Richard Of York Gave Battle In Vain. Red, orange, yellow, green, blue, indigo and violet. A rainbow is caused when sunlight is dispersed through water, usually raindrops but they can occur at waterfalls as well. Acting like a prism, the drops of water refract the light from behind. The various wavelengths are bent at slightly different angles which causes an optical effect for the viewer which we know as a rainbow.
But we don’t care about all that. We just like spotting them. The pleasure of finding one in the sky does not seem to diminish with age, a bit like the excitement of hearing an ice cream van.
I once saw a double rainbow, one beneath another, and stood motionless getting gradually more wet until a third rainbow appeared below the second. A moment I shall never forget.