What's the "een" in Halloween?
in astronomy, sharpness of a telescopic image. Seeing is dependent upon the degree of turbulence in the Earth's atmosphere for a given telescope. Scintillation, the "twinkling" of stars to the unaided eye, is a commonly known result of turbulence in the higher reaches of the atmosphere. Poor seeing in telescopes is more a result of turbulence in the lower atmosphere. This turbulence sets a limit on the features that a telescope can resolve.