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

scientific illustration of the sky, a perspective view of effects from ice crystals for meteological observers

scientific illustration of the sky, a perspective view of effects from ice crystals for meteological observersClick to embiggen

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.