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temperature layers have different densities and, therefore, bend light differently. Light rays from the same object arrive slightly
displaced creating an imperfect or smeared image. These atmospheric disturbances vary from time-to-time and place-to-place. The size
of the air parcels compared to your aperture determines the "seeing" quality. Under good seeing conditions, fine detail is visible on the
brighter planets like Jupiter and Mars, and stars are pinpoint images. Under poor seeing conditions, images are blurred and stars appear
as blobs.
The conditions described here apply to both visual and photographic observations.
Figure 7-1
s
Seeing conditions directly affect image quality. These drawing
represent a point source (i.e., star)
under bad seeing conditions (left) to excellent conditions (right). Most often, seeing conditions
produce images that lie some where between these two extremes.
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