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    Henning Umland's long term almanac. Is it wrong?
    From: Bill Lionheart
    Date: 2016 Feb 23, 09:10 -0800

    I am sorry if this has been covered before but I took a sun sight today 23/02/2016 at 12:06:50 and looked up the GHA and Dec on Henning Umland's long term almanac http://www.celnav.de/longterm.htm which gives GHA of the Sun as  360° 00' 00'' and Dec  10° 45' 39'' S.

    When I worked through the sight my sextant altitude was out by a couple of degrees so I redid the calculation usy pyephem, the Python language Ephemeris library http://rhodesmill.org/pyephem/ .  Here is my code by the way (marsham is just the name of the location)

    import ephem
    marsham=ephem.Observer()
    marsham.date='2016/02/23 12:06:50'
    marsham.lat, marsham.lon = '53.3280922','-1.9948138'
    marsham.pressure=987
    marsham.temp=10
    sun = ephem.Sun()
    sun.compute(marsham)
    print("Sun Altitude and Az %s %s" % (sun.alt, sun.az))
    print("Dec %s" % (sun.dec))
    print("RA %s" % (sun.ra))
    deg= ephem.degrees
    print("GHA %s" % deg(marsham.sidereal_time()-sun.g_ra).norm)
    print("Sextant reading with art horiz %s" % deg(sun.alt*2))

    And the output

    Sun Altitude and Az 26:41:43.2 175:59:18.8
    Dec -9:55:54.7
    RA 22:24:43.19
    GHA 356:21:40.5
    Sextant reading with art horiz 53:23:26.3
    bill@bill-XPS:~/astronav$ python pyephex.py
    Sun Altitude and Az 26:41:43.2 175:59:18.8
    Dec -9:55:54.7
    RA 22:24:43.19
    GHA 356:21:40.5
    Sextant reading with art horiz 53:23:26.3

    Which agrees with what I measured up to index error. Can anyone check the calculations with their own almanac software and see if they agree with me that PyEphem is right?

    Thanks Bill

       
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