Input Options

GV generates images, movies, and tables based on input supplied to it through a web-based form.

The list of observers includes:

GV Observer Options
New Horizons	All instruments and numerous trajectories for encounter planning.
Messenger	Two simple square FOVs (M1, M2).
Rosetta	All instruments and multiple trajectories.
Cassini	Includes UVIS and ISS FOVs.
Galileo	SSI imager.
Voyager 1	ISS WAC and NAC instruments.
Voyager 2	ISS WAC and NAC instruments.
Earth	Observer is assumed to be at the Earth's center. E1 and E2 are simple rectangular FOVs. Operates like an Earth-based planetarium program, useful for planning coordinated observations.
Sun	Useful for planning atmospheric occulations. Includes simple circular FOVs S1, S2, S3.
Pluto	Useful for planning occultations. P1 and P2 are simple circular FOVs.
Juno	[Restricted access] Includes UVS, JIRAM, and JunoCAM FOVs.
LRO	[Restricted access] Includes LAMP FOV.
JUICE	[Restricted access] Includes Alice FOV.

Changing the Observer changes more than just the observer itself, but it reconfigures a number of other GV input options, including:

The set of SPICE kernels used. Different trajectory files assume different planetary ephemerides, and GV handles this carefully.
The list of available instruments (e.g., no need to have New Horizons FOVs if Observer = Cassini).
The list of plotted bodies (e.g., GV will not usually plot the small Saturnian satellites if Observer = New Horizons).
The list of available target bodies (although all bodies are available using the Target = Other Body).
The boresight rotation direction.

For New Horizons and Rosetta, different kernel sets are selectable. A kernel set is group of kernels for one mission, read by GV. Some of these kernels sets are general-purpose, while other have been custom-built for one-off tests. Some include C-kernels (that is, spacecraft pointing usable with SPICE Lookup), but many do not.

New Horizons Kernel Set Examples
Reconstructed (15sci_rhr)	Includes best derived position and pointing info from Pluto encounter. Right-hand rule coordinates. Updated regularly and automatically ingests new kernels changes from SOC. [Recommended]
Reconstructed (15sci_lhr)	Same as above, but using left-handed coordinates. Updated regularly.
Predict (NHOPS v28Jun2015)	Uplinked trajectory and pointing, with simulated deadbands. [Recommended]
Reconstructed (15sci_rhr 10.02s)	Same as Reconstructed trajectory, but offset by dt = -10.02 seconds to adjust for best knowledge of flyby C/A time from imaging data as of 25-Jul-2015.
NHOPS Encounter	Recommended for tour planning; includes C-kernels. [Outdated for Pluto]
Reference Metakernel	Nominal kernel set, useful for planning and data analysis. Does not include all C-kernels. [Outdated for Pluto encounter, but useful for Jupiter and cruise]
ACO-5	Includes C-kernels for Annual Checkout 5
Encounter 20	C/A date of 20-Jul-2015, early encounter candiate
Encounter 5000	C/A distance of 5000 km, early encounter candidate

Rosetta Kernel Set Examples
R-Alice Metakernel	Uses daily updated C-kernels from SOC; used for most purposes.
Recommissioning V5	One-off C-kernel
Study Case 2	One-off C-kernel

To see what files are included in a kernel set, check List Kernel Info before plotting. This will display the entire list of loaded kernels, often along with documentary information about the kernel set's heritage.

[New Horizons and Rosetta only] Upload kernels: For New Horizons and Rosetta, GV also allows the user to upload and manage their own custom set of kernels. These kernels should be compressed into a .zip file and then uploaded via the web interface. If no longer needed, they can be deleted.

Note that kernel sets uploaded in this way are accessible by all users of GV with proper access. Please don't post something you don't want other users seeing. If needed, post an explanatory note with your kernel set (in the supplied field) to help you remember its heritage.

When selected, the user-uploaded kernels are added to the end of the GV's kernel list, where SPICE treats them at highest priority, effectively overwriting any kernels for the same object and time loaded in the default GV kernel set.

