Sunday, May 29, 2016

The Green Flash

The General Hoyt S. Vandenberg steamed southeast at a leisurely eleven knots across the South Atlantic between Ascension Island and South Africa in late September of 1979.  A clear sky, a mild temperature, excellent visibility, and a calm and bright blue sea served as the daily standard in these subequatorial latitudes.  Classified as a range instrumentation vessel, the General Vandenberg conducted vital national defense missions for the federal government.  For this purpose, she carried an army of technicians who worked with a large assortment of electronic gadgets. Most of the crew, myself included, knew little or nothing of what these technicians actually did.  We just sailed the ship for them. 

In the late afternoon one day, several technicians gathered on the outside deck near the starboard bridge wing to watch the Sun set.  The second mate, an older man named George Hebb, stood on the bridge wing, and seeing the technicians gathering, called down to them: “Get some binoculars and watch carefully as the Sun goes down.  The conditions look good today.  You should see the green flash.”

Dumbfounded by this suggestion, they asked George what he was talking about.  He then explained the green flash to them.  In response, they exchanged puzzled expressions with raised eyebrows and laughed at him.  Finally, one of the technicians asked him bluntly, “Have you been drinking?”

“No!!  I have not been drinking!!” thundered the insulted second mate at his skeptical audience.  “What do you take me for?  A Bowery bum?  You guys want to be called scientists and you don’t know how the world works?  Just watch when the Sun sets and you’ll see what I’m talking about!!”

Normally a very congenial and mild mannered man, George Hebb seldom got annoyed. His outburst silenced the “scientists,” however, and they waited and watched the Sun quietly.  Binoculars in hand, I waited and watched, too, as did George on the bridge wing above.  The Sun set slowly, and as predicted, just when the upper limb approached the horizon, the small remaining section of the Sun turned bright green for perhaps two or three seconds.  Then the  Sun set completely, and it was all over.

The assembled technicians had seen the green flash, and so they now believed what the second mate had told them.  Also, they no longer questioned his sobriety.  Vindication!  But their initial reaction on hearing about the green flash was actually quite typical.  Most folks have never heard of the green flash and have never seen it, and as ignorant people often do, they ridicule what they do not know and have not experienced.  Thirty-seven years after this event aboard the General Vandenberg, the green flash has new credibility in the form of a Wikipedia article[1] and YouTube videos[2].  I’ll stand by the simple and straightforward description set down in the American Practical Navigator, however:

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.  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 last to rise.  The shorter wave blue and violet colors are scattered most by the atmosphere, giving it its characteristic blue color.  Thus, as the sun sets, the green image may be the last of the colored 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 generally supposed.  Conditions favorable to observation of the green flash are a sharp horizon, clear atmosphere, a temperature inversion, and an attentive observer.  Since these conditions are more frequently met when the horizon is formed by sea than by land, the phenomenon is more common at sea.[3]

I have seen the green flash many times aboard several ships.  Day after day aboard the General Vandenberg in the South Atlantic, the green flash was clearly visible.  Aboard the Rigel and the Waccamaw in the North Atlantic and the Mediterranean, the green flash was a fairly common event.  I’ve never seen it in the Pacific or the Caribbean, though, nor in the far North Atlantic or the North Sea.  But each time the green flash occurs, it is a magnificent sight to behold, however briefly.  The green flash proves the point that:

They that go down to the sea in ships, that do business in great waters;
These see the works of the Lord, and his wonders in the deep (Ps. 107:23-24).

How fortunate my shipmates and I were to repeatedly witness such a spectacle!  Such a simple and small thing—the last sliver of the Sun changing color from orange to green for the last few seconds of its setting.  Then it disappears below the horizon, and the twilight gradually turns into darkness.  This is the daily transition from daylight to nighttime, and the green flash plays a small but significant role in the drama.  The “wonders in the deep” indeed!

After my Merchant Marine career drew to a close, I thought that I would most likely never see the green flash again.  And, in fact, I did not see it for many years.  Then, quite unexpectedly and in a very unlikely place, I did once again enjoy this opportunity.

Miss Patty and I sailed aboard the ferry John H from New London, Connecticut, to Orient Point, Long Island, on Friday, November 1, 2013.  The ship left New London at 5:00pm, when the Sun was low in the western sky.  While the vessel was crossing the eastern end of Long Island Sound, the Sun cast its low altitude light on a scattered collection of altocumulus and stratocumulus clouds.  This illuminated the sky in a wild assortment of vivid blue, yellow, orange, and pink.  It was a truly spectacular sight.  I remained out on deck to watch this display, and to see the Sun set as well.  As the Sun dropped closer to the horizon, I began to wonder if there would be any chance of seeing the green flash.  The conditions looked good for it.  The air was clear, the visibility excellent, the horizon sharp, but somehow Long Island Sound seemed an unlikely place for it.

Nevertheless, I waited and watched as the Sun approached the horizon and started to set.  Even without any green it was still a magnificent and breathtaking sight.  Then, as the upper limb came down closer to the horizon, I looked more carefully, even to the point of eyestrain, hoping but not expecting to see the flash once again.  Finally, it happened.  Small and faint and fast, the green started in the corners and in a second filled the center of the remaining Sun.  Then it all disappeared as the Sun set completely.  It was quite literally a flash.  It lasted at most a second and a half.  The twilight lingered for a while as the now set Sun illuminated the clouds from below the horizon.  This faded gradually as night came over the sea.  When the John H docked in Orient Point at 6:30pm, the sky was fully dark.

The green flash demonstrates a few points above and beyond the laws of physics as they are described in Bowditch.  First, it illustrates the folly of human wisdom.  The technicians aboard the General Vandenberg laughed at a fully competent licensed officer who knew his astronomy, but he had the proverbial last laugh when Nature irrefutably proved him right.  More importantly, this episode proves one of the laws of truth.  If something is true, then it is true even if someone doesn’t believe it; even if no one believes it, it remains true.

Finally, the green flash speaks to us spiritually.  As one of the many beauties of the natural world, it bears mute testimony to the scientific and artistic genius of a divine Creator.  It calls to mind the Psalmist’s famous exclamation, “The heavens declare the glory of God” (Ps. 19:1), a thought that occurs to me often when I gaze skyward.  No mere human could design, let alone create, the world and the universe that we inhabit.  And yet, we are privileged to enjoy this beauty in the same way that we would study the work of a famous artist.  Many such studies of the heavens have been made, and they have yielded extensive scientific knowledge.  Nonetheless, there remains something transcendent and ineffable about this realm.  In the end, perhaps the best we can do is acknowledge as the Prophet did that:

The heavens were opened upon us, and [we] beheld the celestial kingdom of God, and the glory thereof (D&C 137:1).

[1] See
[2] A few of these are very good; many are mediocre; and some are obvious fakes.
[3] Nathaniel Bowditch (original author), American Practical Navigator: An Epitome of Navigation, Volume 1, Washington, DC, Defense Mapping Agency Hydrographic Center, Publication No. 9, 1977, p. 882.  This book has been issued in many editions, revisions, and expansions  since its first publication in 1802, and has served as the standard reference work for Merchant Marine officers throughout its lifetime.  Aboard ship it is referred to simply as “Bowditch.”

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