Cosmic rays are high-energy particles coming from outer space and are mainly composed of protons and the atomic nuclei of many elements, as well as a small fraction of electrons and Gamma ray photons. Constantly present on our planet, cosmic rays were first discovered by Austrian scientist Victor Hess in 1912.

        Cosmic rays span an energy range of 10^9 -10^20 eV. As the energy of cosmic rays increases, their abundance decreases, so larger area instrument for their detection are required.

        The origin of cosmic rays

        -A mystery of the century

        The majority of cosmic rays are charged particles, which are deflected in the interstellar magnetic field during their propagation. When they arrive at the earth, the original directional information is lost. We are yet to solve the origins of high-energy cosmic rays, thus to find out the mechanism of their production and acceleration.