cosmic ray

American  

noun

Physics.

1. a radiation of high penetrating power that originates in outer space and consists partly of high-energy atomic nuclei.

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cosmic ray Scientific  

1. A ray of radiation of extraterrestrial origin, consisting of one or more charged particles such as protons, alpha particles, and larger atomic nuclei. Cosmic rays entering the atmosphere collide with atoms, producing secondary radiation, such as pions, muons, electrons, and gamma rays. Cosmic rays (and secondary radiation) can be easily seen in a cloud chamber.

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Etymology

Origin of cosmic ray

An Americanism dating back to 1920–25

Example Sentences

The bacteria were then exposed to radiation equivalent to 20 million years of cosmic ray bombardment on the Martian surface.

From Science Daily • Feb. 25, 2026

Their aim is to understand why some cosmic ray sources emit neutrinos while others do not, as well as pinpoint where and how those neutrinos are produced.

From Science Daily • Nov. 26, 2025

Researchers long suspected that the feature reflects the highest energies that cosmic ray sources can reach, marking a shift in the spectrum from one power-law behavior to another.

From Science Daily • Nov. 16, 2025

In 1948, Bristol's cosmic ray physics team, led by Professor Cecil Powell, were hunting for new fundamental particles.

From BBC • Jul. 23, 2024

“Some of the cosmic ray enthusiasts are very likely to urge that nature has furnished us with particles of extremely high energies,” he observed.

From "Big Science" by Michael Hiltzik