What Makes That Fire in the Sky: The Science Behind Sunsets
Updated: May 12
In the evening hours, as the sun descends into twilight, we are greeted by a wave of colors known as a sunset. For a brief moment, we are reminded to pause our chaotic minds to enjoy the splendor above us. If you live in Arizona, you are all too familiar with this daily vibrant experience.
What’s behind the colorful wonder? Sunsets are as scientifically intriguing as they are beautiful. In fact, the reason Arizona has some of the most magnificent sunsets in the world is due to a combination of factors such as air quality, time of year, and chance. However, before we uncover the truth about Mother Nature’s scarlet display, we must first understand the reason why the sky is blue in the daytime.
Why is the Sky Blue?
The sun emits energy onto the Earth in the form of white light. As you may remember from science class, white light is a spectrum of colors ranging from ultraviolet to infrared. The colors vary from short to long wavelengths. For example, blue and violet light have shorter wavelengths compared to red and orange.
When sunlight enters our atmosphere, it is no longer a direct beam of white light. Instead, the blues and purples with shorter wavelengths start bouncing off of nitrogen, oxygen, and various other air molecules in the atmosphere. This process is known as Rayleigh scattering, and it’s the reason why we perceive the sky as blue. Without the atmosphere, our planet would look much different; we would be left with the dichotomy of white sunlight and a black sky.
(Fun fact: The sky is not actually blue…we just perceive it that way. Violet wavelengths are shorter and more prevalent than blue wavelengths, which means the sky should appear purple. However, the cones in our eyes are less sensitive to the color violet than they are to blue.)
If the Sky is Blue, Then Why Aren’t Sunsets?
Another important fact to keep in mind is the Earth’s atmosphere is incredibly thin. Neil Degrasse Tyson puts this into perspective when he compares the planet to a fruit: “The size of Earth’s atmosphere relative to the Earth is the same as the skin of an apple relative to the apple.” When the sun is directly above us, the light has a shorter distance of air molecules to pass through. As the blue and violet light waves scatter around us, we absorb those colors in our eyes.
During a sunset, the same scattering effect takes place. However, the light that was once penetrating vertically through a thin atmosphere above you is now traveling horizontally over the Earth’s curvature. At sunset, the light travels through 10 times the amount of distance in the atmosphere, colliding with numerous air molecules along the way. By the time the light reaches your eyes, all the blues and violets have dispersed elsewhere, leaving behind a trail of warm colors such as red, orange, and yellow.
Does Pollution Enhance Sunsets?
There are many claims that pollution and dust can intensify the beauty of a sunset. This idea likely originated from the afterglow that occurs after a volcano erupts. It’s true that volcanic eruptions may lead to beautiful sunsets, but the bold afterglows only materializes when volcanic particles shoot high up into the atmosphere. Pollution and dust particles, on the other hand, remain low in the atmosphere creating a hazy effect that dulls the colors of a sunset.
Contrary to popular belief, pollution does not enhance this multicolored phenomenon. If that were true, then many of the densely populated cities of the world would be revered for their sunsets, but that is rarely the case. Certain criteria must be met to strengthen the light and colors at sundown, and spoiler alert: pollution will not be on the list!
Ingredients for the Perfect Sunset
Don’t let the title of this section fool you — this isn’t the recipe for our newest Sunset Bath Bomb.
Instead, this is an explanation of what conditions need to exist for the perfect sunset to occur.
Not all sunsets are created equal. It’s also no coincidence that they are highly associated with certain parts of the world,