Neptune Viewer Help
This form enables you to generate a Postscript file showing the
appearance of the Neptune 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, Neptune 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.
A selection of the rings is also drawn. The rings are shown as single
lines in black if illuminated and in gray if shadowed or if the opposite
side is illuminated. The Galle and Arago Rings are plotted as dashed
lines if selected. All rings are assumed circular and coplanar. The
Adams Ring arcs are highlighted with heavier line segments. The user
may select between the two competing models for their motion, as
described by Nicholson et al. (Icarus 113, 295-330, 1995).
The locations and spacings of the arcs are as tabulated by Porco
(Science 253, 995-1001, 1991).
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.
1.0 (February 8, 1997):
Original Neptune viewer on line.
1.0a (August 5, 1997):
Bug fixed that prevented Larissa and Proteus from being displayed.
2.0 (February 1, 1999):
Extended ephemeris time limits and added new option.
Added a viewpoint option including Voyager 2 and parallax
corrections for Earth-based observatories.
Added alternative units (Neptune 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 (January 31, 2002):
Added star name option for diagram center.
Added hour/degree options for right ascensions.
2.2 (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):
Ephemeris updates; updated name for "Hippocamp".
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), Neptune
radii, kilometers (projected at the distance to Neptune) or the fields
of view of Voyager cameras.
Arc motion model:
You may also select between the two competing models for the motion of
the Adams Ring arcs, as described by Nicholson et al. (Icarus
113, 295-330, 1995). The latter (default) appears to be more
consistent with recent Earth-based detections.
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
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.
You may select from any viewpoint on the list.
- Earth's center
- Voyager 2: Valid for the period 1989-Jun-03 to 1989-Oct-03.
- 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
You can decide which moons to include in the diagram. At minimum,
Triton and Nereid are included.
Use the boxes to the left of the list to choose the additional
moons to include. Note that, whatever your choice, the moons appearing
above it in the list will also be shown.
You can decide which rings to include in the diagram. The Adams
and LeVerrier Rings are always shown. Click on the box to the left to
show the Arago and Galle Rings. Note that, whatever your choice, the
rings appearing above it in the list will also be shown.
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.
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
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. 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.
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
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
Neptunian 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.
Enter the width of the line segments to use to highlight the ring arcs,
in units of points (= 1/72 inches).
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Last updated October 14, 2020.