Cassini/Saturn Viewer Help

This form enables you to generate a diagram showing the appearance of the Saturn system at a specified time. All bodies are rendered with terminators and shadows as appropriate. Selected background stars can also be included.

In the diagram, Saturn and the moons are modeled as triaxial ellipsoids, and are drawn with latitude and longitude contours at 15 degree intervals. Illuminated regions are indicated with black lines; unilluminated regions and terminators are shown as light gray. Penumbral shadows are not indicated. Optionally, the 0 and 180 degree meridians can be shown with a heavier line.

The following ring boundaries are drawn: A Ring outer edge; A Ring inner edge; B Ring outer edge, B/C Ring boundary; C Ring inner edge. The rings are shown in black if illuminated and in gray if not. Optionally, the E, F and G Rings can be drawn as dashed lines.

The diagram is oriented with J2000 declination increasing upward and with right ascension increasing to the left. The frame has uniformly-spaced tick marks along each axis. The declination axis is labeled in degrees, minutes and seconds; the right ascension axis is labeled in hours, minutes and seconds.

Each diagram includes a caption that summarizes the key parameters used to generate it.

Limitations. The outer irregular satellites of Saturn are not shown.

Change History

RPX Viewer 1.0 (January 17, 1995): Original Saturn viewer for 1995-6 ring plane crossing observations.
1.1 (December 11, 1995): Revised to use a better ephemeris based on a few 1995 observations.
Saturn Viewer 1.0 (January 28, 1997): New interface, allowing for a choice of ephemerides, greater control over the figure contents and more informative figure captions.
1.1 (February 6, 1997): Additional information at the bottom of the "results" page includes the subsolar and sub-Earth longitude.
2.0 (February 1, 1999):
- Expanded ephemeris time limits and added a new ephemeris option.
- Added a viewpoint option including Voyager 1, Voyager 2, and parallax corrections for Earth-based observatories.
- Added alternative units (Saturn radii, kilometers, and the Voyager camera fields of view) to the field of view options.
- Added background star options.
- Added an option to suppress latitude and longitude lines, producing diagrams that are suitable as drawing blanks for amateur observers.
- Added distances and light travel time to output table.
2.1 (December 6, 2000): Added the Cassini Orbiter viewpoint to support mission planning.
2.2 (July 21, 2001): Updated the Cassini Orbiter tour.
2.3 (January 31, 2002):
- Added new ephemeris option ("Prometheus 2002").
- Added star name option for diagram center.
- Added hour/degree options for right ascensions.
2.4 (January 10, 2003): Added Phoebe.
2.5 (July 14, 2003): Added pericenter markers for F Ring. Updated F Ring orbital elements.
2.6 (August 30, 2007): Added Cassini-discovered moons and the latest ephemeris options.
2.7 (December 1, 2009): Updated the default ephemerides. To reduce confusion, we have removed the choice about what ephemeris to use.
2.8 (January 23, 2013): Anthe and Aegaeon added. Renumbered for consistency among all Planet Viewer tools. Ephemeris updates.
2.9 (January 4, 2016): Ported to new server. Ephemeris updates.
2.10 (October 14, 2020): Ephemeris updates, including the final Cassini tour reconstruction.

3.0 (July 5, 2021): Major new features:

the returned web page now lists the sub-observer and sub-solar longitudes and latitudes for each the planet and each moon.
the diagram page identifies the sub-observer longitude and latitude, as well as the phase angle, of the planet or selected moon.
there is now an option to highlight the prime meridian on the planet and moons.
Viewer requests can now be bookmarked.
the new Output option lets you jump directly to a PDF or JPEG diagram, bypassing the web page.
ephemerides have been updated.
the form now uses a clean, new style sheet.
bug fix: if selected, the anti-solar direction is now more accurate.

3.1 (August 2, 2022):

the JWST and HST viewpoints have been added.
ephemeris updates.

Observation Time

The observation time (UTC) 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.

Field of View

Enter the field of view of the drawing to be generated and select the appropriate units. Units can be seconds of arc (the default), milliradians, microradians, Saturn radii, kilometers (projected at the distance to Saturn) or the fields of view of certain spacecraft cameras.

