Rapid variations, often in the form of pulsations, of the light from stars or terrestrial light
sources.
The apparent brilliance, colour and position of the stars or lights undergo variations, owing to
fluctuations of the refractive index in the positions of the atmosphere through which the rays of
light pass; the phenomenon is thus analogous to shimmer. Other factors being equal,
scintillation of stars is consequently more pronounced near the horizon than at the zenith; for
the same reason the scintillation of lights from terrestrial sources is more pronounced over
plains than on mountain summits.