• navigation
    Taking a reading with a sextant is called "taking a sight."

    Photograph by Thomas J. Abercrombie

    Polynesian Navigation
    The ancient Polynesians navigated hundreds of thousands of miles of the Pacific Ocean using a combination of celestial navigation and piloting. Polynesians were familiar with constellations in both the Northern and Southern Hemisphere. They relied on oral tradition and the history of their ancestors' navigation from different islands.

    They paid attention to regional and seasonal weather patterns. They also recognized different species of plants and animals native to different islands. If a piece of driftwood belonging to a familiar type of tree floated to shore, or a bird known to live in a specific ecosystem flew by, navigators would have an idea of what type of land lay ahead and how far away it was.

    Graveyard of the Pacific
    The mouth of the Columbia River, in the U.S. state of Oregon, is one of the most difficult areas to navigate. Because so many ships and sailors have been lost in the turbulent waters, the mouth of the Columbia is known as the "Graveyard of the Pacific."

    After the Mutiny on the Bounty
    In 1789, some of the crew of the British ship Bounty mutinied (rebelled) against the ship's leader, Lt. William Bligh. Bligh and 18 crew members loyal to him were set adrift in the South Pacific Ocean, a little southeast of the island of Tonga. Bligh and his crew were sent off in a 7-meter-long (23-foot) boat with food and water to last a few days, plus four cutlasses (swords), a sextant, and a pocket watch. They had no compass or navigational charts.

    Bligh successfully navigated more than 6,500 kilometers (3,500 nautical miles) to the island of Timor in 47 days. Bligh's voyage to Timor is considered by many to be the most remarkable feat of navigation in history.

    Shackleton's Endurance
    Ernest Shackleton tried to be the first person to cross the Antarctic continent around 1915. His ship, Endurance, got trapped and crushed in the ice soon after he arrived in the Weddell Sea. The crew was able to get off the ship and manually haul two lifeboats over many kilometers rugged ice. Finally reaching open water, the crew sailed to Elephant Island, where they lived underneath the inverted lifeboats for months. Nobody was coming to save them on Elephant Island, so Shackleton and five others took one of the lifeboats and attempted to sail 1,287 kilometers (800 miles) downwind to the South Shetland Islands. The only navigation they had was a sextant, which uses the angle between the sun (or star) and the horizon (constantly bouncing up and down due to strong Antarctic waves) to calculate latitude. If Shackleton, got the angle wrong, the people on the lifeboat and the people on Elephant Island were all dead, because if Shackleton missed the South Shetland Islands, there isn't any land downwind for 8,047 kilometers (5000 miles). Shackleton must have paid attention in his navigation class. His crew hit the South Shetland Islands in five days. It took them 4 attempts to make it back to Elephant Island. Everyone was still alive on the island, thanks to a sextant and a skilled explorer.

    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 the 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 BCE, 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, and are still the most familiar navigational tools in the world.

    Dead Reckoning

    Dead reckoning involves estimating a currentposition 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 the Earths 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. governments 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 the 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.

  • Term Part of Speech Definition Encyclopedic Entry
    accurate Adjective

    exact.

    Age of Exploration Noun

    (1400s-1800s) period during which Europeans traveled the world by ocean in search of trade.

    almanac Noun

    annual publication containing a calendar, astronomical information, and weather forecasts.

    ancestor Noun

    organism from whom one is descended.

    angle Noun

    slanting space between two lines that ultimately meet in a point.

    antenna Noun

    structure through which electromagnetic signals are received.

    Apollo Program Noun

    (1960-1975) NASA program of space flights with a goal of humans going to the moon and back.

    astronaut Noun

    person who takes part in space flights.

    atmosphere Noun

    layers of gases surrounding a planet or other celestial body.

    Encyclopedic Entry: atmosphere
    Big Dipper Noun

    constellation of seven stars resembling a ladle, prominent in the Northern Hemisphere.

    calculate Verb

    to reach a conclusion by mathematical or logical methods.

    cargo Noun

    goods carried by a ship, plane, or other vehicle.

    celestial navigation Noun

    determining an object's position using the stars and planets as guides.

    channel Noun

    waterway between two relatively close land masses.

    Encyclopedic Entry: channel
    chart Noun

    type of map with information useful to ocean or air navigators.

    Encyclopedic Entry: chart
    Columbia River Noun

    (1,955 kilometers/1,214 miles) river in western Canada and the U.S., draining into the Pacific Ocean.

    compass Noun

    instrument used to tell direction.

    Encyclopedic Entry: compass
    constellation Noun

    group of stars that form a recognizable shape.

    current Noun

    steady, predictable flow of fluid within a larger body of that fluid.

    Encyclopedic Entry: current
    cutlass Noun

    short, curved sword.

    dead reckoning Noun

    method of navigation based on past position to determine a vessel's current position.

    degree Noun

    unit of measurement for latitude and longitude.

