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

Azelio Boriani azelio.boriani at screen.it
Tue Jan 24 11:50:54 EST 2012


Yes, the first real push was the Longitude Act (1714) and the Harrison's
clocks.

On Tue, Jan 24, 2012 at 5:36 PM, Chris Albertson
<albertson.chris at gmail.com>wrote:

> 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
> returned
>
> --
>
> Chris Albertson
> Redondo Beach, California
>
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