Sunlight gives the sky its blue color as it gets getting dispersed by air molecules. This process is termed Rayleigh scattering. Although we are used to seeing a blue sky around us daily, will the sky always be blue?
The sky gets its color from sunlight which comprises all colors of light. As the blue light waves are shorter and smaller than other light rays, they get scattered the most, resulting in a blue sky. As long as the Sun exists, the sky will remain blue. However, other factors, including pollution, global warming, and humidity, change their appearance in different areas.
Before we delve deeper into the reasons that cause the sky to look different, first, we need to understand why it is blue. Continue reading to learn more about the sky’s color!
Why is the Sky Blue?
Although sunlight appears white, it is formed from all light colors. These include the visible light part of the electromagnetic spectrum. Within the spectrum are seven different wavelengths of light, each with a distinct color. While red light has the longest wavelengths, blue light has the shortest.
As sunlight reaches Earth, it hits the air molecules within our atmosphere and gets dispersed in all directions. As blue light has the shortest and smallest wavelengths, it gets scattered the most. This gives the sky its blue color.
However, as we get close to the Earth’s outer atmosphere, the sky becomes a faded blue color. This is because sunlight has not yet traveled far enough into the atmosphere to bounce off various air molecules. So, not enough blue light has been scattered in all directions to give the sky its blue color.
Thus, the closer we get to the Earth’s surface, the more the blue light hits and bounces off from air molecules. Therefore, the blue color of the sky deepens near the ground.
Here is a video that also explains why the sky is blue:
Now that we know how the sky becomes blue let’s discuss why it might appear different.
What Can Make the Sky Look Different?
Even though sunlight always reaches the Earth’s atmosphere and blue light gets scattered, the sky might sometimes appear different.
Pollution
Throughout the year, there are varying levels of aerosols in the sky. Aerosols refer to small air, dust, and fume particles getting released into the air. It is likely for the air to be dustier in some parts of the world during the summer because of warmer and dry weather. The dust increases aerosols in the air and leads to more color variation in the sky.
Similarly, most farmers harvest their crops in the fall, from September to December. The process also produces dust particles, producing many aerosols in the environment. Therefore, the moon particularly appears more orange during the harvest season.
Aerosols change not only the sky’s appearance during the day but also during sunset. Areas with nearby forest fires or volcanic eruptions and cities with more industries have deeper red sunsets because of higher pollution rates.
Another factor that leads to pollution in the environment is Isoprene. Although it is a natural hydrocarbon released by trees and plants, it can harm air quality once combined with artificially made pollutants. Human activities, including factory emissions, mostly cause these.
Isoprene also increases greenhouse gasses in the atmosphere by reacting with OH radicals. These are the primary oxidizing elements in our atmosphere. Thus, when isoprene reacts with them, it reduces the atmosphere’s ability to lower the effects of greenhouse gases.
These factors combine to increase pollution, which makes the sky look colorful with red and orange tones instead of blue.
Humidity
Another reason why the sky might appear different is because of haze. This can make the sky look greyish as compared to a bright blue color. This is common in parts of the world near the water because haze can be formed from both the water vapor from the oceans and salt particles from the seas.
The presence of these elements in the air makes light scatter differently. Therefore, as blue light is not dispersed sufficiently in all directions, the sky appears more whitish than blue.
Although pollutants can make the sunset look more intense, it will have a red hue even if the air is clean. Continue reading to find out why!
Why Is The Sky’s Color Different At Sunset And Sunrise?
The sky should always be blue during the day. If it is not, it means that there is humidity or pollution in the environment. However, it is natural for the sky to change colors during sunsets and sunrises.
During sunset or sunrise, the sky appears reddish. This is also explained through the Rayleigh scattering process mentioned at the beginning of the article. During the day, the Earth is closest to the Sun during its axis rotation. This makes the shortest light wavelength, blue, visible to us.
However, the Sun is farther from us during a sunset or sunrise. So, the light we see has traveled a greater distance through the atmosphere to reach us. This means that the shorter wavelengths become invisible when the sun is lower in the sky because they have already been scattered away without reaching the Earth’s surface.
What’s left are the longer wavelengths. As red-light waves are the longest in the visible light spectrum, we see a red hue during sunsets and sunrises.
Next, let’s discuss whether the sky is blue across our Solar System.
Is The Sky Blue On All Planets?
The sky’s appearance on each planet depends on its atmosphere. The difference in air composition will make light from the visible spectrum scatter differently than air on Earth.
An example is Mars. Here, the atmosphere is thin and comprises carbon dioxide with many dust particles. Hence, the sky on Mars appears orange-colored even during the day.
Conclusion
From the abovementioned information, it can be observed that the sky will always remain blue if the Sun exists. However, its appearance may look different from the ground depending on where you are looking at it from and how clean the air around you is.
