Mars Viewer Help
This form enables you to generate a Postscript file showing the
appearance of the Martian 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, Mars 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 hypothetical rings of Mars are also shown. Their
appearances are based on the model of
Krivov, A. V., and D. P. Hamilton 1997. Martian dust belts: Waiting for
discovery. Icarus 128, 335-353.
In this model, each of Mars' moons generates a cloud of dust. The
Phobos ring is modeled as equatorial but 350 km thick and shifted toward
the Sun by one Martian radius. The Deimos ring is 5300 km thick and
shifted away from the Sun by two Martian radii. It is also tilted out
of the equatorial plane toward the ecliptic by 15 degrees. See the above
reference for the explanations of these surprising properties.
Each ring is shown by a pair of curves, one indicating each of its
vertical limits. The rings are shown in black if illuminated and in
gray if not or if the opposite side is illuminated. The Phobos ring is
shown by solid lines; the Deimos ring by 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.
2.0 (November 9, 1999):
Original Mars viewer on line.
(The version number was chosen for consistency with other tools.)
2.1 (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):
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):
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:
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 field of view of the drawing to be generated and select the
appropriate units. Units can be seconds of arc (the default), Martian
radii, or kilometers (projected at the distance to Mars).
Three 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
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. Enter up to three values
in each box, separated by spaces. The values are interpreted as hours,
minutes and seconds, respectively in the RA box and as degrees, minutes
and seconds in the dec box. Any or all values can have fractional parts.
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
- Named observatories:
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
You can decide whether to include the hypothetical Martian rings in the
diagram. Click on the box to the left to select your option. If
selected, both rings are indicated by pairs of dashed lines above and below
the ring plane to indicate these rings' physical thickness. The Phobos
ring is shown with a solid line and the Deimos ring is shown with a
for a discussion of the models used for each ring.
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 occultations. Objects are marked by
pluses and are labeled by name if the
Moon & Star Labels option is activated.
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 Mars Viewer does not
access a star catalog; instead, it only plots stars from a finite list.
To view the current star list, click
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
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. Enter
up to three values in the RA and dec boxes, separated by spaces. The
values are interpreted as hours, minutes and seconds, respectively in
the RA box and as degrees, minutes and seconds in the dec box. Any or
all values can have fractional parts.
Enter a title for the plot in this box. It will appear centered above
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 Mars' 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.
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Last updated October 14, 2020.