We had a brilliant display yesterday of double rainbows. I have attached a few images from a co-worker Steve Nally. I will tell you there is something very different between the primary rainbow closer to the ground and the secondary bow which is higher up. Can anyone figure out the difference???
More pictures from Kathy Robinson...
The pictures above show what we refer to as a double bow. That is two rainbows that share the sky and shape, but the secondary bow is always further away from the ground. To understand how a double bow works, you have to first understand how the primary bow is formed. We get rainbows when sunlight shines directly into a rain drop, then bounces off the back of the raindrop, and is reflected to your eyes. The water acts like a prism and spreads the light into the full spectrum of colors. When a secondary bow is formed, the light has to bounce twice off the back of the rain drop before it is reflected to your eyes. That means more light is muted by the rain drop (the cause of it being less bright) and like a mirror the colors are flipped backward to the primary rainbow since the light bounces off one more surface of the raindrop. So everytime the light bounces off the back of the drop, the reflection, much like a mirror, is flipped and reversed. This is same thing as when you look in a mirror everything looks backward. Here is a good illustration I drew up. Sorry if it is a bit crude. :)