NavList:

   

Reply

On 15 Dec 2004 at 12:39, Alexandre Eremenko wrote:

> Why did not he measure altitudes?

With a sextant and an artificial horizon one can only measure altitudes up
to 60?. That is enough for this series, and probably many more, but
Thompson (and his contemporaries) never measured altitudes. It just wasn't
part of their procedure.

> Could you also explain the notation: what is TA and what's AA?

True Altitude (TA) and Apparent Altitude (AA)

> And what are the numbers
> +3'48", -4', +2"

These are the three corrections for clearing the lunar distance given by
Witchell's method.

> >perhaps one could work
> >backward from his calculated altitudes to get the DR position.
>
> Perhaps. For this we need to know the time
> used in his alt calculations, and the equation of time
> from his almanac.

The average time for his lunar distance (given at the bottom of the series
of each) is the time used for his altitude calculation. The equation of
time is given in the almanac data for the sun (near the bottom of the post
- 12:24.6 on the 26th and 12:05.0 on the 27th).

> I suppose it was 9:03:45 for Altair and 9:12:47
> (P. M. ?!) local time.

Yes.

Ken Muldrew.

   

Reply