One of the first questions children often pose to themselves about why the sky is blue is “Why does it have color?”. While this question might seem complicated at first, the answer can actually be quite straightforward and easily found online.
Sky filled with air has tiny gas particles called air molecules – we know these as air. Air molecules happen to be just the right size to allow all colors of light besides blue through. When light hits an air molecule it gets scattered like ping-pong; this process is known as Rayleigh Scattering.
Light Scattering in the Atmosphere
Light traveling through the atmosphere is absorbed and scattered by particles, giving rise to its blue hue. Air molecules (mostly nitrogen and oxygen) are the primary culprits responsible for scattering this sunlight; however dust particles, ozone and volcanic ash also play a part in dispersing it.
Sunlight may appear white, but its composition consists of all the colors of the rainbow – red, orange, yellow, green, blue, indigo and violet. When passing through transparent materials such as water, its path bends and changes direction due to refraction – which allows separate wavelengths from within its visible spectrum to travel at different speeds through it.
The wavelengths of light scattered in an atmosphere depend upon both particle size and medium properties. Nitrogen and oxygen molecules are much smaller than visible light wavelengths, so they are very effective at scattering short-wavelength light (blue and violet), but not long wavelength light (red).
Light scattered by these microscopic particles will be scattered into many directions, leading to dimmed illuminations that look different depending on where they reflect off surfaces and appear dimmer. Furthermore, as our eyes are more sensitive to blue hues than red, the diminished illuminations appear slightly bluer than they would otherwise.
Other wavelengths of sunlight are less readily scattered by our atmosphere and appear dimmer, thus explaining why the sky appears blue during the day but red at sunrise and sunset.
At dawn and dusk, the colors appear different because sun rays travel further through the atmosphere obliquely than at other times of year – this means longer wavelengths such as red and orange are more efficiently scattered than blue and violet light. As dawn and dusk occur nearer Earth’s surface than elsewhere during the year when more solar radiation reaches ground level resulting in deeper blue hues appearing in the sky at these times; when sunlight hits higher into the sky this reverse effect takes place; less radiation reaches it then leaves less sunlight reaching ground level resulting in lighter blue skies during these times of year resulting in darker skies overall.
Rayleigh Scattering
Rayleigh scattering is the phenomenon responsible for giving the sky its signature color: when light hits tiny particles in the atmosphere and bounces off them in different directions. These molecules consist primarily of nitrogen and oxygen molecules; its energy depends on wavelength; longer wavelengths like red light are more intensely scattered. Therefore, on a sunny day the scattered light appears blue-tinged.
John Tyndall first noted this effect, later named for Lord Rayleigh who further studied it. Atmospheric molecules tend to scatter 400- to 700 nanometer light (blue and violet wavelengths) more than shorter wavelengths; our eyes being particularly sensitive to blues makes the sky seem always blue!
During the daytime hours, sun rays strike the atmosphere at an angle that ensures maximum Rayleigh scattering. At sunrise and sunset however, as the sun gets lower nearer the horizon these rays must travel further through the atmosphere before hitting their mark; as they do so they refract through denser parts nearer to earth where their original paths take less efficient turns in being dispersed; eventually reaching their original destinations more directly.
Sunrise and sunset sunrays interact more intensely with water vapor and atmospheric gases than during midday, leading to even more effective Rayleigh scattering and less blue and violet frequencies reaching our eyes.
Red and yellow light rays, which our eyes can easily identify, can be distinguished. Sunrise and sunset appear with more vibrant orange- and red-tinged rays compared to midday’s relatively dim blue-tinged sunlight rays.
Scattered blue light is also polarized, giving the sky a deeper shade of blue when seen through sunglasses with polarizing filters. Furthermore, the intensity of scattered light decreases with increasing distance from its source – further adding depth to its hue as you move further away from it.
The Sun’s Rays
As soon as the Sun rises or sets at night, its rays begin lighting the atmosphere. Light passing through an atmosphere is then scattered by molecules in the air that refract or bend different wavelengths of light; shorter blue wavelengths tend to be scattered more frequently than longer red ones and this explains why we see skies that tend toward blue colors.
When white sunlight shines through a prism, its different wavelengths of light travel at slightly different speeds through it – just as when sunlight hits molecules in our atmosphere but with much denser molecules than those found in a prism. Refraction of light through these air molecules is much less dramatic due to their greater density compared to prisms.
As soon as you step out into a field in the middle of the day, you’re likely to notice that the sky looks bluer. This is due to how Sun rays travel higher up into the atmosphere almost vertically and consequently less of the shorter blue wavelengths are scattered and they reach our eyes more readily than their longer red counterparts.
At sunset and sunrise, the Sun’s rays must pass through more atmosphere than normal during their journey from Sun to earth. This lengthy passage causes more blue and violet wavelengths to scatter while shorter red wavelengths pass more easily – contributing their distinct hue to an incredible sunset or sunrise!
Your may have heard some incorrect explanations for why the sky is blue, such as reflecting ocean waves or having an oxygen tint. But in truth, the sky appears blue most of the time for three reasons: our Sun emits light of various wavelengths that scatter through Earth’s atmosphere at different rates; eyes are more sensitive to shorter blue wavelengths; these three factors work in combination to give the illusion that the sky looks blue most of the time.
The Sun’s Position in the Sky
As soon as sunlight hits an atmosphere, its light becomes scattered in all directions, often more strongly at the blue end of the spectrum than other colors – leading to what we know today as blue skies. The Sun moves throughout each day and year along its orbit around celestial sphere that intersects with Earth’s rotation axis; this apparent motion gives rise to sunrise/sunset/moonset events as well as depending on an observer’s geographic latitude.
As it passes through more atmosphere nearer the horizon, the Sun appears lower in the sky nearer its location. As more sunrays pass through our atmosphere and get scattered off by particles like carbon dioxide and nitrogen molecules, less blue light makes its way through into our eyes – this effect becomes most apparent during a solar eclipse when its disk appears to turn deep red in color.
At noon, the Sun shines at its brightest. Depending on your latitude, its rays may also rise over an eastern or western horizon and set somewhere around sunset or sunrise – this time period is known as civil, nautical or astronomical twilight.
Sunlight may appear colorless, but that isn’t entirely accurate. Light contains different wavelengths that collectively add up to the net white hue we perceive when looking at objects. When sunlight hits our eye from these various wavelengths it appears blue because our brain interprets it as coming from above us.
Sky Blue, as we perceive it in our minds, evokes feelings of peace and relaxation. Therefore, Sky Blue makes an excellent hue to incorporate into interior designs in rooms such as bedrooms, kitchens and bathrooms. Sky Blue encourages creative thought while simultaneously encouraging focus in the present moment – which explains why its use often occurs within rooms intended for meditation or relaxation purposes.