Why the Sky is Blue and Sunsets Are Red

Color is more than simply one hue; understanding their interactions is crucial for creating presentations and selecting a color palette for projects.

Tyndall and Rayleigh believed that the blue color of the sky must be due to microscopic particles of dust or droplets of water vapour in the atmosphere.

Blue Light

Light from the sun enters Earth’s atmosphere and is scattered by air molecules, with shorter wavelengths like blue, green, and violet becoming dispersed more than longer wavelengths such as red, yellow and orange rays – thus creating the familiar scene of blue skies during daytime and reddish hues at sunset.

The color of the sky depends on how much light is scattered by air molecules and the colors it contains, along with water molecules. This scattering explains why water appears blue-tinged as well as contributing to gem stone opalescence or bird wings (known as Tyndall effect).

Blue light has the shortest wavelengths on the electromagnetic spectrum and transmits less energy than other colors, reflecting less than other hues; therefore, its reflection makes up most of what we perceive during daylight hours as blue skies. But depending on where we view it from in the sky, we might perceive more or less blue depending on where we stand in relation to its source; at horizon levels it seems bluer since sunlight passes through more atmospheric layers before dissipating as it would above it.

This happens because atmospheric molecules resonate at frequencies more in tune with blue light waves than with any of its counterparts, which causes more blue light waves to be scattered and noticeable than others. When this happens, electrons in molecules become attached faster to blue light wavelengths than it can be absorbed or reflected, leading to its scattering more than expected and giving this wave its unique hue.

As the sun goes down in the sky, light must pass through more and more atmosphere, leading to blue light becoming further scattered while other colors (reds and yellows) pass more easily – this explains why the night sky appears less blue and more white at night, or reddish during a sunset.

As the sun descends lower into the sky, more atmospheric molecules push and pull against its path and spread blue light more freely across it, dispersing more rapidly and scattering other colors more diffusely. This causes blue light to be scattered more widely while filtering out some others.

Rayleigh Scattering

As light from the Sun travels through Earth’s atmosphere, it encounters many molecules that scatter it. This process occurs depending on wavelength – shorter wavelengths like blue light are scattered more while longer wavelengths like red are scattered less. This phenomenon is known as Rayleigh scattering after its primary discoverer; an English physicist from 19th century named Rayleigh developed its basic principles.

Reason why the sky appears blue: light waves scattered by molecules are often affected more strongly by air particles that act like scattering particles than long wavelengths, thus leading to changes in light direction that eventually reach your eyes and give off their signature blue color. Otherwise, some light can simply pass right through or be absorbed by molecules as energy-conserving processes take effect – giving rise to what we perceive as blue skies.

At the horizon, the Sun is closer to Earth and therefore more of its light travels through our atmosphere – which also means more passes through thicker sections – which makes its scattering process more efficient. Molecule density and angle of incidence with atmospheric molecules both play key roles here.

Thus, sun’s rays become more susceptible to being dispersed into our eyes by air molecules, leading to their dispersal through scattering events into your vision and making sunsets often yellow and orange in hue. Other colors of the spectrum are blocked out altogether while only blue and violet light reaches our retinas.

If the molecules in the air were an effective match for sunlight wavelengths, then scattering would be more efficient and we’d see all its colors more vividly. Unfortunately this is not the case due to Mie scattering (named for German physicist Gustav Mie), in which air particles don’t match perfectly to act as effective scattering particles for sunlight.


At sunset, the sky turns red as light passes through thicker air and dust near the horizon, scattering blue light while allowing orange and yellow wavelengths through. Stop signs and tower beacon colors also disappear because their shorter, higher frequency waves have difficulty passing through clouds and dust.

Aerosols are tiny solid or liquid particles suspended in Earth’s atmosphere from Earth all the way out into space, from fog or smoke to emissions from burning fossil fuels or industrial processes. Aerosols may be naturally produced like fog or smoke or they can be man-made like emissions from fossil fuel combustion or industrial processes that emit them. Aerosols range in size from few microns up to million times larger than human hair and come in all sorts of shapes such as jagged volcanic ash bits or round droplets of water and salt that absorb or scatter Sun’s rays depending on chemical composition – naturally or man-made emissions from burning fossil fuel combustion processes emit these aerosols into space.

When the Sun shines through clear fluid, electromagnetic waves of various lengths ranging from UV to radio waves are generated and scattered by its particles, creating a rainbow of colors; longer wavelengths (like blue and violet hues ) tend to be scattered less than shorter ones like greens and reds. John Tyndall first discovered this effect in 1859 by shining a beam through a clear glass tube filled with smoke: light reflected from either end was blue while sideways reflections appeared reddish-orange.

Aerosol particles such as black and brown carbon can warm the atmosphere, while others such as sulfate droplets cool it. Together, aerosols have an enormous influence on Earth’s climate: reflecting solar radiation back onto Earth or absorbing it can both warm or cool the planet; when mixed with clouds they influence rain/snowfall patterns – Mount Pinatubo’s eruption in 1991 released tons of reflective sulfate aerosols which helped cool it by about 0.6degC.


The sky appears blue because sunlight entering our atmosphere scatters in all directions and is directed back toward you; those wavelengths most strongly scattered by air molecules at the blue end of the spectrum appear more blue to us; the remainder gets absorbed into molecules and appears reddish orange to our eyes.

The color of the sky depends on how much dust or pollution there is in the atmosphere and on their size, which affects light scattering; larger dust or pollution particles tend to scatter less blue light than small ones but can obstruct reddish and yellow hues from reaching your eyes.

When the Sun is close to the horizon, its rays must pass through more of Earth’s atmosphere than when it’s high up in the sky, increasing their likelihood of scattering off air molecules at lower temperatures than when higher up in the sky. As such, more shortwavelength blue and violet light reaches your eyes than longer wavelength orange and red lights do.

As the Sun moves toward its horizon at sunset, its rays become more likely to be reflected off clouds lining the sky and back onto their surfaces, casting white hues upon cloud tops while other parts of the atmosphere appear reddish or yellow due to more readily reflecting colors than blue ones. This results in whiter cloud tops while most areas appear reddish or yellowish due to easier reflection than blue hues.

At midday height, when the Sun is at its most intense, its rays strike nearly vertical angles against atmospheric molecules, allowing most of its blue and violet light to pass through without being absorbed by air molecules, giving rise to an array of blue-violet hues from its light sources. As such, its appearance resembles both blue and violet.

As an experiment at home to explore how sunlight travels through our atmosphere, try this easy experiment with milk in a glass of water and a flashlight: when seen from one side of the glass it will appear bluish-white; from its end however it appears more yellow-orange due to more extensive scattering by water molecules than at any point during its journey through space.

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