POIPU, Kauai – I never thought I’d see the fabled “green flash.” After decades of squinting toward the evening horizon, hoping to see what my 8-year-old brain had envisioned as a fountain of green light erupting from the sun, I’d conceded defeat. In fact, one could say I was a member of team Tanqueray Flash—a term I’d serendipitously encountered in a book describing Kauai’s hiking trails.
“The only green flash anyone’s ever seen is through the bottom of a Tanqueray bottle,” the author’s father supposedly grumbled at a columnist who’d described the phenomenon in the LA Times. Gin bottles? Those I knew something about. Green sunsets, not so much.
But two Sundays ago, as I stood on Kauai’s south shore, the sun defied my expectations and turned green as it dove into an ocean spotted with sea turtles and humpback whales. It wasn’t just any green, either: For a few moments, the setting sun was a vivid, otherworldly hue that matched my conception of alien slime.
Somewhat unbelievably, the sun pulled the same trick the next evening, when it again transformed itself into a glimmering green—and it did the same thing again two nights later as it waved goodbye to 2015. Each time, the peculiar color appeared at the fringe of the descending disk, then bled through the rest of the sun as it slid into the sea, leaving the ocean temporarily wearing a ridiculous green cap.
It was nothing like the image my 8-year-old brain had conjured, and spectacularly better than staring through an empty bottle of Tanqueray.
Yet based on my three observations (small sample, I know), “flash” isn’t quite the word I’d use to describe the phenomenon. To me, “flash” implies something quick and bright, like lightning or a camera flash, neither of which is similar to what I saw. The green color was fleeting, to be sure, but it simmered rather than burst, and oozed instead of erupted. It was more of a “green glow” or a “green smear.”
Regardless of what you call it, the green flash occurs because Earth’s atmosphere bends and scatters light from the departing sun. When viewing conditions are just right, green wavelengths reach our eyeballs and the rest are filtered out. Normally, “just right” conditions include a clear, unpolluted horizon that’s free of clouds and haze, which more or less describes a lot of places that aren’t Los Angeles or Beijing; people most commonly report seeing green flashes over the ocean, though a watery horizon is not a requirement.
Green colors can also appear at sunrise, though they’re tougher to see than at sunset, and can sometimes appear just above the sun, rather than being smeared over its disk. And, it turns out, 8-year-old me wasn’t totally wrong after all: A rare class of “flash” actually appears as a ray extending upward from the sun.
So why it is so unusual to see? One explanation is that under normal circumstances, the green flash is so quick that it’s imperceptible unless an inversion layer in the atmosphere helps the color stick around for longer. But I’m not really sure. I suspect it’s something like the recipe I got from one of my favorite bakeries for the most delicious (vegan) cupcakes I’d ever met—even after following the recipe to the letter, my cupcakes didn’t turn out as well. As with those mysteriously good cupcakes, the recipe for green flashes probably involves a bit of secret sauce, because even under the best circumstances, it’s tough to predict when it will appear.
I’m told that seeing the phenomenon from Kauai is nothing special, though it is sometimes extreme enough to temporarily stop table service at restaurants in town. What this suggests to me is that visiting Kauai in winter is pretty much a must-do, for reasons that have nothing to do with mai tais that come in pints, swimming with sea turtles, and braving extremely muddy trails that take you through some of the rainiest places on Earth. We’re used to seeing a lot of colors at sunset, but green isn’t one of them—and when it does appear, the green flash is exquisite.