Skip to main content Skip to Search Box

Definition: cosmic rays from Dictionary of Energy

Physics. high energy subatomic particles, mostly protons and helium nuclei, that travel across space at close to the speed of light. The lowest energy cosmic rays originate in the sun, and higher energy ones from supernovae and pulsars within the galaxy. Those with the highest energy may be extra-galactic in origin, possibly from quasars and active galactic nuclei. Also, cosmic (background) radiation.


Summary Article: cosmic rays
from The Columbia Encyclopedia

charged particles moving at nearly the speed of light reaching the earth from outer space. Primary cosmic rays consist mostly of protons (nuclei of hydrogen atoms), some alpha particles (helium nuclei), and lesser amounts of nuclei of carbon, nitrogen, oxygen, and heavier atoms. These nuclei collide with nuclei in the upper atmosphere, producing secondary cosmic rays of protons, neutrons, mesons, electrons, and gamma rays of high energy, which in turn hit nuclei lower in the atmosphere to produce more particles (see elementary particles). These cascade processes continue until all the energy of the primary particle is dissipated. The secondary particles shower down through the atmosphere in diminishing intensity to the earth's surface and even penetrate it. The size of the shower indicates the energy of the primary ray, which may be as high as 1020 electron volts (eV) or more, many times higher than the highest energy yet produced in a particle accelerator; however, cosmic rays of lower energy predominate. Cosmic rays were long used as a source of high-energy particles in the study of nuclear reactions. The positron, the muon, the pion (or pi meson), and some of the so-called strange particles were initially discovered in studies of this radiation. Cosmic rays were first found to be of extraterrestrial origin by Victor F. Hess (c.1912) when he recorded them with electrometers carried to high altitudes in balloons, an achievement for which he won the Nobel Prize in 1936. They were so named in 1925 by R. A. Millikan, who did extensive research on them. Since then much pertinent information has been collected that have been of use in studying the chemical composition of the universe, but the origin of cosmic rays remains a mystery. However, when they react with interstellar gases, the result is a gamma ray that can be traced back. Spacecraft results indicate that many of the gamma rays appear to come from the direction of supernova remnants. The nature of the acceleration processes by which the primary particles achieve great velocities (very nearly the speed of light) is also still highly speculative. Modern electronic detectors called charge coupled devices (CCDs) are effective cosmic ray detectors; a ray can strike a single pixel, making it much brighter than the surrounding ones. Cosmic rays play a significant role in the natural mutation and evolution of life on earth.

  • See Rossi, B. B. , Cosmic Rays (1964);.
  • Dorman, L. I. , Cosmic Rays (1974);.
  • Friedlander, M. W. , Cosmic Rays (1989).
The Columbia Encyclopedia, © Columbia University Press 2018

Related Articles


Full text Article Cosmic Rays
Science in the Early Twentieth Century: An Encyclopedia

Cosmic rays were discovered during a spate of scientific work on “rays” of various kinds, some of them real and others not, around the turn of...

Full text Article cosmic rays
Astronomy Encyclopedia

Charged particles (protons and the nuclei of heavier atoms) that arrive at the top of the atmosphere and come from cosmic space. Their energies...

Full text Article cosmic rays
The Encyclopedia of Ecology and Environmental Management, Blackwell Science

The Earth is continuously subject to bombardment by cosmic Radiation , or cosmic rays, which originate in space and, to a lesser extent, in...

See more from Credo