Wednesday, January 11, 2006

The Green Flash is Real and I've Seen It

A common topic of discussion among blue-water sailors is whether one has seen the illusive "green flash". Invariably, most don't believe it happens, some believe and maybe one in a couple hundred have actually seen it. I fall into the last category. I have been fortunate enough to see it three times, twice in the Western Pacific and once about 200 nautical miles North of Hawai'i.

When the sun is just below the horizon, some rays are refracted by the atmosphere and are thus visible. That causes twilight. If the conditions are just right, the atmosphere may act as a prism and split the light into its component wavelengths as it passes your position. Just for a fraction of a second, one may see the flash of green (or even violet or blue, which makes sense theoretically, although the green is easiest to see).

The phenonenon is rare because the atmosphere is rarely clear enough, and people rarely observe the sun at just the right time. I know navigators who have observed sunsets hundreds of days at sea and missed it every time.

The beautiful image below was captured by a Finish photographer in 1992. I found it via Google, posted as a Goddard Spaceflight Center Astronomy Image of the Day.

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