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What Makes That Fire in the Sky: The Science Behind Sunsets

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 and 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 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 actually 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 continues taking 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 are shot 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, such as the tropics or deserts. The intensity of sunsets are amplified based on a mixture of factors:

  • Air Quality: As mentioned above, pollution and dust will counteract the vibrancy of a sunset. Instead, the air needs to be clean and dry. Additionally, the summer months are not an optimal time for sunsets because the air circulation remains stagnant (Arizona is an exception to the rule due to the monsoon season).

  • Cloud Coverage: The quality of a sunset can be greatly elevated by the addition of clouds. However, not all clouds are created equal. The density of low-level stratus clouds don’t allow enough light to penetrate through, whereas high-level cumulus and cirrus clouds can enhance the depth of a sunset’s colors.

  • Sun Angles: As autumn rolls into the winter months, the sunlight hits the Earth at a more tilted angle. Therefore, the light has to travel further along the Earth’s curve, filtering out more blues and purples along the way. This deepens the brilliance of the red, orange, and yellow hues.

Arizona has arguably some of the most radiant sunsets — bold and bright, like flames of a fire. Many worthy experiences in life cost money, so take the time to enjoy the complimentary beauty that nature has to offer. Regardless of where you live in this world (humidity and cloud density be damned) allow yourself the privilege of taking a mindful sunset break. Set an alarm on your phone, go outside, and bask in all it’s fiery glory!

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