Jupiter Moon Tracker Help
This form enables you to generate a diagram showing the
east-west motion of the inner satellites of Jupiter
across the planet's disk.
The distance of each selected moon from the planet's axis is plotted in
units of either
or planetary radii. Positive values correspond to bodies on the "morning" side
of the planet (moving toward the observer) and negative values by the "evening"
side. In the diagram, the planetary limbs are indicated by a dark
gray stripe down the middle.
Optionally, the locations of the rings can be added as bands
in lighter gray.
Time increases downward on
The Moon 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):
3.0 (August 2, 2022):
Major new features:
The start and stop times (UTC) of the table can be entered in a variety
of formats. For example, the following all parse to 0:01:02 UTC on July
- JWST, HST, and Earth-based observatories are now supported.
- Moon Tracker requests can now be bookmarked.
- the new Output option lets you jump directly to the table,
bypassing the web page.
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 (ISO 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.
You may specify the point of view of the diagram. By default, the point
of view is the center of the Earth.
You may select from any viewpoint on the list.
- Earth's center
- JWST: Valid for 2021-Dec-25 to 2024-Feb-22.
- HST: Valid for 1990-Apr-25 to present.
- Named observatories:
After each observatory's name, you will see listed its latitude and east
longitude in degrees, followed by its altitude in meters. Note that
only very rarely will a diagram change significantly based on the
particular location of an Earth-based observatory.
Latitude & Longitude:
If your desired observatory or location is not on the observatory list,
you can enter its latitude, longitude and altitude in the three boxes
provided. Latitudes and longitudes can each be specified by up to
three values, interpreted as degrees, minutes and seconds. Longitudes
can be specified either east or west.
If you wish to have an observatory added to the standard list, or to
refine the coordinates of a listed observatory, email the necessary
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
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 planetary 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
By default, when you click on "Submit", you are directed to
a web page that lists the details of the request, a small preview of the
diagram produced, and options to view or download that diagram as PDF,
JPEG, Postscript, or as an ASCII table. Optionally, you can choose to
bypass the web page and
go directly to any one of these four formats.
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Last updated August 3, 2022