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    Re: Round Two: with a bonus ex-meridian
    From: Peter Hakel
    Date: 2013 Mar 8, 14:09 -0800
    The many-body fix at 19:00:00 local time comes out right on the money (see attached sights.xls and many_body_fix.xls):

    Lat: N 20d 38.6'
    Lon: E 120d 48.9'

    For the Achernar ex-meridian, I first advance the above position by 4 minutes and 1 second ( = 0.0669 hours, using time.xls and dr.xls) to the instant when Achernar was observed:

    Lat: N 20d 39.2'
    Lon: E 120d 49.7'

    This longitude has the "GHA equivalent" of 239d 10.3'.  Achernar transited that meridian at UT = 09:50:53 (aries_stars.xls), whereas its observation was made 13 minutes and 8 seconds later (time.xls).

    From ex_meridian.xls I get:
    Lat: N 20d 39.3'
    only 0.1' from the latitude of the DR-advanced many-body fix.


    Peter Hakel



    From: Antoine Couëtte <antoine.m.couette{at}club-internet.fr>
    To: pmh099---.com
    Sent: Friday, March 8, 2013 12:11 PM
    Subject: [NavList] Re: Round Two: with a bonus ex-meridian


    RE : NavList Post # 22641
    Let us change things up a bit with this round of stars. 5 bodies, with one that can be reduced as an ex-meridian of an upper transit (hint it's Achernar).
    We are going a bit faster now so you might want to advance the later sights for accuracy.
    Ship data:
    Date: 16 January 2013
    ZD -9 (note change)
    Crs: 049 Deg
    Spd 14.6 knots
    Height of eye: 83 ft
    Index error: 0.9' on the arc
    Temp 72 deg F
    Pressure 1016 mB.
    GPS fix at 1900-00 is Lat 20-38.6'N Long 120-48.9'E
    Star Data:
    Capella: 1900-27 Hs 40-40.2'
    Aldebaran: 1901-12 Hs 50-13.3'
    Rigel: 1902-27 Hs 32-03.8'
    Achernar: 1904-01 Hs 12-21.2'
    Fomalhaut: 1905-32 Hs 24-43.2'
    Fix a celestial fix at 1900 LT, "error" from the GPS fix, and standard deviation of the intercepts.
    *******************************************************************************
    Hello Jeremy,

    From your GPS Position used as DR, and updated for each observation time, I get:
    CAPELLA -0.5NM/046°4
    ALDEBARAN +0.4NM/088°6
    RIGEL -0.4NM/114°4
    ACHERNAR -0.1NM/181°8
    FOMALHAUT _0.1NM/221°3
    Sdev (i.e. LOP's dispersion) = 0.3 NM
    Position in Bearing 298° from DR and at distance of 0.1 NM
    Lesson learnt : What's the use of the GPS if you can get a Celnav position within 0.1 NM of true Position ?
    Attaboy ! Well done, once again, Skipper !
    Antoine M. "Kermit" Couëtte
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    File: 122735.sights.xlsx
    File: 122735.many_body_fix.xls
    File: 122735.time.xls
    File: 122735.dr.xls
    File: 122735.aries_stars.xls
    File: 122735.ex_meridian.xls
       
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