People commonly associate blue with feelings of openness, stability and order – no wonder it has become so popular for corporate logos and apparel!
When sunlight strikes the atmosphere, its wavelengths disperse in all directions – more efficiently for shorter wavelengths such as violet and blue which gives the sky its distinctive hue.
The Sun
Light is scattered off particles in the air, reflecting and scattering off of them in order to bend (or “shift”) its wavelengths, changing its hue in ways which cause an object’s original hue to change significantly – for instance, sunlight from the Sun appears white; when reaching Earth’s atmosphere it turns blue because shorter wavelengths get scattered more than longer ones.
The Sun is an immense ball of hydrogen and helium gases, along with minor amounts of oxygen and carbon. Its surface, known as the Photosphere, consists of an extremely thin layer of plasma hot enough to produce light as well as other forms of electromagnetic radiation; this ionized layer scatters blue and violet light – the reason for why sky looks blue!
As sunlight passes through our atmosphere it passes through several layers of gases before reaching our eyes. When sunlight reaches Earth it travels through many more layers before being scattered by air molecules – mostly nitrogen and oxygen molecules – before finally arriving in your eyes. Red and yellow wavelengths tend to be absorbed more easily while blue/violet waves scatter more easily, giving us our beautiful blue-toned skies.
John Tyndall was the first person to understand why the sky is blue, discovering in 1859 that light passing through a clear fluid with small particles suspended within it scatters more light of short wavelengths (blues) than long red wavelengths (reds). Experiments could include shining white light through tank filled with water mixed with milk or soap for experimentation purposes – from side views it will appear blue while from front it would become redder in appearance.
At sunset, as the Sun decreases in height in the sky, its light must travel through an atmosphere thicker and deeper than during noon when directly overhead. This requires its rays of light to pass through more oblique angles before traveling further through gases and dust particles before eventually emerging as less blue and more red hues; hence why it appears reddish orange.
The Earth’s Atmosphere
As sunlight passes through our planet’s atmosphere, it is dispersed by gases in our air – this process is known as Rayleigh scattering after English scientist Lord Rayleigh. Light with shorter wavelengths like blue and violet is more likely to be scattered by gases than longer-wavelength light such as red and orange; consequently most sunlight reaching your eyes will likely be blue-tinged in hue.
When the sun is near the horizon, its light has to traverse more atmospheric layers than when directly overhead, meaning its blue light has more time to be scattered and dim. The same holds true during sunrise or sunset when its illumination travels across even wider reaches of our atmosphere.
As the sun’s rays pass through our atmosphere they reflect off water molecules, dust particles, and smog particles – reflecting them back at us through water bodies such as rivers or oceans, giving our skies their blue hue. However, our skies also appear blue because gases such as nitrogen and oxygen contain molecules with smaller radius than wavelengths of visible light and selectively scatter blue light which leaves other wavelengths unaffected by scattering.
Atmospheric gases absorb ultraviolet radiation from the Sun, helping protect our skin from its potentially damaging UV rays.
If the Earth’s atmosphere contained less gases and particles, our skies would likely appear darker and less blue. But it’s important to keep in mind that other factors impact its hue, such as water vapor, air pollutants, chemical pollutants and how our eyes respond to light.
Our brains interpret signals coming from our eyes’ three types of color-detecting cones and monochromatic rods to give us our sense of color, with our perception of blue being an especially well-studied example of how this process interacts. Blue provides one of the more complex examples of how our visual system operates; studying it helps us gain a better understanding of how we see the world around us.
The Moon
When sunlight hits Earth’s atmosphere, some shorter wavelengths are depleted as more powerfully scattered by dust and water molecules, creating bluer-than-redr rays which give us our impression of blue skies.
Scattering occurs most strongly near the ground, explaining why the sky appears lighter near horizon than directly overhead. As one ascends into higher atmosphere, however, light becomes diffused less by particles that scatter it and eventually turns darker in hue as more particles scatter it back out again.
Pollution and water vapor can alter the color of the sky by absorbing and reflecting specific wavelengths of light, such as those produced by pollution and climate change. Mars, for instance, features a permanent layer of dust which gives its skies their signature butterscotch hue – this same haze also causes it to appear redder when setting or rising into view.
Tyndall and Rayleigh made the initial attempt in the nineteenth century to explain why the sky is blue. Their theory suggested that its hue could be caused by small particles of dust and droplets of water, yet such particles are relatively rare and so this theory was later abandoned; Einstein later demonstrated that sky color is determined primarily by absorption and scattering of photons by nitrogen and oxygen molecules in the atmosphere.
An additional factor is how strongly each color responds to our eye receptors: red cones are stimulated less strongly than their blue counterparts and even green cones more so, giving rise to our perception that the sky is blue while actually consisting primarily of reddish-orange light.
Farmer’s Almanac started calling the second full Moon in each month a “Blue Moon,” a tradition which continues today. Contrary to popular belief, this term does not refer to calendar dates or lunar phases but instead refers solely to when such rare phenomena occurs – for instance volcanic ash/smoke, water droplets in the air or certain forms of clouds can all play their parts.
Solar Eclipses
Sunlight passes through Earth’s atmosphere and is scattered by molecules and particles, mostly made up of oxygen-containing molecules and particles, that determine its hues mainly via short wavelength (blue and violet) light waves that reach our atmosphere more often than longer ones (red, orange and yellow) that do. As our eyes have an inherent preference for blue, the sky appears bluer.
As you ascend into the atmosphere, scattering decreases and sky color lightens as more particles than wavelengths of visible light are scattered away by scattering particles much smaller than visible light wavelengths. Lord Rayleigh developed the formula that describes how intensity of scattered light depends upon wavelength – scattering being greater for shorter wavelengths while decreasing for longer ones.
At a solar eclipse, the Moon blocks out the Sun and transforms day into night, providing us with an amazing chance to view its corona as a bright red ring of red. If you have never witnessed one, we highly suggest experiencing one firsthand; its breathtaking spectacle will leave you speechless.
Solar eclipses occur due to the unique alignment between Sun, Moon, and Earth. There are only a few conditions necessary for an eclipse to take place: firstly the Sun and Moon need to be in direct line, while secondly it needs to be exactly between Sun and Earth – failing either of these criteria you won’t see the solar eclipse!
As we’ve previously observed, the Sun emits a broad spectrum of light with various hues. When sunlight passes through our atmosphere and is filtered by gases and particles, its wavelengths are affected more by short wavelengths being scattered more than long ones causing the sky to appear bluer than normal. Solar eclipses change this effect because sun’s rays strike it at less oblique angles which allows more of its shorter wavelengths through to our eyes than during normal days.