The vivid Tucson sunset may simply be molecules filtered through our eyes, but something about it touches the heart.

We’re defining Tucson in 100 objects. The daily series began April 20. Follow along at

Our open horizon is the principal ingredient in our spectacular sunsets.

The sun, after all, is simply a bright, white light in a black sky. You need atmosphere to break that light into its various colors.

Molecules in the air scatter light. When the sun is overhead, the small, predominant ones — oxygen and nitrogen — are scattering low-wavelengths of sunlight, the blues and the violets. Our eyes are better at detecting blues and that’s why we see a blue sky.

When the sun sinks lower, we look through a longer stretch of atmosphere, and most of those colors on the blue end of the spectrum get filtered out.

Our eyes see the reds, oranges, and yellows, said J.J. Brost, science officer for the National Weather Service in Tucson.

That’s why the best sunsets are seen from beaches or mountaintops — anywhere the horizon isn’t blocked.

In Tucson, we have the added advantage of interesting natural features. The sun sets over ridges topped with saguaros and behind distant mountain ranges, each a different shade because of their relative distance.

And now it’s time for “Tucson in 100 Objects” to ride off into a perfect Tucson sunset.

Contact reporter Tom Beal at or 573-4158.