Navigation

Navigation is the methods used to learn where someone is and how to go to another place. Since this is easy when landmarks are visible, the word is often limited to the methods ships or aircraft use. The word navigation was invented in the 15th century from the Latin word navis which means "ship" and is found in other Indo-European languages. Navigation is literally "art of ship mastery" but is also used for 'finding one's way'. The Global Positioning System is the main tool for it.
Simple navigation
One type of navigation was made by the Polynesians and is called Polynesian navigation. Polynesians used different things found all around them to find their way across large areas of open ocean. Other early people also learned how to travel large distances using the natural world. For example:
A long time ago (and still used by some people today) people would watch the stars, the sun and the moon. From this they would know where north was. With charts they could find how far from the equator they were. This is called celestial navigation. Until they had accurate clocks they didn't know their Longitude (how far east or west they were) without seeing landmarks.
Some types of clouds form over land, and waves can bounce off of a shore and travel out to sea.
The time it took to get to a place. When traveling on land they knew it would take them, for example, two days to get from one place to another. This time would most likely stay the same. From this they could travel two days and know they were close to where they wanted to be.
The animals they found helped too. In different places the people would find different types of fish, whales or birds that only lived in one place, or near land. From that they could tell either they were near or far from where they needed to be.
An example of people who used the stars were the Vikings. They knew that the star called Polaris (the North Star) does not change location and points to the north. They would then know the latitude (distance from the equator), by measuring the angle between Polaris and the horizon. They also used animals, especially birds, to know if land was nearby. They also knew that specific kind of clouds form near land and that waves are different near land than at high seas.
Medieval navigation
As time went by better methods of navigation were invented or discovered. Some of these methods are:
Dead reckoning. A ship could throw a log over the side. Attached to the log was a rope with knots tied at regular distances. By counting how many knots went over the side before they pulled the log back in, they knew how fast they were going. They would write this down every day and figure out how much they traveled for the day. This is why a ship's speed is measured in knots.
A compass. It was discovered that the Earth had two poles (North and South) and that these poles had different magnetic charges (positive and negative). Resting a strip of magnetic iron on the point of pin it was found that the strip would spin until it matched the magnetic field of Earth. From this a direction could be taken and paths could be followed. The compass was first invented in China. It was later invented in France in 12th century.
Accurate clocks. With a clock, it was finally possible to know what a person's longitude was. Longitude is the location east or west. Before this, only landmarks and dead reckoning could be used.
Pilotage is when ships look out for special beacons or man made markers, which tell them where they are or to watch out for certain obstacles such as reefs.
People divided the compass into 360 degrees. Then they could give an accurate number for the direction the ship had to follow (the "bearing") to arrive at a harbor. The first navigational sea maps, called "nautical charts", showed the bearings needed to get from one harbor to another.
Modern navigation
Stellar navigation is an improvement on navigating by stars. It uses a sextant, a compass and a very accurate clock called a chronometer. By measuring the altitude of a star (how high it is above the horizon), and its direction on a compass at a known time, the navigator can determine where the ship is. GPS has pretty much replaced stellar navigation, but stellar navigation is still taught in all maritime schools because it does not need special electronics.
Radio navigation was invented in the early 20th century. Hyperbolic navigation uses radio transmitters to find the location of a ship between two or three radio transmitters that do not move.
The Global Positioning System (GPS) replaced other radio methods in the late 20th century. It is a system of satellite transmitters. Travelers use a small receiver to find their location almost anywhere on Earth.