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A Brief History of Human Navigation
Gabriel Spera and Steven R. Strom
Commerce and conquest—perhaps the two greatest drivers of human civilization—have always depended on accurate navigation. Helen of Troy, through her beauty, may have launched a thousand ships, but the Greeks needed something more reliable to guide them to the battle. Fortunately for them (less so for the Trojans), the science of navigation was already well established by the time they set off across the wine-dark sea.
Indeed, the history of human navigation goes back thousands of years. With the rise of mercantilism in the ancient world, traders found that boats provided the easiest and most efficient means of transporting goods. As early as 5500 years ago, merchants in Mesopotamia and Egypt were building vessels large enough to carry goods on a commercial scale. Egyptian sea voyages are even recorded in hieroglyphs dating back to about 3200 BCE. The beginnings of navigation, as an organized study, can be traced to this period.
The mariners who steered these trading vessels needed accurate navigation to get to the next port safely. Typically, they remained close to shore and used geographic landmarks to guide them—a technique known as piloting. If they needed to venture out into the open water, they could make crude approximations of time and latitude by observing the height of the sun. When they traveled at night (which was uncommon), they used the moon, stars, and planets as celestial guides—assuming the sky was clear.
The Greeks and Phoenicians made great strides in navigation and developed techniques that remained in use for thousands of years. By some accounts, the Phoenicians were the first to use the Pole star for maritime navigation and the first to circumnavigate Africa. The Pole star, which remains fixed above the North Pole, was critical for early navigation because it allowed navigators in the Northern Hemisphere to gauge their latitude by measuring its height. The Greeks and Phoenicians also lit bonfires along shorelines at key locations, facilitating travel by night.
About the same time the Phoenicians were charting the Mediterranean, other seafaring cultures were exploring the vast expanses of the South Pacific. Like Western mariners, the Pacific Islanders used stars, currents, and migratory seabirds to find their way. Their star maps were particularly sophisticated, as evidenced by the remarkable distances—literally thousands of miles of open seas—that they successfully traversed.
Mediterranean mariners also learned to keep records of a ship's direction, speed, and travel time to determine position—a technique known as dead reckoning. Starting from a known point, such as a port, the navigator would measure the heading and distance traveled in one day and mark that position on a chart. Each day's ending position would be the starting point for the next day's measurements. The system was notoriously inaccurate. Speed was estimated by watching seaweed or driftwood float by the ship, and travel time was measured by an hourglass.
Beneath overcast skies, navigators relied on guesswork and intuition to determine a ship's heading. A better method arose around 1100 CE, when the Chinese created the first magnetized needle compass. Eight or nine decades later, this invention would appear in Europe, too.
Indeed, the 12th and 13th centuries brought several navigational advances to Europe, including the lead line for determining sounding depths. This period also saw a florescence in the creation of nautical charts and celestial almanacs. Seafarers also rediscovered tools used by the ancient Greeks—most notably the astrolabe and the cross-staff. These devices were used to measure the elevation of the sun or stars above the horizon. To find the latitude of a ship at sea, the navigator would measure the height of the noon sun or a star of known declination and consult an almanac to find out what latitude corresponded to the data for that date.
A similar device was the Arabian kamal, a rectangular plate with a string attached in the center. Before leaving port, the navigator would hold the plate out until its upper and lower edges touched the North Star and the horizon and tie a knot in the string to mark the distance from nose to plate. To return to port from an unknown position at sea, the navigator would sail north or south until the plate again touched the North Star and horizon when held out at the distance marked by the knot, and then sail along that latitude toward port. Most kamals would have several knots to indicate the latitudes of frequently visited ports.
In the 15th and 16th centuries, trade with the Far East and exploration of the Americas intensified, fostering a renewed interest in navigational techniques. Merchants and their backers could not afford to lose even a single ship laden with spices or precious gold. Nonetheless, explorers such as Columbus still relied on dead reckoning and similarly unreliable techniques. Clearly, new methods and instruments were needed.
