‘I’m happy just to be with you
And loving you the way I do;
It’s everything I need to know
Just resting in the afterglow of your love…’
Afterglow; Small Faces 1968
As we write this, the 22nd of March, we also note that the departure time of our popular Champagne Sunset Cruises changes to 18h00 or, for the landlubbers or those without a military background, six o’clock in the evening. As winter approaches the days shorten, the nights lengthen and we must adjust. There is not much point in cruising out of Cape Town harbour aboard a luxurious catamaran just to catch the afterglow of an Atlantic sunset. The joy and spectacle of the daily setting of our own star needs to be savoured like a vintage wine: taking in all the notes and nuances of the enchanting process.
Like snowflakes, every sunset is different. We probably tend to miss the process most evenings during the normal course of our lives, unless there is a particularly spectacular array of colours on show, but at Waterfront Charters the sunsets are so much part of our daily lives and routine that we can’t help but see the differences – great and small – that make each setting unique. Obviously when the cloud cover is ten tenths, we don’t see Sol vanishing at all, so that doesn’t really count, but on every other evening some subtle – or dramatic – atmospheric twist will paint the sky in a new fashion.
These colours all start out as the white light that our sun blasts out in regular fashion; it’s the atmosphere that provides the palette to add the amazing tints to the stream of photons. The array of rainbow colours that make up the white light (think prism here) hit the atmosphere – much thicker at sunset that during the day due to the angle – and some of those colours are scattered out of the beam of light by hitting gas molecules and airborne particles, leaving the other colours to reach our eyes. Blue and green have shorter wavelengths, and without going too much into the science, these are more easily scattered and removed from the beam. The remaining longer-waved red and orange colours then hit the water droplets in the air and are further scattered into the many hues that light up the horizon. With a little nod to the technicalities, the scattering of the shorter wavelengths is called Rayleigh scattering, and the secondary scattering by cloud drops and other airborne molecules is known as Mie scattering, and is not wavelength dependent.
Of course, man has contributed greatly to the Mie scattering by filling the atmosphere with a wide range of pollutants and other larger molecules. This has a noticeable effect on sunset; one of the reasons the evening displays are normally more highly coloured than sunrise is due to the fact that the day has had human-created airborne detritus from industry and travel filling the sky. By morning, much of this has dissipated and so the process begins all over again. But humans aren’t totally responsible for all these molecules; our planet (despite being around four and a half billion years old) is still fiery at heart, and volcanos are continually spewing out clouds of ash that can produce a wide variety of changes to the panorama. Interestingly, these changes are height dependent: in the troposphere ash will mute sunsets, but, as it reaches the stratosphere as tiny sulphuric acid droplets, it can create vivid colours both at sunset and post-sunset. These latter displays are known as afterglows, and are also notable because they can be reflected in the eastern sky; a sort of stereo-vision sunset effect.
So when is sunset, exactly? It’s when the top rim (trailing edge) of the sun disappears over the horizon, whereas sunrise is when the tip of the sun (leading edge) emerges over the eastern horizon, meaning that days are around ten minutes longer than nights in true terms. Who knew? And of course, this is further complicated by the fact that the refraction of light as it passes through the atmosphere means that we can still see the sun although it has actually dropped below the horizon. This refraction also generates that rather odd illusion that the sun is fattening out as it ‘hits’ the horizon: light from the bottom edge is more highly refracted than the top edge, reducing the apparent height of the sun.
But…the best way to see all this is with a flute of chilled bubbly in your hand with your other arm around someone you love, standing on the deck of a luxury Waterfront Charters catamaran. Check out our range of cruises and treat yourself to one of Nature’s most thrilling spectacles. The science may be fascinating, but the romance of the occasion trumps everything.
