A rainbow is one of nature’s most spectacular light shows, appearing as a vibrant arc of color across the sky. This display is actually a trick of light and water, a natural phenomenon you can understand using simple science. It shows how ordinary sunlight can be transformed into something extraordinary when it meets tiny drops of water floating in the air. The appearance of this colorful half-circle depends on a very specific set of circumstances lining up perfectly.
What Does a Rainbow Need to Appear?
To see a rainbow, you need three things: a bright light source, water droplets, and the correct viewing angle. The most common light source is the sun, which must be shining brightly and relatively low in the sky. The water droplets usually come from rain, but they can also be mist from a waterfall or a garden hose spray suspended in the air in front of you.
The final condition is your position as the observer. You must be standing with the sun directly behind you, shining over your shoulder and onto the water droplets ahead. If the sun is too high in the sky, you will not see a rainbow because the light will not hit the drops at the necessary angle to reflect back to your eyes.
The Secret Job of Raindrops
Each tiny raindrop acts like a miniature prism waiting for sunlight to strike it. When a ray of white sunlight enters the front of the drop, it slows down and bends slightly; scientists call this bending refraction. Once inside, the light travels to the back of the water droplet and hits the inner surface. Here, the light bounces back, which is known as reflection.
After bouncing, the light travels back toward the front of the drop where it exits and bends for a second time as it passes back out into the air. This double-bending and single-bouncing path sends the sunlight back towards your eye.
Why Rainbows Have So Many Colors
The reason sunlight separates into many colors is because each color is a different wavelength of light. Each wavelength bends by a slightly different amount when it enters the water drop, a process known as dispersion. Red light has the longest wavelength and bends the least, while violet light has the shortest wavelength and bends the most. This difference in bending angles keeps the colors separated and distinct.
Because the colors always bend by the same amount, they always line up in the same order. You can remember the seven colors of the rainbow with the name “ROY G. BIV,” which stands for:
- Red
- Orange
- Yellow
- Green
- Blue
- Indigo
- Violet
Red is always on the outside of the arc, and violet is always on the inside.