Science Art: Perspective view of the sky…, from “Refraction by Ice Crystals” in Instructions to Marine Meteorological Observers, 1938.

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These are the optical effects you have to be aware of if you’re going to describe the sky when ice-filled cirrus clouds are overhead. Ice crystals refract sunlight differently than water droplets, and you get these curves and halos which a trained meteorologist (of the 1930s) had to be able to record accurately.

It’s from a U.S. Weather Bureau manual for meteorologists that I found in the Biodiversity Heritage Library.