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   CZA - Effect of solar altitude 

  CZAs at different solar altitudes
  Arcs at different sun heights. Altitudes of the sun are on the right. The scale shows distances from the zenith.

The CZA forms only when sun is less than 32.3 high.

When the sun is near that upper limit the arc is faint, diffuse and very close to the zenith.

As the sun sinks the CZA brightens, extends into an arc of increasing radius and becomes narrower.

It is at its best when the sun is about 22 high.