More recently, the late Thor Heyerdahl suggested that these navigators followed the Sun on its westward journey near the equator. Seeing the Sun vanish in the western horizon at evening and then reappear in the East at morning, they could rest assured they would eventually return home. Some have suggested that ancient tales of visiting and returning from the Underworld were in reality coded references to early circumnavigation of the globe.
Indeed, the knowledge of a round globe and the assurance that by traveling continuously in any direction, one would eventually return to known territory was essential in generating the "Age of Exploration."
There are however recorded seafaring traditions some preserved to this day that give us glimpses of how ancient explorers could venture over open sea for hundreds or thousands of miles without needing to circle the globe.
Navigators of the Pacific used cognitive maps for regions that were known to them. Most important of the memorized locations was what Harold Gatty called the "home center." When Tupaia constructed his map for Captain James Cook, he was able to point "to the part of heaven, where each isle was situated" according to Forster, an obvious reference to zenith stars.
However, a zenith star at any particular moment in the diurnal day can also indicate the longitude of a destination. For example, at the start of the solar year, indicated for example by the heliacal rising or setting of a fixed star, the celestial bodies at sunset will be positioned over specific geographical locations in both latitude and longitude.
At a certain time, the zenith star can indicate both the latitude and longitude of a place. As an example, the bearing of this star on the horizon can be estimated by the distance, parallel to the horizon, of the zenith star from the local meridian. The same distance is then used from the corresponding point of the compass.
This relationship will not last long due to the constant spinning of the earth on its axis. However, that location at that particular point in time, what we know as azimuth and elevation, can continue to be associated with the star and the geographical location. The azimuth and elevation at that moment can be a reference to the star and thus we will call it an "etak star" from the Micronesian system of navigational references.
At the same time during the succeeding heliacal rising or setting, the star will again be at about the same azimuth and elevation. The existing slight error is not cumulative and tends to cancel out, so this is a reliable way of correlating geography with the fixed stars both in terms of latitude and longitude.
As long as the observer is in the same geographical location the etak star for any other location will always be the same.
As the zenith star moves into a new position due to the diurnal spinning of the globe, the reference azimuth and elevation, or etak star, marks the place in the sky corresponding to the destination. While the observer remains in the same location, the etak star for the destination will always remain the same.
If the observer, however, moves toward or away from the etak star, the location of the latter will change. Moving toward the etak star, the position in the sky moves closer to the zenith, while moving away drives the etak star closer to the horizon.
Upon reaching the destination, the etak star should be directly overhead in the zenith.
The etak star moves closer toward the zenith as the ship moves closer to the destination.
For navigators trained from childhood to memorize the relative positions of the stars, keeping track of an etak star should not present a difficult task. Even amateur stargazers can rather quickly orient themselves using the polar stars, their general knowledge of the rising/setting points of constellations, the seasonal rising/setting point of the Sun, etc.
When traveling to a destination, the navigator must only be able to reposition the etak star proportionally to the distance traveled. This is what is done using the Micronesian etak system. Depending on the winds and currents, an etak represents a division of the total distance per a unit of time, usually a solar day.
The etak distance is thus relative and in certain conditions the distance covered in a day might be more than 100 miles while in another it is less than 20 miles. By maintaining orientation, the navigator perceives not only the distance covered but the relative change in position in all directions.
There exists some documented evidence of the use of zenith stars for the purpose of obtaining bearings by both the Tongans and Tikopians. Unfortunately few details are given. Even more mysterious are fuzzy references suggesting such usage in traditions concering the Hawai'i-Tahiti voyages. There are many other notices of vague, uncertain usage of zenith or other high stars in the Pacific (Lewis, p. 289ff).
Steering toward an etak star or the related bearing on the horizon is not the same as steering toward the corresponding zenith star. As J.P. Frankel notes, the longitude indicated by zenith stars changes by about one degree every four minutes. However, the etak star bearing changes only according to the change of position of the observer. At most this will usually be no more than a few degrees in an entire day.
And since any error in judgement will be random and thus non-cumulative, they tend to cancel out with each position-fixing. That would mean that longer journeys with more readings would tend to be more accurate in terms of position-fixing than short ones!
Exploring unknown territory
When the navigator ventures into new regions, they could use the home center system to always find their way back to known territory without necessarily needing to circumnavigate the globe.
Even in areas with strong prevailing winds, there are always seasonal wind shifts and current patterns that allow explorers to confidently undertake circular journeys using the etak stars of unknown regions as their guide. The journey of the Hokule`a, a recreation of the ancient Polynesian journeys from Tahiti to Hawai`i and back, demonstrates this clearly.
Some general knowledge about ocean currents could also have helped equatorial ocean exploration. For example, currents traveling just below the equator tend to move in the opposite direction as those just above the equator.
By sailing or even paddling against the wind in periods of light winds, one can explore the nature of currents in unknown regions knowing the breeze will be at your back during the return journey.
Micronesian seafarers of the Caroline Islands were able to chart confusing currents stretching some 1,900 miles east-to-west and 840 miles north-to-south, from Kapingamarangi to the Marianas.
Ancient bearing star
He defined the days of the year by constellations,
He founded the Nebiru station to determine the stars' limits,
That none may go too far or too short,
The stations of Enlil and Ea, he placed by his own,
Having opened the gates on both sides,
And strengthened the locks on the right and left,
In the center he placed the zenith.
These passages are from the Mesopotamian tale of Marduk's slaying of the dragon Tiamat, and his creation of the heavens from the dragon's body.
We have already suggested in the blog that Nebiru may have been both a bearing and zenith star, the "star of the crossing" to the Underworld gateway. The station of Nebiru may have been the etak star of Spica used to set the heavenly bands by which the Mesopotamians divided the equatorial "way of Anu." The gates mentioned above are those through which the Sun rises at twin-peaked Mt. Mashu in the East.
During the latter half of the fourth millennium, at the heliacal setting of Sirius, the star Spica would serve as an excellent zenith and etak star for the dual peaks of Pinatubo and Arayat.
Spica was associated much later in Greco-Roman times with Isis Pelagia, the patroness of mariners. In such a sense, what star would be more suited as a patron goddess for seafarers than the etak star of one's home port?
When the Roman empire adopted Christianity, Isis Pelagia apparently became Maria Pelagia, or the medieval Maris Stella or Stella Maris "Star of the Sea."
Late European representations of the Virgin Mary often show her holding a sheaf (spica) of wheat in her hand similar to the image for the constellation Virgo, or decorated with sheaves. Some paintings show a single star on her robe, which has been interpreted by some as representing Spica (alpha Virginis).
Paul Kekai Manansala
Chaucer, Geoffrey. Romancing the Goddess: Three Middle English Romances about Women, University of Illinois Press, 1998, p. 195.
Finney, Ben. Voyage of Rediscovery, University of California Press, 1994.
Lewis, David. We, the Navigators: The Ancient Art of Landfinding in the Pacific, University of Hawai`i Press, 1994.