Jupiter Moon Tracker Help
This form enables you to generate a Postscript file showing the
east-west motion of Jovian satellites within a specified time period.
The distance of each selected moon from the planet's axis is plotted in
units of either arcsec or Jovian radii. Positive values correspond
to bodies on the "morning" (east) side of Jupiter and negative values by
the "evening" (west) side. In the diagram, the limbs of Jupiter are
indicated by a dark gray stripe down the middle. The locations of the
rings can be added as bands in lighter gray. Time increases downward on
The Tracker tool also allows you to download an ASCII table containing the
numeric values that went into the diagram. The file contains a single header
line followed by the numbers. Columns are as follows:
Modified Julian Date (UTC)
Projected equatorial radius of planet (arcsec)
Distance of first moon from planet's axis (arcsec)
Distance of second moon from planet's axis (arcsec)
1.0 (January 28, 1997):
Original Jupiter Moon Tracker on line.
1.1 (February 11, 1997):
Added a new ephemeris option ("Pre-RPX #2").
2.0 (January 12, 1999):
Revised user interface. Revised method of plotting Gossamer Ring(s).
Added a new ephemeris option ("Post-Galileo").
2.1 (January 31, 2002):
Added a new ephemeris option ("Post-Galileo #2"). Also expanded the
ephemeris time limits for the small satellites.
2.2 (December 1, 2009):
Updated the default ephemerides. To reduce confusion, we have removed
the choice about what ephemeris to use.
2.5 (January 23, 2013):
Renumbered for consistency across all the Moon Tracker tools.
2.6 (January 4, 2016):
Ported to new server.
2.7 (October 14, 2020):
2.8 (June 20, 2021):
The start and stop times (UTC) of the plot can be entered in a variety
of formats. For example, the following all parse to 0:01:02 UTC on July
If you want the gory details of how times are interpreted, click
- 1976-JUL-04 00:01:02.00
- July 4, 1976 12:01:02 am
- 12:01:02 am July 4, 1976
- 1976-07-04T00:01:02Z (PDS format)
- MJD 42963.00071759259
- JD 2442963.50071759259
Enter the time interval to be used for the tabulation as a number in the box,
and select the time unit from the choices provided. Start times and intervals
are rounded to the nearest minute.
Enter the numeric range and units of the horizontal axis. The value
you enter is actually half the width of the diagram; for example, if you
enter 10 Jupiter radii, then the axis will run from -10 to 10. Zero
always falls at the middle of the plot.
Enter a title for the plot in this box. It will appear centered above
Click on the box to the left of each moon that you wish to include in the
diagram and in the tabulation.
Click on the box to the left of each ring that you wish to include in
the diagram. Rings appear as gray vertical stripes on the plot. For
plotting purposes, the rings are shown extending all the way down to
the planet. For the "Gossamer Rings" option, two faint rings are shown
bounded radially by the mean orbits of Amalthea and Thebe.
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Last updated June 20, 2021.