Exploring Our Fluid Earth

Wayfinding is the process of orienting and traveling from place to place. Humans, as well as animals, are capable of wayfinding. For example, pets can return home after escaping their yard, birds migrate long distances, and aquatic animals find their way to a particular beach, bay, or stream during mating season. We use the term wayfinding to include all processes that allow humans and animals to orient themselves, including traveling over unknown or unmarked trails and paths.

 

Fig. 8.2. US Navy officers navigate their warship into a foreign port with the aid of a local pilot and nautical chart.

Image courtesy of US Navy, adapted from Wikimedia Commons

Navigating is a more specific form of wayfinding that implies precise knowledge of where you are and where you are going (Fig. 8.2). The word navigate originated from Latin sailing terms, but today we use the word navigate to include plotting a course over land, water, or air. Navigating involves knowing your position in space compared to a known location and the process of determining how to move (e.g., by hiking, driving, or sailing) from one place to another.

 

 

 

 

 

Early Polynesian Voyagers

Fig. 8.3. The Polynesian voyaging canoe Hōkūle‘a sails near Nihoa in the Papahānaumokuākea Marine National Monument, Northwestern Hawaiian Islands.

Image courtesy of Na'alehu Anthony, National Oceanic and Atmospheric Administration (NOAA)

The early Polynesian voyagers were some of the best wayfinders in history (Fig. 8.3). They were able to find their way across vast reaches of the Pacific ocean basin navigating by the sun, stars, and other natural cues. One of the natural cues that Polynesian voyagers used for navigation is the knowledge that islands block waves and ocean swells (Fig. 8.4). Not only is there a zone of calmer water behind an island (Fig. 8.4A), but an island also reflects (Fig. 8.4B) and refracts (Fig. 8.4C) waves and swells. When waves meet after being reflected, they interact. A seasoned navigator can see or feel this change in pattern, thus locating small low-lying islands that are not visible. In addition to waves, Polynesian voyagers took careful notice of seabirds and isolated piles of clouds on the horizon, both of which could indicate the presence of land (Fig. 8.5).

 

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Fig. 8.4. The figure above shows three examples of how islands can (A) block, (B) refract, or (C) reflect waves and ocean swells.

Image copyright and source

Image by Byron Inouye

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Fig. 8.5. (A) Clouds form over land because of the elevation and temperature differences between land and the ocean. This picture is of the high island of Moloka‘i, Hawai‘i.

Image courtesy of Fatemeh, Flickr

Fig. 8.5. (B) Flat atolls do not have peaks that can be seen from afar. However, navigators can see a reflection of the island in the clouds. This picture is of Kure Atoll, Northwestern Hawaiian Islands.

Image courtesy of NOAA/LT Elizabeth Crapo

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Fig. 8.6. (A) The North Star is aligned with earth’s axis of rotation.

Image by Byron Inouye

Fig. 8.6. (B) In the Northern Hemisphere, stars appear to rotate around the North Star throughout the night. This photo was taken at Mìrow castle in Poland.

Image courtesy of Smiglyluk, Wikimedia commons

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Specific stars are visible at different times of the year or in different geographic locations. Stars always travel east to west in a line. In the northern hemisphere, stars appear to rotate around the North Star (Fig. 8.6). By tracking the movement of the stars, voyagers can determine their approximate location with a high level of accuracy. Polynesian navigators could explore the ocean beyond sight of land and always know how to return home by knowing the general location of an island relative to the rising and setting of particular star groups.

 

 

Fig. 8.7. The Hawaiian star compass was developed by Master Navigator Nainoa Thompson.

Image courtesy of Polynesian Voyaging Society, © Charles Nainoa Thompson

Master Polynesian navigators memorize the rising and setting positions of hundreds of stars. One way of helping to organize this information is the Hawaiian star compass (Fig. 8.7), which divides the sky into eight families of stars occupying 32 houses. The houses indicate the position of stars rising and setting at the horizon. Knowing which star houses are rising and setting means that you are able to chart a course from your starting point to a specific destination. This type of celestial navigation has been used, along with wind direction and wave observation, to find small islands in the vast world ocean. The Polynesian voyaging canoe Hōkūleʻa (Fig. 8.3) uses the Hawaiian star compass (Fig. 8.7) to navigate and has made the 2500 mile voyage from Hawaii to Tahiti many times, using only traditional wayfinding methods.

