As sunlight passes through the atmosphere, its energy becomes scattered by air molecules – this scattering effect being especially evident for blue light.
As such, very little of the direct blue light of the sun reaches your eyes directly, leading to pale skies as you climb higher into the atmosphere.
Sunlight
As the Sun shines upon Earth, its light passes through our atmosphere, where gas molecules scatter or bend its light rays – which gives sky its hue; blue-tinged wavelengths tend to get scattered more strongly than other hues, leaving behind a blueish tint in our surroundings.
Scientists had long recognized that the Sun produced blue light, yet were uncertain as to its source. John Tyndall and Lord Rayleigh proposed that particles in the air such as dust or moisture reflected sunlight back to create the blue hue we see around us today.
When sunlight interacts with these particles, its longer wavelengths such as red and orange light are absorbed by them while shorter blue and violet wavelengths are scattered back in your direction of sight by Rayleigh Scattering; this effect gives sky its characteristic hue.
Water molecules absorb blue and violet light efficiently, and scatter any shorter wavelengths, including reds and oranges, across its surface in such a way as to appear white in our eyes.
As the Sun passes lower in the sky during a day, more of its light passes through our atmosphere and scatters with greater strength than when higher up. This creates a predominantly blue-ish sky at the horizon while closer to the Sun this increases to more pink and orange hues.
Mars has an array of colors with less blue than Earth due to the different temperatures of its atmospheric gases and their ability to absorb and scatter light differently, giving each planet its own distinctive palette of hues. Astronomers are currently exploring why even though the Moon doesn’t have an atmosphere it seems yellow when full.
Atmosphere
Earth’s atmosphere is filled with gases and particles that scatter or absorb light, giving its signature color its distinctive hue. Blue and violet light wavelengths in particular tend to resonate off these particles more strongly, creating Rayleigh scattering which gives sky its distinctive color; longer wavelengths such as red, orange and yellow light pass through unaffected.
The hues of the sky can change depending on time of day and weather conditions, from deep blue during sunrise and sunset, through grey to pink during sunrise/sunset times and purple during twilights – as sunlight travels further through its path through the atmosphere, this could result in unexpected hues being revealed.
Light passing through the atmosphere is scattered in all directions, but higher frequency colors such as blue and violet have more energy-rich wavelengths that disperse more readily than lower frequency colors like red or orange; this gives the sky its characteristic hue.
Light is also diffused by atmospheric particles larger than its wavelengths, such as water droplets and dust, that absorb red- and orange-tinged wavelengths, thus allowing blue and violet wavelengths more freely through.
Air molecules consist of nitrogen and oxygen molecules; while nitrogen is transparent to light, oxygen absorbs it and contributes to giving the sky its blue hue.
At midday, the sky is typically blue due to Rayleigh scattering; but in the evening or at dawn when the Sun is lower in the sky, its reflection causes red horizons due to Mie scattering. This occurs because light that travels farther through atmosphere is scattered more widely than light from further away from Sun.
The Moon lacks an atmosphere, making its surface appear black day or night. Yet on Mars the sky doesn’t appear black; instead it has a thin atmosphere similar to that of the Moon; since light can’t interact with gas molecules directly it doesn’t become scattered, giving rise to what appears as blackness on this world.
Rayleigh Scattering
Lord Rayleigh proposed the theory that our skies appear blue as a result of how sunlight interacts with our atmosphere. Light can bounce off mediums through scattering; usually shorter wavelengths (blue and violet) tend to be scattered more than longer ones like red light, leading to their signature color becoming apparent in our skies.
However, atoms and molecules present in our air are much larger than the short blue and violet wavelengths produced by sunlight, meaning they are less likely to scatter – leaving longer wavelengths, like yellow and red light, uninterrupted through to reach us; our eyes interpret this mix of reflected red and yellow wavelengths as a blue-tinted sky.
Further complicating matters, airborne particles differ significantly in properties from water particles, leading to Mie Scattering: an unusual form of scattering where larger particles behave more like refractors than scatterers and produce what appears to be changing colors from moment to moment. Rayleigh Scattering takes place when smaller particles than light wavelength pass by at high velocity; Mie Scattering occurs when larger ones pass at low speed resulting in moments where sky colors seem to shift continuously.
At noontime during a clear and bright daytime sky, sunlight often passes close to the ground where atmospheric particles are concentrated, where shorter blue and violet wavelengths have already been dispersed before they even reach our eyes. As a result, most shorter blue wavelengths have already dissipated from reaching us, leaving behind mostly yellow-red skies.
As the Sun begins to set, its angle changes and atmospheric density becomes less dense, leading to more Rayleigh scattering and shorter blue and violet wavelengths being scattered further, creating an evening sky that appears bluer. To minimize exposure during these hours, avoid outdoor activities in this period if possible; otherwise be sure to wear eye protection if required.
Reflection
Light is reflected off objects found in our everyday environment to reveal all of the colors of the rainbow, each having their own wavelength, frequency and energy level – violet has the shortest wavelength and highest frequency while red boasts longer wavelength and lowest energy.
Rayleigh Scattering occurs when sunlight passes through Earth’s atmosphere and scatters on gas molecules, creating the sky’s characteristic blue hue. Blue wavelengths tend to scatter more than other colors, giving rise to an illusion that the sky appears bluer.
This phenomenon, commonly referred to as the Tyndall effect, accounts for the blue hue seen across many aspects of nature – from fish eyes and water surface reflection to gem stones such as sapphires and rubies. Sir John Tyndall first studied light scattering back in 1859 when first investigating this form of light scattering.
If you shine a white beam of light into a clear liquid with particles suspended within it, its blue wavelengths will scatter more strongly than red ones – just as happens with sunlight passing through the atmosphere towards reaching our eyes.
Rayleigh scattering helps explain why the sky becomes bluer at sunset and sunrise, when the Sun has to pass through more atmosphere; more blue wavelengths get scattered away by this process and don’t reach our eyes as easily.
Similar to when the Sun is high in the sky, when its light reaches your eyes it has less chance to penetrate before dissipating into space, leading to reddish hues resulting in reduced exposure for your eyes.
Are you curious to understand more about why the sky is blue and other natural phenomena? Look no further than Tappity Meteorologist’s fun, interactive lessons for kids! This app is an excellent way to introduce young ones to science while encouraging them to ask questions about what’s going on around them – this way you can help foster curiosity about our world while stimulating young minds with its wealth of scientific topics such as solar system, weather & climate, ecology etc.