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    Re: Working a lunar
    From: Hanno Ix
    Date: 2009 Aug 5, 22:57 -0700
    Gentlemen:

    I am a novice to CelNav, and I certainly have no experience in lunars.

    Some algorithm occurred to me, though, that I would like to share and discuss. However, given the age of this business,  if it is a valid one I doubt it is new. If anyone has seen it before, please let me know, so I could read up on it. The objective is to find GMT and location.

    Let's make a Gedanken experiment:

    A ship reaches land of unknown coordinates. Land makes it practical for the navigator to measure the meridian passages of Heavenly Bodies rather reliably. Given GMT, he can calculate LAT and LONG. (One shot method.)

    But now we pose GMT as unknown. Sitting on land, measure the meridian passages of, say, sun and  moon which moves. Can I find GMT, too, using the now available data not using the classical moon distance methods?

    If I see things right, there must be a LOP which connects all locations on Earth with a given, fixed difference DT between the meridian passages of sun and moon.

    However, along this LOP, the same DT occurs at a different GMT. In this scenario, the LOP referring to a given DT is pre - calculated, listed in an almanac and annotated with GMT at each LAT. So, by having found the LAT before we just read the GMT of the DT-specific LOP.

    There is another opportunity:

    By accepting preliminarily this GMT, we can calculate LAT again, namely from the meridian passage of the MOON, and compare both values found. If  there is a gross difference we must have made an error. This, by itself, would be of value. Otherwise, though, we have good reasons to accept the GMT we found.

    I appologize if I am talking about  a method I have not gone through myself yet! I fear there is a hick-up in this somewhere. But I would like to hear the critique of you specialist navigators before I spend alot of time trying to do something long known as wrong.

    If, however, you find it sound, and has not done before I will pusue it.

    Best regards




    --- On Sun, 8/2/09, Paul Hirose <cfuhb-acdgw---.net> wrote:

    From: Paul Hirose <cfuhb-acdgw---.net>
    Subject: [NavList 9301] Re: Working a lunar
    To: NavList@fer3.com
    Date: Sunday, August 2, 2009, 3:13 PM


    Antoine wrote:
    > So, my results would not be that bad ...

    Your results are only 1 second different from my program.

    But it recommends the upper limb of the Moon, because the light is
    coming from almost directly above (position angle = 350°). Of course, if
    the "observation" was calculated, this doesn't matter. Even if it was
    really observed, I don't think there is much error because the Moon is
    nearly full (phase angle = 4°), and the cleared lunar distance is not
    very sensitive to altitude.

    My corrected time is 2001-04-08 at 03:21:10.5 UT1 (03:22:14.5
    Terrestrial Time). Position fix from the altitude observations is
    N44°50.48' W011°01.08'.

    I checked the solution by entering the Terrestrial Time, latitude, and
    longitude W11°17'07.2" into the USNO MICA 2.0 program. Longitude equals
    my solution, moved west by delta T (64 seconds) converted to arc (= 64 *
    15 * 1.002738 arc seconds). With these inputs, the outputs from MICA
    should match the observations. (MICA does not compute refraction, so I
    used my program's values.)

      31.4506  Moon altitude
      - .2718  semidiameter
      + .0263  refraction
    ---------
      31.2051  lower limb (calculated)
      31.2050  lower limb (observed)

      17.7536  Mars center
      + .0497  refraction
    ---------
      17.8033  refracted center (calculated)
      17.8033  refracted center (observed)

      64.9266  refracted separation angle
      + .2718  Moon semidiameter
    --------
      65.1984  lunar distance (calculated)
      65.1983  lunar distance (observed)

    The check is good.

    --
    I filter out messages with attachments or HTML.




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