Sky color can be determined by various factors; however, all this starts with visible light physics.
As sunlight travels through Earth’s atmosphere, its light is scattered by nitrogen and oxygen molecules – with blue wavelengths being particularly dispersed, making the sky appear bluer than it would otherwise.
Rayleigh Scattering
The sky is blue because light from the sun passes through our atmosphere and gets scattered, mostly by molecules in the air. Blue parts of the spectrum tend to be more strongly scattered than red and violet due to being smaller than visible wavelengths; this process is known as Rayleigh Scattering after Lord Rayleigh who discovered it back in 1870’s.
Our eyes are more attuned to the blue spectrum than any other, due to our brains misinterpreting scattered light from air as blue sky even when the sun is low in the sky, leading to blue skies being visible at its zenith and red skies near its horizon during sunrise or sunset.
Light can also be scattered in other directions depending on the size and density of scattering particles, with closer-in scattering causing it to appear redder than diffuse scattering. Rayleigh Scattering is one of the primary forms of scattering found in our atmosphere.
As well as Rayleigh scattering, other processes can also change the hue of the sky. Dust and aerosols in particular can change its hue; their main constituents being water vapor and nitrogen; however other gases like chlorine and nitrogen dioxide also linger within our atmospheres.
These other gases don’t contain air molecules and so their smaller sizes allow them to scatter all colors more or less equally (known as Mie scattering). This results in either a blue or gray sky.
Air composition varies with altitude, latitude, season and weather conditions; Rayleigh-Mie scattering plays the primary role in creating its characteristic hue of sky color; other contributing factors could be cloud cover, solar radiation levels and their color as well as density/refractive index variations due to temperature shifts which also contribute to its hue.
Atmosphere
The atmosphere is the thin layer of air extending from Earth into space and filled with gases, dust particles and other chemical compounds that interact with light. From space, its constituent gases appear blue while from Earth-level it appears black – this difference occurs because molecules in the atmosphere scatter shorter wavelengths such as blue and violet more efficiently while absorb and scatter longer wavelengths more weakly; multiple scattering events give sky its color.
Light entering the atmosphere is scattered by gas molecules (mainly nitrogen and oxygen) in the troposphere, where its wavelength exceeds that of visible light wavelength. As these gas molecules are much smaller than visible wavelengths of light, only part of it can be scattered away – this process is known as Rayleigh Scattering and one reason why the sky appears blue.
As light travels upward through the atmosphere, it reaches the stratosphere, which contains fewer gas molecules and less turbulence than lower layers. This layer is generally calm, stretching about 30 miles above Earth. Planes often fly here – which helps explain Australia’s pleasant weather!
Clouds or dust in the air appear white because their particles are larger than wavelengths of light. On the other hand, mountainous areas are known for their blue hazes created by air containing terpenes which react with ozone to form aerosols which produce particles small enough to scatter blue light.
Have you noticed how the sky seems brightest overhead before gradually dimming into pale yellow or red near the horizon? This is due to light from the Sun (or Moon) passing through various atmospheric layers on its way towards reaching Earth, meaning more blue and green wavelengths (shorter wavelengths) get scattered before reaching it while red and orange ones (longer) do reach it.
Why the sky is blue is a multifactorial explanation that includes many variables including chemistry, humidity, temperature and even cloud cover. At its core though, our eyes interpret signals sent from our brains to our senses and interpret these as blue or otherwise.
Clouds
Blue skies can often signal clear weather, but they can also be caused by clouds. Clouds form when water vapor and other gases collide in the air to form dense masses that form layers or clusters, with stratus clouds usually consisting of thin grey layers while cumulus clouds tend to form puffy formations with white tips; cumulus clouds form puffy piles while cirrus are delicate white structures while nimbus clouds produce rain or hailstorms.
The sky’s color varies with light being scattered and refracted through its clouds and also depending on time of day; for instance, during sunset and sunrise it may look red while throughout the rest of the day it remains blue due to refracted and scattered sunlight traveling farther into atmosphere before reaching our eyes, leading it to refracted more in directions away from them compared with red or orange light from sun; shorter wavelengths like blue and violet light from sun are scattered more due to increased sensitivity from our eyes towards blue light from sun than longer wavelengths like red or orange as our eyes are more sensitive towards blue light as sun puts out more blue light than other colors from its sun-powered sunrays than other colors from its light source;
Light scattering by dust and pollution in the atmosphere can also have a dramatic impact on the color of the sky, turning it grey in some cases. Therefore, it is crucial that industrial and urban areas strive towards air purification to achieve clarity of vision.
People used to think the sky was blue because it reflected Earth’s oceans; this theory proved inaccurate; instead, oxygen plays a critical role. Over two billion years ago, blue-green microbes called cyanobacteria emerged in seawater and began pumping large amounts of oxygen into the atmosphere, providing foundation for all plants which convert carbon dioxide and sunlight into energy while producing additional amounts of oxygen as byproducts through photosynthesis; photosynthesis is responsible for most of today’s atmospheric oxygen.
Latitude
Latitude is an angular measurement that measures the distance from Earth’s equator to any particular point on its surface, measured in degrees, minutes and seconds. Used together with longitude lines (also called meridians) it forms a grid system for describing locations on our planet’s surface.
As we move away from the equator, our atmosphere becomes thicker and smoggier, meaning less sunlight reaches our eyes – decreasing blue light dominance while our eyes perceive what remains as neutral white sunlight.
Our planet’s blue hue can also be traced back to our atmosphere being rich with oxygen. Over two billion years ago, blue-green microbes called cyanobacteria formed in ocean waters and performed an extraordinary feat: they converted sunlight into oxygen through photosynthesis – thus raising temperature while increasing water vapor content of our atmosphere as a result of photosynthesis-generated extra oxygen production.
Due to less atmospheric gases and dust particles scattering blue wavelengths of sunlight, they’re able to travel further before being absorbed and reflected back into our eyes – so the sky appears blue during the daytime and red at sunrise and sunset.
Noteworthy is the difference in color of Mars sky to that on Earth due to a different atmosphere that lacks water vapor, thus having less of an effect on light absorption and scattering.
Lines of latitude, also referred to as parallels, run parallel with both the equator and each other. Longitude lines mark them at their intersection at each pole on Earth – the Tropic of Cancer is situated 23 degrees 26 minutes 21 seconds north of the Equator while Capricorn sits 23 degrees 26 minutes 27 seconds south – one degree of latitude covers approximately 111 kilometers while one minute equals 60 seconds.