Cosmic rays can mean any high energy from the cosmos and were only referred to as rays for historical reasons – in that they thought cosmic rays were electromagnetic radiation. However generally cosmic rays refer to high energy particles with mass whereas high energy in the form of gamma rays and/or X-rays are photons. These cosmic particles were discovered in 1912 by Victor Hess when he ascended to 5300 meters above sea level in a hot air balloon and detected significantly increased levels of ionization in the atmosphere.

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