How are rainbows formed. I know it’s about refraction from water droplets, but shouldn’t you see many tiny rainbows instead of one big one.
In: Physics
Why does this keep coming up!? How many times is this question going to trend?
So what you’re actually looking at is a big ball of mist in the sky?
Sunlight is what is called polychromatic light. This means it contains all visible wavelengths (red, orange, yellow, blue, green, indigo, violet) as well as wavelengths of light we cannot see (infrared, ultraviolet, x-ray, gamma-ray and so on). When this light from the sun refracts through a water molecule, all the light is separated. The longer wavelengths (red) will refract at a smaller angle then the shorter wavelengths (blue, violet). This is why we see red at the top of a rainbow and the blue colors at the bottom of a rainbow.
Now to address your question. Technically there are tiny rainbows from one water molecule, but we wouldn’t be able to see this refraction through a single water molecule just because there is not enough light to be received by our eye. It is a sum of all these that produces what we call a rainbow. Rainbows only occur when there are enough water molecules refracting light to be perceived by the human eye.
So, everyone gets their own rainbow?
Well, I once saw three rainbows in a row. One really bright one. One slightly less bright one just underneath and one barely discernible one underneath that one.
Was pretty cool. Doesn’t really meet the definition of “many” though.
If you need a visual to understand (like I do), this youtube video is really helpful:
For me, it’s helpful to remember that a rainbow is a circle. You usually just can’t see the other half. In the inner parts of a circle the spectrum continues. The ultra violet and higher frequencies keep going. Outside the circle, the infra red and lower frequencies continue. A rainbow only appears like it does to us because we can only see a small segment of the spectrum.
I can’t explain why you don’t see teeny ones, BUT when you see a rainbow, you only see one of what’s actually an endless formation of concentric rainbows.
The primary rainbow is the brightest, and if you see purple in it, you are actually witnessing a whole new bow.
Have you ever noticed that sometimes in perfect conditions a primary rainbow seems as though there are “extra” shiney bands below it?
This is called a supernumerary rainbow, and it’s the beginning of the second “disk” in the concentric bands. The blue of the primary one overlaps with the red of the next, and it shows up as purple or violet.
So, you are kind of right. There are many different rainbows. Our eyes are only capable of seeing the brightest of them.
>shouldn’t you see many tiny rainbows
I’ll address this specifically as others have glossed over it.
You would see multiple rainbows if we had multiple suns. And if we were really close to the sun, we’d be dead, but there would also be no rainbows.
The sun is far enough away that the light coming from it acts a bit like a laser. All the light points in one direction. The sunlight hits the water droplets and reflect off it just like shining a laser pointer at a screen.
When you shine the laser pointer at the screen, only that spot on the screen lights up. Now imagine that the color of the light from the laser pointer changed based on where you pointed it on the screen, blue in the middle, through the color spectrum to red on the outside edge. As you move the laser around, you are only seeing specific colors in specific spots. If you expand the laser’s light from a dot to a disc big enough to light up the whole screen, you’ll see all the colors.
Now, while it’s true that each droplet shines all the colors of the rainbow, each of those colors are going in different directions and the only color you see is the one pointed at your face. And like the laser pointer and screen example, what color that is pointed at your face is determined by that droplet’s position in the sky.
I would really recommend looking on youtube for “Walter Lewin Rainbow”, he was a professor at MIT and he’s lectures on introductory physics are amazing. I would recommend watching all his lectures but you know… I’m a nerd.
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