I just finished my ten thousandth watch if Moana with my son, and I do not understand how you can travel by holding your hand up to the starry sky. It would make sense if the stars were stationary relative to your position, but they’re not. A star you measure at 10pm is in a completely different position by 2am. I understand the Disney version is an oversimplification, but how does the real thing work?
In: Earth Science
One of the things I love about Moana is that all the incidental stuff in the movie — the plants and animals, the architecture and culture, etc — is very well-researched*, so the deviations from actual Polynesia are deliberate screenwriting choices rather than mistakes. And that goes for the astronomy too.
In the movie, Moana is sighting by the particular stars that Europeans call Orion, and which the Hawaiians know as “Ka Hei-hei o na Keiki”, or “Cat’s Cradle” — yes, the kid’s game with string. The three stars in the middle we call “Orion’s belt”, and the Hawaiians call “Na Kao”, or “The Darts”.
These stars are distinctive: they lie along the celestial equator, so they always rise in the east and set in the west, no matter where you are on Earth. So first, you can tell what direction you’re heading by spotting them near the horizon. But even better, the *angle they make with the horizon* can tell you what latitude you’re at — more or less. You can see Moana using her hand to check that angle.
[Here’s](https://imgur.com/a/mnETYkz) a quick demonstration I put together with planetarium software. The [first image](https://imgur.com/jfn5r4z) shows Orion setting from Hawaii, the [second image](https://imgur.com/MUaULLP) is from Tahiti, and the [third image](https://imgur.com/HAdxb6R) is from northern New Zealand. As you go south, the three stars are more vertical, perpendicular to the horizon as they set.
The only real simplification Disney made in this shot is that Orion isn’t the only constellation the Polynesians used. They had a number of “star lines” — chains of constellations and star patterns that formed lines in the sky, which could be used to identify direction or latitude at any time of year, even when the sky was partly cloudy. Here’s more info:
http://www.hokulea.com/education-at-sea/polynesian-navigation/polynesian-non-instrument-wayfinding/hawaiian-star-lines/
* I grew up in Hawaii and took a bunch of Hawaiiana classes in school, but I’m not a native. So take my opinion that Moana is “well-researched” with a grain of salt.
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