If you have never seen a green flash before it is a momentary phenomenon that happens under the right circumstances that causes the color of green to be visible for a second or two at the very top of the disc of the sun as it just sinks behind the horizon at sunset. Conversely it can occasionally also be seen just seconds before the sun rises in the morning. One must be very focused at the final moment before the sun disappears because if you blink you might miss it.
The perfect conditions to see a 'green flash' as the sun sets can often be found on your Kauai sunset sails. Perfect conditions generally include a few criteria: seeing the sun set on a flat surface like the surface of the ocean, viewing the sunset from many miles away, having clear and non polluted conditions and having a non cloudy horizon. Since these conditions happen with such regularity on Kauai it is almost a staple for sunset sail boats here.
The cause of the green flash has to do with the refraction of the sun's rays just as it dips into the ocean. The earth's atmosphere will bend the last visible rays of the sun in the same manner as a prism. The colors of the spectrum with the longest wavelengths will disappear first and the shortest will disappear last. Because violet and blue have shorter wavelengths than green you might think that they would be the last color to be seen, and occasionally they are as in the rarely seen 'blue flash' but in order for that to happen the atmosphere needs to be exceptionally clear.
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