Celestron C8-S - Manual (Page 37)

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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 6-1
Seeing conditions directly affect image quality. These drawings 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.