[time-nuts] establishing your position w/o gps
jmfranke at cox.net
Tue Jan 24 17:47:29 EST 2012
The Lunar Distance method was not practical, but it was supported by the
astronomers who felt that a mechanical contraption was beneath the art. Even
Newton, who was the first head of the Longitude Board, would not consider
the use of a mechanical clock. One argument from the astronomers was that
astronomy could determine time but a clock could only keep time.
From: "Chris Albertson" <albertson.chris at gmail.com>
Sent: Tuesday, January 24, 2012 1:26 PM
To: "Discussion of precise time and frequency measurement"
<time-nuts at febo.com>
Subject: Re: [time-nuts] establishing your position w/o gps
> 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
> On Tue, Jan 24, 2012 at 9:54 AM, jmfranke <jmfranke at cox.net> wrote:
>> 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
>> a clock. The term lunar distance was used because the navigator measured
>> 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
>> the Royal Observatory.
>> John WA4WDL
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