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    Re: Pointer star question
    From: Brad Morris
    Date: 2013 Feb 2, 17:10 -0500

    Hi Mark

    "Exact" angular separation between Polaris and Merak will depend upon the initial set of coordinates.  To what resolution do you need the angular separation to be?  An arcminute?  An arcsecond? 

    So rather than just give you an answer, I will give you the tools so that you can compute the distance on your own.  Naturally, I will provide an example with the equation.

    First, find the Right Ascension and Declination of both objects.  I will use
    Polaris
    RA 2h 31m 52.051s
    Dec N 89d 15m 50.64s
    Merak
    RA 11h 1m 50.52s
    Dec N 56d 22m 57.00s

    Since the h.m.s format is difficult to deal with, convert it to decimal.
    Decimal RA=h+(m/60)+(s/3600k
    Polaris
    RA=2+31/60+52.051/3600
    RA=2.5311252778
    Merak
    RA=11+1/60+50.52/3600
    RA=11.0307

    Also, convert the d.m.s format to decimal degrees
    Decimal Declination=d+(m/60)+(s/3600)
    Polaris
    Dec=89+15/60+50.64/3600
    Dec=89.2640666667
    Merak
    Dec=56+22/60+57.00/3600
    Dec=56.3825

    You will need to convert RA to Sidereal Hour Angle.  SHA=360d-(RA*15d/h).
    Polaris
    SHA=360-( 2.5311252778*15)
    SHA=322.0331208333
    Merak
    SHA=360-( 11.0307*15)
    SHA=194.5359 

    The angular separation between the two bodies is then given by

    arccos(sin(dec1)*sin(dec2)+cos(dec1)*cos(dec2)*cos(SHA1-SHA2))

    arccos(sin( 89.2640666667)*sin( 56.3825)+cos(89.2640666667)*cos( 56.3825)*cos( 322.0331208333-194.5359))

    arccos(.8283548032)

    34.069894429 Degrees

    or

    34 Deg 4 min 11.62 sec

    THIS DOES NOT ACCOUNT FOR REFRACTION.

    Now you have the keys to compute the distance between any two stars.

    Regards
    Brad

    On Feb 2, 2013 3:41 PM, "Mark" <m62065@yahoo.com> wrote:

    Hello all! I've been a lurker for several years now but I've been unable to find an exact answer the angular separation between polaris and merak, does anyone know what it is? Thanks, Mark.
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