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From: Paul Hirose (no email)
Date: Thu Jul 15 2004 - 00:27:14 EDT
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 :
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