What Determines the Diameter of a Moon Halo?

AI Thread Summary
The diameter of a moon halo is influenced by the angle of the moon above the horizon and the altitude of cirrus clouds, typically forming a 44° cone around the moon. While trigonometric calculations can estimate the halo's diameter, the actual appearance can vary based on the observer's location and the cloud structure. Different observers may perceive the halo differently, leading to variations in size and position. The phenomenon is complex, and the uniformity suggested by simple calculations may not reflect real-world observations. Understanding the moon halo requires considering both the physics of light refraction and the variability of atmospheric conditions.
jmvizanko
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So I got to see an amazing Moon Halo the other night. My question is, what is really the diameter of the average location in the halo, where the light is bent by ice crystals? Is it really as easy as doing the trig with the altitude to your average cirrus cloud, the angle above the horizon that the moon is at, and the 44° cone that the halo represents? Or have I fundamentally misunderstood the phenomena?
 
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Trigonometry should work.
I don't see the relevance of the result, however. The clouds do not have any structure of that size, and different observers will see rings at different locations (and even different size, with a different altitude).
 

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