[time-nuts] establishing your position w/o gps

Jim Lux jimlux at earthlink.net
Tue Jan 24 20:45:27 EST 2012


On 1/24/12 10:26 AM, Chris Albertson wrote:
> have you ever tried to measure an angular distance using a hand held
> instrument while standing on the deck of a moving boat in the open
> ocean?  try it and you will see why they wanted a clock.     You
> really can't measure an arc minute reliably we should expect about 15
> arc minute accuracy if you are standing on a moving ship.  A few very
> skilled people could do better.
>
> The moon moves what? about 10 degrees per day so in practical terms
> you can get time to about 30 minutes.   But other sources of error
> would add to that.   But still knowing even the hour is very good
> that puts you in the correct time zone
>

you can do much better than that by looking for occultations (and they 
work with the new moon as well).  If you know what day it is, you know 
about where the moon is, and you can look up in a table which stars get 
occulted when.  Then you just watch through binoculars.

I'd say you can get within ten seconds without much trouble, assuming 
you can find the star.








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