An Etymological Dictionary of Astronomy and Astrophysics

English-French-Persian

فرهنگ ریشه‌شناختی اخترشناسی-اخترفیزیک

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speckle lifetime
  عمر ِ پَکال  
omr-e pakâl
Fr.: durée de vie de tavelures  

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.

Etymology (EN): → speckle; → life; → time.

Etymology (PE): Omr “life-time;” from Ar. ‘umr; pakâl, → speckle.