Why is the Sky Blue? – Chemistry

why is the sky blue chemistry

Have you noticed how the sky is an endless sea of blue? Closer to the sun, its hue becomes lighter while moving further from it.

Light travelling through Earth’s atmosphere collides with molecules and particles such as oxygen and nitrogen, scattering light in various directions. Shorter wavelengths like blue are scattered more than longer ones (red). This process is known as Rayleigh Scattering.

Rayleigh Scattering

Sunlight entering our atmosphere is scattered by random air molecules, predominantly oxygen and nitrogen molecules, into many directions by way of reflection off oxygen- and nitrogen-containing particles in our environment. Rays that strike these particles tend to scatter at wavelengths corresponding to blue and violet which, due to being so short wavelengths, scatter more strongly than longer wavelengths like red or yellow which our eyes then interpret as sky color.

Scattering intensity varies with wavelength and particle size; thus causing different colors of sunlight to appear differently when passing through a prism, as its wavelengths get bent or refracted at different angles.

How is the sky blue? At sunset and sunrise, when the Sun moves closer to the horizon, its light must travel through more atmosphere to reach your eye – this means it encounters smaller molecules which scatter blue wavelengths more readily. Meanwhile, nearer the horizon there may also be greater concentration of red wavelengths in the atmosphere which help offset some of this scattering effect.

To make sense of it all, consider the energy of each wavelength involved. Longer wavelengths like red and orange tend to have lower energies than their blue counterparts and will therefore be less affected by atmospheric fluctuations; allowing blue and violet wavelengths more freely pass through, giving the sky its color.

Dust and pollution in the air also create cloudy conditions, while this effect is responsible for creating the characteristic haze found on mountains and tropical regions, where ozone reacts with plant terpenes to form small aerosols which reflect blue wavelengths back.


As sunlight hits Earth’s atmosphere, it is dispersed through gases and particles by scattering. This scattering process is more noticeable for short wavelengths like blue than long ones such as red – hence why we most commonly see blue skies.

A beam of white light directed through a clear tank of water will appear blue due to oxygen molecules scattering blue light more than other colors, just as water molecules do in oceans or when looking down into lakes or ponds, creating an optical illusion known as rainbows.

The color of the sky depends on how much moisture and dust haze there is in the atmosphere and what type of molecules exist within. Mountainous regions can often feature an alluring blue haze created by ozone’s reaction with plant terpenes; this aerosols is only 200 nanometers wide so scatters more blue light. Conversely, pollution or smog may make skies appear brown, yellow or even red in hue.

As you ascend further into the atmosphere, the sky darkens as your distance between Sun and eye increases and sunlight must travel further through atmospheric layers before it reaches you. Atmospheric nitrogen and oxygen particles scatter some of this blue light further reducing how much it reaches your eyes.

Small oxygen and nitrogen molecules scatter short-wavelength blue light more effectively than long-wavelength red light, since blue has shorter wavelengths than other colors.

Additionally, our eyes are more responsive to blue light than green or yellow hues; therefore blue is more noticeable than other colours when reaching our eyes. Indigo and violet wavelengths tend to be scattered more lightly; therefore they appear as being slightly bluer than they really are.


Nitrogen (N) is an element with symbol N and atomic number 7. As a nonmetal element found in Earth’s atmosphere, nitrogen makes up approximately 78%. Odorless, tasteless and colorless, its main uses include making fertilizers and manufacturing high-density foam; additionally it can also serve as refrigerant and is sometimes combined with gasoline to improve combustion more cleanly.

Sunlight striking Earth’s atmosphere is scattered in all directions by molecules and atoms that reside there, with shorter wavelengths (blue and violet) being scattered more than longer wavelengths such as red or yellow light; thus giving the sky its signature blue color.

Higher altitudes tend to produce brighter skies due to more atmosphere being available to diffuse sunlight, which explains why noon-time skies tend to appear bluer than 5 p.m. skies.

Air around us primarily consists of nitrogen, but other gases like oxygen and carbon dioxide also play a part. When white sunlight hits this mixture it scatters to produce its characteristic blue hue, giving us what we know as air.

Nitrogen isn’t the sole factor responsible for turning the sky blue; all atmospheric gases contribute to this effect, with nitrogen being one of the more abundant contributors that contributes to its color. But nitrogen still plays a significant role in shaping its hue.

Nitrogen is an inert nonmetal that does not readily form stable compounds with other elements, making it one of the more disorganized nonmetals to work with. Most often found as a gaseous state, nitrogen may also exist as liquid or solid forms.

Liquid nitrogen can quickly freeze food to preserve texture, moisture and flavor while also being an integral component in medical and fertility clinics to store sperm, eggs and embryos. Solid nitrogen has also found application as part of industrial processes for manufacturing acetone and nitric acid.

Even without an atmosphere, the Moon still boasts an equally blue sky. Its blue hue comes from reflection of sunlight off of dusty surfaces rich with nitrogen atoms – the source of its characteristic hue.


Over time, scientists have provided various answers to this question of sky blue color; many still believe oxygen to be its cause. Unfortunately, this explanation is incorrect for several reasons. First of all, oxygen molecules found in atmospheric air don’t actually emit blue light themselves and instead contain both nitrogen and oxygen which both appear white to our naked eyes. Furthermore, oxygen does not emit its own form of light which could account for its contribution towards sky blue hue.

The blue color of the sky can be explained by sunlight reaching Earth and becoming scattered all around. Blue light in particular tends to get scattered more efficiently due to having shorter wavelengths; as a result, we see blue sky instead of red ones.

Water is an effective reflector of sunlight. It reflects all colors except green and red rays from sunlight, giving lakes and rivers their blue hue. We can test this theory by holding up a piece of paper against any body of water and viewing it closely; without reflection any colors from rainbow, the paper will look gray; however if reflecting green and red light from water body it will turn blue!

Scientists have recently determined that water appears blue due to it absorbing some of the red light that passes through it, with liquid water showing greater absorption than its frozen or snow counterparts. This makes sense, given that liquid water contains large molecular structures which more readily absorb red light compared to smaller oxygen and nitrogen molecules.

Small amounts of ice, like that found in a glass of water, appear white or transparent; however, large masses such as glaciers or Arctic ice sheets will appear blue due to all their trapped air bubbles.

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