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From: Mike Boersma (no email)
Date: Tue Nov 02 2004 - 13:59:26 EST
Given GMT and an almanac, you can still do a noon sight for latitude and
longitude (use the equation of time on the daily page to establish
meridian passage of the sun, the difference between this as observed and
GMT gives longitude; the declination of the sun at noon will give you a
means to get the latitude -- you would need to improvise some elevation
method to determine when sun is at its zenith).
The almanac gives declination information for both the navigational
stars and many minor stars -- if you you can establish when one of these
is at zenith right above you, the declination of the star = your
latitude (perhaps through some sort of plumb bob).
Any meridian passage of a star, planet, or moon will give you longitude
(again you will need to have a elevation method to determine this). GHA
of the star, planet or moon at the time of meridian passage = longitude.
Local sunrise and sunset times can be determined from information in the
almanac and can be used to establish lat and long. The same goes for
moonrise and moonset etc. With the rise and set of the sun, moon,
planet, or star, you do not need an elevation measuring device. You will
want to take into account parallax.
Make a kamal for low altitude elevation measurements.
Bowditch has a good discussion on these kinds of methods as do many
others.
Good watchkeeping (keeping an accurate log) will allow for a good DR
plot which will minimize the inconvenience of not having a sextant.
The same goes for weather conditions which do not allow for the use of
the sextant.
Michael Boersma
Alexandre Eremenko wrote:
> What sort of Cel Nav can you do without sextant?
> (Assuming you have an almanac and chronometer.
> Or your wristwatch and radio to check it).
>
> Apparently yes. I am not speaking of eclipses
> which are rare events. One method was already
> discussed: timing the occultations of stars by
> the dark edge of the moon, a method slightly
> less precise than that of lunar distances because
> the distance is too small, and only available
> for somewhat less than 1/2 of each month,
> when the moon moves with
> its dark edge forwardis:-)
>
> Another method was proposed by Bill in our recent
> off-the-list conversation: timing the rise and
> set of various bodies. Each such timing gives you
> one position line. It is interesting, how precise
> can this method be. (I understand that the
> major obstacle here is refraction).
>
> Alex.
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