The sky appears blue due to sunlight being scattered by gases and particles in the atmosphere, with blue wavelengths being scattered more readily than any other.
At midday, when the sun is directly overhead, its light appears white. But during sunrise and sunset when more of its rays must travel through atmosphere layers to reach us, more blue-violet light gets scattered and becomes red instead of being concentrated onto one surface of our eyeballs.
Air is not completely transparent
The sky is not completely transparent, taking on some color from gases and particles in our atmosphere. When sunlight hits Earth’s atmosphere it interacts with these particles and scatters all around. Blue wavelengths scatter more easily than others so the sky tends to appear bluer than its red counterpart.
That is why the sky appears different on different days. The color depends on factors like dust, pollution and water vapor in the atmosphere – factors which often produce blue skies during the day but which then turn red at sunset and orange during sunrise.
Sunlight consists of multiple wavelengths, which when seen collectively are perceived by humans as white light. But when reaching Earth’s atmosphere, these different wavelengths become scattered differently by gases and particles in our atmosphere – shorter wavelengths such as blue and violet are scattered more readily while longer ones such as red and yellow ones scatter less easily; hence why the sky looks blue during daytime. And for sunset and sunrise this means red skies appear red or orange depending on their lengths of exposure to air molecules in our atmosphere.
Though our eyes can detect all the colors that comprise white light, our brains interpret its wavelengths differently. For instance, red wavelengths tend to be perceived by our minds as extremely vibrant colors while blue ones may seem muted compared with what’s seen with our eyes; hence why sky can seem pink or grey on some days and green or violet on others when lit bright white.
As the sun travels low in the sky at sunset or sunrise, its path must pass through an even thicker layer of atmospheric pressure than when overhead. This causes many more blue wavelengths to get scattered away than at other times allowing red and orange wavelengths through and creating vivid shades seen by our eyes.
Blue light is scattered more than other colors
The blue hue of the sky can be explained by air molecules scattering sunlight. Light with shorter wavelengths (such as blue), is more vulnerable to scattering by these molecules than longer wavelengths such as red. As more blue wavelengths appear in sunlight, its reflection creates an overall blue tint in the sky.
Sir John Rayleigh first described this phenomenon, known as Rayleigh Scattering, in 1870. Sunlight traveling through the atmosphere passes through gases like oxygen and nitrogen – much smaller molecules than visible light wavelength – that serve as candidates for Rayleigh scattering. As soon as sunlight hits these gas molecules it scatters all over. Our eyes tend to respond more favorably towards blue than violet wavelengths; as such this process makes the light appear bluer.
However, this effect can occur with any color of light hitting a gaseous substance – hence why looking through a prism reveals an array of colors. Furthermore, dust, pollen or other particles in the air may have similar wavelengths of light that act upon their colors, altering their hue as well.
One key contributor to the blue color of the sky is water vapor in the atmosphere absorbing light and scattering blue and green wavelengths; water vapor absorbs red- and infrared-bound wavelengths while scattering other wavelengths, explaining why clear days appear slightly less blue than cloudy ones.
As the sun gets lower in the sky at sunset and sunrise, more of its radiation must pass through our atmosphere before reaching our eyes – meaning shorter blue wavelengths scatter more easily while warmer colors (such as orange and red hues ) pass more readily; hence why the sky appears red at these times of day.
Blue light is refracted more than other colors
As sunlight travels from Earth’s atmosphere into its atmosphere, it passes through an array of gases and particles in the air that act like molecules to scatter or bend the light in various ways, often favoring blue and violet wavelengths due to being easier for air molecules to scatter than longer wavelengths such as red or yellow; this effect creates the impression that our sky looks blue during the daytime hours.
Furthermore, our eyes are extremely sensitive to blue hues; and because the Sun emits more energy in this part of its spectrum. As such, even without any further emittance by our star, a bright sky would still appear due to enough blue wavelengths being dispersed by natural means.
This characteristic blue hue of the sky is further amplified by water droplets floating through the air reflecting blue light more efficiently than any other wavelength, lending it its signature hue. However, other factors can alter its hue, such as pollution or the presence of haze or dust particles.
On a clear day, the blue of the sky is created by Rayleigh scattering. When the sun rises or sets it must travel further through a denser lower atmosphere full of dust particles; as it passes over these particle clouds more of its blue and violet wavelengths are scattered by our eyes than when directly overhead resulting in yellower (or even greenish) sunrays reaching us.
Cloudy days diminish the intensity of the sky’s blue, as water droplets scatter only so much light before reflecting it back to our eyes and its reflection off of clouds causes our eyes to perceive a darker shade of blue.
Blue light is absorbed more than other colors
As light passes through Earth’s atmosphere it encounters gas molecules which scatter its light rays; blue wavelengths are more affected than other colors by this scattering process and thus make up much of what we perceive to be blue skies during daylight hours. Violet and red wavelengths remain more consistent as they continue their journey directly toward your eyes.
At sunset and sunrise, sunlight must pass through a thicker portion of the atmosphere than during daylight hours, scattering more short blue wavelengths that then allow longer red and orange wavelengths to reach our eyes and transform the sky from blue to orange or even red depending on where the Sun lies in relation to horizon. As such, these events produce beautiful orange-red skyscapes.
Remembering this fact will keep the oceans looking their blue hue regardless of air pollution levels, rather than due to water absorbent properties. Sunlight hitting an open body of water reflects predominantly in blue and ultraviolet wavelengths, while violet and indigo wavelengths absorb by it and this creates the color we associate with seas and oceans.
The ocean can appear green in places due to the presence of plant life or sediment from rivers and streams that has washed into it, as yellow pigments present in plants or sediment absorb some blue lightwaves while only red and orange wavelengths reflect back to our eyes.
Additionally, blue and violet wavelengths absorbed by water molecules are directed into higher energy states rather than reflecting back down towards Earth, producing an ocean’s characteristic greenish-blue color.
The Earth’s atmosphere does not absorb all blue and violet wavelengths, which allows us to still see stars and other objects at night. When combined with other properties mentioned earlier, this gives the sky its distinctive whitish-blue appearance during the day; at night however, however, our atmosphere becomes almost completely transparent so that we can see celestial objects not lit by sunlight.