Navigation

Navigation is the art and science of determining the position of a ship, plane or other vehicle, and guiding it to a specific destination. Navigation requires a person to know the vehicle's relative location, or position compared to other known locations.

Navigators measure distance on the globe in degrees. Understanding latitude and longitude are very important in navigation. Latitude is a north-south position measured from Earth's Equator and longitude is an east-west position measured from the prime meridian.

There are many different navigation techniques. People have been using some of them for thousands of years.

The earliest navigation methods involved observing landmarks or watching the direction of the sun and stars. Few ancient sailors ventured out into the open sea. Instead, they sailed within sight of land in order to navigate. When that was impossible, ancient sailors watched constellations to mark their position. The ancient Minoans, who lived on the Mediterranean island of Crete from 3000 to 1100 B.C.E, left records of using the stars to navigate, for instance.

Compasses, which indicate direction relative to the Earth's magnetic poles, are used in navigation on land, at sea, and in the air. Compasses were being used for navigation by the 1100s C.E., and are still the most familiar navigational tools in the world.

Dead Reckoning
Dead reckoning involves estimating a current position based on a past position. Dead reckoning factors in speed, time, and direction of travel. When used in sailing, it does not take into account wind speeds or ocean currents. However, the only reference point in dead reckoning is the past position. This can make it difficult to realize when mistakes are made during travel.

Celestial Navigation
For sailors, celestial navigation is a step up from dead reckoning. This technique uses the stars, moon, sun, and horizon to calculate position. It is very useful on the open ocean, where there are no landmarks.

Navigators must be familiar with the different constellations at different times of the year, as well as the different constellations in the Northern and Southern Hemispheres. The most familiar constellation in the Southern Hemisphere, for instance, is the Southern Cross. The stars in this constellation are never visible in the Northern Hemisphere above the tropics. The Big Dipper, a familiar constellation in the Northern Hemisphere, is not visible in the Southern Hemisphere.

Navigators using this method need a tool such as a sextant to measure the angle between objects in the sky and the horizon. They also need an accurate clock and an almanac giving the positions of celestial bodies.

NASA and other space agencies continue to use sophisticated celestial navigation for many of their missions outside Earth's atmosphere. The astronauts and engineers of the Apollo program used celestial navigation to chart their way to the moon and back. The Mars Exploration Rover also uses celestial navigation to communicate information back to engineers and researchers on Earth.

Piloting
Piloting relies on fixed visual references to determine position. This is probably the most familiar type of navigation. With this technique, the pilot must be able to recognize visual markers or identify them using maps or charts. If the pilot misidentifies the markers, he or she could take the vessel off course. Pilots also employ radar or global positioning system (GPS) technology if visibility is poor.

Pilots are one of the most important crew members on seagoing vessels. Pilots navigate ships through difficult passages, such as narrow channels, stormy river mouths, and harbors with heavy ship traffic. With millions of dollars of cargo (such as cars, oil, or military troops) on ships larger than a football field, the pilot must be calm and responsible. He or she must understand the weather, the seabed or lakebed, the channels of a river, and trade winds and currents.

Radio Navigation
Radio navigation is similar to celestial navigation, except it replaces objects in the sky with radio waves being broadcast. The navigator can tune into a radio station and use an antenna to find the direction of the broadcasting radio antenna. Position can be determined by measuring the time it takes to receive radio signals from the stations of known locations on the ground or aboard satellites.

Radar is a type of radio navigation. It originally stood for Radio Detection And Ranging. Radar is a system that measures the time it takes to bounce electromagnetic waves off an object and back to a receiver. The waves that reflect back to the receiver indicate the object's distance.

GPS
GPS, or global positioning system, is a satellite-based navigation system. While the GPS system is funded and controlled by the U.S. government's Department of Defense, anyone with a GPS receiver can use it. The earliest GPS system was launched between 1978 and 1985 with 11 satellites. It now includes about 24 satellites that orbit Earth and send radio signals from space.

The system works much like radio navigation. A GPS device receives a signal from the satellites, and it calculates position based on the time it takes for the signal to transmit and the exact position of the satellites. It is a highly accurate navigation tool.