Start Time

Time of the observation. Appropriate light-time corrections are made; positions calculated are apparent positions, at the specified time, from the observer's location. GV will plot the positions of bodies at every timestep. However, only one FOV is plotted, which is for the start time.

Format is flexible; any standard SPICE time format is acceptable. Examples include:

GV Time Format Examples
January 20 2006	UTC; time assumed to be 00:00:00
2006–31–Jan 01:00:34.12	UTC
JD 2454156.45	Julian date
2015::200 12:12:23	Day-of-year format
2006-180T18:28:12	Day-of-year format
SCLK 5/0504705750.2	SCLK (Spacecraft Clock Time); all missions with SCLK kernels.
MET 51623454.1	MET (Mission Elapsed Time); New Horizons only

Close-approach times can be automatically calculated by entering CA and an optional body name.

GV Time Format Examples
CA	Computes close-approach time to body named in Target field
CA Hydra	Computes close-approach time between Observer and Hydra

A real-time computation can be done by leaving the field blank:

GV Time Format Examples
[blank]	Use current, real-time UTC

End Time

[Optional] GV can plot the motion of solar system objects as seen from the moving observer. If this value is set, then the positions of the bodies are plotted at evenly spaced intervals between the start time and end time. If the start time is before the end time, then the table and plot are generated in reverse order.

Interval

[Optional] If set, then defines a number of discrete timesteps to use when plotting motion of solar system objects, and generating data tables. The input allows for several different formats, such as:

Interval Examples
3 Timesteps	Three equally-spaced steps, between Start Time and End Time.
3 Days	Plot at 3-day intervals, from Start Time to End Time. The number of intervals is determined automatically.
25.5 Seconds	Plot at 25.5-second intervals.

The maximum number of intervals is a hard-coded limit based on computation time:

500, if planets or satellites are being rendered;
10,000, otherwise.

The higher limit is useful for making data tables; GV can usually generate tables of this size in < 1 minute. To use the higher limit, uncheck the boxes to Draw planets and satellites. Rendering bodies takes far longer than computing their position for a table, so use short intervals with caution!

GV's default is to make only one plot (i.e., 1 Timesteps).

Movie

If set, create an animation based on the given input parameters. The movie will be created with the specified start time, end time, and number of timesteps.

The results will be returned in GV's Movie Maker, not the main GV screen. This panel creates a preview of the movie based on user input parameters. The frame rate is user-settable. The movie is generated after being previewed in the Movie Maker. Once generated it can be downloaded in a variety of formats: Animated GIF, MP4, tarball, or raw PNG frames in an HTML page.

NB: GV's Movie Maker has less error-checking than the single frame-by-frame mode of GV. If errors are generated during the movie creation (e.g., for a time range not covered by the kernel), the error message will likely not be reported back to you, and GV may appear to have hung. Check your inputs before making long movies!

Center Position

Position at which the central FOV is pointed. This can be a specified position, or a body name. The position may be specified in terms of J2000 celestial coordinates (RA/Dec), or in terns of ecliptic coordinates (Lon/Lat). Either one of these may be entered in units of

GV Postional Units Examples
Degrees	45.00
H/D MS	4 12 34.4 (HMS, for RA) 4:12:34.4 or 89 14 41 (DMS, for Dec) 89:14:41
Radians	2.12239

GV Reference Frame Options
J2000	Celestial coordinates (i.e., Earth's rotation axis is oriented with Dec=0 deg)
ECLIPJ2000	Ecliptic coordinates (i.e., Earth's orbital plane is oriented with Dec=0 deg)

If a body name (Sun, Io, New Horizons, etc.) is specified for the center position, then its proper coordinates are automatically filled in for its RA/Dec or Lat/Lon.

SPICE Lookup: If selected, then the actual spacecraft orientation (RA, Dec, Rotation*) at the specified time is computed based on the available SPICE C-kernels.

