"The Nature of Light and Colour in the Open Air"

... is a wonderful book. I highly recommend it to anyone who spends time outdoors and lives with their eyes open. (Most people don't) There are hundreds of optical phenomena that can been seen by anyone who takes the time to look, and with the help of this classic book, knows what to look for. I've been lucky enough to see almost every one listed in the book.

It was just starting to rain here with the late afternoon sun shining brightly. With the rains approaching from the east, I knew there would be a great rainbow and I wasn't disappointed. As you can see here, there are two bows visible. Sometimes there is a third one visible outside the second one, but I couldn't make it out this time.

The lower, brighter one is the one most people see. The second fainter one is usually seen when the raindrops are just the right size and the sunlight is bright. As you can see, due to the different path the light takes in the raindrops that produce the outer bow, the sequence of the colors in this bow is reversed.

If you look closely at the larger image, you will see additional violet arcs along the inside of the brighter bow. Due to the very bright sunlight, these were very apparent to the eye, but not as obvious in this image. Also note that inside the brighter bow, the sky is brighter while the sky between the bows is darker. These are because more light is scattered back to the observer inside the main bow, but the light is scattered away from the observer between the bows. Canon 20D - 1/80th, 20mm @ f/18, ISO 100