An air shower is an extensive (many kilometres wide) cascade of ionized particles and electromagnetic radiation produced in the atmosphere when a primary cosmic ray (i.e. one of extraterrestrial origin) enters our atmosphere. The term cascade means that the incident particle, which could be a proton, a nucleus, an electron, or (rarely) a positron strikes an atom in the air so as to produce many high energy ions (secondaries), which in turn create more, and so on. The original particle having arrived with high energy and hence velocity near the speed of light, the products of the collisions tend also to move generally downward, while to some extent spreading sidewise. The overall effect, when the energy of the primary is high enough, is to produce a widespread flash of light due to the Cerenkov effect, and to excitation of air molecules. This can be detected with arrays of mirrors and photocells. The actual arrival of the cascade of particles can also be detected in many cases, also generally with detectors based on the Cerenkov effect.

External links

• Extensive Air Showers
• Buckland Park Air Shower Detector
• Haverah Park Detection System
• HiRes Detector System (current, 2004)
• Pierre Auger Observatory
• AIRES (AIRshower Extended Simulations) : Large and well documented Fortran package for simulating cosmic ray showers by Sergio Sciutto at the Department of Physics of the Universidad Nacional de La Plata, Argentina
• CORSIKA, CORSIKA: Another code for simulating cosmic ray air showers by Dieter Heck of the Forschungszentrum Karlsruhe, Germany
• COSMUS : Interactive animated 3d models of several different cosmic ray air showers, and instructions on how to make your own using AIRES simulations. From the COSMUS group at the University of Chicago.
• Milagro Animations : Movies and instructions for how to make them, showing how air showers interact with the Milagro detector. By Miguel Morales.
• CASSIM Animations : Animations of different cosmic ray air showers by Hajo Dreschler of New York University.