optical properties of the earth's atmosphere vary on short spatial and
temporal scales. Although tenuous, the atmosphere is deep enough for
the integrated optical variations to impose distortions on the otherwi
se plane wavefronts of light from astronomical objects. The departures
from plane wavefronts are of the order of only a few microns but thes
e have a catastrophic effect on imaging by astronomical telescopes. On
e, but very expensive, solution to the problem is to launch the telesc
ope above the earth's atmosphere; another is to reduce the distortions
in the wavefronts by the use of adaptive optics. These latter techniq
ues promise to bring about a revolution in the quality of astronomical
images from which new, exciting astronomy should follow.