Among the many challenges that faced those who ventured onto the open sea was navigation. In the millennia before the 18th-century English clockmaker John Harrison invented a chronometer that enabled sailors to accurately determine their longitude—the last major hurdle in accurate location-finding at sea—how could mariners possibly know where they were, or where they were going, in the vast emptiness? Well, find their way they did, using a host of ingenious methods.
How did mariners of old navigate their way around the open ocean?
Photo credit: © Felix Möckel/iStockphoto.com
Land and air
The first seafarers kept in sight of land. That was the first trick of navigation—
follow the coast. To find an old fishing ground or the way through a shoal, one could line up landmarks, such as a near rock against a distant point on land; doing that in two directions at once gave a more or less precise geometric location on the surface of the sea. Sounding using a lead and line also helped. "When you get 11 fathoms and ooze on the lead, you are a day's journey out from Alexandria," wrote Herodotus in the fourth century B.C. The Greeks even learned to navigate from one island to the next in their archipelago, a Greek word meaning "preëminent sea." They may have followed clouds, which form over land, or odors, which can carry far out to sea.
But what if land were nowhere nearby? The Phoenicians
looked to the heavens. The sun moving across the commonly cloudless Mediterranean sky gave them their direction and quarter. The quarters we know today as east and west the Phoenicians knew as
Asu (sunrise) and
Ereb (sunset), labels that live today in the names Asia and Europe. At night, they steered by the stars. At any one time in the year at any one point on the globe, the sun and stars are found above the horizon at certain fixed "heights"—a distance that mariners can measure with as simple an instrument as one's fingers, laid horizontally atop one another and held at arm's length. The philosopher Thales of Miletos, as the Alexandrian poet Kallimachos recorded, taught Ionian sailors to navigate by the Little Bear constellation fully 600 years before the birth of Christ:
Now to Miletos he steered his course
That was the teaching of old Thales
Who in bygone days gauged the stars
Of the Little Bear by which the Phoenicians
Steered across the seas.
Watching the direction a seabird traveled with food for its young was one reliable method to find the nearest land. Photo credit: © Ken Canning/iStockphoto.com
Bird and wave
The Norsemen had to have other navigational means at their disposal, for in summer the stars effectively do not appear for months on end in the high latitudes. One method they relied on was
watching the behavior of birds. A sailor wondering which way land lay could do worse than spying an auk flying past. If the beak of this seabird is full, sea dogs know, it's heading towards its rookery; if empty, it's heading out to sea to fill that beak. One of the first Norwegian sailors to hazard the voyage to Iceland was a man known as Raven-Floki for his habit of keeping ravens aboard his vessel. When he thought he was nearing land, Raven-Floki released the ravens, which he had deliberately starved. Often as not, they flew "as the crow flies" directly toward land, which Raven-Floki would reach simply by following their lead.
Heeding the flightpaths of birds was just one of numerous haven-finding methods employed by the Polynesians, whose navigational feats arguably have never been surpassed. The Polynesians traveled over thousands of miles of trackless ocean to people remote islands throughout the southern Pacific. Modern navigators still scratch their heads in amazement at their accomplishment.
Like Eskimos study the snow, the Polynesians watched the waves, whose direction and type relinquished useful navigational secrets. They followed the faint gleam cast on the horizon by tiny islets still out of sight below the rim of the world. Seafarers of the Marshall Islands built elaborate maps out of palm twigs and cowrie shells. These ingenious charts, which exist today only in museums, denoted everything from the position of islands to the prevailing direction of the swell.
Currents may be invisible to the untrained, but not to seasoned mariners. Photo credit: © Clicks/iStockphoto.com
Current and wind
Sailors relied on natural forces they could readily comprehend. One of these was
currents. From time immemorial, journeys have been made or broken by these undersea winds. The western-trending currents of the Indian Ocean, for one, are likely responsible for the Indonesian-based race of Madagascar, an African island more than 3,500 miles from the nearest bit of Indonesia. Similarly, the clockwise currents in the North Atlantic helped doom one of the greatest land scams in history: Erik the Red's colonization scheme for the island he cleverly dubbed "Greenland." Of the 25 ships that sailed west from Norway in the year 990, only 14 arrived.
The father of those North Atlantic currents—the Gulf Stream—was named by none other than Benjamin Franklin. While deputy Postmaster-General of Great Britain in the 18th century, Franklin noticed that his mail ships to the American colonies took longer than whaling ships. Questioning whalers, he learned of a powerful current originating from the Gulf of Mexico—hence his name for it—and sweeping northeast into the North Atlantic (and, incidentally, giving the British Isles a climate positively balmy for such a northern latitude).
Like currents, trade winds have always been important to mariners. Those blowing heads on yellowed old maps were not mere decoration. In the Indian Ocean, for example, Indian traders over the ages have ridden the northeast monsoon to Africa in the cool, dry winter and taken the southwest monsoon back to the subcontinent in the hot, wet summer. To make their annual voyages from Tahiti to Hawaii, a journey of several thousand miles, the Polynesians hitched a ride on the prevailing south-easterly wind, setting a starboard tack and sailing northeast.
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| Gnomon |
For millennia, as sailors from the Phoenicians to the Polynesians knew, the heavens remained the best way to find one's north-south position. Increasingly sophisticated devices were designed over the centuries to measure the height of the sun and stars over the horizon. The
gnomon or sun-shadow disk operated like a sundial, enabling the user to determine his latitude by the length of the sun's shadow cast on a disk floating level in water. The Arabian
kamal was a rectangular plate that one moved closer or farther from one's face until the distance between the North star and the horizon exactly corresponded to the plate's upper and lower edges. The distance the plate lay away from the face—measured by a string tied to the center of the plate and held at the other end to the tip of the nose—determined the latitude.
(Reposted from Peter Tyson, Secrets of Ancient Navigators, October 6, 1998, Nova)
(For historical fiction that touches on this topic, see Chapter 3: Look Back of The Coming Wrath)
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