from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun meteorology, astronomy A very rare phenomenon observed in morning or evening when the sun is crossing or immediately below the horizon, in which a momentary flash of blue light appears above the upper rim of the solar disk, caused by refraction of light in the atmosphere.
  • noun nuclear physics A phenomenon sometimes observed when a criticality incident occurs in nuclear materials, inducing a discharge of radiation into the environment.


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