No, not a post about Mark Cavendish and the odds of his winning the green jersey in this year’s Tour de France but about the tantalising, elusive burst of green light that occasionally comes with sunrises or sunsets at sea – at the precise moment leading edge of the sun’s disc rises above the horizon in the morning, or the instant the last of it slips below the horizon at dusk. People who have never witnessed this phenomenon often dismiss it as a myth or optical illusion, but it exists. I have had the optics of it all explained to me by an atmospheric physicist, who described the warping of the first (or last) rays of the sun as they burst over the horizon so that the rays of green light are the only ones through the atmosphere – for just a brief microsecond. It is most readily observed on the flat horizons at sea, particularly when the sky is clear and the atmosphere is still. There is even a violet flash, but this is rarer. I have only ever seen the violet flash once, while sailing through the Doldrums between West Africa and Brazil on a clear still morning when the sea was like glass.
I have seen the green flash, on the other hand, many times, as recently as this morning when I watched the sunrise from the hilltop house where I am staying. It was beautiful and very, very transitory. It is never an easy thing to photograph. I had my camera trained on the spot where I knew the sun was about to rise and my reflexes (and the camera’s) were nearly quick enough to catch the green flash in its prime. It was fading to yellow-green when the shutter closed. So here it is. I’ll do Mark Cavendish another time.