The refraction of light rays passing through Earth's atmosphere, due to variations in the density and temperature which produce corresponding variations in its refractive index. Atmospheric refraction gives rise to a shift in the apparent direction of a celestial object; the effect increases the observed altitude of an object and is greatest (just over half a degree) for objects on the horizon.
Unusual density variations close to the surface may produce mirages, shimmer, and other deceptive effects.
Related categories• OPTICS AND OPTICAL PHENOMENA
• ATMOSPHERIC PHENOMENA AND STRUCTURES
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