Navigation - Lat and Long by Finbar

Since the beginning of our voyage, we have been using GPS (Global Positioning System) to determine our position. This has allowed us all to concentrate more on learning to sail. Now that we are all more confident we have been relying on it less and less.
Navigation is the process of finding your position relative to your destination and then, after plotting the shortest, easiest and safest route to that destination, calculating the information needed to follow that route.


The hardest part of this process used to be the first, finding your position. However, with the advent of satellite§ navigation (GPS) this has become simply a mater of pressing the right buttons. Before the days of synthetic hydrocarbons[1] and silicon chips, navigators had to use other means. While on long sea passages, out of sight of land and any landmarks, the only way to calculate your position was to use the sun and the stars. These navigators had charts to tell them the relative positions of land, relative of course to the position of all the other land. The problem was to pinpoint their position on the oceans. This is why they created a numerical system to indicate any point on the globe.
Upon the surface of the world the mariners superimposed an imaginary grid, similar to those that can be seen in textbooks and maths examinations. The difference between this grid and the graphs in exams is that graphs are drawn on flat paper, where as the world is not flat (as all enlightened people should know), but round like a sphere. It is, in actuality, not a perfect sphere, as it bulges out at the equator and is slightly flattened at the poles, both caused by the effects of the centrifugal force caused by the Earth’s rotation. This is how the navigators solved the problem of an approximately spherical Earth. They took the equator, the line that circles the Earth equidistant from both poles, as the starting point for the horizontal lines. Then they drew lines parallel to the equator, these are called lines of latitude. Therefore the farther away the circular lines of latitude were from the equator the smaller their circumferences became, decreasing in size until they reached the poles.
            The latitude lines are labelled 0˚ at the equator up to 90˚N at the North Pole and 90˚S at the South Pole. They are labelled with a degrees sign because they are equal to the angle that is made when a line is drawn from the equator to the centre of the Earth, to the point on Earth’s surface where you are standing. That is why latitude is measured in degrees. So every different angle has its own line circling the earth. If a more precise measurement is required, degrees are split into 60 minutes, which are again split into 60 seconds. However seconds are rarely used anymore, instead decimals of the minutes are used.
While on our voyage we have kept a log every hour noting down, among other things, our GPS position. It was exiting to watch as our latitude slowly decreased, first showing 49˚54´N (Lizard Point) then 42˚11´N (Bayona, north west Spain) then 37˚09´N (Cape Saint Vincent, south west Portugal) and now down to our current latitude 33˚03´N (Porto Santo, Madeira Archipelago).
The vertical grid (longitude), to indicate how far around the Earth you are, is more complicated as there is no starting point like the equator. So an arbitrarily line to start counting from had to be chosen. These vertical lines run straight from the North Pole to the South Pole and back again on the other side, and they are called lines of longitude. This means that if you were to cut the earth in two along one of these lines of longitude you would always get two equal halves. Any line that you can do this with is called a great circle, or meridian. The only line of latitude that is a great circle is the equator.
The choice of the longitudinal great circle from which to start counting, the prime meridian, was a source of political argument. England chose Greenwich, France chose Paris and several other countries nominated there own prime meridians. Eventually it was decided that Greenwich would be the international prime meridian, however the French continued to use Paris for some time afterwards.
In contrast to our steadily decreasing latitude, our longitude has gone from west to east and back again. Starting at 5˚10´W (Lizard Point) then west to 11˚08´W (Bay of Biscay) turning east along the Algarve coast as far as the Guadiana river 7˚27´W and now currently 16˚07´W (Porto Santo).




[1] Synthetic Hydrocarbons: Any synthetic substance that is composed of chains of hydrogen and carbon i.e. plastic, glass fibre, synthetic fabric, Ex

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