[*] When using SPICE Lookup, the spacecraft rotation angle is computed and applied properly internally, but the results are not visible in the Roll Angle input box.

Other Body: If selected, then the body entered into the box next to the selection menu is used. This allows for use of target bodies not explicitly listed in the pull-down selection menu. The named target can be any valid NAIF name or code.

GV Example Target Names
Phobos, equivalent to 401
537, equivalent to Jovian moon Kale
0, equivalent to Solar System Barycenter
Pluto Barycenter, equivalent to 9
Pluto, equivalent to 999
Galileo Orbiter, equivalent to -77

Even though all NAIF IDs are recognized, kernel files for all bodies may not be available. New kernels and bodies can usually be added easily; please ask.

Juno Pointing

[Juno only] When selected, GV uses a special Juno-specific mode for spin pointing. The spacecraft spin axis (+Z) is pointed to a specified location, and the FOVs are drawn as they would be with the spacecraft spinning about this axis. The FOVs are not targetable individually, although UVS may be pointed to the extent allowed by its scan mirror.

When Juno Spin Pointing mode is selected, several of GV's other input panels are dimmed, indicating they are disabled. For instance, it is not possible to set the Target position or an FOV Footprint, because the spacecraft is rotating.

Juno Spin Axis +Z Options
Earth, Jupiter, Sun	Point +Z toward the named body.
Orbit Normal	Point +Z toward the Orbit Normal. Orbit Normal is defined as the cross product of the Juno-to-Jupiter position vector with the Juno-to-Jupiter velocity vector.
RA/Dec	Point +Z to the specified RA/Dec or Lon/Lat position. Degrees.
+Z Offset dRA/dDec	A positional offset (in RA/Dec, or Lon/Lat) which is added to the position computed for the Spin Axis field. This offst is added arithmetically; it is not necessarily the same as an additional rotation by dRA/dDec. Degrees.

Spin Phase: Rotate the FOV position of the Juno UVS instrument by the specified angle about +Z. This allows the UVS FOV to point to any position in a 360° swath of the sky. Degrees. See also Plot FOVs: UVS Swath.

Mirror Slew: Using the UVS scan mirror, offset the UVS FOV position by the specified angle about the spacecraft +Y axis. At the same time, rotate the FOV by an identical angle about the spacecraft +X axis. Degrees.

Neg Orb Norm: [Output] This is a returned value which indicates the negative orbit normal position. It is retuned only when selecting Juno Spin Axis toward Orbit Normal, and does not include the +Z Offset dRA/dDeg angle. Degrees.

Plot Orientation

Rotates the plot a specified angle clockwise -- e.g., "10 degrees relative to s/c +X up." The entire plot is rotated, including axes. There are essentially two rotations performed: one so that the specified direction points up, and then an optional rotation beyond that.

Plot Orientation Options
Sky North	[Default] Rotate so that the plot is oriented with the North Celestial Pole (NCP, for J2000) or North Ecliptic Pole (NEP, for ECLIPJ2000) toward the top.
Body North	Rotate so that the pole of the target (e.g., Pluto) is north. This does not work for SPICE Lookup mode, because GV is unable to determine the target name from a C-kernel alone. However, in such cases you might consider rotating relative to an FOV such as LORRI or Alice.
LORRI Up Alice Up	[New Horizons only] [Rosetta only] Rotate such that the major axis of the specified FOV is upright. [Experimental -- results not guaranteed]
S/C +X S/C +Y S/C +Z	Rotate such that the specified spacecraft axis is upright.

