Thousands Of Miles Dead Reckoning | StarTalk

We're featuring my interview with traditional Polynesian ocean Voyager 9 OA Thompson, and I had to ask him how the ancient Polynesians navigated 2400 miles from Hawaii to Tahiti without being able to calculate longitude. Let's check it out.

Okay, imagine you're standing on the beach at Waikiki. You're looking over the horizon to where Tahiti is, and then imagine you draw one line—like an arc—to the west side of Tahiti and the other line to the east side. That's your target. It's less than a degree, so your destination is not in view because it's far beyond your line of sight.

So, your destination spans an angle from where you're standing in Waikiki, and as long as you navigate inside that angle, nothing else matters, right? Because you're gonna get to your target on the other side. Really, really smart. In fact, it seems to me your angle can be wider than that because you just have to get your destination within your horizon, and then you can just reckon to it—50 miles?

Yeah, yeah, 15 miles. So, you have a 30-mile angle. So, it's really the width of 30 miles at the distance of where you're headed—that's your angle. 2,400 miles away though, is... thirty?

Oh yeah, that's narrow, but still, it's a known problem, right? Yes. So, but there's so many unknowns in the navigation that it's not a GPS; it's not a coordinate system. You don't have longitude. You need instruments, and you need tables, which we don't have. It's a dead reckoning system, so you only know where you are by memorizing where you come from.

If you memorize your complement, you gotta be awake. You know, we stay up 21, 22 hours a day, so it ain't easy. Here's what you do—slip this in your...

So, what's that? That same sex? I see he didn't take it. [Laughter] [Music]