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    Re: Lunar4.4. vs Frank's online calculator
    From: Paul Hirose
    Date: 2023 Apr 26, 23:41 -0700

    I duplicated the results of Modris Fersters with Lunar 4.4 (DE441
    ephemeris).
    
    time
    2023-04-02 18:40:00.00 UT1
    2023-04-02 18:41:09.48 TT
    +1m09.48s delta T
    
    position
      24°00.00' +56°00.00'  east lon, north lat
    0.0 meters (0 feet) above ellipsoid
    
    atmosphere
    10.0 C (50.0 F) at observer
    1010.0 mb (29.83″ Hg) air pressure
    50.0% relative humidity
    
    Moon
      44°11.89' computed unrefracted center altitude
         15.02' unrefracted semidiameter
          0.98' refraction
      44°27.90' apparent upper limb altitude
    148°17.17' predicted azimuth
    
    Venus
      16°52.49' computed unrefracted center altitude
          3.14' refraction
      16°55.63' apparent center altitude
    278°45.19' predicted azimuth
    
    My program recommends Moon upper limb and Venus far limb. It also has a
    "center of light" option. But in this case, Venus phase angle is 58°, so
    I don't think there's much error if observe Venus center and ignore
    phase. The easy way is to select "center" for the Venus distance limb
    (in the program main window). Then the output omits a correction for
    Venus SD:
    
    topocentric apparent Moon to Venus angle:
    104°03.44' center to center, unrefracted
          3.25' refraction
    104°00.19' center to center, refracted
        -15.02' Moon near limb refracted SD
    103°45.17' computed Moon to Venus
    
    The last line is identical to his value. But is it correct? You can get
    azimuth, altitude, and angular diameter from the JPL Horizons online
    ephemeris. (Does not give semidiameter.) Apply refraction to the
    altitudes, then compute separation angle. Subtract Moon SD. (Lunar 4.4
    says refraction has no effect on SD at 0.01' precision.)
    
    https://ssd.jpl.nasa.gov/horizons/app.html#/
    
    Careful - observer coordinate order is longitude, latitude, height.
    
    There is an option to apply standard refraction, but I have never used it.
    
    I would investigate this myself, but it's time to go to bed.
    
    --
    Paul Hirose
    sofajpl.com
    
    

       
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