# NavList:

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

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Re: I need help with my first noon sun sight
From: Trevor Kenchington
Date: 2003 Dec 20, 12:27 +0000

```Jim,

Explaining the difference between your Methods 1 & 2 is easy. For Method
2, you started from the time of meridian passage quoted in the almanac
to the nearest minute. You cannot expect calculations based on that to
be accurate to anything better than the nearest minute. Since both of
your calculations round to a time of 1308, they are in full agreement to
this level of accuracy. If you want the time of meridian passage to
the nearest second, you can't use your Method 2.

I think that your problem with your method 8 is that you have read off
the Equation of Time for 1200 GMT on 14 September but you are applying
it to an observation after 1600 GMT that day. If you check the almanac,
you will see that the Equation of Time increased by 10 seconds in the 12
hours after 1200 GMT. Hence, in the four hours to your local noon, it
must have increased by 4 seconds (to the nearest second). Apply that
correction and your Method 8 will agree with your Method 1 to the
nearest second.

Trevor Kenchington

You wrote:

> Please see my calculations below for 3 ways to predict the local zone time
> for meridian transit of the sun on September 14, 2003 at my position of L
> 46o 11.1' N, Lo 63o 08.0' W (GPS Fix).  I cannot understand why Methods 1, 2
> and 8 produce different predictions.  Can anyone spot the reason?
>
> I made a time diagram of this problem, though I am not sure that it is
> correct, and it gives yet a third answer:
> http://jimthompson.net/boating/CelestialNav/NoonSunSight.htm#Time%20Diagram
> (ignore the rest of what I have written on that page -- I am still muddling
> through this).
>
> Thank you,
>
> Jim Thompson
> jimt2{at}jimthompson.net

--
Trevor J. Kenchington PhD                         Gadus{at}iStar.ca
Gadus Associates,                                 Office(902) 889-9250
R.R.#1, Musquodoboit Harbour,                     Fax   (902) 889-9251
Nova Scotia  B0J 2L0, CANADA                      Home  (902) 889-3555

Science Serving the Fisheries

```
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