An Etymological Dictionary of Astronomy and Astrophysics

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).

See also: → elastic; → scattering.