FOV Position

Position of the selected FOV in the sky. By default, the FOV is centered on the target. Options are:

GV Position Options
Degrees from Target	e.g., 4 deg in RA and Dec from the target
Radii from Target	Distance in body radii; e.g., 3 R_Jup from Jupiter.
RA/Dec degrees	Absolute position, in degrees.
RA/Dec (H/D)MS	Absolute position, in Hours / Degrees / Minutes / Seconds.
Degrees along Limb	Positions the FOV center on the limb of the target body. The two angles entered are not interpreted as RA & Dec, but are used as: RA: Counterclockwise degrees around the limb. The zero-point is arbitrary. Dec: Degrees inside (-) or outside (+) limb; 0 = limb itself.
Degrees Roll from Nadir	In this mode, the FOV begins pointed 'downward' at the target center. A slew is then performed, according to the angles specified. The two angles entered in this case are: Roll: Side-to-side slew, in degrees. Referenced relative to spacecraft velocity; i.e., orbit normal. Pitch: Front-to-back slew, in degrees. Referenced to orbit normal. In this pointing mode, only a Roll or a Pitch may be performed; you maybe get incorrect results if you combine them.

FOV Footprints

This allows for plotting of mosaics and scans, such as:

"Cover Pluto with a 4x4 LEISA mosaic, spaced at 0.5 deg intervals, in a lawnmower-type scan pattern, with a slew every 75 seconds."

The following options are available. A footprint refers to a single placement of the FOV; a mosaic is made up of many different footprints.

GV Footprint Settings
# of Footprints	The size of the mosaic, for instance, a 1x10 mosaic (10 frames, linear) or a 4x4 mosaic (16 frames, square).
Footprint Spacing	The center-to-center spacing between footprints. If this spacing is less than the FOV width, the footprints will overlap
Footprint Path	If Draw is selected, the path between the footprints will be drawn, to show the order in which the scan is to be performed. Three scan patterns are possible: Lawnmower Zamboni Typewriter
Footprint Ref. Frame	The default mode is Inertial, in which case footprints are placed on the sky instantaneously with no correction for target motion or rotation. If Target mode is selected, then body motion and rotation is considered (e.g., for performing a mosaic at closest-approach to a body). Target mode requires use of a Footprint Interval.
Footprint Interval	[Optional] The delay in seconds between subsequent footprints.

Keep in mind that GV doesn't model spacecraft inertia, pointing stability, or deadbands. The Footprints mode is for sketching out mosaic patterns, not performing sequencing.

Center FOV

Name of the FOV to point. Options include all remote sensing instruments, plus the spacecraft boresight.

CtrPlot on: Allows the final plot to be centered on the target (e.g., Pluto), or the FOV (e.g., LORRI). If the values set in the FOV Position are zero, then the the Target and FOV positions are both centered.

Plot Radius

Angular size of the plot.

Plot Radius Options
Degrees	Selected value is the plot radius, in degrees. The width is an arclength, not a positional difference -- e.g., near the poles, a 5 degree radius plot covers a far greater region of the sky than near the equator.
Target Radii	Plot size is based on size of the target. For instance, with Target=Jupiter, set Plot Radius=1 to make Jupiter exactly fill the plot window in the width direction. If multiple timesteps are plotted (e.g., many timesteps of Jupiter, all of which can have different sizes), then the plot radius is based on the size at the central time, midway between the start and end times.

Plot FOVs

FOV (field-of-view) footprint plots for each of the instruments can be individually selected. The list of FOVs available is set by the Observer. In most cases the FOV positions are read directly from the relevant SPICE files.

For NH PEPSSI, sector 0 is indicated with a heavy outline.

For Rosetta Alice, the top portion is indicated with a heavy outline.

Plot FOV Options
S/C Boresight	Plot a red + within a circle, at the spacecraft's defined boresight location.
S/C Axes	Mark and label the endpoints of the spacecraft's six principle axes (+X, +Y, +Z, -X, -Y, -Z). [New Horizons only] GV will also plot the projected s/c +Y and +Z vectors, originating from the s/c boresight. This allows for easy determination of (e.g.) spacecraft roll angle relative to the Sun.
Mark Boresights	Plot a + at the boresight of every instrument FOV.
Color FOVs	Plot the FOVs in different colors (one per FOV). A legend is given below the plot.
Line Thickness	Allows the FOVs to be plotted thicker, making them more visible. Default = 1. Using Line Thickness > 5 causes some graphical artifacts due to IDL's plotting routines.
STK Colors	[New Horizons only] Make the colors for LORRI, LEISA, MVIC, Alice, and REX match those used by STK.
Alice Rows	[New Horizons only] Plot lines for the individual detector rows of the Alice Airglow FOV. Rows 5, 10, 15, and 20 are plotted in bold.
UVS Swath	[Juno only] When in Juno Spin Pointing mode, draw the pair of 360° arcs tracing out the rotational footprint of Juno-UVS as the spacecraft rotates about its spin axis.

