Cruising rarely visited islands in French Polynesia

It's an ill wind and it's not blowing any good. An unseasonal high-pressure system has spiraled from Antarctica, cartwheeled across the Tuamotu Archipelago and brought our ship, National Geographic Orion, to Tahanea atoll in search of smooth waters.

Thousands of years ago Polynesian navigators crossed these same waters, sailing from Samoa and Tonga in their double-hulled canoes to settle the Society Islands, Hawaii, Rapa Nui (Easter Island) and Aotearoa (New Zealand). Genetic research indicates these seafaring Polynesians originated in Taiwan about 5200 years ago.

"This large scale migration was one of the greatest maritime achievements in human history," says Tom Ritchie, senior naturalist with Lindblad Expeditions. "Each new island they settled was the equivalent of us trying to reach Mars."

While most passengers have retired to their cabins a few have gathered on the NG Orion's bow, absorbed by the vastness of the night sky. With the lights turned off, the Milky Way floats just out of reach, a million pinpricks in a purple shawl.

"Close your eyes and feel the roll of the deck, the splash of waves, the direction of the breeze," says Ritchie, during his talk on celestial navigation. "The Polynesians used the stars, sun, currents, birds and even clouds to navigate the 165 million square kilometre expanse of Pacific Ocean".

Since leaving Tahiti two days ago we've gained sense of the magnitude of the Pacific Ocean – the largest of the Earth's oceanic divisions - and the remoteness of the Tuamotu Islands. Part of French Polynesia the Tuamotus are composed of 80 islands and atolls stretching across an area as large as Western Europe.

It was here between 1966 and 1996 that France conducted almost 200 nuclear tests. The thrill of seeing places I've only read about balanced is by the sorrow that comes from learning that the "controlled explosions" are still causing cancer and health issues today. "Tahiti was exposed to 500 times the legal limit of plutonium," says Ritchie. "Even Greenland sharks still carry radiation from the fallout."

It's day three when we navigate a narrow channel to enter the deep lagoon of the uninhabited Tahanea atoll. From the bridge we watch Captain Tim Cashman negotiate the unchartered waters in true expedition style. While the early Polynesians relied on a 32-point mental compass, the NG Orion's military-grade sonar and shallow hull bring us safely where few ships venture.