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    Re: GMT from Jupiter's moons
    From: Paul Hirose
    Date: 2004 Jul 14, 21:27 -0700

    The JPL HORIZONS system can calculate planetary satellite phenomena. Here's
    what Io will be doing tonight, as seen from Palomar Mountain, California
    (local time). The columns in the table are explained in the machine-generated
    comments below.
    
    HORIZONS is a little difficult if you're an occasional user; I needed six
    tries to get the table right. This was, however, the first time I've ever
    attempted such a computation. Fortunately the turnaround is fast, at least
    during off-peak hours. Basically, I sent the command email, went immediately
    to my inbox and downloaded email. The reply from JPL was already waiting.
    
    It's very useful to save some of your old command emails when they work right.
    Then you can simply edit and submit them for subsequent jobs.
    
    To compute the satellite visibility code (the rightmost symbol in the table
    below), HORIZONS uses the equatorial radii of the primary and satellite with
    no allowance for oblateness. I would be interested to hear how much difference
    this makes, compared to the tables George mentioned. The tabulated separation
    angle in arc seconds is the center-to-center distance. The table is adjusted
    for light-time. I used an hourly tabulation, but it can made be as fine as
    desired.
    
    Note that Io is behind Jupiter at sunset, but emerges after astronomical
    twilight.
    
    
     Date_(ZONE)_HR:MN      ang-sep/v
    *********************************
    $$SOE
     2004-Jul-14 18:00 *m    43.593/*
     2004-Jul-14 19:00 *     30.385/*
     2004-Jul-14 20:00 *     16.571/O
     2004-Jul-14 21:00 N      3.195/O
     2004-Jul-14 22:00       12.358/U
     2004-Jul-14 23:00       26.260/u
     2004-Jul-15 00:00       39.673/*
     2004-Jul-15 01:00       52.237/*
     2004-Jul-15 02:00       63.662/*
     2004-Jul-15 03:00       73.693/*
     2004-Jul-15 04:00  m    82.105/*
     2004-Jul-15 05:00 Nm    88.710/*
     2004-Jul-15 06:00 *m    93.359/*
    $$EOE
    *******************************************************************************
    Column meaning:
    
    TIME
    
      Prior to 1962, times are UT1. Dates thereafter are UTC. Any 'b' symbol in
    the 1st-column denotes a B.C. date. First-column blank (" ") denotes an A.D.
    date. Calendar dates prior to 1582-Oct-15 are in the Julian calendar system.
    Later calendar dates are in the Gregorian system.
    
      The uniform Coordinate Time scale is used internally. Conversion between
    CT and the selected non-uniform UT output scale has not been determined for
    UTC times after the next July or January 1st.  The last known leap-second
    is used over any future interval.
    
      NOTE: A time-zone correction has been requested. See header.
    
      NOTE: "n.a." in output means quantity "not available" at the print-time.
    
    SOLAR PRESENCE
      Time tag is followed by a blank, then a solar-presence symbol:
    
            '*'  Daylight (refracted solar upper-limb on or above apparent
    horizon)
            'C'  Civil twilight/dawn
            'N'  Nautical twilight/dawn
            'A'  Astronomical twilight/dawn
            ' '  Night OR geocentric ephemeris
    
    LUNAR PRESENCE
      The solar-presence symbol is immediately followed by a lunar-presence
    symbol:
    
            'm'  Refracted upper-limb of Moon on or above apparent horizon
            ' '  Refracted upper-limb of Moon below apparent horizon OR geocentric
                 ephemeris
    
     ang-sep/v =
      Target-primary angular separation and visibility. The angle between the
    center of target object and the center of the primary body it revolves around,
    as seen by the observer. Units: ARCSECONDS
    
      Non-lunar natural satellite visibility codes (limb-to-limb):
        /t = Transitting primary body disk,  /O = Occulted by primary body disk,
        /p = Partial umbral eclipse,         /P = Occulted partial umbral eclipse,
        /u = Total umbral eclipse,           /U = Occulted total umbral eclipse,
        /- = Target is the primary body,     /* = None of above ("free and clear")
    
    
     Computations by ...
         Solar System Dynamics Group, Horizons On-Line Ephemeris System
         4800 Oak Grove Drive, Jet Propulsion Laboratory
         Pasadena, CA  91109   USA
         Information: http://ssd.jpl.nasa.gov/
         Connect    : telnet://ssd.jpl.nasa.gov:6775  (via browser)
                      telnet ssd.jpl.nasa.gov 6775    (via command-line)
         Author     : Jon.Giorgini{at}jpl.nasa.gov
    
    
    

       
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