Did you know : Some colourful facts

Did you know : Some colourful facts
Image Credit- Nicky on Pixabay


How is a rainbow formed? Why do soap bubbles shimmer? Why do rainbow-like colours appear when light strikes oil floating on water? What is it that the sun looks red at sunset?

Since childhood, we have been amazed and surprised to see its sudden appearance. These look magical to us and sometimes we are spellbound to observe this breathtaking beauty. Let us understand the science behind this natural phenomenon.


How is a rainbow formed?

A rainbow always appears in the sky after rain falls when the sun shines. Most of the time it appears in the evening or in the morning because, for the formation of a rainbow, the sun needs to be low in the sky, at an angle of less than 42° above the horizon. The lower the sun in the sky, the more of an arc of a rainbow we will see. A rainbow is always formed in the direction opposite to the sun. A rainbow is not a “thing” and it does not exist in a particular “place.” It is an optical phenomenon.

In simple words, a rainbow is made when sunlight is reflected and refracted through the water droplets in the atmosphere. How is a rainbow made? Well, you know that sunlight looks white, but it’s made up of different colours – red, orange, yellow, green, blue, indigo, and violet. When white sunlight passes through the raindrops, the raindrops act like tiny prisms. They bend the different colours in white light, so the light spreads out into a band of colours – red, orange, yellow, green, blue, indigo, and violet -the colours of a rainbow.


Why do soap bubbles shimmer?

Isn’t it lovely to feast your eyes upon the glistening soap bubbles as they glide up in the air? If you blow from a plastic pipe, lather between your hands, or produce by the detergent in a washing machine, in any case, the bubbles seem to shimmer with colours that bear between red, yellow and purple even if they meet small amounts of light.

The reason behind this are the properties of light. When light rays move from one transparent medium to another – in this case, from air to the bubble, some rays go through, and some rays bounce back or are reflected. Some light rays bend at the point where air meets the bubble.

When light bends, it is called refraction and it is what causes soap bubbles to change colours. The more the light rays deviate, the more blue rays from the spectrum will become visible to the human eye. Less deviation makes the red parts of the spectrum visible. In effect, the surface of the bubble acts like a small prism that separates the various light rays into their individual wavelengths, and these appear to us as shimmering colours.



Why do rainbow-like colours appear when light strikes oil floating on water?

When oil is poured into water, it spreads out to form a very thin film on the surface of the water as oil is not soluble in water. However, this film is of varying thicknesses. In some places, it is a molecule thick, whilst, in others, it is much thicker.

When light passes through the oil, some of it is reflected off the different layers of oil, whilst some carries on, and is reflected off the surface of the water lying below. Because the light waves have now travelled different distances before being reflected, they mix, producing a spectrum of colours. As a result, a rainbow-like pattern is shown on the oil surface, and this phenomenon is called thin-film interference.


Why does the sun look red at sunset?

We have all enjoyed the beauty of glorious sunsets when the sun appears to be fiery red and attract all nature lovers. Why is the Sun, which is shiny white at noon, red at sunset? It is because sunlight or what we call ‘white light’ is made up of different colours, each having a different wavelength of a different colour.

During a sunset, the sun’s rays are slanting, and they go through a much longer path in the lower atmosphere. The lower layers of the atmosphere have many more suspended tiny particles called aerosols that are suspended even in the cleanest of air. Aerosols come from many sources like soil, salt from the ocean, plants, and the burning of fossil fuels or chemical air pollutants.

As the lower layers of the atmosphere have more aerosols, their scattering effect is magnified, and more hindrance causes more scattering. This results in more red light being scattered towards you than any other colours and that is why the sun looks bright red at sunset.

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