BBC Science Focus

HOW TO NAVIGATE USING THE STARS

Polynesian master voyagers don’t need modern compasses to navigate their way around the vast waters of the Pacific.

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Long before the advent of modern science and technology, Polynesian navigators could travel vast distances across the Pacific between New Zealand in the southwest, Hawaii in the north and Easter Island in the southeast. Those navigation­al practices had almost vanished by the 1970s – but the Polynesian Voyaging Society on Hawaii has since revived the knowledge with the help of Mau Pialug, a traditiona­l navigator from the Micronesia­n island of Satawal.

Kālepa Baybayan was one of a handful of Pialug’s students, and he has now become a master navigator in his own right. He says a key tool is the ‘star compass’. This is not a physical object but a mental construct – the navigator memorises positions of the stars in the night sky, and when they rise and set, to orientate the canoe.

The stars are useful in other ways too: the altitude of a star changes with the canoe’s latitude. This means a skilled navigator with a detailed knowledge of the night sky can

pinpoint the canoe’s north-south position from the height of a given star above the horizon, using an outstretch­ed hand as a measuring tool. “You know when you are approachin­g land because the stars will tell you by their altitudes,” says Baybayan.

The navigator also uses passing flotsam and mental arithmetic to judge how fast the boat is moving, and keeps track of the canoe’s wake relative to the orientatio­n of the canoe itself to judge the degree to which winds are driving the boat off-course. Both factors must be taken into account if the navigator is to mentally calculate the canoe’s approximat­e east-west position. The navigator must track all of these factors – and many more – for days on end. “The trip from Hawaii to Tahiti is 2,400 nautical miles: it’s going to take you about three weeks to get there,” says Baybayan. “It’s a mental challenge to do this without notes or writing. But it gives incredible satisfacti­on to complete a voyage successful­ly.”

 ??  ?? Hold your hand outstretch­ed with the thumb touching the horizon. Each part of your hand measures a particular altitude (for example, the width of little finger is 1°). Here, the altitude of Polaris (the North Star) is being establishe­d
Hold your hand outstretch­ed with the thumb touching the horizon. Each part of your hand measures a particular altitude (for example, the width of little finger is 1°). Here, the altitude of Polaris (the North Star) is being establishe­d

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