Saturn Viewer Help
This form enables you to generate a Postscript file 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.
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.
If you zoom in on Hyperion, its orientation will be incorrect because
the SPICE data files do not contain a model for its chaotic rotation.
Prometheus and Pandora's rotations are not corrected for their orbital
wanderings.
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 beta (January 4, 2016):
Ported to new server. Ephemeris updates.
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 (PDS format)
- MJD 42963.00071759259
- JD 2442963.50071759259
If you want the gory details of how times are interpreted, click
here.
Enter the field of view of the drawing to be generated and select the
appropriate units. Units can be seconds of arc (the default), Saturn
radii, kilometers (projected at the distance to Saturn) or the fields of
view of the Voyager or Cassini cameras.
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 ansa: The diagram will be centered on the ansa of the
selected ring. 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.
You may specify the point of view of the diagram. By default, the point
of view is the center of the Earth.
Observatory:
- Earth's center
- Voyager 1: Valid for the period 1980-Aug-23 to 1981-Jan-01.
- Voyager 2: Valid for the period 1981-Jun-01 to 1981-Oct-22.
- Cassini: Valid for the period 2000-Nov-09 to 2008-Aug-09.
- 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
Mark Showalter.
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 be included. Note that, whatever
your choice, the moons appearing above it in the list will also be
included.
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).
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 Jupiter 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
Mark Showalter.
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.
Enter a title for the plot in this box. It will appear centered above
the diagram.
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.
The diagram is rendered to scale, which means that some of the smallest
Saturnian 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.
If you activate this option, all latitude and longitude lines will be
suppressed in the diagram. This produces a diagram that is suitable for
amateur observers to use as a drawing blank.
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.
You have the option of placing a dot at the location of the pericenter
of the eccentric F Ring in the diagram. Select whether you want to mark
no rings or the F Ring. Also enter the size of the dot, in units of
points (= 1/72 inches).
Saturn Viewer Form |
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Last updated 4 January 2016.
Mark Showalter