NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: R: Re: Exercise #15 Day's Run (almost)
From: Jeremy C
Date: 2008 Aug 11, 15:57 EDT
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From: Jeremy C
Date: 2008 Aug 11, 15:57 EDT
Celestial Running fixes are as you describe (Terrestial Running fixes are a
different matter altogether) which is to say several LOP's advanced or retarded
over a span of several hours. I would tend to agree that the LAN sun and
Moon lines (both shot within a minute) crossed would constitute a fix by
themselves, while the AM sunline advanced to noon would be considered a checking
LOP that would be more questionable due to the effects of set and drift on its
advance.
However, there is a catch here. The sun and moon lines were shot at
about 12:20 LT and we are looking for a 1200 position for the noon slip and to
calculate the "day's run." Therefore, both of these lines must be retarded
19 and 20 minutes respectively to give us a 1200 position which, along with
the advanced AM sunline, give us a 1200 Running fix.
The general practice in the US system is to advance any number of AM
sunlines to noon and advance or retard LAN to noon to give us the 1200 running
fix. This position is thought of as a bit questionable, and often times
the DR lines are run from AM stars to PM stars without correction by the noon
position, although I am sure there is a lot of variation due to the Captain's
preference.
Jeremy
In a message dated 8/10/2008 5:06:53 A.M. Eastern Daylight Time,
fedeastro.rossi@libero.it writes:
Jeremy,
I've just worked the first part of the exercise, but I got to a slightly
different result.
In fact I use to define a running fix one which is derived from observations
well spaced in time, e.g. a couple of hours before LAN, LAN and a couple of
hours after LAN: in this case I assume the center of the (hopefully) small
triangle formed by these three LOPs as being the Fix. In this case only one
LOP is really spaced in time, i.e. the sun LOP of the morning, while LAN and
moon LOP are only a few minutes apart, so I would rely on the latters to
calculate the 1200 fix which is then 15deg 13.7' N 145deg 00.0' E.
What do you think?
Federico
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