Srinisspace - Science Behind Everything - Rainbow explained

Have you listened to the conversation of Mithran & Maha about rainbow??

So who wouldn’t want to enjoy a rainbow on a rainy day? Everyone one of us would have seen a rainbow in our childhood and enjoyed it. But have we ever think why rainbow appears and what it exactly made up of? In this post, we will see how the rainbow appears and what is the scientific explanation behind it.

What is a Rainbow?

Rainbow is an optical illusion. In reality, the rainbow doesn’t exist or it does exist all the time but we are unable to see it.

Little confusing? Yes, what I said is actually true.. Every one of us would have studied about the rainbow and its colors in our school science.

White is a combination of all colors and black is the absence of visible light. Each and every color in the color spectrum has a wavelength. Rainbow is a natural phenomenon in which white color is scattered to different colors according to their wavelength and so visible to our eyes.

How Rainbow appears??
Usually Rainbow appears in the early morning or evening shortly after rain. Certain conditions need to be met to see a rainbow,

The sun(light source) should not be more than 42° to the horizon.
The observer should be in east facing(in the morning) or west-facing(in the evening).

The droplets should be in mid-air between observer and sun.
The scientific explanation for a rainbow is reflection retraction and disperse of light. Since the water drop is in a spherical shape, it reflects and retracts the sunlight. Let's see how it appears,

  1. ,The light encounters the side of the water drop.
  2. Some part of the light reflects while others retract inside the water drop.
  3. The retracted light reaches the backside of the water drop.
  4. If the sun is at 0° to 42° to the horizon, then the retracted light portion will be at 0° to 42° to the backside of the water drop. Between this angle, most of the light will be reflected back to the drop.
  5. The reflected light reaches the other side of the drop and some of them retracts again, while the remaining reflects back and it continues on.
  6. When the refraction happens, different wavelengths refract differently, according to their wavelength. Violet, with a shorter wavelength, refracts more and Red, with a longer wavelength, refracts less. So we have violet in the inner circle and red in the outer circle of the Rainbow.When the light finally refracts and exists from the drop, according to their wavelength, it is visible to the human eyes with various colors.
The visible colors in the rainbow are Violet, Indigo, Blue, Green, Yellow, Orange and Red (called as VIBGYOR to easily memorize it).

Fun facts:
  • Rainbow is actually a circle. Since we observe it from the ground, we are seeing an arc. If we observe it from the flight, we can see a full circle of the rainbow.
  • The same phenomenon can occur in the night also. If the moonlight is bright enough, then we can see a moonbow.
  • A double rainbow is a phenomenon in which two rainbows are visible. In theory, all rainbows have a secondary rainbow, but their visibility is faint when compared to the primary rainbow.
  • Sometimes at the time of sunrise or sunset, if a rainbow happens to occur, the shorter wavelength colors like blue & green scatter easily and so a rare red rainbow occurs.
  • In different mythologies, rainbows are considered as a bridge of gods or sign of God for a good omen.