Viewed from above sea level, the sky takes on an even darker blue color as more blue wavelengths get scattered through the atmosphere than other hues.
Rayleigh scattering, which affects all gases smaller than light wavelengths, plays a part.
Light Wavelengths
Sunlight contains all of the colors of the rainbow – including blue – which make up its spectrum, which then gets scattered in our atmosphere to form what we know as sky. As light enters our atmosphere, it interacts with gases such as oxygen and nitrogen; their molecules are much smaller than visible light wavelengths and so easily scatter its waves, known as Rayleigh scattering after Lord Rayleigh first discovered this effect in 1871. According to Rayleigh’s observations, scattering amounts are directly proportional to fourth power of wavelength; meaning shorter wavelengths (such as blue) are more easily scattered than longer ones such as red.
As light travels through the atmosphere, it becomes polarized by interactions with dust or water droplets. Since some of this light is drawn towards oxygen molecules and scattered heavily in one direction, contributing to what gives Earth’s sky its signature blue hue.
Violet and blue wavelengths of light (the shorter ones) are also more effective at scattering due to being more sensitive to their environment; this explains why the sky appears blue at ground level while darker blue hues dominate at higher elevations where sunlight has further to travel through the atmosphere.
Other factors can impact the intensity of Rayleigh scattering, such as atmospheric density and dust or pollution levels. Such conditions can also have an effect on sky appearance; when there are an excessive number of clouds or haze it can make the sky appear muggy or gray.
Sky colors change when the sun nears either horizon or setting, as this requires sunlight to travel farther through the atmosphere and therefore magnify Rayleigh scattering, meaning less violet and blue light from the sun reaches our eyes resulting in darker skies at sunset or sunrise than during other parts of the day.
Atmospheric Molecules
Air molecules in our environment are much smaller than visible light wavelengths, so they scatter sunlight more effectively than larger parts of the atmosphere – this phenomenon is known as Rayleigh scattering and it accounts for why our skies appear blue.
What gives our sky its blue hue is due to shorter wavelengths such as blue and violet being dispersed more heavily than longer red and orange wavelengths; we perceive more blue wavelengths due to being closer to what our eyes respond most readily to.
But this is only half of the story. Atmospheric conditions at sunset can have a huge effect on the color of the sky; due to dust and water vapor concentrations affecting Rayleigh scattering.
When the sun is low in the sky and there is an abundance of dust or water vapor in the atmosphere, its color appears darker than usual as less light is scattered by small particles, thus less blue light reaches us directly.
When the sun is high in the sky and there is very little dust or water vapor present, light scattering by smaller particles in the atmosphere increases and more blue light reaches us.
Both effects can be traced back to one root cause – the size ratio between atmospheric particles and wavelengths of light that they scatter. When this ratio is equal, no change occurs and sky remains blue.
At certain times of day, the sky can appear white because near the horizon the path of sunlight through the atmosphere is 10 times longer than overhead and its photons scatter more often, resulting in reds and greens becoming as intense as blues – creating the effect that when added together they yield white.
Light Attenuation
As light travels through the atmosphere it is scattered by air molecules (mainly nitrogen and oxygen ). This process, known as Rayleigh scattering, is responsible for giving sky its blue hue. Light waves coming from the Sun must travel through a lot of atmosphere before reaching you, making their wavelength weaker; blue wavelengths tend to be scattered more often than longer ones such as red or yellow ones.
John Tyndall and Lord Rayleigh discovered that scattering efficiency depends on an inverse fourth power of wavelength: S(lambda)(lambda)4. This indicates that shorter-wavelength violet and blue light is much more strongly scattered than longer wavelengths, rendering short wavelengths much less bright. Rayleigh scattering accounts for much of the sky’s beautiful blue color; though other causes also contribute such as dust particles or aerosols may partially obstruct it.
Sunlight contains several other colors, such as yellow and red, that do not experience Rayleigh scattering; instead they experience Mie scattering; this occurs when various atoms and molecules in the atmosphere scatter light at specific frequencies or polarisations – creating an effect similar to that of a prism that divides its spectrum into its component colours.
Rayleigh and Mie scattering can have a wide-ranging impact, altering not just blue parts of the spectrum but all wavelengths to some extent, producing blue skies even though the Sun produces white light.
This explanation for Earth’s blue sky can also apply to any planet with an atmosphere, including other solar systems such as Mars or Venus. Other planets’ skies may appear slightly different due to variations in composition of gases as well as concentration of small particles such as dust or water droplets – these factors all influence sky colors significantly and often contribute to stunning sunsets on other worlds.
Rayleigh Scattering
Light from the Sun interacts with molecules in Earth’s atmosphere and light rays are scattered all directions by molecules. Blue and violet wavelengths tend to be scattered more intensely than other colors – giving the sky its distinctive blue hue. Understanding why blue wavelengths scatter more strongly is crucial to correctly interpreting its appearance and color.
Light traveling through the atmosphere passes through gases such as nitrogen and oxygen; their particles are much smaller than visible light wavelengths and ideal candidates for Rayleigh scattering. As light rays pass through gas molecules, they are randomly scattered in all directions – this process is known as Rayleigh scattering after 19th century British physicist Lord Rayleigh who pioneered its use.
Scattering intensity decreases as a fourth power of wavelength; longer wavelengths are therefore more likely to pass unimpeded through atmospheric layers.
Refracting light by means of diffraction, sunlight scattering by atmospheric molecules is also affected by its direction; for example, it’s strongest near Earth’s surface while weakest at its edge.
Scattering depends on a range of factors, including atmospheric density and composition as well as particle count; for instance, an atmosphere containing large amounts of dust, pollution or water vapor could result in reddish hues due to scattering.
Polarization is another factor influencing scattering; its intensity depends on atmospheric molecules’ angular momentum and rotational energy, and can best be observed with blue light which tends to be polarized forwards.
Blue wavelengths of sunlight are scattered more strongly than other wavelengths, leading to them making up most of the visible light that we perceive. But this does not explain why sunset and sunrise skies appear bluer – instead, this phenomenon results from sunlight travelling ten times further through the atmosphere than it would do directly overhead; this long path results in sky becoming much whiter nearer the horizon due to no longer depending on Rayleigh scattering for illumination.