Cosmic ray
High-energy particles raining continuously on Earth from space. Most are protons, coming from the Sun and from far across the galaxy.
In 1912 Victor Hess took instruments up in a balloon to about 5,000 metres and confirmed that radiation grows stronger with height[1]. Radiation had been assumed to come from the ground, so this was evidence of something arriving from space. Hess received the 1936 Nobel Prize in Physics.
When cosmic rays hit the atmosphere they create showers of new particles. Before accelerators existed, cosmic rays were almost the only way to study high-energy particles, and the positron was found among them[2]. For satellites and astronauts they are a cause of equipment faults and radiation exposure. Voyager 1's departure from the region dominated by the Sun was recognised by a sudden rise in cosmic rays from the galaxy.
Related terms
- PositronA particle with the electron's mass and a positive charge. It is the electron's antiparticle; when the two meet, both vanish into light.
- Cloud chamberA device that makes the path of a charged particle visible as a trail of fine water droplets.
- Van Allen beltDoughnut-shaped regions where high-energy protons and electrons are trapped by Earth's magnetic field. There is an inner and an outer belt.
- HeliopauseThe boundary where the flow of particles from the Sun (the solar wind) is stopped by the gas between the stars — one definition of the outer edge of the solar system.
On the timeline
Sources
- V. F. Hess, “Über Beobachtungen der durchdringenden Strahlung bei sieben Freiballonfahrten,” Phys. Z. 13, 1084–1091 (1912).
- C. D. Anderson, “The Positive Electron,” Phys. Rev. 43, 491–494 (1933).