In addition to the moons of Jupiter, there was a method in direct
competition with Harrison. It was the Lunar distance method. The Lunar
distance method used the position of the Earth's moon against the zodiac as
a clock. The term lunar distance was used because the navigator measured the
angular distance from the moon to various stars to establish the moon's
position and then the time was deduced from lunar position tables.
Developing the lunar distance tables was part of the reason for establishing
the Royal Observatory.
John WA4WDL
--------------------------------------------------
From: "Chris Albertson" <albertson.ch...@gmail.com>
Sent: Tuesday, January 24, 2012 11:36 AM
To: "Discussion of precise time and frequency measurement"
<time-nuts@febo.com>
Subject: Re: [time-nuts] establishing your position w/o gps
On Tue, Jan 24, 2012 at 3:16 AM, Attila Kinali <att...@kinali.ch> wrote:
On Tue, 24 Jan 2012 11:04:08 +0000
"Poul-Henning Kamp" <p...@phk.freebsd.dk> wrote:
In message <20120124115848.312d60bd4fccce4f3e71c...@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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