One thing I love about the weather is how fascinating it can be to anyone of any age. It is something much larger than any of us. And it’s something that we have little to no control over.
And while that can be a little uneasy at times, there are some things, like rainbows, that can bring a sense of comfort and peace.
So what causes this phenomenon? Let’s first start with the basics of light. All light moves at 186,282 miles per second, which is better known as the speed of light.
However, when light passes through glass or water — both are known as a medium — it slows down.
The sun is considered a white light. White light is made up of all colors; red, orange, yellow, green, blue, indigo and violet are visible to the human eye.
Each one of those colors has a unique wavelength, which allows for the human eye to see a color signature.
The wavelengths range from largest to smallest on the scale. Red will have the longest wavelength and violet will be the smallest.
And the wavelength directly reflects the medium that the light travels through. So in the case of a rainbow, the light is passing through the medium of water.
So given that background, let’s start to build on the formation of a rainbow. Rainbows occur after a storm passes or when there is a storm in the distance.
For a person to see a rainbow, there must be light and there must be a medium — in this case, the light is given off by the sun. The medium is the rain drops, or water, from the storm that will change the wavelength of the light from the sun.
The sun will hit the spherical surface of the raindrops and scatter into all seven colors. This scattering is called “refraction.” But not only is the light refracted, it is also reflected when it hits the raindrop, so that the colors come bouncing back. And to get down to specifics, it reflects back at an angle of 40 to 42 degrees relative to the path of its original light source, the sun. I’ll touch on this more when we address why rainbows are always seen as an arc.
First, a couple of key points: To see a rainbow, you must always have the sun behind you and raindrops in front of you. When looking at a rainbow, you also must remember it isn’t flat — that is just the way your eye sees it. It’s the same reason we see the sun or moon as flat, even though we know it is not.
Finally, rainbows are actually circles, not semi circles. We describe them as arcs, because that is all that we can see. The second half is actually lost in the horizon. But, if you were to see a rainbow from a top-down approach, like from an airplane, you could actually see the entire circle the rainbow makes.
Now, let’s get into the science of why we see them as arcs from the ground, or as I just noted, full circles from above.
Light is refracted and reflected off rain drops at a 40-degree angle. The easiest way to think of the path of the light is like an empty ice cream cone. Imagine yourself at the tip of the cone looking outward. Remember you are seeing the reflection from a 40-degree angle, which coincidentally takes the shape of a cone with your eye as the point. When you look down the cone, you see a circle — just as rainbows are actually full circles.
Since rainbows are solely a function of light, you can’t catch them or touch them. Perhaps this adds to their majestic beauty, and that pot of gold we will never see!