As sunlight passes through Earth’s atmosphere, its light is scattered by gases and particles – particularly blue wavelengths which tend to be dispersed more efficiently than other colors resulting in beams with bluish tints.
Scientists had difficulty pinpointing why the sky appears blue. Its color can be explained by how small molecules scatter sunlight.
Sunlight
Sunlight contains an amalgamation of all colors of the rainbow; combined they make white light. As sunlight passes through Earth’s atmosphere it gets scattered a bit by air molecules; violet waves get scattered more than others due to Rayleigh scattering; this process causes sky areas to look whitish-blue; however red and yellow light wavelengths tend to get scattered less rapidly, meaning when direct sunlight reaches your eyes it has a slight blue tint.
This same effect explains the blue haze you see when looking up at mountains or viewing a forest fire sky: air particles smaller than wavelengths of blue light scatter it more than red and yellow wavelengths, giving off its characteristic hue. But standing next to someone covered with this blue hue wouldn’t show as tinted blue due to your eye not picking up their color so strongly.
This phenomenon also helps explain why sunrise and sunset skies appear to be whiter; since sunlight passes more quickly through the atmosphere during these times than during normal daytime conditions, more time for blue Rayleigh scattering to take place and give rise to its signature effect of creating white hues in the atmosphere.
Mie scattering is another process responsible for making the sky appear white; it occurs when sunlight hits clouds or dust particles in the atmosphere and scatters in ways not as obvious as Rayleigh scattering, allowing shorter red and yellow wavelengths to reach your eyes more effectively; making the sun seem oranger than it would without clouds or Mie scattering.
Atmosphere
Light is scattered when it strikes molecules in the air, making the sky appear blue but sometimes grey or white at times. This phenomenon, called Rayleigh Scattering after Lord Rayleigh who first observed it in 1870, creates what’s known as Rayleigh Scattering; his model demonstrated this phenomenon by showing how when more minute particles like oxygen and nitrogen molecules were involved, more blue and violet light was scattered than longer wavelengths such as red and green light rays; but when there is more particulate matter like dust, smoke or water vapor this effect lessened, leaving a more uniformly blue sky all year round.
Clear and sunny days usually result in beautiful, blue skies; however, when there’s fog or haze it may turn grey near the horizon due to air not having enough small water droplets to scatter light and give it its characteristic hue.
Scientists are currently conducting studies to establish how much the sky might lighten if we implement one of the controversial geoengineering techniques being considered to combat global warming, such as spewing sulfur dioxide into the atmosphere to lower solar radiation reaching Earth and spew it down onto its surface. If implemented on a grand scale this would diminish sunlight reaching our planet’s surface and potentially turn its once brilliant blue skies white in hue.
Note that, while ozone is beneficial in protecting us from UV rays, it also absorbs longer red and orange wavelengths of sunlight that could otherwise be overpowered by Rayleigh scattering and cause the sky to appear darker in tone.
Clouds
What determines whether or not the sky appears blue depends on the size of particles that scatter light. On clear days, small airborne molecules scatter short wavelength light more efficiently than longer wavelength forms like red, yellow and green rays to give the sky its characteristic hue of blue.
But as explorers climbed ever higher into the mountains, they noticed that as they reached the horizon the sky gradually faded from blue to white – an observation which puzzled scientists for centuries until Lord Rayleigh used a prism to demonstrate that sunlight passing through our atmosphere scatters into different colors.
Sunlight contains all of the visible colors of the rainbow: violet, indigo, blue, yellow, orange and red. Each of these hues has a specific electromagnetic wavelength length range between 300 nanometers to 700 nanometers – shorter wavelengths have more energy which is absorbed by atmosphere while longer ones scatter widely causing sky to appear bluer.
Clouds can transform a once blue sky into one that appears whiter, when light passes through and interacts with large droplets that scatter visible wavelengths evenly, giving off a white appearance to the sky.
Volcanic eruptions or dust storms, on the other hand, can disperse sunlight into many different colors. When near the horizon, this phenomenon is called Mie scattering; larger particles in the air like smoke and dust tend to scatter red light more efficiently than other wavelengths; hence why sunsets often have yellow or orange hues and why Edvard Munch’s The Scream has that unnerving red tint.
Mie Scattering
We love the blue of our skies because of light scattering. Tiny particles like nitrogen and oxygen molecules in the atmosphere scatter light at short wavelengths, creating what’s known as Rayleigh scattering; longer wavelengths such as red and green do not get dispersed as easily.
So it can seem gray or white depending on where and conditions one lives, while its hue depends on pollution levels and humidity; when air quality is very dry, its bluer shades appear stronger while in humid weather they might have lighter tones of blue hues.
Mie scattering can create the appearance of white skies on bright and sunny days. This phenomenon occurs when clouds contain water droplets or vapor (fog-like conditions). As sunlight passes through these particles, they effectively scatter all wavelengths equally to give an appearance of white light – this explains why clouds and mist may look white during bright sunshine days.
Mountain vistas often display a band of white near the horizon due to mountain haze forming from gases emitted by vegetation that react with ozone in the air and form fine particles 200 nanometers wide that scatter blue light. Forest fires, volcanic eruptions or other natural or man-made events may contribute to its creation; otherwise it can form naturally or due to atmospheric conditions anywhere. This type of whiteness is commonly referred to as “blue haze.”
Rayleigh Scattering
As sunlight penetrates into the atmosphere, it interacts with tiny particles of nitrogen and oxygen molecules much smaller than visible light wavelengths – providing ideal conditions for Rayleigh scattering to disperse light evenly across space, producing white light illumination. Shorter wavelengths like blue are scattered more effectively than longer ones such as red; hence generating blue skies as seen below.
However, the sky doesn’t just remain blue due to weather alone – its colors also change depending on season and time of day; at sunset for instance, due to dust accumulation in the atmosphere it may appear more orange or red than usual.
As the Sun moves lower in the sky, more atmosphere passes between it and your eyes – meaning more blue and violet light are scattered away, leaving only redder tones to reach our eyes.
Mie Scattering also contributes to the appearance of blue skies, occurring when sunlight reflects off clouds and atmospheric particles and causes them to appear white while also giving the surrounding sky its blue hues.
One of the primary determinants of sky color is cloud size and composition, particularly small cloud types which tend to appear whiter, while larger clouds often take on a blue tint due to their greater light-scattering abilities than their smaller counterparts – which explains why sky bluer hues appear nearer the horizon as there are less clouds directly overhead.