Step back in time with me, if you will. Back to high school and into the one class that struck the most fear into your heart. Algebra or calculus, perhaps? Maybe it was English composition (dangling participles and comma splices, anyone?). In my case it was science class with all its associated trappings – the maze of abbreviations on the periodic table, the smell of formaldehyde, Bunsen burners gurgling with unknown liquids – which is why I chose writing as my career. It’s much less intimidating. At least it was until David W. of New York City wrote in with this month’s question – one that requires a scientific answer. My palms are sweating already! Let’s get to it before my brain seizes up altogether:

What makes desert sunsets so spectacular?

The Sonoran Desert is renowned for popsicle-hued red and orange sunsets that have captivated both amateur and professional photographers for generations. In order to understand exactly what causes these brilliant natural displays, we have to back up a step and start with another question: Why is the sky blue?

Ordinary white sunlight is made up of colors from the full spectrum, from red all the way through violet. On its travels to Earth, most sunlight passes through the atmosphere relatively undisturbed, but on occasion a light particle (a photon) collides with an air molecule (emissions, dust and moisture particles called aerosols) and bounces off it in a process called scattering. How strongly light is scattered by air molecules depends on its color (or wavelength), with light from the blue-violet end of the spectrum being more likely to bounce off air molecules than light from the red-orange end. As a result, enough bluish light is scattered into our eyes to make the sky appear blue.

Now, fast forward to sunset when sunlight light travels a much longer path through the atmosphere to reach us than it does at noon. During this process, so much violet, blue and green light is “scattered out” that it is mostly red, orange and yellow light that gets through. Because the desert air is very dry and relatively free of particulates (compared to many other cities), there aren’t enough large aerosols here to obscure and dim the light of the setting sun, which contributes to the sunset’s brilliance. And, desert air frequently contains smaller aerosols like airborne dust that can actually intensify the sunset’s colors. The result is a breathtaking show of Mother Nature’s artistic ability!

Tags: Sonoran Desert, Sonoran Explorin'

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