My heart leaps up when I behold a rainbow in the sky
In Chapter 22 a contrast was drawn between some meteorological optical effects—rainbows and some ice crystal halos—observed during the day, from those potentially observable from nearby light sources at night. This Appendix summarizes some of the salient features of rainbows and one of the common ice crystal halos.
So what is a rainbow, and what causes it? A rainbow is sunlight, displaced by reflection and dispersed by refraction in raindrops, seen by an observer with his or her back to the sun. The primary rainbow, which is the lower and brighter of two that may be seen, is formed from two refractions and one reflection in myriads ...