How and why is a rainbow formed in the sky

The first person to give a scientific explanation for this weather event was René Descartes in 1637. Descartes' explanation was based on the phenomena of reflection and refraction of light rays in water droplets.

At the moment that a ray of light enters a drop of water, this light is refracted into various colours. In addition, the direction of the light ray also varies somewhat. Upon reaching the end of a drop of water, the light tries to escape it. However, some of it is contained and is reflected back. Since the drop is curved, the light will be sent back at a 138º angle. It is this precise angle that explains rainbow formation.

When an observer sees this phenomenon, all the colours of the water drop form a 138º angle, producing an arc, caused by the sun's rays . However, usually you can observe only part of the arc because the other part is cut off by the ground. Still, it's possible to see a complete arc or even a full circle around the edges of a waterfall if the sun is behind you.

It's also interesting to know that if you move a little to one side, the light you observe will be a different one. Therefore, from each position you'll be able to see a different rainbow. It's also possible that two people, even if they're together, can see a completely different rainbow.

You can see double rainbows or even triple rainbows. This can be explained because the light refracts inside the drop of water before escaping it, thus causing more colour reflections. However, the second rainbows are often much fainter than the initial ones. They also tend to appear larger, because they come back at a 130° angle.

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