Star Tracker FOVs

[LRO-GV only]

The LRO Star Tracker FOV's ST1 SUB1 and ST2 SUB1 are sub-FOVs within the ST1 RECT and ST2 RECT FOV's. The instrument can use any 254 x 12 (or 12 x 254) portion of this array as the FOV. The coordinates are specified by entering a list of four integers - e.g., "3 256 3 14", in the order "x0 x1 y0 y1". These values are user-specified and are not retrievable using SPICE Lookup.

If no values are supplied, then GV assumes a default value for the Sub-FOV positions.

The same coordinates are used to plot both ST1 SUB1 and ST2 SUB1.

Roll Angle

Rotation angle in clockwise degrees, around the instrument's boresight axis starting at a given zero-point. For New Horizons, the rotation angle zero-point can be set several ways.

GV Roll Angle Options
NCP (North Celestial Pole)	For angle 0 degrees, the spacecraft is rolled about the boresight until the scan axis (-Z) reaches its minimum separation to the NCP.
NEP (North Ecliptic Pole)	For angle 0 degrees, the spacecraft is rolled about the boresight until the scan axis (-Z) reaches its minimum separation to the NEP.
Orbit Normal	For angle 0 degrees, the spacecraft is rolled about the boresight until the scan axis (-Z) reaches its minimum separation to the orbit normal vector. The orbit normal is defined as the vector product of (observer-to-target-body-center) X (velocity of observer). Using Orbit Normal mode requires using a named target, not an RA/Dec position. For MVIC scans of Pluto near C/A, this orientation (for 0 deg) keeps the HGA roughly Earth-pointed, and allows for far-to-near or dark-to-sunlit scans. Because Orbit Normal is based on the orbit to a named body, it cannot be used when Target = SPICE Lookup is set, because GV can't tell from the kernel alone what the target it.
Solar Normal	Same as Orbit Normal, but relative to Sun instead of the target body.

In the terminology used by New Horizons Mission Operations, these three options specify the external reference vectors.

Objects

GV can plot stars, solar system objects, and instrument FOVs. Each object can be plotted, or plotted with a label attached.

GV Object Types to Plot
Planets	GV calculates positions for the nine planets. Latitude/longitude grids are drawn, and the lit and unlit portions are indicated. Bodies are assumed to be spherical, with their size taken from their equatorial radius. Plotting Jupiter also plots its main ring. The Sun is always plottted. Pluto's SPICE ID (999) reflects its planetary status, so GV will always consider it a planet.
Satellites	GV calculates positions for selected satellites of Jupiter, Saturn, Uranus, Neptune, and Pluto. If selected, orbits of satellites will also be plotted, with 360 points per orbit. Orbital plotting assumes satellites have zero eccentricity and inclination, and should be used with caution. For precise calculations, plot the positions using the Timesteps option.
Stars	GV plots stars from the HD and Tycho-2 star catalogs. Searching for stars is slow, especially for HD and for plots wider than a few degrees. For wide plots, turn off star plotting unless necessary.

Each object has a series of possible options.

