A

David

Darling

seeing

Seeing is the blurring of a stellar (point-like) image due to turbulence in Earth's atmosphere. Seeing estimates are often given in terms of the full-width in arcseconds of the image at the points where the intensity has fallen to half its peak value. The typical value at a good site is a little better than 1 arc-second. Amateur astronomers often used the five-point Anontiadi scale, which rates seeing as I (perfect), II (good), III (moderate), IV (poor), and V (very bad).