How Are Rainbows Made?
Do We Only See Rainbows When It's Raining?
The short answer is no. Of course, the ones we commonly see are during a period of rain. When light passes through a prism, for example, we see an end result of color. When we first learned about the behavior of light and the speed in which it travels, consider what was also learned in science classes with the prism. As light, or white light, hits the prism, the behavior of the light is dispersed (scattered) at different angles and exits as different colors depending on the way it refracts, or bends. When the ray of light bends as it passes from an angle in one medium (such as air) into another medium (such as a glass prism), the speed of light changes, which is called refraction.
What Makes a Rainbow?
According to history, the refraction of light related to a glass prism was investigated by Sir Isaac Newton in the 17th Century. He had determined that each ray of light based on its angle as it entered a certain medium would produce color as it left the medium source. Naturally, to study the scientific or mathematical implications of how the behavior of white light chances may sound a bit convoluted so to read about this subject with visuals is more helpful.
If someone were to explain how there are different colors which constitute white light, the understanding of the process becomes more possible to grasp. The colors that combine together to create white light are red, orange, yellow, green, blue, indigo and violet. Depending on frequency, or wavelength, of each of these colors, will determine how the colors are arranged on the rainbow. Longer frequencies produce red light and shorter frequencies produce violet.
After a rain shower, there are multitudes of raindrops that float in the air. Light from the sun comes into contact with these raindrops and as it enters them, the light bends and and as it passes through the raindrop, it generates a specific color dependent on its frequency. Imagine that each raindrop is like a mini-prism.
When a second rainbow (or double rainbow) is witnessed, it is produced similar to the way described above. However, light from the sun is reflected twice before it leaves the raindrop.
Why Does a Rainbow Look Like Part of A Half Circle?
The light in a rainbow travels in a curved path, or arc. It always appears we see half of an arc, but rainbows are actually formed as a circle. Keep in mind, also, that a rainbow is formed when the sun is behind the viewer. There is what is called an anti-solar point from which the rainbow seems to form around. The horizon gets in the way of our being able to see the whole circle of the rainbow. If the sun is going down, we can see more of this colorful phenomenon and likewise when the sun is higher, we see less of it.
The Physics of Rainbows Video
The video below provides another good explanation of the behavior of light in creating rainbows. While the narrator of the video is speaking at a fast pace, if you keep up with the explanation and the video images, it provides a better understanding.
Catching a Rainbow
I think it would be challenging for each of us to recall the very first time we saw a rainbow, but as children, when we were wowed by them. We tried to count the different colors in them and after the experience was gone, we wondered when it would happen again. As adults, many of us still get excited when we see one. It's art in the sky.