Rainbow The Optical Illusion


Nature has elements that instantly mesmerize humans, whether it’s the presence of mountains, trees, oceans, sky, flowers, or the beauty of snowfall and rainfall. However, these wonders aren’t present everywhere in every country or city. Some places may showcase specific natural marvels, but one universally enchanting aspect of nature is rainfall. It’s a gift from nature that can be witnessed almost everywhere. Rain is a significant blessing, bringing joy not only to people but also serving as a necessity and source of happiness for the entire Earth and its diverse species, including animals, fish, birds, and insects.

This rain is not just rain; rather, when it arrives, it brings along additional wonders. Among those wonders is a beautiful phenomenon known as the rainbow. Most of us have likely seen it after rain, displaying seven colors. It is a fascinating sight for people, especially children. Whenever it rains, many people eagerly wait for the appearance of the rainbow.

But have we ever thought about how a rainbow actually forms? Why don’t we see a rainbow after every rain? Often, a rainbow is visible when there is sunlight during the rain. The answers to all these questions can only be understood when we will figure out how a rainbow is formed and what physics is behind it.

Science behind Rainbow:

Before the 17th century, there were many misconceptions about the rainbow, such as it being only purple in color, some believed it had three colors, and others thought there was a pot of gold at the end of the rainbow. Some even considered it a mystical gate to another world that could be crossed. In certain cultures, it was seen as a divine bridge.

But then Sir Isaac Newton conducted an experiment in which he passed white light through a prism, revealing that the white light dispersed into seven colors. One day, he darkened his room completely by covering it. He created a hole in his window through which sunlight could enter. When sunlight passed through the hole and through the prism, it became apparent that sunlight is comprised of seven colors: red, orange, yellow, green, blue, indigo, and violet.

Formation of Rainbow:

So, we have observed that a rainbow always appears when it’s raining and sunlight is present. In fact, raindrops also act as prisms. When it rains, sunlight reflects on these raindrops , internal reflection occurs in the water droplet, then it refracts . As a result, sunlight disperses into seven colors. Each color refracts at a different angle: red at 42°, orange at 40°, yellow at 38°, green at 36°, blue at 34°, indigo at 32°, and violet at 30°. This sequence is based on the different wavelengths of each color, with red having the longest wavelength and violet having the shortest wavelength.

Sometimes, it also happens that it’s raining, sunlight is present, but we still don’t see a rainbow. This is because these colors are not tangible; they involve reflection and refraction. A rainbow will only be visible when it’s raining, the sun is behind us, and the incident light and refracted light angles lie between 40° to 42°.

Shape of Rainbow:

Whenever we see a rainbow, it always appears as a half-circle. However, in reality, a rainbow forms in a full-circle shape. The reason we see only half of it is that the other semicircle is beyond our visibility. If observed from aircraft or taller buildings, the full circle of the rainbow becomes visible.

Types of Rainbow:

Rainbow doesn’t form in only one form infact rainbow infact it has many other versions.Rainbow has following types;

Primary Rainbow:

As we discussed, a rainbow forms when sunlight undergoes internal reflection in water droplets, followed by refraction and dispersion of light. The primary rainbow occurs when the sunlight undergoes internal reflection only once. Normally, the rainbows that form are primarily of this type, following the sequence ROYGBIV.

Secondary Rainbow:

The secondary rainbow forms when sunlight undergoes two internal reflections in a water droplet. When this rainbow forms, we see two rainbows—one dark and one light. The dark one is the primary rainbow with the sequence ROYGBIV, and the sequence of the second rainbow is VIBGYOR.

Supernumerary Rainbows:

Supernumerary rainbows are formed when light waves undergo numerous interactions. These rainbows appear very faint and are visible between the primary and secondary rainbows. This phenomenon is another precious optical illusion gifted by nature.

Lunar Rainbow:

A very interesting type of rainbow is the lunar rainbow, also known as a moonbow. It forms when moonlight refracts and disperses through water droplets or raindrops. However, observing a moonbow can be challenging because it is dimmer compared to primary rainbows, given that sunlight is brighter than moonlight.

Now, whenever it rains, enjoy the rainbow along with keeping in mind the science behind it. Look at the rainbow with a different perspective. It’s a part of nature that illustrates how everything is perfectly synchronized in the natural world.



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