Why Do Rainbows Occur?
Dearborn Biology for Better
A rainbow is one of the most beautiful occurrences in nature. All it takes to form is water and sunlight, but its conditions must be met. First is the water. In order for a rainbow to form, it requires there to be water droplets in the sky, which is why we see them after it rains. Next would be the sun. The sun must be low in the sky, or more specifically, less than 42 degrees above the horizon. There is also a third crucial part to a rainbow’s visibility and that is you. You must be standing where the water is in front of you and the sun behind you. The reason behind these conditions is what happens to light when it enters the water droplets. Light, as it enters the water droplet, begins to slow down due to the water being denser than air. This slower speed makes the light bend as it reflects off the back of the droplet and comes back out the way it came in but at a different angle, and bends again as it enters the air. This bending is what makes all of the colors. Sunlight is made up of wavelengths, each creating one of the colors of the rainbow. They separate because each wavelength has a different length causing them to bend differently. Red is the longest wavelength and bends the least, and each wavelength gets shorter and bends further until violet, which is the shortest wavelength and bends the most.
Now that the rain and sun are in the correct positions, the focus is on the position of the viewer. The viewer must be between the sun and the water, where the sun is behind them while they look at the rainbow. The reason is the way light travels. The light rays leave the sun to later enter the water droplet. When it enters the water, it reflects off the back and comes back in the direction that it came, which is where the viewer must be for their eyes to be able to collect the light inorder to see the rainbow form. A rainbow is a beautiful phenomenon that can only be appreciated when the perfect environmental conditions are met.
How Are Rainbows Formed?, Met Office, 24 May 2018,
“What Causes a Rainbow?” NOAA SciJinks – All About Weather, National Oceanic and Atmospheric Administration, 9 Nov. 2020, scijinks.gov/rainbow/.