The sky is blue due to small molecules in the atmosphere scattering shorter wavelengths more effectively, known as Rayleigh scattering.
As sunlight hits clouds, its light is scattered by larger water droplets or ice crystals which scatter all colors equally so white light remains visible. Light tends to travel upwards or to the sides, creating whiter upper regions than less exposed bases of clouds.
The Sun’s Light
As sunlight passes into our atmosphere, it passes through gases and particles such as gaseseous molecules that scatter it across all directions; shorter wavelengths like blue light are more efficiently scattered back towards their source – hence why sky appears bluer.
When the sun is high in the sky, its rays come into contact with atmosphere at near vertical angles, where their majority encounter air molecules which absorb more of violet and blue light before radiating it away to other directions resulting in our eyes seeing a saturated blue hue that gives midday skies their characteristic appearance.
As the Sun lowers in the sky and its rays are scattered by more of the atmosphere, more long wavelengths such as reds and yellows pass through, giving rise to yellows or even reds being visible as it descends toward sunset or rises at sunrise.
Sunlight contains all colors of the visible spectrum – including white. However, when sunlight hits Earth and interacts with our atmosphere, blue light scatters predominantly and produces a sky that is predominantly blue.
For us to understand this phenomenon, it is necessary to analyze the composition of our atmosphere. This consists primarily of nitrogen, oxygen and water vapor – two gases while water vapor exists as liquid form – with smaller water molecules than gas molecules forming our atmosphere being interacted with more directly and dispersed more easily into space.
Water vapor and air molecules interact to form clouds, composed of droplets or, more commonly, ice crystals that interact with each other to form water droplets or, more commonly, ice crystals. Since these particles are smaller than air molecules and scatter all colors of light equally but blue light more effectively than others – hence why clouds appear white against a blue sky background.
Nitrogen and oxygen react with sunlight in similar ways, forming beautiful clouds of all sizes – from puffy cumulus clouds to wispy cirrus clouds – in every kind of weather condition.
The Earth’s Atmosphere
The Earth’s atmosphere is an enclosed layer of gases surrounding our planet, composed of water vapor, nitrogen, oxygen and other gases. When sunlight hits this atmosphere it refracts through and scatters off these substances creating blue hues due to shorter wavelengths being scattered more efficiently than longer ones.
As sunlight passes through clouds, it interacts with water droplets much larger than atmospheric particles in the sky, and this interaction scatters all colors equally resulting in whiter skies as all their hues are spread around equally by these larger particles in the clouds.
As sunlight passes through clouds, its beams are also refracted upwards or to the sides, creating whiter tops than their bases which receive less light. The same principle holds for vapor-filled clouds known as contrails which is why those clouds often appear white against blue backgrounds.
Cloud bases appear white due to the condensed water that makes up their composition. When water evaporates it forms liquid droplets which float in the air – these liquid drops give clouds their distinctive white hue. When sunlight hits these droplets it gets deflected through Mie scattering as their molecules are much smaller than wavelengths of sunlight, meaning that shorter wavelengths of sunlight are scattered more efficiently by them.
Light reaching smaller particles in the atmosphere is scattered in all directions, leading to its blue-white coloring of skies and clouds we see today. Furthermore, this hue intensifies during sunset and sunrise when Sun nearer to ground and lower density allows more Rayleigh scattering to occur allowing more blue light absorption while other visible colors scatter freely leaving more or less intact visible colors intact, explaining why skies tend to appear blue at these times and clouds are usually whiter during these hours.
Water Droplets
Sky color results from light reflecting off molecules in the atmosphere through Rayleigh scattering, named for physicist Lord Rayleigh. Shorter wavelength forms of light such as blue are more likely to get scattered by these tiny gas molecules in our atmosphere compared to longer waves such as red and orange due to them having smaller wavelengths than visible light waves.
Water droplets are tiny clumps of vapor suspended in the atmosphere that resemble mist, fog, smog or clouds. Although often mistaken for such things as mist or fog, these droplets actually resemble tiny dust particles with two hydrogen atoms bound together with one oxygen molecule and held in place by atmospheric pressure (the same force which keeps you sitting securely when sitting up).
As sunlight passes through a cloud, it interacts with its water droplets. Since water molecules are larger than individual atoms and molecules that make up atmospheric gases, they scatter light evenly across all colors, giving the sky its blue appearance. A similar process takes place inside rain clouds; however, their larger droplets disperse less light efficiently so reducing how much light reaches their base and making the cloud appear grayer.
Large clouds can absorb all of the sunlight reaching them and appear white; however, most clouds do not tend to be very large.
Gray clouds near the ground and producing precipitation (rain) are most frequently seen at night, while white ones in the upper atmosphere typically hovering at heights above 16,500 feet – commercial planes fly between 30,000-45,000 feet for reference – are known as cirrus, cirrostratus, altocumulus and nimbostratus while cumulus stratocumulus and nimbostratus form when moist air rises and condenses before cooling and becoming saturated with water vapor before precipitation begins forming precipitation.
The Tyndall Effect
As light passes through Earth’s atmosphere, it scatters in all directions by colliding with gas molecules. Shorter wavelengths such as blue and violet tend to scatter more than longer ones like red and yellow – giving the sky its characteristic hue of blue – this process known as Rayleigh Scattering.
Sunlight hitting water droplets or ice crystals in clouds is scattered evenly in all directions due to being much larger particles than atmospheric ones that make up our sky. When an atmosphere molecule is exposed to light, its electric fields temporarily polarize it by pushing electrons towards one direction – however when exposed to another color of light the electrons scatter randomly once again due to resonance from within its internal structure with light waves entering.
However, water droplets and ice crystals are so large that their vibrations don’t coincide. As a result, all colors of sunlight are distributed equally across the sky, giving it its distinctive hue.
The Tyndall Effect was named for Irish physicist John Tyndall. It’s a type of Rayleigh scattering which occurs when light passes through small drops of liquid, where its refraction process slows down, allowing molecules in water to interact with it more directly, thus enabling certain wavelengths of light emitted from clouds to be absorbed and then reflected back out again by them.
This phenomenon explains why laser beams can be seen through fog, milk appears white and clouds at sunrise and sunset appear yellow or orange-hued – due to sunlight passing through more of the atmosphere, which causes more blue light to scatter from clouds allowing more red and yellow hues through to reach earth, giving rise to their unique orange/red coloration.