Navigation

The art of finding the way from one place to another is called navigation. Until the 20th century, the term referred mainly to guiding ships across the seas. Indeed, the word "navigate" comes from the Latin navis (meaning "ship") and agere (meaning "to move or direct"). Today, the word also encompasses the guidance of travel on land, in the air, and in inner and outer space. One of the earliest navigation instruments was the plumbline, used to measure the depth of water. The log was used to determine the speed of the ship relative to the water.


There are four standard techniques:Piloting;Dead Reckoning;Electronic navigation;Celestial navigation;

Piloting is a simple method in which the navigator directs a vessel from one place to another by observing such landmarks on the earth's surface as lighthouses, beacons, buoys, prominent rocks and cliffs, and by measurements called soundings of water depths.

Dead Reckoning involves keeping careful track of the ships direction and distance in different ways from the origin in order to predict it's location.In dead reckoning, east-west travel was facilitated by maintaining the Sun at the same degree above the horizon. Pointing a finger of an extended arm at the Sun at noon and maintaining every day the same angle the arm makes with the body, would guarantee a true east or true west direction. Changing the angle, that is, lowering or raising the arm, would cause a shift in the direction away or towards the horizon. In dead reckoning, a pilot could calculate the distance traveled in an hour or a day by measuring the time that it took a floating device to travel the known length of the ship, from the bow to the stern.

Electronic Navigation is a modern technique that is the most common and advanced method using the capabilities of RADAR.A pulse is sent that deflects of ships,buildings etc. and a RADAR image is plotted representing the bodies around the vessel.

The Loran C system sends electronic pulses from stations at known locations on the shore. The travel time of the signal from the stations to the ship is used by a Loran C receiver to automatically calculate latitude and longitude. This allows a navigator to plot the ship's position precisely on the nautical chart

The more recent modern system however is Global Positioning System that measures the distances with the help of numerous satellites.

Celestial Navigation uses the motion of the Earth relative to the sun and other stars to determine position. In the northern hemisphere, the star most used by the celestial navigator is Polaris, the north star. This is a bright star that appears to be directly over the North Pole. The Earth moves about it's axis and hence the stars appear to be moving accordingly in a circular manner.The Polaris is the center of this circle and hence helps to pinpoint North.This is comparitively difficult towards the South Pole where there is no central star to guide the way.Timings of sunset and sunrise need to be noted and corresponding positions are calculated generally with a chronometer or sextant.