One such instrument, developed around the turn of the 17th century, was the quadrant, essentially a quarter of a circle with a plumb bob suspended from its apex. To determine latitude, the user would site the sun or a star along one vertice, letting the plumb line fall across the curved 90-degree scale, indicating the angle of elevation. Of course, staring directly at the sun is not without its drawbacks. Thus, a variation of the quadrant, known as the back-staff, soon gained preference, as it allowed the user to face away from the sun to make the necessary measurements.
Subsequent advances in optics led to the invention of the sextant in 1731. This instrument uses mirrors to generate images of the sun and horizon. To determine the height of the sun, the user would tilt one mirror using a calibrated dial until the image of the sun was precisely superimposed upon the image of the horizon. Not only was the instrument more precise, it was easier to use on a rolling deck.
Of course, sailors on the high seas were not the only ones who needed to know their position; explorers and cartographers traveling through the wilderness also needed such information. The sextant, however, was essentially unusable when the horizon was obscured by mountains or forests. To compensate, instrument makers began developing devices with artificial horizons. These advances would later play an important role in the development of the airplane and the submarine, which operate above and below the horizon.
Still, while latitude measurement improved, longitude measurement remained out of reach. Precise timekeeping seemed the logical approach, but the best clocks of the day lacked the precision or robustness to withstand choppy seas.
(Map courtesy of Dr. Seymour Schwartz) |
The "longitude problem" was so vexing that England established a Board of Longitude in 1714 and offered 20,000 pounds sterling to whoever could resolve it. Some of the greatest minds of Europe joined the race for a solution. Some believed that variations in Earth's magnetic field held the key, while others insisted on celestial techniques. John Harrison trumped them all by building a chronometer that lost less than one second per day during long sea voyages. Still, the board was reluctant to confer the award on someone who was not a member of the established scientific academy, and Harrison—greatly embittered—had to wait until 1763 to collect his prize.
Harrison's chronometer gradually gained favor, and the pace of navigational advancement slowed during the industrial era. Still, the ability to move and communicate over long distances by telegraph and railroad spurred the need for civil and military time coordination. Thus, in 1884, at the height of the British Empire, Greenwich, England, was established as the world's Prime Meridian. Previously, each major nation established its own prime meridian and local time; the promulgation of Greenwich Mean Time did away with these, and standardized navigational readings throughout the globe.
After a period of relative quiescence, the 20th century brought an unprecedented wave of navigational advances. The century opened with the first transatlantic radio transmission by Marconi in 1901, followed by the first airplane flight by the Wright Brothers in 1903. These two events would soon become closely linked, in navigational terms. The rapid acceptance of the airplane necessitated navigational improvements, as pilots were essentially in the same boat as mariners centuries before. As a result, many navigational advances of the 20th century focused on aeronautical and astronautical techniques, although ships and ground vehicles also benefited from this work.
By the 1920s, the development of radio navigation was underway. By 1935, England had conducted a successful trial of the first radar system. By 1939, a chain of working radar stations was in place along the south and east coasts of England—and this system proved critical in the Battle of Britain the next year.
Radio direction finding thus became the standard for aircraft navigation, eliminating the need for celestial techniques. Radio in turn gave way to inertial guidance—which is essentially a highly sophisticated form of dead reckoning.
The Global Positioning System, of course, brought a revolution as great as any in the history of navigation. With the advent of GPS, users anywhere in the world could easily (and cheaply) determine their position with remarkable accuracy by passive reception of satellite signals.
But the story is far from over. As civilization reaches farther into space—where terms such as "horizontal" and "vertical" hold little meaning—new navigational techniques will be required. The earliest space flights used special sextants that measured the angle between the edges of Earth or celestial bodies to determine position. These sextants have since been replaced by electronic devices. Even geosynchronous satellites have begun using GPS signals for orbit determination.
As space vessels venture out beyond the reaches of the inner solar system, they will encounter new navigational challenges. Some of these will be met through techniques that resemble those used by the first sailors thousands of years ago. Others may require a whole new way of thinking about location and time.
