# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Multi-Moon line exercise in 2 parts
From: Christian Scheele
Date: 2009 Aug 13, 22:46 +0200

Sorry for hijacking your thread, Jeremy. How far south of the Cape of Good
Hope will your trip take you? (I was googling Cape Hope...) It must be quite
far south if you are planning on shooting a lower transit. I should have
completed your moon exercise by then. I'm in Cape Town.

Christian Scheele

----- Original Message -----
From: "Christian Scheele"
To:
Sent: Tuesday, August 11, 2009 8:19 PM
Subject: [NavList 9474] Re: Multi-Moon line exercise in 2 parts

>
> Thanks for taking me through this, I was hoping somebody would do so. You
> say that determining the azimuth is impractical is impractical. This is
> why
> times of sunrise/sunset at one of the equinoxes are chosen as point of
> departure in the exercise on the ION webpage that I was drawing attention
> to, allowing its solution. I agree, it is impractical.
>
> Are you of the opinion that Charles Cotter's method to determine the
> passage
> of time between the sun's meridian passage and its maximum height is a
> simplification, however acceptable in view of its purpose? I understand
> that
> you are an expert on Cotter. I was thinking that an exact result would
> require a kind of integral in order to take the changing dh/dt of the sun
> into consideration, both as far as the change in declination as well as
> the
> observer's own movement are concerned. Cotter apppears to be assuming
> constant values for dlong and dlat. I'm not too strong on the maths side,
> so
> I'm stuck at this point.
>
> Is anybody further on Byrd and Weems?
>
> Christian Scheele
>
> George Huxtable wrote:
> ....
>> normal altitude navigation, altitudes are measured, routinely, to within
>> 1
>> part in 5000 of the maximum range of 0 to 90 degrees. To do similarly
>> well
>> by using rate-of-rise, you would have to measure that to within 1 part in
>> 5000 also. To do that by timing the rising or setting of the Sun, which
>> can
>> be over in 2 minutes, would call for timing that to a fortieth of a
>> second
>> of time, and for establishing contact of the Sun's limbs with the sea
>> horizon to within a third of a second of arc. It's completely
>> impractical,
>> just as establishing position around that circle by a measurement of
>> azimuth
>> is completely impractical. Only at sea, mind you. On land, measurement of
>> azimuth can be highly precise.
>>
>> Jeremy has provided the list with useful real information by which we can
>> assess the drawbacks of the proposed "rapid-fire" method. From his
>> he takes a realistic view of its limitations. So should we all.
>>
>> George.
>
>
> >

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