Astronomers use ground-based detectors, high-altitude research balloons, artificial satellites and other methods to detect cosmic rays. Ground-based detectors, often spread over large areas (for example, the Pierre Auger Observatory is an array of detectors spread over 3,000 square kilometers), identify and analyze the secondary particles (electrons, positrons, photons, muons, etc.) produced in a chain reaction of particle interactions triggered by the collision of cosmic rays and Earth's atmosphere. The properties of the original cosmic ray particle, such as arrival direction and energy, are inferred from the measured properties of the extensive air shower, which is the cascade of secondary particles collectively showering down through the atmosphere. There are two kinds of ground-based detectors: Surface detector arrays analyze the air shower at a unique altitude, whereas air fluorescence detectors record the shower development in the atmosphere, based on the interactions of air shower particles with nitrogen molecules in the atmosphere. Modern "hybrid" detectors, such as the Pierre Auger Observatory in Argentina and the Large High Altitude Air Shower Observatory in Sichuan, China, take advantage of the complementary nature of these two. Moreover, scientific balloons (such as the one used in Cosmic Ray Energetics and Mass Experiment) and satellites (such as China's Dark Matter Particle Explorer or DAMPE telescope) can also be used to observe pure cosmic rays at very high altitudes and in outer space.