    Department of Defense Noun

    department of the U.S. government whose mission is "providing the military forces needed to deter war and protect the security of our country."

    destination Noun

    place where a person or thing is going.

    determine Verb

    to decide.

    ecosystem Noun

    community and interactions of living and nonliving things in an area.

    Encyclopedic Entry: ecosystem
    electromagnetic wave Noun

    movement produced by an electric burst or charge.

    Equator Noun

    imaginary line around the Earth, another planet, or star running east-west, 0 degrees latitude.

    Encyclopedic Entry: equator
    estimate Verb

    to guess based on knowledge of the situation or object.

    Global Positioning System (GPS) Noun

    system of satellites and receiving devices used to determine the location of something on Earth.

    globe Noun

    scale model of the Earth, or sometimes used to mean the Earth itself.

    Encyclopedic Entry: globe
    harbor Noun

    part of a body of water deep enough for ships to dock.

    Encyclopedic Entry: harbor
    Henry the Navigator Noun

    (1394-1460) Portuguese prince.

    horizon Noun

    line where the Earth and the sky seem to meet.

    Encyclopedic Entry: horizon
    landmark Noun

    a prominent feature that guides in navigation or marks a site.

    latitude Noun

    distance north or south of the Equator, measured in degrees.

    Encyclopedic Entry: latitude
    longitude Noun

    distance east or west of the prime meridian, measured in degrees.

    Encyclopedic Entry: longitude
    Mars Exploration Rover Noun

    one of two robots (Spirit and Opportunity) sent by NASA to explore the surface and atmosphere of Mars.

    Minoan Adjective

    (3000-1100 BCE) civilization of the Mediterranean island of Crete.

    mouth Noun

    place where a river empties its water. Usually rivers enter another body of water at their mouths.

    Encyclopedic Entry: mouth
    mutiny Verb

    to overthrow authority.

    NASA Noun

    (acronym for National Aeronautics and Space Administration) U.S. agency responsible for space research and systems.

    navigation Noun

    art and science of determining an object's position, course, and distance traveled.

    Encyclopedic Entry: navigation
    observe Verb

    to watch.

    open sea Noun

    part of the ocean not belonging to any country or nation. Also called the high seas.

    oral tradition Noun

    history, characteristics, and mythology of a culture transmitted through vocal, not written, methods.

    orbit Verb

    to move in a circular pattern around a more massive object.

    Encyclopedic Entry: orbit
    piloting Noun

    method of navigation based on fixed visual references to determine a vessel's position.

    Polynesia Noun

    island group in the Pacific Ocean between New Zealand, Hawaii, and Easter Island.

    prime meridian Noun

    imaginary line around the Earth running north-south, 0 degrees longitude.

    Encyclopedic Entry: prime meridian
    radar Noun

    (RAdio Detection And Ranging) method of determining the presence and location of an object using radio waves.

    radio navigation Noun

    method of navigation based on the source of radio waves being broadcast to determine a vessel's position.

    radio signal Noun

    radio wave used to transmit and receive messages.

    radio wave Noun

    electromagnetic wave with a wavelength between 1 millimeter and 30,000 meters, or a frequency between 10 kilohertz and 300,000 megahertz.

    relative location Noun

    general spot where something is located; its place in relation to something else.

    sailor Noun

    person who works aboard a ship.

    satellite Noun

    object that orbits around something else. Satellites can be natural, like moons, or made by people.

    seabed Noun

    the floor of the ocean.

    sextant Noun

    tool used by navigators to determine latitude and longitude.

    Southern Cross Noun

    constellation visible in the Southern Hemisphere.

    star Noun

    large ball of gas and plasma that radiates energy through nuclear fusion, such as the sun.

    sun Noun

    star at the center of our solar system.

    trade wind Noun

    winds that blow toward the Equator, from northeast to southwest in the Northern Hemisphere and from southeast to northwest in the Southern Hemisphere.

    traffic Noun

    movement of many things, often vehicles, in a specific area.

    transmit Verb

    to pass along information or communicate.

    tropics Noun

    region generally located between the Tropic of Cancer (23 1/2 degrees north of the Equator) and the Tropic of Capricorn (23 1/2 degrees south of the Equator).

    Encyclopedic Entry: tropics
    turbulent Adjective

    violent or chaotic.

    venture Verb

    to take a risky or dangerous opportunity.

    visibility Noun

    the ability to see or be seen with the unaided eye. Also called visual range.

    weather Noun

    state of the atmosphere, including temperature, atmospheric pressure, wind, humidity, precipitation, and cloudiness.

    Encyclopedic Entry: weather
    weather pattern Noun

    repeating or predictable changes in the Earth's atmosphere, such as winds, precipitation, and temperatures.

    William Bligh Noun

    (1754-1817) British naval officer.

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