GV Object Options
Draw	Draw the body. Stars are plotted as points of varying size; the magnitude scale automatically adjusts. Planets & satellites are rendered using the surface style chosen below. Bodies are assumed to be spherical with equatorial radius; for higher precision, use limbs mode.
Label	Label the body. For stars the ID, magnitude, and type (if available) are listed. If multiple magnitudes are available, the brightest one is used.
Orbits	Plot the orbits of planets and/or satellites if drawn. For planets, the trajectory plotted is for the planet itself, not its barycenter. For all orbits, note that what GV shows are orbits and not paths. That is, GV plots the position that the body would take if it moved right now, but with the observer anchored in its current position. Thus, you will not see (e.g.,) Pluto's retrograde motion from the Earth, which depends on observer motion. What you will see is a projection right now of Pluto's entire orbital ellipse onto the sky. For satellites, what GV does is probably what you want it to. For planets, be careful to understand what it does. GV draw the orbits using a fixed timestep through the orbit. The path may be inaccurate if the observer is very near the body (e.g., within a few days of New Horizons' Pluto encounter).
Barycenters	Plot the center-of-mass of the system. This option is only enabled if GV has one or more barycenters in its list of targets (e.g., Pluto Barycenter for NH-GV).
Rings	Plot any defined rings of the planets. Currently the following rings are defined: Jupiter: Inner and outer edge MU69: Sunflower orbits (that is, normal to the sun vector) at 3500 km and 10,000 km
Solar Vector	[New Horizons only] Plot a vector showing the projection of the Sun's direction onto the sky plane, as viewed from the spacecraft boresight. The scatter angle (sometimes referred to as the SciOps LORRI scattering angle) is the position angle, measured CCW from +Y_SC, of this solar vector. Negative scatter angles refer to CW rotations from +Y_SC. The angular distance to the Sun can be seen from the phase angle, which is available from the Solar Sytem Data Table, or with a mouseover on the target.

Objects are plotted in the following order:

Stars
Planets and Satellites, in order of decreasing distance
Barycenters
FOVs

Tip: There are three ways to identify objects in a plot:

Click the Label box to print labels next to each object.
Create a table (see below), which lists all objects and their parameters.
Move the pointer over the objects, and a label will appear identifying it.

Stellar Catalog

There are three options for the star catalog:

Tycho-2	(c. 2000). 2.5 million stars with two-color magnitudes (B and V) but no spectral types, complete to roughly V=11.5, although with some data to V=16. Positions are accurate to ~ 0.05", and are adjusted in GV for proper motion. Compared to HD, Tycho-2 has better positions, is more complete, and is much faster to search.
HD	(c. 1924). 272,150 stars with two-color magnitudes (photographic and photovisual) and spectral types, complete to V=8.5 or so. Positions are poor (~1") and no proper motion is available. Missing magnitudes are indicated by -999, which is never a valid data value.
USNO–B1.0	(c. 2004). 1.04 billion stars with five-color magnitudes (B1/R1/B2/R2/I), compete to V=21. Positions are accurate to 0.2". Photometry is 'marginal' (0.3 mags). Searching the USNO-B1.0 is quite slow because of the catalog's size. If you do, use it only on small fields, and/or with a sensible magnitude limit.

Support for the 2MASS catalog can be incorporated with minimal effort; if desired, please ask.

Stellar Mag Lim or Range

Takes either one value, or two. Delimiter is hyphen, comma, or whitespace. If no value is passed, V=8 is assumed.

GV Stellar Range Examples
7	Plot only stars brighter than V=7
-1-5	Plot stars between V=-1 and V=5
4 10	Plot stars between V=4 and V=10.

Some catalog stars have no listed magnitudes. These stars are plotted by default if one value is supplied to GV in the Stellar Mag Lim Range; they are never plotted if two values are supplied. See Exclude Missing Magnitudes.

Stellar Type Filter

[Optional] A list of stellar types to plot. List is a series of single characters which are matched against the stellar type. For instance, OB plots only stars which have O or B in their spectral type field. Ignored for catalogs with no spectral types.

Available filters are O, B, A, F, G, K, M, GK, KM, GKM, OB, OBA, and OBAF.

