BLUE skies are something that people are used to seeing, particularly during the summer months in the UK.
Here, we look at the reasons why the sky appears this colour, and what other shades it can appear.
Why is the sky blue?
The reason the sky is blue is because of the way that light reacts with the Earth's atmosphere.
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.
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Light travels as waves of energy, which are scattered all over the place when the sunlight separates.
It appears blue because blue light scatters more than any other colour on the spectrum.
The sky appears white when the sun is high in the sky, 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 is common for the sky to appear in different colours, such as red, yellow or pink.
However, sometimes the sky will appear in some more unusual colours, which may be confusing to some.
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.
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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.
There have even been instances of the sky appearing in shades of purple and lilac.
In 2018, purple skies were seen across the UK during sunrise.
This was attributed to low pressure systems moving in from the Atlantic ocean.
Is the sky blue on other planets?
Other planets in the solar system have a different atmosphere to Earth's, meaning the sky would be a different colour.
This is because light reacts with other atmospheres differently.
For example, the atmosphere on Mars is a lot thinner than the Earth's one.
It has an atmospheric volume less that one per cent than what is found on Earth.
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."