Diagram Center

Four different methods of specifying the diagram center are supported. Click on the box to the left of the option you wish to use.

Body: The diagram will be centered on the location of the selected body.

Ring or orbit ansa: The diagram will be centered on the ansa of the selected ring or orbit. Specify the east or west ansa using the second box. Note that east is toward the left in the diagram.

J2000 RA and dec: The diagram will be centered on the specified pair of right ascension and declination coordinates. The first box is for the RA and the second box is for the dec. You may also specify whether the RA is in units of hours or degrees. Enter up to three values in each box, separated by spaces; these values are interpreted as degrees/hours, minutes and seconds, respectively. Any or all values can have fractional parts.

Star name: Enter the name of a star as it appears in the current list. The name must match exactly.

Moon Selection

You can decide which moons to include in the diagram. At minimum, the moons Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Hyperion, Iapetus and Phoebe are included. Use the boxes to the left of the list to choose the smallest set of moons to include. Note that, whatever your choice, the moons appearing above it in the list will also be shown.

Ring Selection

You can decide which ring to include in the diagram. At minimum, the A, B and C Ring boundaries are shown. Click on the box to the left to show the F Ring, the E Ring core and the G Ring. For each selection, the rings appearing above it on the list will also be included. If selected, the E, F and G Rings are plotted as dashed lines to distinguish them from their brighter counterparts. The F Ring is plotted with accurate eccentricity and inclination, using the model of Bosh et al. (Icarus 157, 57-75, 2002).

Background Objects

You have several independent options for including background objects in the diagrams. These options make it possible to render diagrams around the times of stellar or spacecraft occultations. Objects are marked by pluses and are labeled by name if the Moon & Star Labels option is activated.

Standard stars: Check the box to include any of a standard list of stars that happen to fall inside the field of view of the diagram. The Neptune Viewer does not access a star catalog; instead, it only plots stars from a finite list. To view the current star list, click here. This list is updated periodically at the request of the users; if you would like to have a star added to the list, email the necessary information to pds-admin@seti.org.

Additional star: In addition to or instead of the standard stars, you can specify one additional star to be included in the diagram. Check the box to the left and enter the star's RA, dec, and name in the three boxes. You may also specify whether the RA is in units of hours or degrees. Enter up to three values in the RA and dec boxes, separated by spaces; the values are interpreted as hours/degrees, minutes and seconds, respectively. Any or all values can have fractional parts.

Other bodies:

Check each box to mark the location of the specified body or spacecraft in the diagram.

Title

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

Moon and Star Labels

Optionally, the diagram will be generated with the name of each moon and star written above and to the right of its center. You may select the size of these labels in points, where a point is 1/72 inches.

Moon Enlargement

The diagram is rendered to scale, which means that some of the smallest moons may be very hard to see. You may enter a minimum plotted size for moons in this box. If a nonzero value is used, the smallest moons will be easier to see. The size is in units of points, equal to 1/72 inches. A value of ~4 may be appropriate.

Ring Plot Type

You have three options for how Saturn's A, B, and C rings are plotted. In the "Transparent" option, the ring boundaries are drawn but everything behind the rings is shown normally. In this case, the rings do not cast shadows. In the "Opaque" option, the rings are opaque from the A Ring's outer edge all the way down to the planet. The rings do cast shadows and objects behind them are invisible (including objects that would normally be visible interior to the C Ring). In the "Semi-transparent" option, objects behind the rings are subdued in gray but are still visible. The rings do cast shadows. This option generates the most realistic view but, because of limitations of the toolkit used to generate the diagram, generates a Postscript file up to twice as large as with the other options.

Pericenter Markers

You have the option of placing a dot at the location of the pericenter of each eccentric ring in the diagram. Select whether you want to mark no rings, just the Epsilon Ring, or all eccentric rings. Also enter the size of the dot, in units of points (= 1/72 inches).

Highlight Prime Meridians

If you select this option, then the 0 and 180 degree meridians will be shown with a heavier weight.

Output

By default, when you click on "Generate diagram", 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, or Postscript. Optionally, you can choose to bypass the web page and go directly to the diagram in one of the three formats.