Saturn Moon Tracker Help
This form enables you to generate a Postscript file showing the
east-west motion of Saturnian 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 Saturnian radii. Positive values correspond
to bodies on the "morning" (east) side of Saturn and negative values by
the "evening" (west) side. In the diagram, the limbs of Saturn 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 (March 14, 1995):
Original Saturn Moon Tracker
for 1995-6 ring plane crossing observations.
1.1 (December 11, 1995):
Revised to use a better ephemeris based on a few 1995 observations.
1.2 (January 28, 1997):
New interface, allowing for a choice of ephemerides, greater control
over the figure contents and more informative figure captions.
2.0 (January 12, 1999):
Revised user interface.
Expanded ephemeris time limits and added a new ephemeris option
("New Prometheus fit").
2.1 (January 31, 2002):
Added a new ephemeris option
("Prometheus fit 2002").
2.2 (January 10, 2003):
2.3 (August 8, 2008):
Added Cassini-discovered moons and the latest ephemeris options.
2.4 (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):
Anthe and Aegaeon added.
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 Saturn 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 main rings are shown extending from the A Ring's
outer edge (136780 km) all the way down to the planet. The E Ring is
plotted between 3 and 5 Saturnian radii, although it actually extends
outward much further.
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Last updated June 20, 2021.