Cosmic Rays

Overview

Cosmic rays are high-energy particles from space that travel near the speed of light. Virtually all cosmic rays are atoms of hydrogen, helium, and other elements that have been stripped of their electrons. Such particles are deflected by the magnetic fields of stars, planets, and other celestial objects as they travel through space, making it difficult to determine their source. However, research suggests they originate from powerful astronomical phenomena, such as exploding stars

In the early 1900s, observations of small electric currents in the atmosphere were attributed to radioactive elements in the ground, which could ionize atmospheric atoms with their radiation. In 1912, while flying hot-air balloons, Victor Hess found that this radiation increased at high altitude, suggesting a cosmic origin. Before experiments revealed that it was affected by Earth's magnetic field and therefore composed mostly of charged particles, this ionizing radiation was mistakenly named after gamma rays—high-energy light.

As powerful versions of particle accelerators, collisions between cosmic rays and atmospheric atoms produce showers of rare particles. Analyses of these showers have validated the special theory of relativity, revealed the existence of antimatter, enabled scientists to track changes to Earth's surface, and contributed to the development of the Standard Model.

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