What is a navigation ??

Navigation is the art and science of determining one's position so as to safely travel to a desired destination. Different techniques have evolved over the ages in different cultures, but all involve locating one's position compared to known locations or patterns.

Modern Navigation

Simple navigation begins with pilotage which is knowing your position in familiar territory by orienting oneself to visual landmarks. One can also use a map, nautical chart or aeronautical chart to perform pilotage in unfamiliar locales. Maps are normally used on land where they depict surface features such as roads that might be followed; charts are used on sea and in the air where they depict obstacles that must be avoided. A compass can assist in orienting the map or chart, obtaining bearings to landmarks and for maintaining a steady direction of travel. A sextant can be used to measure the angle of a star above the horizon or the angle between two terrestrial landmarks.

Where landmarks are not visible, other techniques must be used. Dead reckoning allows the navigator to deduce their position by advancing their position on a chart using their known course, speed and time of travel. After compensating for the effect of winds or currents, an estimated position is derived. Celestial navigation is most often used out of sight of land using the Sun, Moon, stars and planets as reference points. In addition to the sextant mentioned above, celestial navigation requires an accurate time source such as a chronometer and a nautical almanac. A calculator or sight reduction tables ease the required spherical geometry calculations. Some facility for plotting the resultant lines of position is also required.

The basic technique of the navigator is to derive a line or circle of position. This can be accomplished by taking the bearing to or distance from a landmark and plotting the resultant line of position or cicle of position on his chart. Where two lines of position intersect establishes a fix. If only one line of position is available, this may be evaluated against the dead reckoning position to establish an estimated position. A third line of position is always sought in order to verify the first two lines of position. The three lines of position rarely meet exactly but normally form a triangle (called a "cocked hat") on a chart. The size of the triangle is affected by many factors, the vessel may be within or occasionally outside the triangle, but as a general rule the larger the triangle, the less certain the position.

Lines (or circles) of position can be derived from a variety of sources: a) celestial observation (actually, a short segment of the circle of equal altitude, but generally represented as a line, b) terrestrial range (natural or man made) when two charted points are observed to be in line with each other, c) compass bearing to a charted object, d) radar range to a charted object, e) on certain coastlines, a depth sounding from echo sounder of hand leadline. There are some older methods seldom used today such as "dipping a light" to calculate the geographic range from observer to lighthouse

Radio aids to navigation provide additional electronic reference points to the navigator, and in some cases, handle the plotting work as well. Satellite systems such as GPS measure the distance to artificial satellites to determine position. Increasingly, Electronic Chart Display and Information Systems take these electronic inputs to provide a moving chart showing the travelers location on an electronic chart display. However, it is prudent for the traveler to always know, practice, and have the materials at hand for manual navigation in the event that electronic aids fail or electrical power is lost.

Navigation is the art and science of determining one's position so as to safely travel to a desired destination. Different techniques have evolved over the ages in different cultures, but all involve locating one's position compared to known locations or patterns.
The earliest form of navigation was "land navigation". Marine navigation began when pre-historic man attempted to guide his craft, perhaps a log, across the water using a form of piloting which uses familiar landmarks as guides. Dead reckoning was probably next, used to navigate when landmarks were out of sight. While celestial bodies were used to steer by, celestial navigation, as known today, was not used until the motion of the sun and stars was understood. The voyage of Pythease of Massalia, between 350BC and 300 BC is one of the best records of an early voyage. Use of a magnetic compass could allow a course to be maintained. The log and a sand glass could be used to determine distance run. This allowed a dead reckoning estimate of the ship's position to be calculated. When approaching land the lead line was used to assist with landfall. Nautical charts were developed to record new navigational and pilotage information for use by other navigators. The development of accurate celestial navigation for taking lines of position based on the measurement of stars and planets with the sextant allowed ships to more accurately determine position. Most sailors have always been able find absolute north from the stars, which currently rotate around Polaris, or by using a dual sundial called a diptych.
When combined with a plumb bob, some diptyches could also determine latitude. Basically, when the diptych's two sundials indicated the same time, the diptych was aligned to the current latitude and true north.
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