Many people mistakenly believe that the sky’s color comes from reflecting off of oceans; this may partially be true but more accurately the sky takes its blue hue from long wavelengths of light absorbed by water bodies.
Water molecules absorb reds, oranges and yellows more readily while reflecting back blue wavelengths onto surfaces that then direct these shorter wavelengths toward your eyes.
Rayleigh Scattering
The sky’s hue can be explained by light scattering by gas molecules in the atmosphere – an effect known as Rayleigh scattering – which occurs under cloudless conditions. Rayleigh scattering is an elastic form of scattering wherein scattered light reflects and diffracts in all directions equally, while intensity depends on an inverse of wavelength multiplied by four (i.e. violet/blue wavelengths are more likely to be scattered than red-hued wavelengths, hence making the sky appear bluer).
John William Strutt, 3rd Baron Rayleigh first observed this phenomenon in 1870s London. He observed that when sunlight hits air molecules it is scattered, with this amount depending on its wavelength. Light is most likely scattered by molecules smaller than visible light’s wavelength such as nitrogen or oxygen in air; due to their small size they absorb or scatter photon energy easily without losing much energy, leading to visible light being scattered by them more than by larger particles such as atoms and molecules.
Rayleigh Scattering is also one of the key reasons that oceans and lakes appear blue when seen from above. When sunlight enters water bodies, molecules absorb longer wavelengths such as red rather than reflecting shorter blue wavelengths – this selective scattering leads to what we commonly perceive as blue water when seen from above.
Not the only cause, but a major one, for why the sea appears blue is sunlight interact with water molecules to cause their color change – hence why even on cloudy days the ocean seems so vibrantly blue from above. Many assume that its color comes solely from reflecting light from above but this explanation falls short; part of its hue can come from reflection; but most of its hue is caused by interaction of sunlight with molecules of water which make up its bulk of this colour change; thus leading people to believe this theory.
Water Absorption
The ocean doesn’t reflect its surroundings in order to appear blue; instead it does so due to how water absorbs and scatters light. Water molecules are better at absorbing long wavelengths like reds, oranges and yellows while shorter wavelengths such as blue and violet tend to get scattered by particles within it; similarly why we see sky as blue – these wavelengths tend to scatter easily than others.
Additionally, particles in the water – such as salt or debris from dead sea animals – cause additional scattering of blue wavelengths, making the surface appear blue even when the sun shines directly upon it. This means that most of its visible spectrum gets reflected back out into space instead of reflecting directly back onto it – creating the appearance of an ocean surface as blue as ever.
But the sea is not an unadulterated body of water – it contains various substances dissolved within it such as sand and mud which absorb light, leading to less blue hues as you explore deeper into its depths.
One other cause is that ocean surfaces contain lots of phytoplankton that contain chlorophyll pigments, which absorb blue and green wavelengths of sunlight while reflecting only red and purple ones back out into space. Phytoplankton tend to take on green hues from this, though they will occasionally also reflect back blue wavelengths when sunlight passes through them.
If you were walking on the Moon, the sky wouldn’t appear blue because it doesn’t contain an atmosphere to give the illusion of blueness. On Earth however, our atmosphere – including oxygen from breathing – makes the sky seem bluer.
At its core, what causes red skies over deserts, forests, and ice is reflection off surfaces; while blue light is being absorbed and scattered by Earth’s atmosphere. Overall, our atmosphere appears blue due to absorbing long wavelengths of red and orange light while scattering violet wavelengths around.
Sunlight Reflection
The sky’s blue color can be seen reflecting in the ocean surface, yet this does not account for all its blueness. When seen from low angles, water appears grayish rather than blue due to not absorbing all of the light hitting it; instead it only reflects about 6% back at us.
Water molecules vibrate best with blue light wavelengths than longer-wavelength wavelengths like red or orange light; as a result, any light that hits it gets scattered, giving water its characteristic blue color.
Have you ever noticed how the ocean seems to glitter when neared at sunset or sunrise? This phenomenon occurs due to sunlight striking water surface and being scattered, particularly nearer the horizon where shorter blue wavelengths tend to get scattered more than longer red ones; leaving behind more red and yellow to reach our eyes and creating those characteristic orange and red hues in the sky.
As well as this, the surface of the ocean contains both organic material and sediments from rivers that drain into it, both of which fall within an optimal size range for scattering blue light efficiently. Furthermore, phytoplankton (algae) living on its surface contain chlorophyll pigments that absorb blue light strongly; this phenomenon predominantly impacts shallow waters where most phytoplankton live; however it doesn’t impact deeper waters where more of it exists.
Due to this phenomenon, the ocean typically appears dark blue near deep water depths while lighter hues near continents. This gradient becomes especially noticeable during calm winds and waves conditions; during stormy conditions however, storm-generated winds and currents often stir up sediment that settles at the bottom of the sea bed resulting in milky-brown waters due to wind-driven currents stirring up sediment deposited there from previous storms.
The sky appears blue because its color is determined by water properties and absorption and scattering of blue, violet and red wavelengths by air molecules – this process accounts for most of the illumination seen above ground.
Cloud Cover
The blueness of the sky doesn’t originate with ocean currents or waves; rather, it comes from how sunlight scatters through atmosphere due to gases and particles present therein. Blue light wavelengths tend to get scattered more than red and yellow wavelengths due to this Rayleigh Scattering effect – meaning more blue light gets scattered when there are less clouds present and vice versa! So that explains why more open skies appear bluer.
The ocean’s iconically deep blue hue derives from water molecules in seawater selectively scattering blue wavelengths of sunlight more than other colors, further enhanced by reflection from skylight onto its surface. Variations in water clarity, depth and viewing conditions can alter which shade of blue we perceive by our eyes.
As sunlight penetrates our planet’s atmosphere, it is reflected back out in all directions by gas molecules present. Due to a thicker atmosphere at lower altitudes, longer wavelengths pass more easily through than shorter ones, creating uniform sky colors across Earth.
However, short wavelengths of blue light tend to be reflected back more strongly due to molecules acting as effective Rayleigh scatterers than other gases such as helium or nitrogen in the atmosphere.
On a sunny, clear day with pleasant weather conditions, the sky often appears blue even if the ocean appears green or brown. Furthermore, reflecting off of water surfaces gives them a deeper hue than they would without this effect.
Why does the sky appear yellow or red at sunrise or sunset? When the Sun is low near the horizon, its light has to travel further through the atmosphere before reaching our eyes – this causes shorter wavelengths such as blue and green to be scattered more than they would at higher altitudes, giving longer wavelengths like red and orange more of an opportunity to reach our vision.