The Green Flash

[tartansailor]

Greetings,
I wrote this for the Nyack Boat Club news letter many, many years ago and just happened to run across it while looking
for something entirely different. Being the 4th of July I offer it for your enjoyment.

THE GREEN FLASH

The term Green Flash means different things to different Nyack Boat Club skippers. To the denizens of the popular watering hole up the street it probably means an inspiration! To Lightning champion wannabees it probably conjures up memories of floggings and humiliations at the stern of a certain green woodie skippered by Gary Urban in years past; but to our Nyack blue water sailors, they know that it is a common celestial phenomenon.
For the benefit of the very few landlubbers in our midst I would like to invite your attention to an excellent description found in Bowditch: American Practical Navigator, 1977, p882.
“As light from the sun passes through the atmosphere, it is refracted. Since the amount of bending is slightly different for each color, separate images of the sun are formed in each color of the spectrum. The effect is similar to that of imperfect color printing in which the various colors are slightly out of register. However the difference is so slight that the effect is not usually noticeable. At the horizon, where refraction is maximum, the greatest difference, which occurs between violet at one end of the spectrum and red at the other, is about 10 seconds of arc. At latitudes of the United States, about 0.7 second of time is needed for the sun to change altitude by this amount when it is near the horizon. The red image, being bent least by refraction, is the first to set and the last to rise. The shorter blue and violet colors are scattered most by the atmosphere, giving its characteristic blue color. Thus, as the sun sets, the green image may be the last of the color images to drop out of sight. If the red, orange , and yellow images are below the horizon, and the blue and violet light is scattered and absorbed, the upper rim of the green image is the only part seen, and the sun appears green. This is the green flash.”
“The phenomenon is not observed at each sunrise or sunset, but under suitable conditions is far more common than is generally supposed. Conditions favorable to observation of the green flash are a sharp horizon, clear atmosphere, and temperature inversion. An attentive observer may see this phenomenon, which is more common at sea, as many as 50% of sunsets and sunrises”
“Duration of the green flash (including the time of blue and violet flashes) of as long as 10 seconds has been reported, but such length is rare. Usually it lasts for a period of about ½ second to 2½ seconds with 1.25 seconds being average. This variability is probably due to changes in the index of refraction of the air near the horizon.”

Richard Papp

[David Morton]

Yes Indeed! Witnessed by my own self, several years ago on the West Coast, while watching the sunset at Half Moon Bay Golf Links. A somewhat mollifying experience after an afternoon of stinking up the golf course. Even more mollified by the multiple martinis that followed...

David