Blue skies are something most of us take for granted. But its color could change dramatically throughout history Thierryand scientists say he can do it again.
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According to Finn Berridge, science communicator at the Royal Greenwich Observatory (UK), there are two main factors that make the sky blue on a sunny day.
“The first is the Sun,” he explains. “Normal sunlight is white, meaning it contains all the colors of the rainbow: red, yellow, green, and blue.”
The second is the composition of the atmosphere. The sky contains many tiny particles, such as nitrogen, as well as oxygen and water vapor, which scatter light in all directions, Burridge explains.
Blue light has a shorter wavelength than most other colors and spreads out more, filling the sky with blue.
This process is known as Rayleigh scattering after Lord Rayleigh, the British physicist who developed the theory in the 1870s.
At sunrise and sunset, sunlight must pass through much more of the atmosphere because the Sun is lower in the sky. Blue light is scattered so much that it bounces away from us. This allows less scattered reds and oranges to reach our eyes, creating the beautiful sky we see.
The sky on Mars is usually candy yellow during the day and turns bluer near the Sun during sunrise and sunset.
Earth’s bright blue sky is unique in the solar system, says Burridge.
Although some planets, such as Jupiter, are believed to have a faint blue upper atmosphere similar to Earth’s, it is much less bright.
Being farther from the Sun, Jupiter only gets about 4% of the sunlight we get here, “so it doesn’t have the intense and beautiful blue skies we have on Earth,” explains the promoter.
On some planets, the story is quite different.
Mars has a thin atmosphere, so Rayleigh scattering is rare. Instead, its many dust particles, which are larger than the nitrogen and oxygen in our atmosphere, scatter the light in different ways.
This is called Mi scattering and results in a red or yellowish sky with blue sunsets.
The blue sky that we know today on Earth is a relatively recent phenomenon in the long history of the planet.
Although there is no way to know exactly what the sky looked like in the past, scientists believe that its color may have fluctuated depending on the gases that were present in the atmosphere at the time.
When the Earth formed about 4.5 billion years ago, its surface was largely molten.
One theory states that the early atmosphere, as the planet cooled, consisted mostly of gases from volcanic eruptions and other geological activity, such as carbon dioxide, nitrogen and small amounts of methane, with very little oxygen.
Graphics showing young Earth in orange, today’s blue planet in green and blue, and future Earth in white and yellow.
Over time, life appeared on Earth in the form of ancient bacteria, which added a large amount of methane to the atmosphere. The light shining on this methane turned it into more complex organic compounds that produced an orange haze in the sky, similar to the air pollution in some cities today.
A major change occurred about 2.4 billion years ago with the Great Oxidation Event, when the first organisms called cyanobacteria began to use photosynthesis to convert sunlight into energy, releasing large amounts of oxygen in the process.
Oxygen began to accumulate in the atmosphere until it reached significant levels, finally dispersing the methane clouds. As the modern atmosphere formed, the sky took on the blue color it has today.
In the short term, the blue sky of the Earth will not disappear. Although pollution, wildfires, volcanic eruptions, and dust storms can temporarily change the color of the sky, these effects are short-lived.
After the huge eruption of Krakatoa volcano in Indonesia in 1883, spectacular red and even green sunsets and blue moons were observed, which are believed to be caused by particles such as sulfates and ash in the atmosphere that scatter light in a different way than we are used to.
Claire Ryder, associate professor of meteorology at the University of Reading in the UK, says the overall color effect of aerosols (solid or semi-solid particles in the atmosphere) may depend on their relative sizes.
“We tend to get very strong coloring effects, especially at dusk, when the aerosol particles are all the same size,” he says, because they enhance dispersion in the same way.
Particles in the air caused by pollution can turn the sky white.
“If there is a range of particle sizes, each different-sized particle will interact differently with different wavelengths, creating a mixture of colors,” he explains. When produced at the same time, they can combine, creating a whitish or brown haze. Sometimes this can happen with volcanic eruptions or dust storms, as well as with air pollution.
She says it’s worth considering how climate change might affect the color of our skies in the future.
“As temperatures rise, we’ll release more water vapor into the atmosphere,” he suggests, “which could allow aerosol particles to swell with moisture, increasing their dissipative power and sky-whitening effect.”
“On the contrary, if emissions of pollutants are reduced in the future, we may have bluer skies,” he notes.
But all these changes may not matter much on an astronomical time scale.
For a lasting change in the color of our sky, we would need a dramatic change in the composition of our atmosphere, says Burridge.
“Nothing of this magnitude is going to happen anytime soon unless we have a huge meteorite,” he suggests, “but that probably won’t happen.”
He estimates that it will take at least 1 billion years before the sky is no longer blue.
In about 5 billion years, our Sun will become a red giant star like this one.
As the Sun ages, its brightness will gradually increase. In about 1 billion years, it will emit about 10% more light than it does today, Burridge says.
“This will warm the Earth, pull carbon dioxide out of the atmosphere and eventually start to evaporate our oceans.”
This would probably release a lot of oxygen into the atmosphere and even make the sky a deeper blue for a short time.
But once that oxygen is gone, Burridge says, the sky will change to a “white, yellowish, very hot, more Venus-like atmosphere.”
Even further into the future – about 5 billion years from now – the Sun will begin to run out of fuel and turn into a red giant.
“As time runs out on Earth, the first ingredient, which was the blue light from the Sun, will be lost,” says Burridge.
“When the Sun starts to die and swell into this huge, very, very red star, the atmosphere we have left on Earth will take on a really crimson hue.”
“There won’t be enough people left to see it,” says Burridge. “I hope people have gone to the stars in search of another blue sky.”
