The Science Behind: Rainbows (Part 1)
Cover page- Sara Chaudhari
"Be a rainbow in someone else's cloud"
"Friends are like rainbows, always there you cheer you up after a storm."
"When it rains look for rainbows."
"Count your rainbows, not your thunderstorms."
Rainbows are symbols of hope, of pride, of happiness, but why? The internet is filled with inspirational quotes about rainbows but before we count or become rainbows I think we should understand what rainbows really are.
Now, essentially a rainbow is just light hitting water droplets.
Most often rainbows are found when it's raining, but they also appear around waterfalls, sea spray or fog.
Rainbows are formed when light hits the water at precisely forty-two degrees.
I'm sure most of us have heard the myth that pots of gold can be found at the ends of rainbows. Now, let me tell you why it is a myth: Rainbows are optical illusions!
Rainbows don't actually exist at one specific spot in the sky!
Those leprechauns tricked us!
The appearance depends on where you're standing and where the light is shining.
Usually, the source of light is right behind the person seeing the rainbow. The center of a primary rainbow is called the 'antisolar point' or the imaginary point directly opposite the sun.
Rainbows are a sum of the refraction and reflection of light. Refraction and reflection are both phenomena that are involved in the change of a wave's direction. A wave that's been refracted may look 'bent', while a wave that's been reflected may seem to 'bounce back' from a surface.
When light enters a water droplet, it is refracted. Then by the back of the droplet, it is reflected. Then, as the reflected light begins to leave the droplet is refracted again, at multiple angles.
Rainbows can be found in all sizes, so what determines the radius of a rainbow?
The radius is determined by the refractive index of the water droplets.
A refractive index is the measure of how much a ray of light bends as it passes from one medium to another.
A droplet with a high refractive index will produce a rainbow with a smaller radius. For example, saltwater has a higher refractive than freshwater. This means that rainbows formed by rain will be bigger than those formed by sea spray.
If you've ever seen a rainbow from an airplane, then you probably already know that rainbows are actually full circles.
However, on the ground, you can only see the rainbow above the horizon. Each person's horizon is a little different, so no one can actually see a full rainbow from the ground. In fact, nobody actually sees the same rainbow! Each person has a different antisolar point, therefore the "end" of the rainbow for you could actually the beginning of the rainbow I see.
In conclusion, rainbows are amazing! They are one of nature's many tricks.
In the next article, I will elaborate on why we see specific colors in rainbows and why we sometimes see double-rainbows.
Until then...
Stay Curious ;)
Love,
Sarah
Sources:
https://www.nationalgeographic.org/encyclopedia/rainbow/
https://ssec.si.edu/stemvisions-blog/science-rainbows