An Etymological Dictionary of Astronomy and Astrophysics

One of the parameters that characterize atmospheric → seeing. It is the diameter of the largest aperture that can be used before → turbulence starts to degrade the image quality. As the turbulence gets stronger, the Fried parameter, denoted r₀, becomes smaller. The Fried parameter is wavelength dependent:
r₀ ∝ λ^6/5.
On best astronomical mountain tops it ranges between 20 and 30 cm for λ = 5000 A.

See also: Named after David L. Fried, who defined the parameter 10 1966; → parameter.