The Antoniadi scale for seeing.

Descriptions of seeing conditions are very subjective. In order to try to standardise this area of observing, most planetary and lunar observers use the following seeing scale:

I

Perfect seeing, without a quiver
II

Slight quivering of the image with moments of calm lasting several seconds
III

Moderate seeing with larger air tremors that blur the image
IV

Poor seeing, Constant troublesome undulations of the image
V

Very bad seeing, hardly stable enough to allow a rough sketch to be made

When observing, the seeing conditions should be noted in the observing log.

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