Pronunciation: (ri-frak'shun),[key] —n. 1. Physics.the change of direction of a ray of light, sound, heat, or the like, in passing obliquely from one medium into another in which its wave velocity is different.
2. Ophthalm. a. the ability of the eye to refract light that enters it so as to form an image on the retina.
b. the determining of the refractive condition of the eye.
3. Astron. a. Also called astronomical refraction. the amount, in angular measure, by which the altitude of a celestial body is increased by the refraction of its light in the earth's atmosphere, being zero at the zenith and a maximum at the horizon.
b. the observed altered location, as seen from the earth, of another planet or the like due to diffraction by the atmosphere.