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> *From: *Jacquelin Hardy
> *Date: *2026 Aug 16, 13:45 -0700
>
> I found something strange :
> for example, on a 4 stars fix spread on a 20 minutes period, they don't
> seem to carry all the sights to the same time of one specific star , DR
> updated with course and speed of the ship.
> If this is not done, of course, the fix will be a large triangle,
> especially at 25 knots...

Here is the Nautical Almanac algorithm for direct calculation of
position from azimuth and intercept:

https://archive.org/details/isbn_9780707741062/page/282/mode/1up

It's not necessary to adjust a round of celestial observations to the
same time. Suppose you had a device to track a celestial body and
continuously display its azimuth and intercept with respect to your dead
reckoning position. You would see the output remain almost constant over
a span of several minutes, since DR error doesn't change much.

Thus, you can plot estimated position at some convenient time, say the
nearest whole hour, and plot azimuths and intercepts from a round of
sights as if all had been taken at that time and place.

However, that simple scheme only works if each sight was reduced for the
time and DR of the observation. Electronic calculation or HO 211 allows
this. But if sights are reduced for assumed positions selected to give
whole degrees of latitude and hour angle, intercepts can be tens of
miles even when the dead reckoning is dead accurate.

--
Paul Hirose
sofajpl.com

   

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