 

Early Viking Wayfinders

 

Fig. 8.8. Vikings sun compass works similarly to a sundial.

Image courtesy of liz west, Flickr

Another group of wayfinders noted for their early exploration and seafaring fortitude were the Vikings. Before the Vikings, Europe was navigated mostly along, and within sight of, the coast. Because they were so far north, Vikings tended to do most of their exploring and voyaging during summer months when the weather was good and the sun was out for longer periods of time. The high latitude also meant that the nights were very short in the summer, making it difficult to rely on the stars for navigation. There is archeological evidence that Vikings used sun compasses (similar to sun dials, see Fig. 8.8) to navigate. The angle of the shadow cast by the sun would help the navigator establish a heading depending upon the time of day. This information would allow Vikings to gauge latitude. With this navigational ability, Vikings could venture farther from land, exploring the open ocean, confident in their ability to return home.

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Magnetic Compass

Voyagers have used a variety of instruments and techniques to safely navigate the oceans. Perhaps the best-known navigational tool is the compass. A magnetic compass is a navigational tool that points towards the earth’s magnetic poles.

 

 

Fig. 8.9. A magnetic compass points to the earth’s magnetic North.

Image courtesy of Shyamal, Wikimedia Commons

A magnetic compass is an indispensable navigational tool for determining direction of travel (Fig. 8.9). Although Global Positioning System (GPS) units have mostly replaced compasses, compasses are still used by many professionals. SCUBA divers, for example, use compasses because GPS units do not work underwater. Simple compasses are sealed round containers. They have a magnetized pointer that is held in the middle of the compass with a pin that allows the pointer to spin freely and align itself with the earth’s magnetic field. The point that pivots to the north is often painted red. To magnetize an iron or nickel pointer, it must be repeatedly rubbed on a lodestone, a naturally magnetized rock called magnetite, to impart a permanent magnetic field.

 

An object with a permanent magnetic field is called a permanent magnet. An example of a permanent magnet is a refrigerator magnet. A magnet has its’ own magnetic field, which can interfere with a compass reading. Compasses do not work well close to permanent magnets or in areas with a lot of iron.

 

 

Fig. 8.10. (A) The location of magnetic north compared to geographic north. Note the movement of magnetic north over time. (B) The location of magnetic south has also moved over time.

Images by Byron Inouye

When using a compass, the needle does not point towards the geographic North Pole, but instead points towards magnetic north. Magnetic north is located in Northern Canada, but moves due to magnetic changes in the earth’s core. You can see this change in the location of magnetic north in Fig. 8.10 A. Magnetic south is located off the coast of Antarctica and is also moving (Fig. 8.10 B). The angular difference between the location of the geographic North Pole and magnetic north is called magnetic declination and varies depending on your location (Fig. 8.11 A). In Honolulu, Hawai‘i the magnetic declination is 9° 46’ East (Fig. 8.11 B).

 

Latitude and Longitude

Ocean explorers not only needed to know their direction of travel but they also needed to know their current position on a map. Maps use latitude and longitude coordinates to identify unique locations (Fig. 8.15). Parallels of latitude are imaginary reference lines that form complete circles around the earth parallel to the equator and parallel to each other. Except for positions located right on the equator (0°), parallels of latitude are described by the number of degrees either north (N) or south (S) of the equator.

 

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Fig. 8.15. The equator and the parallels of latitude (A) are equally spaced as seen in an equatorial view of the world and (B) can be seen to form complete circles when viewed from the North or South Pole.

Image copyright and source

Images by Byron Inouye

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Meridians of longitude are imaginary half-circles running from the North Pole to the South Pole. Every meridian must cross the equator, and since the equator is a circle, the equatorial circle can be divided into 360°. These divisions of the equatorial circle are used to label the meridians. The 0˚ meridian (also called the prime meridian) is drawn through Greenwich, England. Meridians are numbered east and west from the prime meridian (Fig. 8.16). Lines of latitude and longitude form an imaginary global grid system. Any point on the globe can be located exactly by specifying its latitude and longitude.

