# NavList:

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

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Re: Old style lunar
From: Alexandre Eremenko
Date: 2004 Dec 15, 23:47 -0500

```In my previous message, I was not sure,
to add or to subtract the time equation.
If one adds it, the Altair alt computed from
Thompson data was 8d 38',
which is close to the value predicted by Frank's
calculator: 8d 45.1'.

So in any case, the large error in Thompson's
latitude can be explained by the errors in
his altitude computations.

It seems that the sad fate of the Lewis and Clark
Lunars did not teach the people who developed
"procedures", that it is better to take altitudes
simultaneously with the Lunars, rather than compute them.

Alex.

On Wed, 15 Dec 2004, Alexandre Eremenko wrote:

> Taking the time equation into account,
> I obtain that Altair's altitude, computed from
> Thompson's data was 12d33'24".
> (I SUBTRACT time equation from his time 9h3m45s,
> and then use the formulas from my previous message
> cited below).
> What procedure he could possibly use to obtain his
> altitude, I don't understand.
>
> On Wed, 15 Dec 2004, Alexandre Eremenko wrote:
>
> > I tried to repeat Thompson altitude computation.
> > I use the formula
> > sin h=sin L sin Dec +cos L cos Dec cos LHA,
> > where L is the latitude (I use Thompson's value 50d47'24")
> > Dec is the star's declination (I use Thompson's value 8d22'25" N
> > for Altair)
> > LHA=(RAstar-RAsun-LocTime)
> > I use Thompson's values RAstar=19h41m3sec for Altair
> >                         RAsun =16h11m13sec
> >                        LocTime=9h3m45sec.
> >
> > I obtain h=10d35'40".
> > How did Thompson obtain a different value of 10d54'19"?
> > What does his DR long have to do with this at all?
> > Or he used some different method to compute altitudes?
> >
> > By the way, what exactly was his watch supposed to show?
> > I mean what is 9h3min45sec, exactly?
> > The time elapsed from his Local Noon (=sun culmination)?
> > Or the time corrected for the equation of time?
> > (In any case my altitude calculation does not agree with his one).
>
> Alex.
>

```
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