Why is the sky red and orange at sunset?

color during sunset - feature

If someone asks us what a perfect sunset would look like, we will for sure describe it in hues of reds and oranges. These enriched colors would set an ideal mood to end our day in a calm and relaxed manner. A marvelous sight to behold until we see it again!

However, this is not as common as the blue skies during the day. Sometimes, the sunsets are in hues of pink, purple, or simply blue to grey as the darkness sets. So, what exactly happens in the sky to give it a wide range of color splashes every day?

Meteorologist Alex Hill explains that light travels from the sun through the atmosphere, resulting in the multi-colored sky.

The science behind

Earth is full of secrets, no doubt! We might have taken a thousand pictures of the setting sun. But did we ever wonder from where the color comes?

The atmosphere comprises numerous gas molecules such as nitrogen, oxygen, carbon dioxide, water vapor, argon, and other gases. As the sunlight passes through these gas molecules, it interacts with them and gives the light a wide range of colors to the sky.

Although sunlight appears more or less colorless, it is composed of plenty of colors ranging from violets to blues on one end and reds to oranges on the other extreme. Similarly, the wavelengths in this spectrum lie between 0.47 μm to 0.64 μm.

Light is made up of various wavelengths, which enables us to see color. Blue light has a shorter wavelength and can quickly bounce off molecules in the atmosphere. This phenomenon is the exact reason why the sky is blue during the daytime.

Light scattered into various colors with different wavelengths (source)

Simultaneously, the red light has longer wavelengths and is not scattered as quickly and effortlessly. When the sun sets, the soft light beams are composed of larger wavelengths towards the red and orange color spectrum.

However, since blue light is scattered out of sight during the sunset and sunrise, the sky does not precisely appear blue.

That’s not all there is to a miraculous sunset. Did you know that it would be impossible to observe these spectra of colors in the absence of clouds?

The phenomenon of light is also the reason for the red and orange hues at sunset. But, clouds are essential to observe these events. The rays are reflected when the scattered molecules hit the clouds. If there is nothing to reflect the light, we are certainly not going to see the shades.

Dust as Pollution affects the vibrancy of sunset

The presence of external particles in the air also has a considerable impact on the color of the sky. The appearance of dust particles and smoke significantly moderates down the vibrant colors in the sky. This occurrence is more valid for sunset than sunrise, as dust particles in the evening are much higher than in the morning.

Pollutants partially obstruct the refracted light particles from reaching the viewers on the ground level. Hence, it notably tones down the various shades in the sky. No wonder the sunsets in countrysides and coastal regions are more vibrant compared to the urban locations.

As explained by A.R. Ravishankar, director of chemical sciences at NOAA Earth System Research Laboratory in Boulder, Colo, to get reddish sunsets, aerosols are required.

Therefore, if the atmosphere consists of more aerosols, getting a red and orange sunset is higher. Aerosols are the minute liquid particles present in the atmosphere that originate from natural and anthropogenic sources.

Bridge at mist, Stockholm, Sweden (source)

Natural aerosols are formed during forest fires, mineral dust, sandstorm, sea spray, or volcanic eruption. It is not a surprise that a volcanic eruption is enough to cause red and crimson sunset all around the globe. Anthropogenic aerosols are produced due to the burning of fossil fuels and internal combustion in car engines.

Volcanoes have painted the skies with one of the most spectacular reddish skies in the history of sunsets. They inject sulphuric acid into the atmosphere, capable of giving that crimson hue to the sundown as they travel along with the wind.

After the 1883 volcanic eruption in Indonesia, outstanding sunsets appeared all around the globe. Similarly, after the wildfire in the Pacific Northwest and central Canada, north-central West Virginia received a beautiful red and orange sunset for a few weeks.

Light has to travel a long distance during the sunset

The sun is nearer to the horizon during the sunset. And, the light beams have to travel a longer distance compared to the sunlight during midday. They also have to pass through a dense environment to reach our range of vision.

A phenomenon known as Rayleigh scattering enables the tiny light beams from the sun to scatter in different directions. As a result, most of the lights of shorter wavelengths, blue, violet, and green, are dispersed far and wide multiple times.

Distance between the sun and earth (source)

This dispersion leaves behind only the light molecules with longer wavelengths, the red and orange glow. Hence, this makes it easier for the red light to travel faster, giving us fiery sunset hues. This red hue is technically the last remaining survivor in the spectrum of color.

Fun fact

Human eyes are more sensitive and receptive to blue light than violets. And, if it were the other way round, the sky would appear violet instead of blue!

Seasons affect the sunset

In the summer seasons, the sunset tends to cover the entire sky with reds and oranges. However, in the winter season, we get a distinctive band of these colors. This difference is mainly because, in summers, many dust particles obstruct the light molecules and scatter them further apart, giving a diminished haze to the sky.

Four seasons and their respective skies (source)

To conclude

Orange and deep red sunsets are magical and Instagram-able. However, it might also indicate that the air is heavily polluted with harmful particles such as aerosols. Next time you watch a beautiful sunset, keep in mind the fantastic phenomena in the atmosphere to bring you this dazzling view.