The Elastic Scattering of Light, as Viewed Through a Flute

“Long on the wave reflected lustres play.”

Samuel Rogers, The Pleasures of Memory, 1792

Sunset, at it’s most prosaic, can be defined as the disappearance of the sun over the westerly horizon. That horizon can be any geographic feature – from mountains to African plains to oceans. It can even be a spectacular manmade skyline, like New York or Hong Kong, that is silhouetted in front of the red orb. At Waterfront Charters we have embraced this daily occurrence, and one of our great joys is sharing the spectacle with entranced guests. Each evening is different; the clouds, the lighting, the rolling sea where ‘reflected lustres play’. Our experienced skippers and crew members are equally entranced by the ever-changing aspects; it is impossible to be complacent about this wonder of Nature.

At Waterfront Charters we salute the sunset, and one of our great joys is sharing the spectacle with entranced guests.

Of course, like all natural wonders, there is science at play. Knowing the background in no way lessens the impact of what we are watching; if anything it adds to the magic. For starters, there is the continual change in the moment of sunset, but this is no lottery: it has been pinpointed daily to the second. You too can do this! All you have to know are your exact latitude, longitude and elevation. And a few other minor details, like the axial tilt of the earth and its daily rotation time, the variances in the planet’s movement in its annual elliptical orbit around the sun, and the Earth and Moon’s paired revolutions around each other. Put that all together in your pocket calculator, press ‘delete’, then look up the sunset time in your daily paper or online. Simple!

The ever-changing palette that is painted across the evening sky.

Our cruises are tied in to the continual changes in sunset time, of course. If we had to maintain a single departure time throughout the year the Sunset Cruises would vary in length from around ninety minutes to three hours. (Although I doubt we’d get many complaints about the extended cruise.) A reminder here to make sure that when you book your sunset cruise you make a note of the time of departure; watching the sunset from Quay 5 in the V&A Waterfront may still be a great experience, but knowing that the luxury boat you missed is bobbing off the Cape coastline without you aboard may lessen the pleasure.

Then there are the colours; the ever-changing palette that is painted across the evening sky. From dramatic reds through the spectrum to pastel yellow and orange, the sun never runs out of artistic ideas. Once again, science can tell us all the reasons, and we believe this adds to the experience. That spectrum mentioned above is caused by the sun’s white light being scattered by air molecules and airborne particles (sadly, pollution can occasionally be beautiful…), and the shorter wavelengths – the blues and greens – scatter more strongly, leaving the longer wavelength orange and red hues that typify a sunset. Add in the water vapour that is suspended in the atmosphere, and the longer wavelengths are scattered even more, causing the red light to dominate, which is called ‘diffused sky radiation’. (For those who really want to know the detail, this is called Rayleigh Scattering, after British physicist Lord Rayleigh, and is ‘the predominantly elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the radiation.’ Now you know.) There is another effect that must be taken into consideration, and this is known as Mie Scattering: the effect of clouds upon the already scattered light. Put all this together and…here’s a thought: hold up a flute of bubbling liquid as you stand on the deck of one of our beautiful boats and look at the sky through this. You can call it Effervescent Scattering, then drink the chilled sparkling wine and feel a bit of sunset course through your system. Perfection!

The bottom edge of the Sun’s disk is refracted more than light from the top, reducing the apparent height of the solar disk.

There is one other illusion that that needs to be addressed: why does the sun look flatter as it settles, seemingly trying to push itself into the ocean? Simple answer: light from the bottom edge of the Sun’s disk is refracted more than light from the top, reducing the apparent height of the solar disk. Its width is unaltered, so the disk appears wider than it is high. Intriguingly, the refraction plays another trick on the eyes too: the sun you are looking at has already set; what you are seeing is the light bent up and over the horizon. On second thoughts, we prefer the thought of the sun shoving its way into the Atlantic, although there might be a little more steam if this was the case.

Waterfront Charters Sunset Champagne Cruises: the perfect way to witness Nature, Science, Scattering, Refraction and Effervescence. The perfect way to celebrate the end of a day; with like-minded friends and family, aboard a luxury boat on the iconic Atlantic Ocean. There is an alternative too: if you are an adrenaline junkie as well as wanting to experience all of the above, choose a Sunset Cruise aboard one of our two high-powered speedboats. No champagne (too delicate for this adventure), but you can quaff a delicious beer or thirst quenching soft drink after a thrilling ride, and raise your bottle to that huge ball of fire as it slips below the waves. You have 365 options every year – like snowflakes, no two are alike!