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    Re: Beginner Meridian Passage Question
    From: Zorbec Legras
    Date: 2004 Sep 2, 03:58 -0500

    ----- Original Message -----
    From: Bill 
    Date:         Wed, 1 Sep 2004 14:51:44 -0500
    To: NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM
    Subject:      Beginner Meridian Passage Question
    ============================
    
    
    first things first
    
    >> are there name [...] ?
    
    1? for the line segment from the north horizon to the pole?
    Call it lattitude.
    zenith to elevated pole = colatitude
    zenih to horizon = 90?
    zenith - colatitude = latitude.
    
    2? pole to zenith,
    Colatitude (90?- latitude) see above
    
    3? zenith to equator
    Latitude
    
    4? equator to southern horizon,
    Colatitude.
    
    5? Zenith to horizon
    90? by definition
    
    
    
    6? the unseen semicircle "through the nadir" ?
    The "visible" apparent path of the sun is called "semi-diurnal arc",
    So you can call the invisible path "invisible semi-diurnal arc".
    The whole path is called "diurnal circle".
    semi diurnal =>  arc cos P =  tan Lat * tan decl
    A star is circumpolar if the colatitude is smaler than the declination.
    
    (90? - Lat) < decl [same name] => circumpolar and visible.
    (90? - Lat) < decl [diff name] => circumpolar and never visible.
    
    Second...
    >> When looking at times of meridian passage [...]
    
    Upper transit occurs when LHA (AHg) is 0?
    lower transit occurs when LHA is 180?
    
    A circumpolar heav. body does have two transits, upper and lower.
    You can know your latitude by observing the two transits of an unknown circumpolar star.
    (true altitude upper transit + true altitude lower transit)/2 = latitude.
    
    And the misconceptions...
    
    >> -"I am guessing the same is true for the Southern Hemisphere"
    Do not speak about southern or northern hemisphere.
    The pole in the same hemisphere of the observer zenith is called : elevated pole.
    
    >>"[...] twice in a sidereal or solar day."
    mean solar day is 24h.
    mean sideral day is 23h 56mn 4 sec.
    It is not the same reference point.
    
    
    
    --
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