How a Rainbow is Formed

• The birth of each rainbow begins with millions of tiny rain droplets.  The rain droplets serve as a type of reflector of light.  White light enters one individual rain droplet and exits as one specific color of the spectrum.  Without millions of rain droplets, a rainbow would not occur.  If you only had a few rain droplets you would only see a few colors.  This is typically why rainbow appear after a rain storm.

• Each rain droplet has a function in the formation of the rainbow. Sunlight enters the rain droplet at a specific angle and the rain droplet separates the white light into many different colors.  This angle is a fixed measurement between your eye and the sun.  What color is refracted depends upon the critical angle,                   which is the angle the sunlight strikes the back of the rain droplet.  Red light bends the least, exiting the rain droplet at a 42 degree angle, while Violet light bends the most, exiting the rain droplet at a 40 degree angle.  All of the other colors of the rainbow exit the rain droplets at some angle between 40 and 42 degrees, thus making up the colors of the rainbow ROYGBIV, this order never changes.

• Each rain droplet reflects all colors at a given point and time, but only one color comes back to your eye, requiring million of rain droplets to create a rainbow.  As the rain droplets fall through the sky, the colors of the spectrum being reflected and refracted are constantly changing.

• Rainbows form a complete circle, however only half is visible.  The horizon only 
• Picture from the web site of the Department of Physics and Astronomy, Arizona State University                                                             allows us to see half of the rainbow circle, so we see just an arc.  What causes the rainbow to have a circular formation is the way that rain droplets fall.  The rain droplets do not fall is flat sheet, however they tend to fall at various distances and speeds.  On some occasions you can see a full circle around a garden hose.

• The perfect time and place to look for a rainbow you need bright sunlight to your back and rain clouds off in the distance in the direction of your shadow. If it is later than 4:30 in the afternoon or earlier than 8:30 in the morning at these condition there is a very good chance you will be able to see a rainbow in the sky.  Other places you may see rainbows formed are fountains, in the ocean as the waves crash against the rock which create a mist in the air, waterfalls, sprinklers and mist from a garden hose.