Ask any child what color the sky is and they are likely to say blue – however a clear midday sky doesn’t always appear so hued.
As sunlight enters our atmosphere, it passes through gases such as nitrogen and oxygen that scatter light of all colors; blue light being spread far more than violet or red hues.
Rayleigh Scattering
Light that interacts with our atmosphere becomes scattered like billiard balls colliding, and this phenomenon is called Rayleigh Scattering. Named for Lord Rayleigh who first described it in 1870, Rayleigh scattering works by redirecting light’s momentum and wavelength away from ground-bound locations to upward or sideways ones; shorter wavelengths tend towards groundbound locations while longer ones get scattered upward or sideways – this means blue wavelengths tend to hit your eyes directly while violet or red wavelengths get directed upward or sidewards or sides of our field of vision – thus giving blue wavelengths an advantage over longer ones when trying to hit each other – just like hitting each other billiard balls would do when encountering resistance – or as in our atmosphere! One form of scattering called Rayleigh Scattering first described this way back in 1870 by Lord Rayleigh who first described this type of scattering which works by redirecting momentum and wavelength direction: Lord Rayleigh described this method first described it first described it; its name after its creator Lord Rayleigh who first described this method back then in 1870! Rayleigh scattering works by redirecting momentum and wavelength direction by alteration: shorter wavelengths more likely towards ground; longer ones more likely towards upwards or sides redirected upwards or sides thereby meaning blue wavelengths get directed into your field of vision while violet/red wavelengths get scattered upwards or sides of field of vision! This way light gets scattered by changing momentum/wavelength reorienting it at 1870! This means blue lights get directed towards ground while violet/red wavelengths will first described the process. It works similarly.
Light entering your eye from any point in the sky is composed of all wavelengths; your brain interprets this mixture based on what proportion of blue and violet wavelengths reach your eye (and how sensitive your eye is to them).
Eyes are generally most sensitive to wavelengths between 400-700nm, with blue wavelengths being the ones we react best to – thus explaining why the sky appears blue despite more violet and red wavelengths entering the atmosphere.
However, the intensity of blue and violet wavelengths reaching your eyes varies with altitude. As you ascend into the atmosphere, concentration of molecules that scatter light declines; this means light becomes less saturated with blue as molecules disperse it further afield; as a result, skies appear paler and whiter as you ascend higher into space.
As you lower in altitude, more blue wavelengths enter your eyes. Furthermore, as blue and violet wavelengths decrease in proportion in the air, your eyes become stimulated more strongly by red and green wavelengths which become increasingly frequent; hence your retinal receptors respond with even greater force to them.
If all colors were distributed uniformly across our sky, it would appear white. Luckily, however, other particles in our atmosphere act as scatterers that give it its characteristic hue; dust and aerosols act like scatterers by dispersing light wavelengths more or less equally across their size spectrums, dispersing all colors more or less equally across its spectrum.
Mie Scattering
Mie scattering differs from Rayleigh scattering by taking advantage of electromagnetic waves colliding with spherical particles; their size and refractive index both impact how light is scattered; these factors also determine coloration effects as well as power distribution. Mie scattering formulas are quite complex; nevertheless, its basic principles can be summarized as follows.
Scattering functions (m,x) measure the ratio between particle refractive index and background media refractive index, where dimensions do not apply, such as media refractive index. They can be identified continuously over angles from 0deg to 180deg by integrating.
As light travels through the atmosphere, it becomes scattered in all directions and may take on different hues depending on its wavelength – that’s why the sky appears blue nearer the horizon but redder farther out, with higher elevations featuring more molecules to reflect off and spread the light than at lower levels.
Scattering occurs due to our eyes being comprised of three types of color-sensitive cones and monochromatic rods that send signals back to our brain to form colors; with blue being the predominant hue, our eyes naturally perceive blue hues.
All gases are Mie scatterers and would produce a clear blue sky if they did not absorb radiation (and consequently reduce in size), however certain gaseous components (like chlorine or nitrogen dioxide ) can absorb light and create a colored sky. Furthermore, dust and aerosol can scatter light adding another color – such as on Mars which has high dust concentrations that add another shade.
All this scattering explains why you cannot see the Sun directly overhead: too long has passed for its blue light to reach you from beyond the horizon. Additionally, this phenomenon accounts for why sunset and sunrise appear red instead of blue as short wavelengths of violet are more likely to be scattered than long wavelengths of blue.
Clouds
As sunlight enters Earth’s atmosphere, gaseous and particulate matter scatter it. Blue light waves are scattered most strongly due to gases and particles in the atmosphere; thus creating the blue hue seen in our skies. Other colors including red are scattered as well, although less strongly.
The same process explains how clouds make the sky appear blue: when water vapor condenses into clouds, their blue-tinged reflection reflects more strongly than any other part of its spectrum, while other wavelengths scatter less and are absorbed. As a result, when looking up from below or viewing sunsets respectively, sky appears bluer.
Apart from blue wavelengths, other parts of the visible spectrum are also scattered by atmospheric conditions and thus make up part of its composition and temperature. Therefore, sky can appear different colors depending on what composition and temperature are found therein.
Scientists have studied how atmospheric conditions impact the color of the sky over time, finding that volcanoes often create an atmosphere rich with more small molecules that turn the skies bluer during an eruption.
Humidity also plays an influential role in shaping the hue of the sky, as water vapour in the atmosphere tends to condense when exposed to moisture, making the atmosphere appear muggy and making sunlight difficult to reach its target destinations. If there’s more water present, more humidity will likely result from its presence and cause it to feel muggy – leading to darker skies overall and harder sunlight reaching earth’s surface.
Overcast skies often appear grey due to large water droplets in clouds which soak up most of the light, creating an appearance similar to darkness.
When you spot clouds in the sky, try pointing your thumb towards it to observe their shape. A cloud that’s smaller than your thumb could be classified as a puffy wisp known as a cirrus cloud, while ones larger may be tower-like cumulus clouds with an anvil shape or tower shape cumulus clouds. Furthermore, categorization by altitude also works; low clouds near ground level or near troposphere level should be categorize as such while higher ones would sit above it all.
Dust
Viewed from Earth, the sky appears blue due to Rayleigh and Mie scattering; however, this effect is only possible because there’s so much air in our atmosphere; without air there would be more red tint than blue in its hue; hence why tropical countries or bushfire-ridden regions typically show less blue in their skies due to damp conditions with high levels of particulate matter such as dust or pollution reducing its overall illumination.
As sunlight enters the atmosphere, its presence becomes much more dispersed due to different wavelengths being different sizes. Violet light has an extremely short wavelength with high frequency and energy output which allows it to hit nitrogen and oxygen molecules more readily and bounce off them quickly.
Contrarily, blue light waves are larger than molecules of nitrogen and oxygen in air molecules; thus causing them to get scattered out across space so quickly you can no longer detect them. Red and yellow waves, on the other hand, tend to scatter much less easily by air molecules; hence why sky looks blue from earthly views while appearing reddish when seen from space.
Planetary atmospheres also influence the color of their skies, such as Mars with its dusty atmosphere; photos taken by Mars rovers show its sky is salmon-colored. Venus features thicker carbon dioxide and nitrogen layers than Earth, creating darker skies that appear more yellow.
Air on Earth is never completely clean; it is always polluted with microparticles of various sizes that range from skin cells shed by you and your loved ones, pollen, dirt, road grime and road dust blown about by wind currents. Luckily, most particles smaller than wavelengths of visible light are scattering blue wavelengths more effectively, so that when looking directly up at a clear sky or when viewing from mountains or airplanes the sky appears darker nearer the horizon than it does looking straight up.