Exclude Missing Magnitudes

[HD catalog only] A few percent of the original HD catalog stars have magnitudes which are missing, and erroneously listed as 0.00. Because these stars may be deceptive, GV can exclude them from the catalog search results. GV will also exclude these always if a range of stellar magnitudes is passed (e.g., 3, 10).

Surface Style

Change the way that planets are displayed. Options are:

Wireframe	Shows a grid, with lon/lat markers and N/S pole indicators. The lit/unlit portion is indicated with a change in color. For Earth, continents and DSN station locations are shown. Wireframe uses the most accurate projections, and is recommended for all times when the observer is near the body (e.g., in-orbit missions, or close approaches at < several radii). Other projections can be inaccurate for close distances.
Pluto LHR	Shows a grid, with longitude markers and N/S pole indicators. Uses left-handed convention (LHR) for Pluto and Charon, which is the default.
Pluto RHR	Same as above, but uses right-handed convention (RHR).
Albedo	Project an albedo map onto the surface. The lit and unlit portions are indicated by a brightness change and a visible terminator. The wireframe grid is superimposed. Available for Mars, Earth, Moon, Jupiter, and Pluto only. For Pluto, the Albedo map used is from Stern & Buie (1996).
Albedo NH	[New Horizons only] Use 'latest' released albedo map, updated frequently through encounter.
Composition	Shows a composition map. Wiregrame grid and terminator are superimposed. Available for Pluto only. The Pluto composition map used is from Grundy & Buie (2001).
Elevation	Shows a digital elevation model (DEM). Available for Moon only
I/F V I/F B	Show a map of I/F for V-band or B-band. Pluto: Based on data in Buie et al 2010, slightly revised by M. Buie in 2015. Charon: Based on data in Buie et al 2010. I/F data is only available for Pluto and Charon.
I/F V Contour I/F B Contour	Same as I/F, but adds contours.
I/F V (2008) I/F B (2008)	Shows a map of I/F for V-band or B-band. Created from a preliminary map that was later published in Buie et al 2010. Pluto: Based on data in Buie et al 2010. Charon: Based on data in Buie et al 2010. This is a legacy setting; in general the newer I/F mode should be used, not this one.
Aurora	Plot the north and south auroral ovals (blue). Also plots the auroral ovals for Io (red), as well as Io's footprint (black). Available for Jupiter only. Data supplied by Randy Gladstone.
Wireframe, No Fill	Same as Wireframe mode, but draws only the limb and terminator (no grid lines, and the body's not filled in). Because the body is 'see-thru', this can be useful for planning occultation observations.
Wireframe, DSK	Use SPICE Digital Shape Kernels (DSKs) where available. This allows for plotting of bodies such as asteroid Lutetia and comet Churymov-Gerasimenko, for which detailed 3D shape models have been developed and incorporated into GV.

Label Lon / Lat

By default, GV labels the longitude / latitude grid of most bodies. If this box is unchecked, then the lon / lat grid is drawn, but the coordinate values are not printed.

Projection

Sets the method of mapping sky coordinates onto the display.

GV Projection Methods
Rectangular	RA and Dec (or ecliptic Lat and Lon) are mapped linearly to X and Y. This is simple and works well for observations which are not close to the zenith. At high values of Dec, distances and shapes become distorted; GV properly plots their distorted shapes. For New Horizons, this projection system usually works fine, because all of its targets are near the equatorial plane. In order to use Surface Style settings which wrap an image onto a body (such as Albedo, Composition, and DEM), you must use Rectangular projection.
Spherical	Shapes and and angular distances are not distorted (that is, planets appear nearly 'circular'), but lines of constant RA and Dec become curved. Spherical modes are recommended in particular for observations near the poles, or for very wide angles (many tens of degrees), where the Rectangular projection becomes less useful. Requires Units = Degrees, and Surface Style = Wireframe. Spacecraft orbital missions, especially polar orbiters, should usually use one of the Spherical modes because they are the most accurate across the entire sky.
Spherical with Grid	Same as Spherical, but also draws a grid of RA and Dec lines.

