EVER looked up on a clear day and thought to yourself, "why is the sky blue?" Why not green or hot pink?
The answer is simple(ish) science, but it may not be quite what you'd expect.
Why is the sky blue?
The sky appears to be blue due to the way that light interacts with Earth.
As sunlight strikes gas particles in the atmosphere, the light separates into all the colours of the rainbow.
This effect is known as Rayleigh scattering, which is named after the man who discovered it, Lord Rayleigh.
Light travels as waves of energy, which are scattered all over the place when the sunlight separates.
The sky is blue because blue light waves scatter more than other colours.
When the Sun is high in the sky, it appears white, which is its true colour.
We see a much redder Sun at sunrise and sunset.
This is because sunlight passes through a thicker layer of our atmosphere, scattering green and blue light as it goes.
Redder light is allowed to pass through and illuminate the clouds in a stunning array of red, orange, and pink.
Why does the sky turn yellow or orange?
It's fairly common to see the sky turn different shades of red or pink.
But sometimes the sky can be more unusual colours, and it can be quite disquieting if you haven't seen it before, and don't know what it is.
In March 2022, dust clouds turned the skyline of the capital orange, and left a rust-covered film on cars.
It was caused by Saharan dust, carried by strong winds that propel it to high altitudes.
The dust can then travel worldwide, as far as the UK.
It's fairly common in the UK, and occurs when Saharan dust storms meet with southerly wind patterns, according to Met Office.
But though it looks beautiful, it can be dangerous to health of some people.
Dust storms are a source of natural particles, including very small materials, potential allergens, and pollutants.
These can be dangerous for people who have lung conditions such as asthma and other allergies.
Other times the sky will appear yellow.
A striking example of this is when the sun appears blood red, while the sky appears to be yellow.
According to the Met Office, sunsets are often red or orange because they're lower in the sky, so sunlight has to move through a thicker layer of the atmosphere before it is scattered, deflected, and seen by human eyes, and we see perceive longer wavelength red and yellow light.
Is the sky blue on other planets?
Other planets don’t have an atmosphere like ours and so their skies would look different.
On Mars, for instance, the atmosphere is about one per cent the thickness of Earth's.
As a result, light wouldn't scatter as much as it does on our planet.
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According to the Royal Museums Greenwich website: "We might expect Mars to have a very faint blue coloured sky, but due to the haze of dust that remains suspended in the air, the daytime sky on Mars appears more yellow.
"This is because the larger dust particles absorb the short wavelength blue light and scatter the remaining colours to give a butterscotch hue over the Martian sky."
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