an air shower. Detectors on the ground that can sense either photons or particles or both can pick up enough information to work out something about the originating photon or particle.
On the ground are detectors that pick up very small amounts of EMR. They may be directed at the sky, or to detect particles reaching the ground, tanks of water may be used: they produce Cherenkov radiation more easily.
From the theory of Cherenkov radiation production, data from a number of such detectors, including timing, yield information regarding characteristics of the photon or particle that triggered.
Examples of Cherenkov telescopes:
Also using Chernkov radiation are detectors of other particles, such as the neutrino detector, IceCube, which detects the radiation produced in a large volume of ice.