Fried parameter

The Fried parameter, often called \( r_0 \), is a measure of the quality of astronomical images affected by Earth's atmosphere. It describes the largest size of a clear, steady patch of the sky before atmospheric turbulence blurs the view. Think of it like a "coherence size": a bigger \( r_0 \) means the atmosphere is steadier, allowing clearer observations, while a smaller \( r_0 \) indicates more turbulence and fuzzier images. Essentially, \( r_0 \) helps astronomers understand and quantify atmospheric effects on telescopic observations, guiding the design of adaptive optics systems to correct for these distortions.