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

Chris Albertson albertson.chris at gmail.com
Tue Jan 24 11:36:05 EST 2012

On Tue, Jan 24, 2012 at 3:16 AM, Attila Kinali <attila at kinali.ch> wrote:
> On Tue, 24 Jan 2012 11:04:08 +0000
> "Poul-Henning Kamp" <phk at phk.freebsd.dk> wrote:
>> In message <20120124115848.312d60bd4fccce4f3e71c136 at kinali.ch>, Attila Kinali w
>> rites:
>> >All this talk about telling the time using stars or the sun made me wonder
>> >how did people tell what position their telescopes had back in the days
>> >before GPS?

Sailingships and trade was what pushed this.   At the time of Columbus
he was able to know his latitude within a few 10s of miles but even
after returning to Europe he did no know how far around the world he
had sailed.  Was it 1/3rd or 2/3rds?  They had no way to know.    The
problem was that on one had a clock that should keep time well enough.
 They used hour glasses on board ship for short duration time keeping
but those were of no use on a longer ocean crossing.

Later they discovered the idea of common view of the moons of Jupiter
and they could measure the time from local noon some even on Jupitor
while a person back home did the same thing.  Later when he got back
home they compare notes and then know the difference in longitude.
 Good ocean going clocks were still centuries away.    But in the
1500's they could only know the location after the fact when they


Chris Albertson
Redondo Beach, California

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