 

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Fig. 8.16. (A) Longitude lines are drawn between the North Pole and the South Pole. (B) Longitude is measured in degrees from 0° to 180° east or west of the prime meridian.

Image copyright and source

Images by Byron Inouye

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For a review of the concepts of latitude and longitude see Locating Points on a Globe.

 

Determining Latitude and Longitude

One instrument that can help to determine latitude is a sextant. A sextant is a navigational tool used to measure the angle that a celestial body, such as the sun, moon, or a star, makes with the horizon (Fig. 8.17 A). The sextant operates on the principle that if two objects can be viewed simultaneously with two mirrors, then the angle reflected by the two mirrors is the angle between the two objects (Fig. 8.17 B). This angle is an estimate of the latitude of the observer, adjusted for the time and date of the instrument reading. If the sextant is being used to observe the sun, filters are put in place to avoid eye damage.

Fig. 8.17. (A) The major components of a sextant: the telescope, the index mirror, the horizon mirror, the index bar and the arc.

Image courtesy of Joaquim Alves Gaspar, Wikimedia Commons

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Fig. 8.17. (B) Steps to calculate latitude at sea are seen through the telescope of a sextant. Click the image to see the animation.

Image copyright and source

Image courtesy of Joaquim Alves Gaspar, Wikimedia Commons

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Longitude was more difficult for early explorers to estimate because it required an accurate chronometer, or timekeeping device, which could be used to compare the time on the ship to the time at a fixed point. As explorers moved west or east, the sun rose earlier or later, and set correspondingly earlier or later, affecting the perceived time of day. For early explorers, the most accurate timekeepers relied on pendulums, which were useless on swaying ships, so longitude had to be estimated using a series of complex equations based on lunar observations. More often, however, early explorers estimated longitude by a technique called dead reckoning.

 

 

Fig. 8.18. A chip log, consisting of a weighted board and spool of rope, is used with an hourglass to estimate a ship’s speed.

Image courtesy of Rémi Kaupp, Wikimedia Commons

Dead reckoning is used to calculate distance traveled by estimating a ship’s speed over time. Estimating speed can be as simple as noticing the time it takes bubbles to pass along the length of the boat. But, to be more precise, ships often used a chip log. A chip log was a weighted board attached to a uniformly knotted line (Fig. 8.18). When thrown overboard, the chip log stayed in roughly the same place while the knotted line unspooled from the boat for a set period of time (such as the time needed for sand in an hourglass to move from one side to the other). Sailors measured the ship’s speed by counting the number of knots passed during the prescribed time span. The name of the unit “knot,” which stands for nautical miles per hour, arose from this method of measurement. Together with a compass direction heading, the ship’s navigator would estimate the ship’s current position using the estimated speed and time traveled from a previously determined position. This method of determining location does not take into account the effects of currents, wind, or inaccuracies in the measurement of time.

 

Navigation Achievements

 

Fig. 8.19. Captain Bligh’s South Pacific voyage started in Tonga and ended on the island of Timor.

Image by Narrissa Spies, courtesy of Google Maps

In 1789, the crew of the British Royal Navy ship Bounty mutinied against the captain near Tahiti in the South Pacific. Captain William Bligh and 18 crewmembers loyal to him were set adrift in a large rowboat. After a brief stop in Tonga, Captain Bligh was able to use the method of dead reckoning to navigate across more than 6500 km of ocean, to the island of Timor in Southeast Asia in just 44 days (Fig. 8.19). He accomplished this impressive feat using only a compass and simple sextant. Amazingly, all crewmembers survived except for one, who was murdered by native islanders early in the journey. To this day, Captain William Bligh’s voyage remains one of the greatest recorded feats of navigation in Western history.

 

The use of dead reckoning declined when John Harrison, a British clock maker, developed the first chronometer that kept accurate time at sea. This technical achievement revolutionized naval navigation as it allowed for accurate longitude positioning. By the early 19th century, chronometers had become cheap enough to be utilized on almost all voyaging ships.

