Why Do Rainbows Form?

What is a Rainbow? How is the Rainbow Formed? How Many Types of Rainbows are there? Why are Two Rainbows Never Same?
why do rainbows form

We all have seen a rainbow when the sun comes out of the clouds after the rain. But, why exactly do rainbows come out like that? In this article, we will discuss why do rainbows form and why the rainbow is curved. So, let us begin this colorful journey!

1. What is a Rainbow?

Rainbow is a natural phenomenon that occurs due to refraction, reflection, and dispersion of light. Because of this dispersion, we can see seven colors in a rainbow. It is often in the shape of an arc, but in actuality, it is a full circle. Color bands in the rainbow include violet, indigo, blue, green, yellow, orange, and red or VIBGYOR in short. (See Why is the sky blue?)

2. Why do Rainbows Form?

When the sun shines after the rain, its light passes through the raindrops. These raindrops act as a prism, reflecting and refracting the white light. When white rays of the sun exit the raindrops, it diverges into seven colors, thus forming a rainbow.

3. Why are Rainbows Curved?

Rainbows appear curved because of the angle we see them from. Rainbows are a complete circle but from land, it is not possible to see a full circle rainbow. To see a full circular rainbow, we need to be at a higher altitude, like a skyscraper or an aircraft. (See 10 Facts About Plane Smoke)

4. When do We See a Rainbow?

We can see this natural phenomenon when the sun is behind us and its rays enter the raindrops at the angle of incidence. These incident rays are then refracted inwards within the raindrops. Rainbows form when these rays are reflected after touching the end wall of the raindrops and then again get refracted before they exit the raindrops. Finally, they reach our eyes and we can witness the rainbow. (See Where Is The Eye Of The Hurricane?)

5. Where do Rainbows Form?

Rainbows occur when the sun rays touch them from a low altitude. This is why we can see a rainbow in the morning towards the west side and towards the east in the evening.

  • A rainbow can be formed in the spray of the waterfall and is known as a Spray Bow. Such a rainbow can also be formed from the spray created by oceanic waves.
  • Furthermore, a rainbow can be formed where there is dense fog and is known as Mist Bow. (See Places with best rainbows)

6. Why are Two Rainbows Never Same?

Sometimes, we have witnessed two rainbows in which one is clearly visible, while the other one is not so clear. This phenomenon happens when the sunlight is reflected twice within raindrops. The second rainbow always forms above the first rainbow. A secondary rainbow forms at 10 degrees outside the primary one. Refraction, reflection, and dispersion of light are the three primary principles depending upon the amount of light, the position of raindrops, and the viewer’s position. Therefore, the arc, color bands, position, and the width of its color bands differ from the view of people watching it. (See What are the top 10 favorite colors?)

Why Do Rainbows Form?

7. Why is the Second Rainbow in Mirror View?

Why do rainbows form in the mirror view is because when the sun rays enter raindrops, they are reflected twice before they exit. Thereby, it results in the second rainbow with reversed color pattern. (See Why Do Earthworms Come Out in the Rain?)

8. How Long does a Rainbow Last?

Why do rainbows form is now understood, but how long does this phenomenon last? It does not last longer than an hour usually, but there may be exceptions at times.

  • In 1994, the rainbow over Sheffield, England lasted 6 hours, from 9 am to 3 pm. It was the longest-lasting rainbow mentioned in the Guinness Book of World Records until 2017.
  • In 2017, some professors and students of the Chinese Culture University witnessed the new longest-lasting rainbow near the mountains of Taipei, Taiwan. That rainbow lasted from 06:57 am to 03:55 pm, making it approximately 8 hours and 58 minutes long.

9. How Many Types of Rainbows are there?

Based on the place of their appearance, the rainbows are classified into the following categories:

  • A reflected rainbow is visible on the water surface just below the horizon.
  • A reflection rainbow appears when the sunlight gets reflected by a water body before entering the raindrops.
  • Moonbow is the rainbow that appears from the same phenomenon, but the only difference is that instead of sunlight, there is moonlight. It is therefore also known as a lunar rainbow.
  • When a rainbow occurs after the shower at early sunrise or sunset although, all the seven colors of the rainbow do not get a chance to be visible. In such a situation, the red color with the longest wavelength scatters the most, resulting in a red rainbow or monochrome rainbow.
  • Sleet is the phenomenon when ice pellets fall in the form of precipitation. So, the rainbow formed in such a situation is formed in the same way. The only difference is the light passes through the ice pellets instead of raindrops, and hence the rainbow thus formed is known as a sleet bow.
  • Fog bows are formed due to smaller clouds and fog droplets instead of raindrops. These fog droplets diffract light resulting in white rainbows with faint red bands on the outside and blue bands towards the inner circle. They can appear anywhere where the air is chilled and fog is thin.
  • Supernumerary rainbows occur when sunrays hit waterdrops of size 1 mm or less. In this type, there are one or multiple faintly colored bands inside the primary bow of a rainbow featuring several pastel colors.
  • Double rainbows occur when sunrays reflect twice inside raindrops. The color pattern is reversed in the secondary rainbow compared to the primary rainbow. Between these bows, there lies a dark unit called Alexander’s band.
  • Why do rainbows form with the same color band is because when two rainbows split from the same point, it is known as a twinned rainbow. It is a rare phenomenon with the same colors in each of them. Unlike the double rainbow, the colors in the twin rainbows are in the same pattern and not in the reverse order.
  • Extraterrestrial rainbows are believed to occur in Saturn’s moon, Titan. Here, the radius of the rainbow is 49 degrees and the reflection is due to methane in the atmosphere. 

10. How did People View Rainbows Earlier?

Because of its magical appearance and mesmerizing beauty, early humans got enthralled with it as well. They were considered to be pathways from the Gods or Heavens. Arcus or Iris, the Greek goddess, was personified as a rainbow in several paintings discovered from those times. This is depicted in paintings where she took the form of a rainbow. According to a mythological tale, Goddess Iris used to scoop water in her pitcher and pour it on clouds to make a rainbow to Mount Olympus. This rainbow was a pathway or a bridge between the land of Gods and the Earth. (See 18 Fun Facts About Space)

So today, we found out about the phenomenon of why do rainbows form and how we see rainbows in different color bands and places. 

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