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Poor Seeing = Turbulence

Notes:

What is the source of poor seeing? The animation will not be visible on the web version so I will describe what is missing.

Let us say that you want to observe a bird from the bottom of a swimming pool. The day is perfectly calm and the entire system is at thermal equilibrium. Thus the water will have no current in it. The bird will be clearly visible with almost no distortion. Note that it will not appear at the location apparent from the bottom of the swimming pool. That is because the air bends (refracts) light differently than the water.

What is visible in the web drawing is what happens when the pool is stirred. Now small parcels of turbulence race across the pool between the eye and the bird. These parcels differ in size, temperature, and density. They refract light differently. The result is the path of the light between the bird and the eye varies greatly. The image of the bird is wildly distorted in random ways.