Secrets of Ancient Navigators: Land and Air

How did mariners of old navigate their way around the open ocean?

By Peter Tyson

 Photo credit: © Felix Möckel/iStockphoto.com

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.

  Read More