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    Re: Lunars with Young's formula: always off by several minutes
    From: Paul Hirose
    Date: 2018 Nov 4, 21:12 -0800

    On 2018-11-02 16:15, William Porter wrote:
    >
    > *Moon-Aries 19Oct18 18:46:47U Obs distance (near): 41deg 16.8’*
    > Lat: 51.432 deg Long -0.219 deg
    > *Ephemera:*
    > Moon (from USNO polynomials)
    > RA: 332.155 deg Dec: -13.891 deg HP:3274” AD:1784”
    
    I don't agree. First, the time. I assume "19Oct18 18:46:47U" is UTC.
    Currently UTC is 37 seconds behind TAI, and TAI is a fixed 32.184 s
    behind Terrestrial Time. Therefore, TT at observation time = 18:46:47 +
    37 s + 32.184 s = 18:47:56.2 = .783289 day.
    
    The applicable polynomial coefficients are:
    
    R.A.   322.7938744    12.0578390    -0.1199279     0.0092096
    0.0018500    -0.0000684
    
    Dec.   -16.3099733     2.8134374     0.3553752    -0.0179380
    -0.0005172    -0.0000195
    
    H.P.     0.9060852     0.0032932     0.0013016    -0.0000520    -0.0000059
    
    (http://asa.usno.navy.mil/static/files/2018/lunarpoly_2018.txt)
    
    With a calculator and the polynomials I get geocentric apparent coords:
    
    332.1701° -13.8970°  RA, dec (true equator and equinox of date)
    .9094° (3274″) HP
    
    An independent computation with my astronomical software confirms those
    values. The position is .95′ different from what William got. I do agree
    with his parallax. Don't know what his AD:1784” means.
    
    
    > Aries
    > RA J2000: 19:50:47=297.696deg
    > *PLUS TO A FIRST ORDER APPROX, 18.8years’ precession at 360/25771 deg year=0.263deg=297.959deg*
    > *Thank you Navlist for helping me find this error*
    > Dec, ignoring precession for now: 8.868 deg
    > GST-UT: 1:52:47 (from astropixels.com)
    
    The Aries computation I will skip since I don't know what's going on.
    
    > 1) Preparation
    > GST (GHA Aries) = 20:39:34 = 309.890 deg
    > GHA moon = 337.735 deg
    > GHA Altair = 12.194 deg
    > “d”, observed distance = 41.528 deg after adding semi-diameter
    
    My geocentric values:
    309.8858° Greenwich apparent sidereal time
    337.7156° GHA Moon
      11.9647° GHA Altair
    
    (UT1-UTC is negligible since it's only 32 milliseconds.)
    

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