Why are Southern California sunsets so beautiful in the winter?

The days are growing shorter as we head toward the winter solstice, but the trade off is that we here on the coast get treated to some absolutely gobsmackingly beautiful sunsets.

That led KCRW staffer Jill Smayo, who took the stunning sunset photo, to ask Curious Coast: “Why are sunsets in Southern California so much more dramatic in the winter than in the summer?”

Chuck McPartlin of the Santa Barbara Astronomical Unit, our city’s amateur astronomy club, had the answer.

The earth, if you remember your high school basics, rotates at a tilt of 23.5 degrees relative to the ecliptic plane. That is, as earth travels in its orbit around the sun, it’s spinning at an angle. This is why the northern hemisphere experience winters at the same time the south gets its summers. Also, the earth’s orbit in not a perfect circle.

Here’s an illustration from NASA that further explains it:

Image from NASA’s SpacePlace blog

“The orbit around the sun is elliptical,” said McPartlin, “so the earth’s motion around the sun changes. In the winter it is moving faster (as it hits the shorter curve of the oval). And we’re closer to the sun during our wintertime. Three percent closer, but enough to make the sun’s apparent motion in the sky different.”

Therefore, our winter twilights last just a bit longer.

The beautiful colors from a sunset are caused by the atmosphere. As the sun gets lower and lower in the sky, its light passes through more and more air layers—compared to noontime, when the sun is directly overhead. And those layers are filled with dust and water particles. This causes the sun’s light to bend as if through a prism, scattering the blue light in favor of reds, oranges, and purples.

On top of that, if there are inversion layers on the horizon—a warmer layer of air trapped under a colder one—you will see that “mirage” effect, as the light is bent through the different layers. That’s what causes the sun to look like a lava lamp bubble sometimes or makes the Channel Islands resemble a spaceship.

“That’s almost a guarantee of a beautiful sunset,” says McPartlin.

Santa Barbara Island as seen through an inversion layer, also known as a Fata Morgana mirage. Photo courtesy of Suzanne Guldimann

That splitting of the spectrum can sometimes result in a great final moment.

“Your eye is much more sensitive to green and it’s one of the last ones refracted into your eye. We call it the ‘green flash,’ he said. “In fact, if you are able to, you can watch the green flash, and then run up a hill and see it again.”

A Green Flash captured just before the sun sets.

And if you’re wondering the best part of the year for a sunset, it’s right now. Between the September Equinox (Sep. 22) and the winter solstice (Dec. 21) is the best time according to McPartlin.

The Central Coast and South Coast are great places to watch the sunset. We face the ocean, so there’s nothing in the way of the horizon. And we’re neither close to the equator nor the North Pole, so that extended twilight is going to be right in that sweet spot.

We live in one of the best places in the world… to watch sunsets. See you at the beach!

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