Why is the Sky Really Blue?
Sky blue color results from air molecules scattering light. Short wavelengths like blues bounce around more, while longer ones such as red can just wiggle through more freely.
Rayleigh scattering was first developed by Lord Rayleigh in 1871.
The Sun
One major contributor to why the sky appears blue is due to sunlight hitting Earth’s atmosphere, where light travels through various layers of gas particles that are smaller than visible light waves – typically oxygen and nitrogen particles but also including water droplets and dust – that scatter or bounce light in different directions, producing the blue hue associated with our sky.
Scientists John Tyndall and Lord Rayleigh first proposed this explanation in 1870’s; later Albert Einstein would further refine and test this theory experimentally.
Daylight hours see the Sun above us, giving off its brightest rays to illuminate the sky. At night, however, its position closer to the horizon means its light takes longer to reach us and may get scattered more often; consequently, nighttime skies tend to appear paler nearer the horizon than during daylight hours.
Also, at night the Sun appears more orangish-yellow due to air molecules scattering its reddish-orange surface more heavily than its blue surface – due to cooler temperatures allowing its blueish-white surface more readily available for light scattering.
Sky is mostly blue because billions and billions of blue light photons have been directed toward us by atmospheric particles, while some light is absorbed by clouds causing it to look white, with any excess being reflected off Earth’s surface and giving the sky its color.
The Earth’s Atmosphere
Sunlight contains various wavelengths, each color representing its own frequency. Lower wavelengths like red and orange light travel further through Earth’s atmosphere than its higher ones like blue or violet light; blue light gets scattered by gaseous particles or molecules in the atmosphere and makes our skies appear bluer; this phenomenon is known as Rayleigh scattering. Molecular airborne molecules (mostly nitrogen and oxygen molecules) tend to scatter these wavelengths more; hence why they make the sky appear so blue!
At ground level, the sky appears blue; as you travel higher into the atmosphere and further away from it, its color becomes paler due to light scattering off particles further away. Likewise, this also explains why the Moon appears black since there is no atmosphere present and light must travel even farther before reaching its surface.
Lakes and oceans appear blue because of a similar effect: when sunlight hits open water, shorter wavelengths absorb by water molecules while longer ones scatter off in all directions.
As soon as you look down upon a lake from space, its blue wavelengths can easily be seen reflecting off of it while other spectrum is being absorbed by its waters. To reveal these hidden blues further and darken the sky more dramatically using a polarizing filter – similar to how ocean looks through glass of water – simply darkening out sky with filter can reveal this hidden blue and uncover hidden details within.
At sunrises and sunsets on Earth, this same effect creates the characteristic blue tint seen around sunrises and sunsets: as Sun rays travel further through Earth’s atmosphere than through outer space, more blue light is scattered away, leaving longer-wavelength redder sunlight to reach our eyes instead. Mars, with no atmosphere whatsoever, does not show this phenomenon at sunset either – though its permanent dust cloud does lend some hint of blue tones to its sky at this time of day.
Blue-Green Microbes
Blue-green microorganisms known as cyanobacteria first emerged two billion years ago in the ocean, performing photosynthesis – the process by which sunlight and carbon dioxide convert into energy with an oxygen byproduct as an extra bonus. Cyanobacteria proliferated through the oceans, pumping oxygen into our atmosphere until its concentration reached what it is now; without them we wouldn’t have our blue skies today!
Sunlight bounces off water’s surface, reflecting back some wavelengths while also absorbing other wavelengths, with longer wavelengths like red absorbed by its molecules while shorter violet wavelengths tend to scatter more, giving the sky its blue tint.
Cyanobacteria have another effect: they produce pigments with shades of blue, violet, green and yellow that emit “structural colors,” responsible for coloring bird feathers, poison dart frog skin and even human eyes. Some structural colors are inherited; while others may be acquired through living organisms to absorb more sunrays and reduce UV damage.
Streptomyces coelicolor bacteria produce an effective antibiotic called psittacofulvin that provides resistance against feather degradation by bird pathogen Bacillus thuringiensis, while another bacteria Pseudomonas aeruginosa produces a phenolic compound known as pyocyanin that kills off rival microbes while helping stabilize cell membranes.
Cyanobacteria produce an array of phenolic compounds that produce every color visible to us – from bright reds and blues that create vivid landscapes to dark greens and purples that give the sky its deep blue hues. These pigments, known as anthocyanins, provide antioxidant protection necessary for their survival in harsh environments.
As we ascend deeper into the atmosphere, the air becomes denser and less transparent; light scattered by molecules has difficulty reaching our eyes directly; this explains why the sky appears paler as we approach its edges.
Sky directly overhead may appear dark blue or even bluish-violet due to reduced air molecules at higher altitudes; only shorter wavelengths of light are scattered by them, leaving most of it to pass through and reflect off of water molecules below.
Water
As sunlight passes through Earth’s atmosphere, it interacts with gases and particles found within. When light strikes these molecules, it scatters in all directions in a process known as Rayleigh scattering; this is what gives sky its characteristic blue hue. Blue photons tend to be scattered more due to shorter wavelengths. Red and green wavelengths tend to travel further into atmosphere where they’re less likely to be scattered by Rayleigh scattering.
Scientists have made great strides in understanding how the atmosphere scatters light, leading to blue skies. Air molecules with more surface area tend to bounce off of one another more easily and scatter light – hence why mountain valley or sea-level environments tend to have more of a blue hue than city skies.
Water can act as an effective filter. It helps filter out harmful UV radiation from the sun while at the same time absorbing some of the scattered light caused by other molecules in the atmosphere – giving bodies of water more vibrant blue skies.
The color of the sky depends heavily on humidity and pollution levels in the air, with humid weather giving rise to deeper blue hues while pollution often tints it grayer or hazier than usual. Yellowstone National Park boasts cerulean skies while cities may exhibit more muted hues like industrious gray or murky twilight hues.
At sunset and sunrise, the horizon of the sky may also appear orange or red due to lower sun positions that require its light to pass through more atmosphere before reaching your eyes. As such, shorter blue wavelengths scatter further, creating space for longer red and orange wavelengths that reach you instead.