Seasons of the Sun

How many times has it happened as you drive? All at once you reach a certain spot on the road, a certain place in your mind, a certain moment between dusk and dark. You grip the steering wheel in wonder. What lies ahead is not just sky, but an impossibly exquisite work of art. Abstract layers of glowing tints that Crayola could not attempt to capture, that poets try in vain to describe.

Sunset.

Not the boulevard, the phenomenon.

And what to answer when the toddler asks, from the rear, “What makes the sky so pink?”

After flubbing such a query the other day, we phoned Edwin Krupp, director of the Griffith Observatory, for an answer. “It’s not as daunting as it might seem,” he said.

“The main principle is that we on Earth are looking through a window. That window is Earth’s atmosphere--a 20-mile-thick layer of air that envelopes our planet. The colors of a sunset depend on what’s in that atmosphere, the distribution of light through whatever . . . “

Kids would never accept a “whatever,” so we asked for further illumination.

The sun transmits rays of light made of all colors of the rainbow mixed together, Krupp said. The light travels 93 million miles through space and then penetrates Earth’s atmosphere, which contains all sorts of gunk created by people and nature: dust from dust storms, soot from wildfires, ash from volcanic eruptions and unsavory pollutants generated by man and machine. It is the sun’s rays, beaming through these microscopic particles in the atmosphere that create the colors we see in the sky, said Krupp. When the sun is high in the sky at midday, we perceive the sky as blue.

But at sunrise or sunset, the sun is at a low angle on the horizon. At that time, its rays must penetrate much more of the atmosphere than at midday. Very colorful sunsets happen when the particulates block certain waves of light, allowing predominantly red light to reach our eyes. The 1991 eruption of Mt. Pinatubo in the Philippines caused “spectacular purple sunsets all around the Earth,” said Krupp.

“But doesn’t the time of year affect the colors of a sunset?” we asked. And why do some people swear that Southern California’s famous summer “smogsets” are more dramatic than the crystalline pinks and yellows of a winter sky at dusk?

Krupp repeated: “It’s what’s in the atmosphere at the time of sunset that determines what it will look like.”

Clouds may be related to season, he allowed. “If you are standing in Malibu . . . and clouds pepper a winter sky, scattered out to the West--and the sun is setting--it will shine up on the clouds from below, and each different cloud formation is like an artist painting a different picture.”

Understanding the science of it all has not made Krupp immune to the glories of nature.

“Sunset is inspirational and romantic all over the world,” he said. “In Paris they call it l’heure bleue--they even named a perfume after it.” In Los Angeles, he said, his favorite place to view the sunset is . . . the Griffith Observatory, of course. “It takes on an absolutely stunning golden glow with the last rays of sun,” he said.