Why is the Sky Blue?
Have you ever found yourself looking up on a sunny day and wondering why the sky appears blue? Turns out there’s an excellent explanation!
The color of the sky is determined by how sunlight interacts with our atmosphere. Sunlight passes through air molecules, scattering in all directions with blue hues being more heavily dispersed than reds.
Rayleigh Scattering
Sunlight contains all of the colors of the rainbow – red, orange, yellow, green, blue, indigo and violet – yet appears white to us here on Earth due to Rayleigh Scattering by tiny particles in our atmosphere. This phenomenon accounts for why skies appear blue.
The atmosphere contains tiny particles of gases such as oxygen and nitrogen that are much smaller than visible light wavelengths, making them perfect candidates for Rayleigh Scattering. As sunlight passes through these clouds we call atmosphere particles they scatter light all directions – more intensely so than longer wavelengths such as red. This results in its characteristic blue color.
Rayleigh Scattering alone cannot determine how blue or clear the sky appears; other factors, including atmospheric density and angle at which sunlight passes through can have an impactful influence. When full of dust or pollution particles or when volcanic eruptions take place, for instance, skies may appear hazy and reddish-tinged.
When we look up at a clear sky, its scattering by gas particles creates a bright blue color. This same phenomenon happens on other planets – which explains why many appear to have blue skies!
Scientists have devised models to predict the appearance of a planet’s sky by taking into account information about its composition and interaction with sunlight. This model takes into account factors like color variation over time and how clouds could alter its hue. Additionally, clouds could provide additional data as they influence sky color prediction.
Astronomer Greg Foot demonstrates in this video how atmospheric pressure at various heights affects the sky’s color and how this correlates with temperature in air. To provide further evidence of his explanations, he launches a weather balloon and films its journey up to twenty thousand metres, tracking how its colour changes with altitude – thus giving him enough information for creating a graph to demonstrate this correlation between atmospheric pressure and temperature with regards to color of sky.
The Sun
Our Solar System revolves around our star, the Sun. This massive ball of plasma powered by nuclear fusion at its core provides light and heat needed for life on Earth.
As sunlight reaches Earth’s atmosphere, it is dispersed through various gases and particles in the air, with blue wavelengths being dispersed more than other colors – hence why sky appears bluer.
Blue light from the Sun passes more readily through Earth’s atmosphere than other colors, which becomes especially apparent at sunrise or sunset when low on the horizon; shorter blue wavelengths have further to travel through our atmosphere before reaching our eyes while longer wavelengths such as red or orange have less scatteredness so can go directly through to us.
Though the sky may appear blue due to Rayleigh Scattering, its true colors lie elsewhere. When white light shines through a prism and split into its component colors by reflection off various objects – including clouds and ocean water – prisms separate it into these spectrum hues; when we look at leaves our brains interpret green reflected from them as white light!
The Sun is an incredible bright object. A medium-sized star, it has been in its main sequence for approximately 4.6 billion years and its surface has an irregular mottled pattern caused by constant radiative energy and magnetic field emission. At surface level its temperature reaches about 6000F; but interior temperatures can be 10 million times hotter! Composed primarily of hydrogen with only 2 percent helium added for good measure, its diameter nearly forms a perfect sphere and it takes between 225-250 million years for one orbit of our Galaxy!
The Earth’s Atmosphere
Atmospheric gases – more commonly referred to simply as “air” – contain many different kinds of gas particles with exactly the right sizes to allow most wavelengths of sunlight through. Blue light tends to get bounced around more by each gas molecule and ends up getting scattered more widely than all the other wavelengths – this phenomenon is called Rayleigh Scattering.
Atmospheric gas molecules scatter light, producing the iconic blue hue we associate with the sky. Other wavelengths of light can easily absorb into or are blocked out completely by our atmosphere, with molecular nitrogen (78%) and oxygen (21%) being the dominant constituents. Our atmosphere also contains smaller amounts of argon (1 percent), water vapour (1 percent), carbon dioxide (0.0395 percent – steadily increasing), methane (0.0018 percent) and other inert gases, along with minute solid and liquid particles that make up its structure.
As you ascend in altitude, the atmosphere thins out until it finally fades into space; but even at this height there are still remnants of Earth’s atmosphere to be detected.
The troposphere is the area closest to Earth’s surface in which most weather occurs and clouds gather. Additionally, this layer contains ozone which absorbs much of the harmful UV radiation produced by sunlight.
Rainbow Haze in Mountain Regions can also be traced to Ozone levels; this haze consists of smog and dust particles containing organic compound terpene that react with Ozone to form small aerosols (droplets) 200nm in size that can further be dispersed via various atmospheric processes including Mie Scattering, Rayleigh Scattering or optically active substances like chlorofluorocarbons.
Other Planets
On other planets, atmospheres can alter light differently and give their skies different hues. Mars features a thin atmosphere composed of carbon dioxide with some fine dust particles – this mix scatters blue light less than red or yellow light; thus producing more white than blue skies on Mars compared to its counterparts on other planets; hence the sky appears redder during sunrise/sunset due to more blue being scattered by gases and dust particles than from other colors.
Sunlight contains all of the colors of the rainbow: red, orange, yellow, green, blue, indigo and violet – in equal amounts. However, when reaching Earth’s atmosphere it becomes slightly bluish due to tiny particles scattering more blue end of spectrum light than others. A similar effect can be seen if one shines a flashlight through milk (a favorite holiday activity); although technically colorless light comes through, its hue changes slightly due to scattering through milk particles.