“…A green which no artist could ever obtain on his palette, a green of which neither the varied tints of vegetation nor the shades of the most limpid sea could ever produce the like! If there is a green in Paradise, it cannot be but of this shade, which most surely is the true green of Hope.” —Jules Verne, “Le rayon vert”
It is so seldom seen that it’s almost mythical, but the famously elusive “green flash” that occurs just after sunset is a real phenomenon.
Sunsets appear red because the colors red and orange have longer wavelengths than green and blue, but as the sun sets the astronomical horizon refraction causes the atmosphere to act as a prism, separating and bending the colors. The longer wavelengths are dispersed, leaving green and blue but these colors are technically too faint for the human eye to detect. It requires another phenomenon caused by refraction to reveal the green flash.
The appearance of the sun slipping below the horizon is actually a mirage, projected above the sun as it moves below the horizon. When conditions are exactly right, refraction and dispersion intensifies and magnifies the green light, producing a visible flash above the solar mirage.
The phenomenon usually appears to turn the disappearing edge of the sun green, giving it the name “Neptune’s wink.” It can also appear as a zigzag of green above the edge of the sun, or more rarely, as a ray—Jules Verne’s “rayon vert.”
A winter sunset on a south-facing Malibu beach offers an ideal opportunity to look for the green flash. Santa Ana conditions or clear weather following a weather front are the best times to look for the flash. Clear skies are essential, and the best viewing opportunity comes when the inversion layer traps a lens of cooler air that acts as a magnifying glass, increasing the density gradient in the atmosphere, and intensifying refraction.
The green flash can also sometimes be seen at sunrise, when the process is reversed and the flash appears immediately before the sun begins to appear above the horizon. In the Santa Monica Mountains an east-facing view where the sun rises from behind a mountain ridge offers the best chance of catching the phenomenon before sunrise.
The flash lasts for only a second or two—blink and you’ve missed it. Digital cameras are more sensitive than the human eye and can sometimes catch the phenomenon even when the photographer doesn’t.
Even the diminished light of the setting sun can damage the eye’s retina, so it is important not to look directly at the sun until the final moments of the sunset, just before the disk slips out of view and what is visible is the mirage, not the actual sun.
Technically, the green flash occurs at every sunrise and sunset, but it requires the right conditions to be visible to human observers. Tradition says that seeing the green flash brings good fortune. The opportunity to look for this atmospheric phenomenon at sunset on a winter beach in Malibu is, in and of itself, good luck, regardless of whether or not one catches a glimpse of Verne’s “true green of paradise.”