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    Re: getting GHA from MICA
    From: Mike Burkes
    Date: 2014 Mar 21, 12:51 -0700
    Hi folks,cannot resist this;Was not MICA the sheriff played by Paul Fix on TV series The Rifleman? OK let me have it!!!
    Mike Burkes
     

    From: cfuhb-acdgw---.net
    To: m_burkes---.com
    Date: Wed, 19 Mar 2014 14:56:02 -0700
    Subject: [NavList] Re: getting GHA from MICA


    Sean C wrote:
    > Question: Is calculating the sidereal time and then the apparent geocentric equator of date position the only way to get the GHA of a body?
    
    I don't have the latest MICA version, but 2.0 has "Apparent Topocentric
    Equator of Date (LHA, Dec)" as one of the choices for position type. In
    theory, that will give you GHA if the topocenter is very close to a pole
    and at 0 longitude.
    
    For instance, at 2014 March 19 at 1700 UT1, compare Moon LHA from N89 59
    59 W000 00 00 to a GHA computed by subtracting the geocentric apparent
    RA from Greenwich apparent sidereal time.
    
    220 01 11.6  topocentric LHA
    220 01 11.5  RA - GAST
    
    I converted LHA from hours to degrees.
    
    If you set the topocenter at exactly 90 north, MICA's LHA is a couple
    degrees in error. Of course one could argue that LHA and azimuth are
    undefined at a pole. However, my software does the common sense thing
    and computes as if you were on the specified longitude and an
    infinitesimal distance away from the pole. That happens with no extra
    effort by the programmer if the coordinate transformations utilize
    vectors and rotation matrices.
    
    --
    I filter out messages with attachments or HTML.
    
    View and reply to this message: http://fer3.com/arc/m2.aspx?i=127287
       
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