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 degrees 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 plot.

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:

Change History

Time Limits

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 4, 1976:
  • 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
If you want the gory details of how times are interpreted, click here.

Interval: 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.

Observatory: You may select from any viewpoint on the list.

  • Earth's center
  • JWST: Valid for 2021-Dec-25 to approximately two years after the present day.
  • HST: Valid for 1990-Apr-25 to approximately two months after the present day.
  • 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 information to pds-admin@seti.org.

Moon Selection

Click on the box to the left of each moon that you wish to include in the diagram and in the tabulation.

Ring Selection

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.

Plot Options

Scale: 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.

Title: Enter a title for the plot in this box. It will appear centered above the diagram.


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.