 

Veteran Polynesian voyagers rely on their knowledge of the stars, waves, weather, and wildlife to travel long distances across the ocean. New navigators gained these skills by carefully observing nature and learning from their elders. Polynesians did not have a written language so information was passed down orally from generation to generation. Unfortunately, by the mid-20th century a lot of this knowledge was lost, following contact with the west and changing traditions. To provide evidence for the purposeful navigation abilities of Polynesians and serve as a source of cultural inspiration, in 1976 the Hawaiian voyaging canoe Hōkūleʻa (Fig. 8.3) sailed to Tahiti without instruments, using only traditional methods of navigation. Since then, traditional Polynesian voyaging has undergone a revitalization across the Pacific ocean basin. Hōkūleʻa has journeyed around the world using traditional wayfinding techniques like the Hawaiian star compass (Fig. 8.7), spreading a message of cultural and envionmental stewardship. Additional polynesian voyaging canoes such as the Hawaiʻiloa (Fig. 8.20) and Makaliʻi have been constructed, and have sailed throughout Polynesia using only traditional navigation methods. The Makaliʻi made its virgin voyage in 1995 to the Marquesas Islands and Tahiti, more than 2500 miles away from its starting point in Kawaihae, Hawaiʻi.

 

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Fig. 8.20. The Polynesian voyaging canoe Hawai‘iloa is dry docked at the Marine Education Training Center on Oahu, Hawai‘i.

Image copyright and source

Image courtesy of Narrissa Spies

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Learn more about Hōkūleʻa and follow her voyages at Polynesian Voyaging Society.

 

Modern Navigation Tools

Modern navigation instruments include remote sensing devices that can detect distant objects such as other ships, buoys (floating navigational aids), islands, or coastlines at night or during the day, in clear weather or dense fog. A common remote sensing device is radar (radio detecting and ranging), a rotating instrument that scans surrounding areas by transmitting high-frequency radio waves that reflect off objects they encounter (Fig. 8.23 A). The reflected wave is picked up by a receiver on the ship, revealing information about the size and location of the object it bounced off (Fig. 8.23 B). Radar can also be used to detect severe weather such as hurricanes and storm clouds (Fig. 8.23 C and D).

 

Fig. 8.23. (A) A rotating radar antenna atop the US Navy aircraft carrier USS Theodore Roosevelt is used to detect other ships within 65 km.

Image courtesy of US Navy, adapted from Wikimedia Commons

Fig. 8.23. (B) Radiowaves emitted from a radar antenna strike an object and return to the antenna. Click to see the animation.

Image courtesy of National Oceanic and Atmospheric Administration (NOAA) National Weather Service

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Fig. 8.23. (C) A radar screen shows an outline of the coast, as well as a hurricane approaching land.

Image courtesy of National Oceanic and Atmospheric Administration (NOAA) National Climate Data Center, adapted from Wikimedia Commons

Fig. 8.23. (D) A radar screen at a navy submarine base in Yokosuka, Japan is used to navigate a ship.

Image courtesy of Toshinori Baba, Wikimedia Commons

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The technique of echo sounding uses sound waves in a fashion similar to radio waves in radar (Fig. 8.24 A). Echo sounders such as fathometers or sonar (sound navigation and ranging) are instruments that measure water depth using sound waves. These devices emit sound waves into the surrounding water and listen for returning sound waves that have reflected, or bounced off, other objects such as the ocean floor, whales, or submarines. The distance is calculated from the time it takes for a sound wave to travel to the object and back (Fig. 8.24 B). This information is crucial in helping navigators avoid running their ships aground.

 

Fig. 8.24. (A) A diagram of a US Navy oceanographic survey ship that shows how echo sounding is used to map ocean floor features.

Image courtesy of US Navy

Fig. 8.24. (B) Reflected sound waves emitted by a sonar instrument helps detects a distant object underwater.

Image courtesy of Georg Wiora, Wikimedia Commons

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Fig. 8.25. Three satellites are needed for a GPS receiver to determine the latitude and longitude of a location.

