This article was first published by The Conversation. Space.com's Expert voices: Op-Ed and Insights was contributed by the publication.
Professor in Astronomy at Nottingham Trent University, Daniel Brown
According to Dulux, the color 2022 will be "bright sky," according to the paint manufacturer.
This light, mellow blue might be familiar to you. You might see a similar hue depending on the time of day and where you are looking.
But take some time to look at the sky, from the horizon to the expanse in front of you, in all weather conditions and from dawn until night, and you'll be amazed at the variety of colors it contains. Over the hundreds of years, physicists worked to discover why the sky has so many colors, including a multitude of blues, reds, and even greens. This is what we have learned and what you should be aware of when gazing at the sky and contemplating "bright skies".
Related: The 'Ring of fire,' solar eclipse wows skywatchers. (Photos).
Comparison of Dulux color Bright Skies against a blue sky with little water vapor near the horizon (left) and a cloudier, which indicates higher levels (right). Image credit to Daniel Brown, Author supplied
Different electromagnetic waves make up the sun's radiation, each associated with a different colour. Blue waves are shorter, yellow waves slightly longer, and red waves even longer.
These waves look white when they are viewed together. This light must travel through the atmosphere before reaching our eyes. Atmospheric molecules are smaller than the wavelength of sunlight's light. These molecules scatter the light in different directions as it hits them. Rayleigh scattering is the name for this effect.
This causes more of the bluer, shorter wavelength light to be scattered and makes the sky appear blue everywhere you look. The sun's light is no longer able to emit the longer wavelengths of blue, so it becomes yellower.
The sky can be seen directly from the Deer Shelter Skyscape installation, which James Turrell created at the Yorkshire Sculpture Park. (Image credit: Daniel Brown)
The daytime sky may not be the same color as the night. Dulux bright skies are more common closer to the horizon. This is because the blue is lighter or washed out more.
This is Mie scattering. It is similar to Rayleigh scattering, but is caused by larger particles (e.g water vapor or small particles of pollution). These particles are able to remove the blue, yellow, and red color components of a white beam of light in equal amounts and they do not affect the color of light passing through the atmosphere. Rayleigh scattering can also cause the sky to turn whiter.
The influence of white in the sky's blues becomes stronger towards the horizon, where the light must pass through more of Earth’s atmosphere before reaching the observer. Nature's visualisation of the current atmosphere is formed by the various shades and tones of blue that are observed. The more particles present, the whiter it will appear.
Horace Bndict De Saussure (18th-century Swiss geologist and alpine explorer) developed a tool that can measure how many particles are suspended in a sky. It is also known as a cyanometer and it allows the observer to see the sky in 53 colors.
Modern version of the cyanometer. (Image credit: Daniel Brown)
Twilight ozone blue
Skywatching at dusk will reveal a spectacular display of color. It captures intense red tones, especially in the direction of the setting Sun. Rayleigh scattering means that the evening sun travels through more of the atmosphere than the sun's afternoon light. This can make the aerosols more colorful and extended if they are higher up in our atmosphere, such as volcanic eruptions.
The sky will turn a bright blue once the sun has sunk below the horizon. Rayleigh and Mie scattering cannot explain this phenomenon. This is because of the presence ozone, a colorless or pale-blue gas that absorbs light and then breaks it down.
The sun's rays must pass through more atmosphere in order to reach us. This is often the case when it travels beyond the horizon. The ozone absorbs the red and orange light from the sun, making the little amount we see in the twilight skies blue.
Night of red and blue-green
If you venture out at night, in a location free from light pollution and its orange glow, you may notice that the night sky isn't black despite not having any sunlight. Sometimes, however, you can see what is known as air glow. This is because our atmosphere emits a faint light. This is due to the formation of atoms mostly oxygen and nitrogen at altitudes between 60 and 190 miles (100-300 kilometers).
Although this glow is always visible, it is usually too faint to be seen. It can make the sky a dark red or green color. It can be captured with cameras more sensitive than the eyes. Our eyes see only a greyish blackness at low light levels.
These colors show us how light interacts with our atmosphere. Through this science, we have also learned how to detect and analyze the light from other planets. In 2001, the first measurements of atmospheric traces were made for HD 209458b (sometimes called Osiris in the constellation Pegasus). Scientists discovered water traces in the atmosphere of an exoplanet (K2-18b) in 2019, which has temperatures that could support our current understanding of life.
This article was republished by The Conversation under Creative Commons. You can read the original article.
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