Rare green flash at sunset is more than pirate folklore

ORLANDO, Fla. – Have you ever watched the sunset on a clear evening and briefly seen a flash of green on the horizon?

The chances of someone seeing this phenomena are slim. In fact, under the right conditions it happens so fast that most people blink and miss it. The flash of green is so rare and unpredictable it’s often thought of as a myth or legend among mariners and in movies such as “Pirates of the Caribbean.” It’s better than folklore, it’s science.

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The green flash spectacle is due to Rayleigh scattering. This is the scattering of light particles without a change in wavelength. In this case, the atmosphere becomes a prism, scattering the light into the different colors people see. During the day, the sky looks blue because the sun is higher in the sky, resulting in a shorter distance for light to travel so the colors aren’t scattered or separated well.

During sunrise or sunset, the sun is closer to the horizon and the light has a longer distance to travel and bend, resulting in more color division by the time it meets the human eye. When the color red or orange appears, shorter wavelength colors are separated more than the longer wavelength light, so we see more longer wavelength colors.

In order to see a green flash appear where the sun is, the conditions have to be perfect. It needs to be a clear night with no haze or clouds around. The view matters too. There has to be no obstructions in the view of the horizon and there has to be a very distinct edge. This is why most green flashes are seen over the flat horizon of an ocean, but it can also be seen on land over a long distance. As the sun sinks under the very specific conditions, a green burst of color will appear for roughly one to two seconds.

This same flash can happen at sunrise too, but is even harder to catch because the sun is coming up, dipping very low on the horizon but making it easier on the eyes. Remember that it’s dangerous to look directly at the sun as it can damage the eyes.

The green flash is so rare to see, most think they’re seeing things that aren’t there.

Back to the folklore. In the movie “Pirates of the Caribbean: At World’s End,” the deck crew refer to the flash of green light right as the sun is setting, saying it’s a soul coming back to this world from the dead. Another saying is if someone sees the green flash they will never go wrong in matters of the heart. An English weather proverb says Glimpse you ‘ere the green ray, Count the ‘morrow a fine day.

Despite these sayings, it all comes down to weather science. Pretty cool, right?