Image courtesy of National Oceanic and Atmospheric Administration (NOAA) Pacific Services Center

Global positioning systems (GPS) are a common technology that use satellites and receivers to determine a precise location on the earth. GPS is used for nautical navigation as well as air traffic control and everyday car travel. GPS receiver devices send a signal to three or more satellites. The distance between the receiver and the satellites is determined by the amount of time it takes the signal to travel to each satellite (the speed of the signal is already known). A minimum of three satellites is needed so that the receiver can triangulate its position based on the information provided by each satellite (Fig. 8.25). If a GPS receives information from four satellites, in addition to latitude and longitude it can calculate altitude (height).

 

Advances in technology have allowed modern navigators to sail the world ocean safely. In contrast to the long voyage of Captain William Bligh in 1789, the same trip today would be relatively simple with the aid of GPS, radar, and sonar. However, modern sailors still learn to use traditional compasses and sextants in case their advanced tools fail (Fig. 8.26).

 

Fig. 8.26. (A) A sailor uses a sextant aboard the US Navy aircraft carrier USS Harry S. Truman

Image courtesy of US Navy

Fig. 8.26. (B) A sailor uses a magnetic compass to navigate along a shoreline.

Image courtesy of US Navy

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Nautical Charts

Nautical charts are the road maps of the seas used by sailors and navigators for locating positions and plotting courses. Good nautical charts are crucial for safe ocean navigation. When used in conjunction with other navigational tools like a magnetic compass, sextant, and chronometer, a skilled sailor can travel confidently across the entire ocean. Nautical charts show features that are important to navigators; in addition to the coastline, nautical charts may feature seafloor depth, local tides and currents, navigational aids (e.g., buoys, lighthouses, channel markers, etc.), magnetic compass  bearings, latitude and longitude, and submerged hazards (e.g., shipwrecks, coral reefs, military restricted areas).

 

 

Fig. 8.27. In this nautical chart for a harbor, the location of the area is given in degrees of latitude (on the left side) and longitude (along the bottom). The numbers in the ocean (blue area) represent the seafloor depth in meters. This chart shows the main ship channel (between the dotted lines), buoys equipped with different signals, and a compass rose to show direction.

Image by Byron Inouye

Examine the nautical chart shown in Fig. 8.27. North is at the top of the chart, latitude scales are on the sides, and longitude scales are at the top and bottom. Grid lines indicate meridians of longitude and parallels of latitude. On this chart, the main ship channel, and other important navigational features, are noted. Some nautical charts show whether buoys are equipped with lights, horns, bells, whistles, or gongs, in order to alert navigators to maritime hazards. A compass rose is included to show direction.

 

A compass rose is a figure used to indicate compass direction on maps and nautical charts (Fig. 8.28 A). On a modern nautical chart, the compass rose has two concentric circles each divided into 360 degrees (Fig. 8.28 B). The outer circle indicates true geographical direction and has a star at 0˚ (360˚). True direction is used on maps and charts. The inner circle on the example in Fig. 8.28 B indicates the magnetic variation from true north for the location of the chart on which this compass rose was located; it is turned at a 4 degree angle to the outer circle. Recall that this magnetic variation is also called magnetic declination. The magnetic north pole of the earth continually changes position, and the amount of magnetic variation differs in different locations around the world (see Fig. 8.10 and Fig. 8.11). Nautical charts indicate the amount of magnetic variation and the yearly rate of change for these locations.

 

Navigational Disasters

Uncertainty in navigation and location has led to some interesting historical events. For example, the Solomon Islands, originally made known to Europeans by explorers in 1567, were discounted as myths or mirages for 200 years because their location was not charted correctly! Subsequent voyagers were unable to find them again until 1767.

In 1629, the Dutch merchant ship Batavia ran aground on some islands off the coast of western Australia. Her skipper had misestimated the position of the ship. Following the wreck, mutineers from the ship murdered at least 110 other crew and passengers.

In another famous story, a large male sperm whale rammed and sunk the whaling ship Essex in 1821. The crew was lost for months due in part to their inability to navigate correctly in their small whaleboats. Only a few crewmen survived. Their story was the basis for Herman Melville’s novel Moby Dick.