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    Re: alternative to running fix
    From: Richard B. Emerson
    Date: 2000 Aug 07, 1:43 PM

    [I inadvertantly replied to Barrie directly instead of sending the
    reply back via NAV-L.  I'm quoting Barrie's initial post and my reply,
    intended for NAV-L in general, after Barrie's latest response.  I've
    also prefixed all of that with a couple additional remarks.  Got that?
    -  RBE]
    For the really intrepid and capable, it's possible to shoot Venus
    during the day on a really clear day if the Sun's glare doesn't
    intrude.  An accurate prediction of Venus' altitude and bearing is
    essential to finding Venus and, of course, it helps if Venus is at its
    brightest.  Anyway, that's how the theory goes.  Has anyone ever
    managed a sextant sight with Venus during the day, even from dry land?
    S/V One With The Wind, Baba 35
    Barrie Hudson writes:
     > Of course Planets and the Moon. Given a suitable sun planet angle
     > Venus gives an excellent mer.alt for Lat. Jupiter also can be
     > observed for mer.alt but is a little tricky to pick up. The Moon in
     > its waxing stage affords a good daytime cross with the sun, when
     > Venus is available a 3 LOP fix is obtainable but watch those Moon
     > upper limbs.
     > Barrie Hudson
     > "Richard B. Emerson" wrote:
     > > Barrie Hudson writes:
     > > > A very interesting discussion with some points on prudent navigation. From
     > > > my experience the sun run sun is a traditional
     > > > method of getting noon position. An a.m P/L say at 0930 is run up to the
     > > > Latitude ZT the position then is run forward or
     > > > run back the few minutes to establish the noon pos. If you wish you can run
     > > > your Latitude up to a PM P/L. One thing
     > > > I always noticed is that the AM star sight never agreed with the Noon
     > > > position and over the voyage it was proved invariably
     > > > that landfalls fell in with star sight positions. In a long passage this
     > > > reliance solely on the sun run sun running fix and scrapping
     > > > the star position means days of accumulated error and big surprise at
     > > > landfall.
     > >
     > > In a sense, where's the surprise?  Assuming a reasonably good grouping
     > > of LOP's from morning or evening stars, you get a full position fix.
     > > With sun lines crossing the DR track, at best all you ever have is an
     > > estimated position or most probable position and a DR track based on
     > > the assumptions that gave that EP or MPP.  The running fix from there
     > > is based on subsequent assumptions on top of those used to form the
     > > initial EP; an assumptional "house that Jack built."  That said,
     > > however, it's been my experience that the error, with reasonable care,
     > > is not enough to produce a "big surprise".  Also, the above argues for
     > > learning to shoot at least planets as well as a few stars, if not the
     > > moon in addition to shooting the Sun.
     > >
     > > Hewitt Schlereth, in his new book Celestial Navigation in a Nutshell,
     > > makes a very nice arguement for learning to shoot Venus after getting
     > > one's Sun skills down.  It's always either in the evening or
     > > morning sky when a usable horizon is likely to be available, and,
     > > because of its brightness, readily identifiable.  Jupiter is often
     > > almost as bright and, in some years, obligingly present when Venus
     > > isn't.
     > >
     > > Rick
     > > S/V One With The Wind, Baba 35

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