NavList:

Good evening Modris
This is the reason I was worried although I might just be confused.  As you know, I often am.  I’m assuming the faintly draw grid is of the celestial sphere (CS) and not lat & long on the Earth.  Therefore, you’ve calculated the observer’s zenith on the CS, and as the Earth and the CS have a common axis, you’ve got latitude cracked.  To get longitude you need to know GHA Aries which it would be nice if you could look up in tables.  Unfortunately, GHA Aries, if my memory serves me correctly, isn’t the same for the same time and day from one year to the next.  You must wait four years for them to be the same. 

That’s why I think you need the second photograph or the hint of Gary navigating boldly using sextant alone.  The fact that it’s close to the two equinoxes might or might not be another clue.  Alternatively, why not keep adding 90W on Google Maps, and if the other three positions come out in the middle of an ocean or darkest somewhere or other, then it’s French Polynesia.  DaveP