Raindrops to Rainbows: How they paint the sky

September 27, 2024

Many people worldwide consider rainbows a meteorological, optical phenomenon associated with a clash of rain and sun. Admired by many, becoming a popular and aesthetically pleasing Instagram story, there is more to rainbow formation than what meets the eye. They don’t just appear, instead, they appear when sunlight slows down and is submerged by water droplets, through a process known as refraction.

Refraction:

This is the bending of light and sound as it passes through either a liquid, solid, or dense gas, this could be a window, wall, or in the case of rainbows we see in the sky, this will be through water droplets. The light bends as it enters the raindrop and then reflects off the back of the droplet, causing the light to refract again, and as it exits the raindrop and enters the air it bends dispersing more colours, this is what we refer to as the rainbow.

Reflection:

When the light enters the raindrop, it is then reflected off the back of the water droplet and refracted again out into the air. Internal reflections can happen more than once; however, the brightest rainbows are a result of just one reflection.

Dispersion:

This happens after the light has been refracted for the second time within the water droplet the white light that entered the raindrop then disperses into the full spectrum of wavelengths, otherwise known as the seven colours that make up the rainbow (red, orange, yellow, green, blue, indigo and violet.)

Where do the Rainbow’s colours come from?

Sunlight consists of various wavelengths, that travel at different speeds when passing through denser air. This disruption of sunlight travel causes the white light to disperse into different colours. The colours we see within the rainbow. The longer wavelengths appear as red, whilst the shorter wavelengths are blue and violet.

A rainbow is an optical illusion; it doesn’t necessarily exist in a specific spot in the sky. The appearance of a rainbow can differ depending on where you’re standing, your position to the sun, and the angle you are looking at can all impact the appearance of a rainbow. TOP TIP: To get the best view of a rainbow, ensure you are standing in front of the sun, instead of directly facing it.

Conclusion:

Sadly, much to many people's dismays, there is no treasure waiting for us at the end of the rainbow! In fact, the adored meteorological phenomena that we are seeing is merely an optical illusion that is unique to every angle one views it.

Rainbows are the result of sunlight being scattered from raindrops, through a process of three crucial steps:

Refraction
Reflection
Dispersion

The wavelength's variety of speeds causes the white light to disperse into the seven colours of the rainbow, the rainbow's outer layers, including red and orange travel faster than the inner layers including indigo and violet.

FAQ's:

What are the colours of a rainbow?
A rainbow typically displays seven colours: red, orange, yellow, green, blue, indigo, and violet.

Why is a rainbow shaped like an arc?
A rainbow appears as an arc because the angle the light is refracted, reflected, and refracted again within the water droplets is the same for each colour. This consistent angle creates a circular pattern, but we usually see an arc because the ground cuts off the full circle.

Can rainbows form at other times besides after rain?
Rainbows can form in any scenario where there are water droplets in the air and sunlight. This includes mist from waterfalls, fountains, ocean spray, and just misty air.

What is a double rainbow?
A double rainbow occurs when light is reflected twice inside the water droplets, resulting in a second, fainter rainbow appearing outside the main one. The colours of the secondary rainbow are reversed, with red on the inner edge and violet on the outer edge.