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    Re: Star proper motion
    From: R.H. van Gent
    Date: 2001 Nov 20, 1:37 PM

    Aubrey O'Callaghan wrote:
    
    > I am astro navigation writing some software for my HP49G and have been
    > looking for star proper motions for calculation of SHA.
    > I have found a good website (http://www.alcyone.de/SIT/SIT_en.htm). However
    > I have some questions about the proper motion.
    > Looking up the proper motion of Sirius
    > (http://www.alcyone.de/SIT/mainstars/SIT000499.htm) get some conflicting
    > answers depending upon the source, which should be used to get the Nautical
    > almanac equivalent ?
    
    Hi all,
    
    The best source for stellar proper motions nowadays is the Hipparcos
    catalogue that is now available at
    
      http://astro.estec.esa.nl/Hipparcos/hipparcos.html
    
    First, you will need to know the Hipparcos number of your star.
    
    For that, go to
    
      http://astro.estec.esa.nl/Hipparcos/HIPcatalogueSearch.html
    
    input the approximate J2000 co-ordinates, a tolerance (say 0.1 degree)
    and a limiting magnitude (say 4). You will then obtain a short table of
    all stars brighter than the limiting magnitude measured near to that
    position with precise co-ordinates, magnitudes and proper motion
    components with their errors - with a bit of luck there will be just one
    star. Click on the star number for more details.
    
    You can also make a plot of your search region with
    
    
    http://astro.estec.esa.nl/SA-general/Projects/Hipparcos/apps/SelectArea.html
    
    but do not use it when the star is very close to one of the celestial
    poles (you will not easily find Polaris in this way).
    
    Note that the proper motion components are given in milli-arcseconds per
    year. For correcting the RA co-ordinate, divide the RA proper motion
    component by 15 * cos(decl.) to obtain the proper motion in seconds of
    time.
    
    In the case of Sirius there is also a 50-year oscillation in RA and
    decl. due to the presence of a white dwarf companion (Sirius B).
    
    Regards,
    
    ========================================================
    * Robert H. van Gent * Tel/Fax:  00-31-30-2720269      *
    * Zaagmolenkade 50   *                                 *
    * 3515 AE Utrecht    * E-mail: r.h.vangent{at}astro.uu.nl *
    * The Netherlands    *                                 *
    ********************************************************
    * Homepage: http://www.phys.uu.nl/~vgent/homepage.htm  *
    ========================================================
    

       
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