Scintillation of Stars

(or twinkling of stars), rapid variations in the brightness and color of stars; these variations are particularly noticeable near the horizon. More than 100 variations per second can occur. Stellar scintillation is caused by the refraction of light rays in rapidly moving jets of air that have different indices of refraction because of the differing densities of the jets. Owing to dispersion, a ray separates into rays of different colors. These rays propagate along different paths, and the closer the star is to the horizon of the observation point, the greater is the degree of divergence of the paths. The distance between the red and violet rays can reach 10 m at the surface of the earth. When polychromatic stellar rays pass through the atmosphere along different trajectories, they encounter different air jets, which collect or scatter the rays in different ways—just as a convex or concave lens would. The rays of the various colors simultaneously strike the observer’s eyes, and as a result, the observer will see a continuous variation in the brightness and color of the star.