When optical waves, whether they originate from starlight, incandescent sources,
or lasers, propagate through the clear atmosphere of the earth, they experience
distortions due to small temperature variations. The two most common
manifestations of this phenomena are the twinkling of stars and the shimmering
of "heat" over hot pavement or surfaces. The small temperature variations, on
the order of 1 ° C or less, are related to the sun's heating of the atmosphere and
turbulent motion of the air due to winds and convection. The small temperature
perturbations cause changes in the velocity of the light as it passes through the
atmosphere, which in turn causes distortions in the intensity (twinkling), phase,
angle-of-arrival, and displacement (quivering) of the light beam.