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    Re: Constellations in "Moana"
    From: Brad Morris
    Date: 2019 Jun 29, 13:37 -0400
    Assume a star at 17°S.  

    Tahiti is roughly 17°S.  At sunrise, the azimuth to that star is 72°12' from Tahiti.

    Hawaii is roughly 19°N.  At sunrise, the azimuth to that same star is 108°01'.

    It is unexplained how their star compass accounts for this, if at all.  If not, the boat steers an arc.

    That also assumes they could magically transport themselves instantaneously.  They cannot.  The distance is stated at 2400 miles.  At 3 knots*, it will take ~33 days for the crossing, under the assumption they can sail directly at Hawaii.  The declination of the star doesn't change, so there is no seasonal variation.  I must therefore retract my comment 2 about seasonal variation.  I was replacing a star with the sun or moon, which does have seasonal variation.  My own, unforced, error.

    Brad


    *two large wetted hulls, 60 feet long was the description, with tiny corresponding sail area in the image.  It won't capsize but it certainly isn't a foiling cat like SailGP's F50s which have been recorded at 48 knots (a sailboat at 48 knots, wow!).  Those are awesome to see, next at Cowes UK in August.  Saw them in NY in person, highly recommended.

    On Sat, Jun 29, 2019, 11:17 AM Brad Morris <NoReply_Morris@fer3.com> wrote:
    After guessing your top secret password (I really must change the password on my luggage*), I had a look at the video.

    I was interested in the Polynesian Navigator's description of how he uses the stars as a compass.  He described 32 houses for the stars and how he set the direction of his vessel by them.  It ignores how seasonal changes will alter the azimuth of the star, but that could be explained away by proclaiming the navigator memorized this variation (he did not so state and Tyson didn't pick up on it.) 

    360°/32 houses =11.25°/house.  This implies a steering error of ~5.625°.  As I understand it, the direction of travel was from the Tahitian Islands to the Hawaiian Islands.  This is theorized in anthropological studies and I cannot be certain this is true.  The change in latitude is ~36° from Tahiti to Hawaii.  This will change the relationship of the star / house compass in a very gradual way, resulting in a curved path if the star house compass was used as described.   How they would precisely hold any course over long distances is difficult to understand. 

    So after sailing 2400 miles, with
    1) a 36° change in latitude subtly altering your house/star compass relationship
    2) a seasonal variation of the star house relationship and
    3) a ~5.625° steering error 
    you would be off by a few hundred miles at destination. 

    It is a darned good thing that the Hawaiian Island chain is 1600 miles long! This is not a miraculous navigational feat.  Kind of like sailing west and running into a continent (Columbus / Vikings / Egyptian Mummies with cocaine in their system/etc).

    Anyway, that's my $0.02 from the peanut gallery.  I know we have discussed Polynesian Navigation before, but I do not recall any instrument such as the star house compass described.

    Brad



    *joke blatantly stolen!

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