An Etymological Dictionary of Astronomy and Astrophysics
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In a → collision between two → particles, the reaction in which the total → kinetic energy of the system, projectile plus target, is the same before the collision as after.
In the interaction of → electromagnetic waves with particles, the scattering when the → wavelength (→ frequency) of the → scattered light is the same as the → incident light (→ Rayleigh scattering, → Mie scattering).

→ elastic; → scattering.

A type of scattering when the → scattered radiation has a → wavelength different from that of the → incident radiation (→ Raman scattering, → fluorescence ).

→ inelastic; → scattering.