An Etymological Dictionary of Astronomy and Astrophysics

The circumstance in which there are not enough pixels in a star’s image. The number of pixels that make up a star’s image is determined by the relationship between the telescope focal length, the physical size of the pixels, and the size of the star’s image. With an undersampled image it is not possible to obtain accurate estimates of the star’s image size or its position. Undersampling occurs when the atmospheric seeing conditions are exceptionally good and the pixel size not small enough.

See also: → under-; → sampling.