NAVIGATION Navigation is the science of planning and following a route For centuries sailors had no way to chart their course other than to use math to figure out their location Tn the third century BCE the Greek mathematician Eratosthenes had the idea of placing an imaginary grid around the Earth The grid had lines running from north to south and from east to west In around 120 BCE a Greek astronomer named Hipparchus used math to plot locations on these lines He used a method modern mathematicians call triangulation Early ships like this Phoenician galley usually stayed close to shore so sailors Could navigate by using landmarks on coast the
SCIENCE FILE Triangulation is based on the idea that someone who knows the length and angles of one side of a triangle can figure out the length of the other two sides ooooo FILE MEASURING LATITUDE A position north or south on Earth is called latitude A position from east to west is called longitude Sailors found their latitude by measuring the angle of the sun or stars above the horizon They then used a version of triangulation to figure out their position on the globe Sailors measured the angle of the sun or stars in degrees of elevation The first sailors held out their arms and used their fingers as a rough measure In the ninth century Arabian navigators invented a device called a kamal The kamal used knots in a string to measure angles Dead Reckoning Before it was possible to measure longitude sailors used dead reckoning to calculate their position This method was based on the ship's last known position called a fix The sailors used their speed direction and how long they had been sailing to figure out their new position If one fix was wrong however later fixes became even more inaccurate On a long voyage sailors might think they were hundreds of miles from their true position oooooooooooooooooo The kamal was a piece of wood with a knotted string One of the knots was held in the teeth and the kamal was held out at arm's length Matching up the edges of the board with a known star and the horizon gave the sailor latitude his
The sextant gets its name because its In the 1750s the English mathematician curved scale covers John Bird invented the sextant This instrument about 60 degrees or measured the angle between any two objects one sixth of a circle In Latin sextans It helped sailors calculate latitude accurately means one sixth MARINE CHRONOMETER From the late fifteenth century the ships of Europe's navies explored the world Europeans set up new trade routes and colonies or overseas settlements Sailors needed a way to measure longitude For this they needed to know the exact time Most clocks and watches kept time poorly on sea voyages The problem was solved in 1735 The Englishman John Harrison built an accurate watch called a marine chronometer It compared the time on the ship with the time in London That helped sailors figure out their position by studying the position of the sun For the first time precise seafaring navigation possible was
SCIENCE oooooS FILE FILE USING RADIO In the late nineteenth century naval commanders began to use radio for navigation Scientists invented a Radio Direction Finder RDF before World War I 1914 1918 Ships and aircraft carried a special antenna The antenna picked up signals from two different radio posts The RDF used the signals to do triangulation This calculation helped engineers to figure out the position of the ship or aircraft Radio was the main means of sea and air navigation during the twentieth century GPS In 1974 the first Global Positioning System GPS satellites were launched into space GPS satellites broadcast a continuous signal that is picked up by receivers on board ships The GPS identifies a ship's precise location These days even the smallest of sea vessels carries GPS Engineers working for the US Army test updated Radio Direction Finder equipment in 1929 The round device is an antenna for receiving signals radio
