Rainbow

Getty Images has 82 pages of rainbows so the choice was hard but very enjoyable.  

When I lived in Santa Fe there was one in the western sky each day around 5 pm above Los Alamos in the Jemez Mountains. Sometimes there was a pair. But if you want to read something poetical about the beauty of a rainbow you're in the wrong place. My nature is more scientific, so here you'll get as brief an explanation as possible.

A "rainbow" occurs when sunlight shines on and interacts with drops of water. The keys are that . . .

• Rain and sunshine must be in different parts of the sky, 
• The observer is between the rain and the sunshine, and 
• The angle of light hitting the raindrops is between 40 and 42 degrees. 

When those requirements are met each raindrop will be refracted to produce one color, slightly different from all the rest. Together those millions of raindrops produce a rainbow in its well-known cascading shades.  That's all there is to it.