A rainbow begins as a million tiny rain droplets. When white light from the sun enters the rain drop at a specific angle rain drop separates the white light into many different colors. This angle is a fixed measurement between your eye and the Sun.
Which color is refracted and seen by your eye depends on the angle at which the sunlight hits the back of the raindrop. Red light bends at a 42 degree angle and violet light at a 40 degree angle, with the rest of the colors coming in between. The colors change as the angle changes as the rain drops fall but the order of the rainbow colors is always red, orange, yellow, green, blue, indigo and violet.
Rainbows appear as an arch in the sky, but in truth they are a circle. The
Earth’s horizon prevents us from seeing the full circle, so we only see about half, thus the arch. Sometimes you can form a full circle rainbow by using a garden hose and causing a spray of water drops in the air.
The best way to see a rainbow is bright sunlight to your back and rain clouds in the direction of your shadow. You can also see rainbows as a result of water mists from waterfalls, the ocean and even a lawn sprinkler.
Have you ever wondered what causes a rainbow to appear on an oil slick in a parking lot? Here’s why. If the ground is wet, the oil spreads on top so very thin that the oil’s thickness reaches the wavelength of visible light. When this happens, the oil/water mix allows you to see color.
This only works when you view the oil slick from an angle because the angle affects the distance the color has to travel from the puddle to be reflected towards your eyes. If you see it from different distances, the colors will change.
You can also see a rainbow of colors in a soap bubble. When light hits the surface of the bubble part of the light is reflected back from the outer surface and part from the inner surface. As the two waves of light travel towards your eye they interfere with each other and the result is a mix of color.
If the light waves get too close together you see almost no color and when waves reinforce each other the color is more intense. When the bubble wall gets thinner as gravity pulls the chemical content to the bottom the two wavelengths cancel each other and the bubble becomes nearly invisible.
Many Americans are familiar with the Irish tradition that a pot of gold awaits at the end of the rainbow, but this is not the only country where rainbows and superstition mix.
In the United Kingdom children were taught to drive away rainbows by making a cross on the ground with two sticks. This may stem from a Norse legend that believed rainbows carried the souls of the dead. In Austrian legends, the souls of children walk a rainbow bridge to heaven.
Materials: Flashlight, clear plastic cup, water.
Process: Darken a room, turn on the flashlight, place the cup on top of the light and add water to the cup.
Result: A rainbow will be reflected on the ceiling. This happens because the water creates a prism which splits the light into different colors.