Q: How are double rainbows formed?
A: A double rainbow - the correct term is secondary rainbow - occurs in the same way as the rainbow in front of it, but the only difference is that two reflections are coming from the same area of rainfall, says Brent McRoberts of Texas A&M University." You need just the right angle to see two rainbows," he explains. "The secondary rainbow is always a little bit fainter in appearance because the sunlight is reflected internally twice by the same raindrop. Also, notice that the colors will always be reversed in a secondary rainbow. This is again caused by the way the light is reflecting off the raindrops."
Q: Is rain always needed to form a rainbow?
A: Yes it is required, says McRoberts. "For you to see a rainbow, the sun always has to be behind you and you must be facing an area of rainfall with the sun at your back," he adds. "When sunlight strikes the area of rainfall, the light is scattered from the raindrop and it produces colors of the spectrum, from light purple or violet to red. Raindrops lit up by sunlight produce a spectrum of colors caused by bending of the light, so a different angle to the rainbow can produce different colors to your eyes. You can create a rainbow yourself by taking a garden hose and turning it on, and with the sun at your back, create a water spray. If you look at the spray at just the right angle, you will see the spectrum of lights form - a rainbow. Areas of the country that have high amounts of rainfall, such as Hawaii and Florida, naturally will have the most rainbows."