# 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 11, 20:19 +0200

```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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