Their imposing canoes vanished long ago. But thousands of years before Global Positioning Satellites, LORAN coordinates or even the sextant, seafaring Polynesians navigated their twin-hulled outriggers across open seas, far from sight of land. By the year 1300 AD, they had populated all of the islands of the Pacific, including the last to be inhabited, New Zealand. This much is known.

Exactly how they found their way across Oceania is a complete mystery. That long ocean voyages were possible was proven in the 1950’s by Thor Heyerdahl’s Kon Tiki. Unfortunately, what was actually demonstrated was that colonists could drift downwind, with the ocean currents from South America and ending up amongst the islands. This is the wrong direction: the overwhelming anthropological and archaeological evidence shows that Polynesia was colonized from the west side of the Pacific Ocean from Asia initially, thence to the east.

Modern sailors in the Pacific islands of Micronesia use an intriguing and foolproof means to find their way: the star compass. Stars trace long arcs across the sky each night, swinging from east to west. Although the times advance by four minutes each night, the positions along the horizon at rising and setting are the same night-to-night and throughout the year. When kept off the bow, stern or at a certain angle to the rigging, such rising or setting positions reliably indicate the ship's course. Since the rise and set azimuth does depend somewhat on the observer's latitude, long voyages were divided into sections called etaks that allowed for this variation.

At sea, sighting a chosen star low on the horizon gives a sailor a point of reference, an azimuth or bearing to follow. The sailor simply steers towards stars rising or setting in the direction of the intended landfall. When a star rises well clear of the horizon or sets below it, another guiding star can be chosen to hold the course. In Tahiti, the sequence of stars was called the avei’a or “star path”, and rarely are more that ten stars are needed over the course of the night. In Micronesia, the present day star compass has 32 points consisting of four cardinal directions and 28 intermediary rising and setting star-points. Local navigators reportedly know the positions of over a hundred fifty stars. Knowledge of patterns of stars in constellation was essential if low clouds or twilight interfered.

The star compass relies on favorable weather and, of course, nighttime skies. During the day and inclement weather, sailors use other natural phenomena for navigation. Rising and setting of the Sun and Moon, swell refracting about a distant island, and clouds building over land masses are readily apparent. More subtle are the reflection of white sand or green coral lagoons in clouds, floating vegetation debris, and even frigate birds and terns flying for roosting or feeding grounds. There is little question that the first voyagers of the Pacific Island relied on many means to find land. Though risky, colonization was not accidental and fortuitous. There is ample cultural evidence that there was extensive trade and deliberate migration to new islands.

To succeed all that is really needed is a direction, a heading or vector from here to there, far simpler than the European coordinate system of latitude and longitude. While latitude is simple enough to determine by the altitude of Polaris or the elevation of the Sun at noon on a given date, finding longitude demanded either an impractically precise clock or impossibly accurate astronomical positions. Solving this longitude problem led to the hijinks and skullduggery endured by John Harrison. The life's work of this 18th-century English clockmaker is engagingly recounted in Dava Sobel’s book Longitude.

I’m always amazed at the gadgetry when I go on the bridge of a modern seagoing vessel: monitors, keypads and laptops threaten to overtake the ship’s wheel. It appears that no one is at the helm: mates are watching the screens or the seas ahead. The shiny brass sextant is more decorative than functional. Latitude and longitude flash on one screen, beamed down from GPS satellites above. Captain Jerry is transfixed on the flashing arrow on the computer screen that is our course. Despite all this technology and computation, he is sailing by what is a modern-day avei’a, a virtual-silicon version of the Polynesian navigator’s star compass.

Moondark is written by Doug Miller and published on the web, in the Delmarva Star Gazers'Star Gazer News and in the Delaware Astronomical Society's FOCUS. Please address comments and suggestions to dmiller@udel.edu. This document was last revised on 22 September '00. All text and images copyright © 2000 Douglas C. Miller, All Rights Reserved. This material may not be reproduced in any form without prior permission.