SEA SIGNS

THE SUN

In the eleventh instalment of our Sea Signs series William explores how the sun affects our adventures and shares tips for navigating by the great ball of fire.

11. THE SUN.jpg

THE SUN

Tracking the sun’s progress through the sky can reward us in all sorts of ways; for some, shifting a scantily dressed body into perpetual alignment with this great ball of fire is the secret to a perfectly even tan and a day well spent. For others, synchronising with the sun’s motions provides a framework to live by; an emotional guide, even. The rising sun, like the Spring Equinox, is a time of anticipation. This is followed by noon, or the June Solstice, when the sun is burning brightest, along with our energy levels. This never lasts long enough though, because soon it’s sunset, or the Autumn Equinox; a time for quiet reflection. And after all that excitement, we ultimately need to rest; this is a good use of midnight, or the December Solstice, when we hunker down and try to remember what the sun felt like. 

 

To make the most of the sun we need to understand its movements - or lack of - because although the sun appears to move across the horizon, it is in fact stationary. It’s the earth that is moving, rotating 360 degrees every 24 hours. This means that the earth rotates 15 degrees every hour, a crucial figure that we’ll come back to time and again in this feature. The infographic below helps explain the theory; when you’re at Line A, you are entering the area lit by the sun and the effect is ‘sunrise’ in the east. In six hours, you’ve moved 90 degrees and are now at Line B. This is ‘local noon’, the moment the sun is highest in the sky and due south. Six hours later you’re at Line C, leaving the area lit by the sun with the effect of ‘sunset’ to the west. For the next twelve hours you’ll be in the darkness, obscured from the suns rays until returning back to Line A.

ANIMATION: EARTH ORBIT, DAY

While the earth is rotating on its axis, it’s also orbiting the sun. This is half the cause of seasons; the other half is a mars-sized asteroid that crashed into the earth millions of years ago, knocking it over by 23.5 degrees [the rock fragments then created the moon – but that’s a whole other story]. For now, the main thing to remember is that the earth is tilted at 23.5 degrees, so as it orbits the sun once a year the northern and southern hemispheres receive differing amounts of sunlight. This is what creates seasons. At the December Solstice, the Northern Hemisphere is tilted away from the sun, so we receive less light and experience winter. Six months later, the Northern Hemisphere is tilted towards the sun, so we receive more light and experience summer. The times directly between the Solstices are known as the equinoxes with both hemispheres receiving equal amounts of light; equi means equal and nox means light. 

 

Now that we understand how the relative positions of the sun and earth create days and seasons, we can put the theory into practice and play some games. The first is perfect on summer days when you’re planning to be at the beach for a long time - but it only works if you arrive in the morning. Start by sticking a piece of driftwood in the sand and placing a shell or pebble at the end of the shadow. As the shadow moves with the sun, keep placing markers at the tip of the shadow and by the afternoon you should have a great arc that curves in towards the stick. Now draw a line between where the arc is closest to the stick, and with the base of the stick itself, and it will point due south. This is because when the sun is due south [at local noon] it is also highest in the sky, meaning it casts the shortest shadow on a north/south axis. 

“draw a line between where the arc is closest to the stick, and with the base of the stick itself, and it will point due south”

For something a little quicker, there’s a fantastic trick to finding south using your watch. Point the hour hand at the sun and imagine a line halfway between it and 12 o’clock. This will be due south. I must have been told this trick a dozen times, and I could never remember which way around it went, so when I was planning this feature I decided to put a little thought into the theory and discovered how it works; now I understand the principle I’ll never forget again. The key is to remember that at 12 noon the sun is due south, and it moves westwards through the sky at 15 degrees every hour. Now imagine the watch face as a compass, and you will see that every hour represents 30 degrees. This means that the hour hand moves around the clock face at twice the speed that the sun moves around the horizon, which is the secret to the trick. So, at 3 o’clock the hour hand has moved 90 degrees from its noon position, but the sun has only moved 45 degrees from its noon position of due south. This is why the ‘imaginary’ line pointing south is half the distance from noon as the hour hand.

 

As well as giving us a sense of bearing, the sun can tell us exactly where we are. Firstly, you need to imagine the earth’s surface sliced into vertical and horizontal cuts, officially called Parallels of Latitude and Meridians of Longitude. To remember which is which, I imagine longitude running along - so if you are travelling along the equator, it is your longitude that is changing. There are 360 degrees of longitude, with each one measured up to 180 degrees east or west of an imaginary line running from North Pole to South Pole and passing through Greenwich.  In contrast, your latitude is the angular distance north or south of the equator, with the North Pole being 90 degrees north, the Equator being 0 degrees and the South Pole being 90 degrees south. Being a long and thin set of islands, Britain’s latitude ranges a huge amount, from 49 N in Lands End to 60 N in the Shetland Isles. 

PRODUCT VIDEO: STAR COMPASS

Now for the magic; by measuring the height of the sun above the horizon you can work out your exact longitude and latitude. For this you need a watch, a book called the Norie’s Nautical Tables [showing the position of the sun throughout the year] and a sextant [stifle the giggles]. Before your mind gets carried away imagining unusual toys, this is in fact a very serious tool and its name has purely intellectual origins; it comes the Latin for one sixth, because its frame is 1/6 of a circle. Although sextants look intimidatingly complex, they actually only take a few minutes to master and their function is very simple; to help you measure the height of the sun above the horizon. By doing this at exactly 12 noon, and comparing your reading with where the Almanac says the sun should be, you can quickly work out your latitude, or position north of the equator.

 

Now for your longitude. This is based on the theory that the earth is rotating 15 degrees every hour, or 1 degree every 4 minutes. With your watch set to Greenwich Mean Time, you can work out your longitude by finding the time difference between your local noon [when the sun is highest in the sky] and that of Greenwich. For example, if your sextant readings show that local noon was at 12:04, your longitude must be 1 degree west. Bisect this with your latitude and you have an exact position, anywhere in the world! If you’re in Britain your longitude should be between 10 W and 1E; if you find local noon at 1pm Greenwich Mean Time, you must be 15 W and out in the Atlantic Ocean, so to get back to Britain you need to head east – and after this feature you’ll have no trouble navigating with just the sun as a reference. 

In the next and last Sea Signs feature William will uncover what we can learn by watching people in and around the water.

About this series

Every day the sea is different, a  result of the ever-changing interaction between the moon, sun, tides, wind, waves,  buoys, boats and the beach. While the picture may appear complex, like a piece of classical music, it is essentially just an arrangement of simple elements, or notes. By dismantling the machine into its component parts and exploring each one in detail we can create order out of chaos; clarity out of confusion. That is the  purpose of this series 'Sea Signs'.

When we are young we learn to navigate urban environments; what traffic lights  mean or how to cross a road. What many of us aren’t taught is how to read nature’s  signposts; how to judge wind by watching birds or what weather different clouds  bring. Then there’s a whole technical world of buoys and boats with different light  sequences, colours and signals communicating messages. My goal in this series is to  share with you all the signs – both natural and man-made - that you may encounter in  your adventures along the coast so you can read them as well as any yachtmaster  skipper or crusty old seadog. 

With this knowledge, nothing is going to slip under your radar.