An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

A measure of the blurring and degradation of the image of astronomical objects caused by → turbulence in the Earth's atmosphere, including the telescope environment. Seeing causes the images of stars to break up into → speckle patterns, which change very rapidly with time. See also → Fried parameter; → differential image motion monitor.

→ see; → -ing.

Šekân "wrinkle, plait; curl; rupture, breach," variant of šekan "fold, curl; ripples on water," from šekastan "to break, split;" Mid.Pers. škastan "to break;" Av. scind-, scand "to break, cleave;" Proto-Iranian *skand- "to break, cleave;" PIE sken- "to cut off."

The angular size of a stellar image for long exposures, as determined by the ratio λ/r₀, where λ is the wavelength and r₀ the typical size of → turbulence patches. → Fried parameter. The most common seeing measurement is the → full-width at half-maximumof the seeing disk. → Airy disk.

→ seeing; → disk.

An optical instrument that follows the variation of → atmospheric turbulence by continuously measuring the → seeing conditions.

→ seeing; → monitor.