An Etymological Dictionary of Astronomy and Astrophysics

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Fried parameter
  پارامون ِ فرید  
pârâmun-e Fried
Fr.: paramètre de Fried  

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 ∝ λ6/5.
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.