If you've got a globe of the Earth in your house, turn it so that the Tuamoto Archipelago in Polynesia is at the centre of your view - and you'll find from that vantage point in 'space', Earth looks like a water planet, with barely any land in sight on the visible 'disk' of the Earth.
Then consider that the ancient Polynesians settled many of the tiny islands that dot that great expanse of inhospitable ocean, and you have to wonder how they were able to do so - Easter Island itself is around 1000 miles from the nearest habitable land. For centuries, European academics put the settlement of these various islands down to accident - without any of the complex instrumentation used by European navigators, Pacific Islanders obviously just drifted around until they lucked out by hitting land (seriously, can you imagine hopping in a small boat with the intention of just drifting till you found something?).
Opinions on how Polynesians reached these small islands began changing in the second half of the 20th century though, especially after the 1972 publication of Dr David H. Lewis's We, the Navigators: The Ancient Art of Pacific Landfinding in the Pacific. Lewis did extensive research on Pacific literature before embarking on a 9-month voyage along with elderly navigators from nine different archipelagos.
What Lewis, and others, found, was that traditional Polynesian navigation was a precise 'science', that used an array of techniques - including using celestial objects (the Sun during the day, stars at night), the movements of wildlife (e.g. birds), the way the swell changed, and even phosphorescence in the sea!
A fascinating recent article at The Conversation delves into some of the techniques of celestial navigation used by the ancient Polynesians, some of which were included in the recent animated movie Moana:
To calculate their position on Earth, voyagers memorised star maps and used the angle of stars above the horizon to determine latitude. For example, the top and bottom stars of the Southern Cross are separated by six degrees. When the distance between those stars is equal to the bottom star’s altitude above the horizon, your northerly latitude is 21º: that of Honolulu.
When the bright stars Sirius and Pollux set at exactly the same time, your latitude is 18º South: the latitude of Tahiti.
Voyagers measure the angles between stars and the horizon using their hands. The width of your pinkie finger at arm’s length is roughly one degree, or double the angular diameter of the Sun or Moon.
Hold your hand with the palm facing outward and thumb fully extended, touching the horizon. Each part of your hand is used to measure a particular altitude.
As fascinating as the celestial navigation techniques of the ancient Polynesians are, in recent years another scholar has discussed an even more intriguing, mysterious navigational method. Marianne George, who has a PhD in cultural anthropology, sailed with David H. Lewis in 1993 to the Santa Cruz Islands, and both were surprised to learn that there was an elderly traditional navigator there by the name of Te Aliki Koloso Kahia Kaveia, who offered to share his knowledge about Stone Age methods of navigation:
[W]hile David Lewis and I were at his home in Taumako, and just after we spent a day and a half going through a copy of Lewis' We, the Navigators with him, Kaveia pointedly asked David "Would you like to know the Polynesian navigation system?"
Kaveia covered the usual techniques, such as pointing out "a succession of ten main navigational stars as they rose through the night, and based on feeling the swells moving under my boat he named and described the patterns of swell refraction and reflection in the open sea." He also described a complex system of understanding the winds. But he also pointed out something new: Te Lapa, or 'The Flashing', a water-bound light phenomenon that appears to emanate from land.
Use of te lapa is usually only done within about 120 miles from shore. So, strictly speaking, it may be regarded as a piloting method rather than a navigational method. But since most Santa Cruz Islands, and most Pacific islands, are located within 100 or so miles of each other, te lapa is a method that Kaveia used frequently.
...Some oceanic lights are well known and documented, and many of these have very credible scientific explanations. This is not the case with te lapa.
Both George and Lewis, under Kaveia's tutelage, were able to observe te lapa (George herself sailed 25 separate voyages with Kaveia, or under his direction, over the next 15 years). According to George:
Te lapa is generally described by Kaveia and other Taumako/Vaeakau voyagers as white and lightning-like. I saw it white or magnesium-white colored, like lightning...
...According to Kaveia, the lightning-like te lapa bolts are straight lines... My eyes could see that there was a beginning and end of the line of light bolts coming toward me. It happens so fast -
in just a fraction of a second - that it is not easy to see or describe. But what I have seen confirms Kaveia's assertion that the bolts are instantaneous, straight in form, and that they emanate straight from land.
In 1998, while showing me te lapa...Kaveia said to me, "So it is like the islands are sending these bolts of light lines out, and if we look for them when we are at sea then many times we can see them and know the exact direction toward the island.
There is still no known cause of te lapa. It is a fact that more than 80% of ocean life makes light (bioluminescence) - including "one deep sea jellyfish that can be seen over 300 feet away" and a squid that "sends out photon torpedoes when threatened" - so perhaps there is some link between te lapa and bioluminescent ocean life. However, researchers have yet to find a solid explanation that explains the phenomenon - not least the fact that it appears to be directional from land up to 100 miles away.
In her article on te lapa ("Polynesian Navigation and Te Lapa - 'The Flashing'", in Time and Mind 5:2), George discusses some other possible explanations. Could islands and their surrounding reefs emit electrical charges that 'jump' to other islands, just as lightning jumps from clouds to earth? Or could it be a non-electric form of light that is reflected and refracted by swells that act as lenses? Or perhaps te lapa is caused by magnetic or electrical fields created by tectonic energy emissions.
Unfortunately, George says, the scientists who might be capable of resolving the mystery "have never seen it - or do not know about it yet", and so the phenomenon remains largely unexamined.
Beyond science though, George even goes so far as to suggest the explanation could be non-physical, that te lapa might be "a phenomenon seen only by people who are psychically and spiritually connected to the ocean as a result of decades of seatime and experience with life there."
But ultimately, George says the topic deserves further research - by employing high-tech low-light cameras, confirmation of any physical source should be possible, and could lead to new understandings about light, waves, islands, the ocean and ocean animals.