The Green Flash
Image courtesy Mila Zinkova
Near the end of Trail of the Jaguar, as Clayton Porter is paddling a sea kayak north across the Gulf of California (Sea of Cortéz) at sunset, he describes witnessing a brilliant green spark of light just as the last rim of the sun disappears below the sea’s horizon: the Green Flash.
The Green Flash is a very real but seldom-seen phenomenon caused by refraction in the earth’s atmosphere. As the sun nears the horizon, its light passes through more and more atmosphere from the perspective of a viewer on the ground or in an aircraft. More atmosphere equals more refraction. Right at the horizon—especially a sharp horizon, and especially over water—the sun’s different wavelengths of light are subject to different effects. Vapor in the atmosphere absorbs orange and yellow, and air molecules scatter the violet, leaving red and green/blue-green light passing directly through the atmosphere toward a viewer. But long-wavelength red light refracts less than the shorter-wavelength blue/green, which means we see essentially two minutely overlapping suns. The rim of the “red” sun dips below the horizon seconds before the rim of the “green” one—hence the Green Flash, visible by a diligent observer under ideal conditions.
I’ve been lucky enough to see the Green Flash twice. The first time was, believe it or not, in the driver’s-side rear-view mirror of Roseann’s 1978 Land Cruiser FJ55. We were heading inland from the Pacific coast of the Baja Peninsula, and I had a view of the sun as it set over the ocean. Just as it disappeared I gasped, alarming Roseann who had no idea what I’d seen behind us. What I’d seen was a perfect brilliant pinpoint of electric emerald, a slow strobe that winked out as instantaneously as it had appeared.
The second time was actually planned. I was helping run a Tucson Audubon Society Marine Ecology Institute at a remote lodge on the Sonoran coast of the Gulf of California. A fellow instructor and I were discussing the Green Flash, and made plans to watch for it. He then mentioned that someone had told him it was possible to see two Greens Flashes in succession if you scaled a ladder at top speed after spotting one, and looked again.
Sadly we had no ladders, so we hit on a plan B: we’d sit on chairs on the veranda of the lodge, concentrating on the horizon, then leap onto them if we saw the flash.
The first afternoon we sat, glancing sideways at the sun as it touched the horizon, then peering intently as the last arc of it contracted and . . . vanished. Nothing.
We debated the reason for this. High on the probability list was the fairly rough conditions on the water that day. Perhaps, although the horizon looked sharp to us, it was actually too broken up and moisture-laden to reveal anything?
Next evening was the same routine, except this time we slacked off a bit and were sipping ice-cold Pacifico beers as the time neared. Again the arc diminished—and just as it vanished an emerald strobe winked at us.
Beer bottles went flying as we leaped up and vaulted onto the chairs. We spun around and peered at the horizon while two fellow staff members who’d been watching us rather than the sun collapsed in hysterics. But the solar system decided that one Green Flash was enough for us that night.
I’ve since read that the Green Flash can sometimes be seen with a setting moon—or even the planets Jupiter or Venus (presumably using a telescope). It can also be seen at sunrise, although this is understandably even more difficult since it’s harder to know exactly where to watch. Airline pilots flying westward see the flash frequently, as sunset is protracted. On the other hand, near the equator the green flash is of much shorter duration than at higher latitudes, since the sun sets at a more perpendicular angle.
So the next time you’re on a west coast on a calm, clear day, pay particular attention to sunset. You might get cosmically lucky. In the meantime, Goggle “Mila Zinkova green flash” to see more of her stunning images and video.
