4 min read

Hesperian Red

The Color of Sunset
sunset light in garden
The garden of Hesperides. Image created by David Lukas

In the garden of Hesperides, in the far western corner of the world, there is an orchard. In this orchard, there are apple trees that produce golden apples and are carefully tended by Hesperides, the nymphs of evening and sunset in Greek mythology.

Or, if you prefer, the sun's electromagnetic rays are scattered by atoms in the atmosphere due to Rayleigh scattering.

No matter which of many stories you believe in, humans have long speculated on the causes and reasons for the brilliant, fleeting colors of sunset. Are they symbols of death and closure, magical signs, or thresholds? Science can now give us a clear and simple answer, yet we still marvel and celebrate this mystery every time it happens.

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On a clear day we see the sun as yellow and the sky as blue, when in fact the sky has no color, and the sun is a white ball. All the colors we see are artifacts produced as the sun's rays are filtered by their passage through the earth's atmosphere.

sun and sky
Blue skies are the result of blue light being scattered in the atmosphere. Photo by David Lukas

Depending on how far rays have to travel through our atmosphere, we end up seeing different colors. In the middle of the day with the sun directly overhead, rays travel a short distance; and when the sun is low in the sky, at sunrise and sunset, rays travel a much longer distance.

sun's relationship to earth
At low angles, the sun's rays travel a much greater distance through the atmosphere. Image created by David Lukas

The sun's electromagnetic energy includes all parts of the visible spectrum, so the sun's color is white. But gases and particles in our earth's atmosphere absorb and scatter parts of the spectrum, giving the sky different colors.

Every sunset is different. Photo by David Lukas

In the middle of the day, with a shorter distance to cover, the sun's rays encounter fewer gases and particles so more blue color reach the earth's surface and the sky looks blue to us. But at sunrise and sunset, with a longer distance to travel, the rays strike many more gases and particles, scattering more of the blue colors so we don't see them, and allowing oranges and reds to become the dominant colors we see instead.

the colors of sunset
Increased dispersion of blue wavelengths allows more orange and red colors to reach our eyes at sunset. Image created by David Lukas

Ultimately, this process happens every sunrise and sunset, but the intensity and quality of the colors we see are dictated by whether clouds beyond the curvature of the earth's surface are blocking these low-angle rays of light or not.

Sunset colors are best when they're reflected onto the bottom of clouds. Photo by David Lukas

It also matters whether low- or high-pressure systems are impacting the density of gases and particles in the atmosphere over the horizon, which is why proverbs such as "red sky at night" can be fairly accurate indicators of changing weather.

Hints of sunset under a moody, stormy sky. Photo by David Lukas

Growing up on the Oregon coast, I always loved the idea that the red colors of sunset are coming at us from over the curvature of the earth, as if they were a window into another world. To this day, no matter how much science I read about wavelengths and atmosphere, this deeply personal, mystical connection still matters the most to me.

One final band of red light over the curvature of the earth. Photo by David Lukas