NavList:

   

Reply

Bill,I don't understand what you're try to convey.If you took the noon sight
while the DR was 30 m to the east the resulting GHA of the Sun would reflect
that.The 120414zt time is only valid for the one EP.30 miles farther to the
east(118*13'43"W)the time of local m.p. will be before 120414zt.
I'm calculating the zone time(local)of local apperrant noon(local meridian
passage)and the EP position of the vessel at that time.If the noon sight is
taken when the Sun is centered on the local meridian the resulting
altitude(when reduced)will give an estimation of the latitude.Because the
Sun at this time is 180* north or south of the DR or EP the resulting * ' "
of the GHA of the Sun will approximate the ships' longitude.One has to then
open the N.A. and retrieve the whole degree,minutes and secounds of the GHA
of the Sun for the time the sight was taken to approximate the
longitude.Thus obtaining both estimates for lat and lon.
As Joel stated taking double altitudes and Fred stated comparing ZT and GMT
will also show the longitude at a noon sight.
Timeing the shot is very important in this method.I was 12 sec. late on the
1-15-04 noon sight and the resulting position shows this error.The noon
sight on 1-16-04 was 1 sec. late as to the calculated zt time of m.p.,along
with a slower travel speed,and the resulting approximation of longitude was
much closer to the gps position.
Does this clear up what I was trying to get across?

-----Original Message-----
From: Navigation Mailing List
[mailto:NAVIGATION-L@LISTSERV.WEBKAHUNA.COM]On Behalf Of Fred Hebard
Sent: Thursday, January 22, 2004 14:12
To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM
Subject: Re: Timed Noon sights for position


Yes, it overcomes most objections, although the procedure is fairly
inaccurate, up to about 100 miles, compared to time shots a few hours
before and maybe after noon.  But Doug is saying that's better than
nothing.  Also, Doug appears to be using a different procedure in his
detailed posting.

On Jan 22, 2004, at 4:58 PM, Joel Jacobs wrote:

> Let me suggest, that if Doug had the time, he could start taking
> sights, say
> 5 minutes before Meridian Passage, record his first reading, and if he
> wants
> a series of readings, until Meridian Passage, record that, and then
> preset
> his sextant to the first altitude he observed, and take the time when
> the
> sun reached that altitude on the downside after passage. Averaging
> those two
> times should allow him to solve for long.
>
> That's more time than he wanted to allocate to this, but it shouldn't
> it
> overcome the objections relative to getting long from a noon sight.
>
> Joel Jacobs
>
>

   

Reply