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

The time scale on which a stellar image changes significantly due to → atmospheric turbulence. It is proportional to the ratio r₀/Δv, where r₀ is the → Fried parameter and Δv the standard deviation of the distribution of wind velocities weighted by the turbulence structure coefficient. Typical lifetimes in the visible range from about 3 to 30 milliseconds.

→ speckle; → life; → time.

Omr "life-time;" from Ar. 'umr; pakâl, → speckle.