Show Data Tables

Output HTML-formatted tables listing the position of each visible object.

FOV Output Table Values
FOV Name	FOV name or S/C principle axis name
FOV Boresight Position	RA/Dec, in degrees
FOV Boresight Position	RA/Dec, in HMS (RA) or DMS (Dec)
Solar Elongation Angle	Angle between boresight and center of Sun.
Spatial Resolution	Resolution in km/pixel, if Target is set to a named body. Assumes square pixels with fixed angular resolution, and the range is assumed to be from the center of observer, to the sub-observer point on the target.

Quaternion Output Table Values
Q1 Q2 Q3 Q4	Display a table listing the pointing quaternions for each footprint location. Quaternions are 4-element unit vectors, and are printed in both SPICE order and STK order. A third format, Engineering order, is not printed. Quaternions specify rotations, and there is a 1-to-1 correlation between SPICE's internal 3x3 rotation matrices, and the 4-element quaternions. Rotations are from [0,0] to the specified instrument pointing (e.g., from RA=0, Dec=0 in J2000 coords.) For more information on the three similar-but-incompatible conventions for quaternion signs and orders, see the NAIF M2Q documentation.

Star Output Table Values
Catalog ID	ID number or name of the star.
Position	RA and Dec, in degrees. For the TYC2 and USNO-B1.0 catalogs, the positions reflect the stars' measured proper motions as of the time of observation.
Magnitudes	Listed for each filter available HD: Photographic and Photovisual magnitudes TYC2: B_T and V_T magnitudes USNOB-1.0: U, B, V, R, and I magnitudes
Stellar Type	[HD catalog only] Type if known

For the solar system, all objects calculated are listed, whether visible or not.

**Solar System Output Table Values**
Name	FOV name or S/C principle axis name
Position	RA/Dec, in degrees. All positions indicate apparent position at given UTC, with light-time correction.
Position	RA/Dec, in H/DMS
Position	Ecliptic Lon/Lat, in degrees
Distance	AU
Distance	km
Angular Diameter	Microradians
Phase Angle	[Sun - Target_Center - Observer], in degrees
Solar Elongation Angle	[Sun - Observer - Target_Center], in degrees
Sub-Solar Lon/Lat	On body, in degrees, planetographic.
Sub-observer Lon/Lat	On body, in degrees, planetographic.
Sub-satellite Lon/Lat	On primary, in degrees. For satellites only. For example, for Charon, the Sub-satellite Lon/Lat indicates its position above Pluto's surface.
Pole angle	Degrees. Angle between (projection of body's rotation axis onto sky) and (vector from observer to North celestial pole). There has been an error in the Pole Angle computation identified, causing <1 deg errors in pole position for Europa and a small number of other satellites. If this affects you, please let me know.
UTC date/time	Time of observation, at observer
Julian date/time	Time of observation, at observer

Pluto's coordinate system is calculated internally using left-handed coordinates (LHR). However, the data tables list a row for Pluto and for Pluto [RHR]. The latter is identical to the fomer, but with latitude and longitude calculated using right-handed coordinates (RHR).

Note that the RHR coordinates tabulated are based on simply flipping the pole by 180°. This will not necessarily give the same results as using the Pluto RHR mode. This is because Pluto's pole has changed definitions several times:

pck0008: [default for many NHGV kernel sets]
pck0009: Changes Pluto pole location by ~3° from previous.
pck0010: Changes Pluto pole location by 180° from previous. [default for Pluto RHR]

Plutocentric Solar Heliographic: Lists the observer's position and velocity in the Plutocentric Solar Heliographic coordinate system (PSH). This is a coordinate frame useful for New Horizons' plasma instruments.

Pluto Solar Heliographic (PSH) Coordinate System
+X_PSH	Points from Pluto center, to the Sun center position, in degrees E.
+Y_PSH	Is in the H x X_PSH direction, where H is the solar spin axis (pointing N) position, in degrees N.
+Z_PSH	Completes the right-handed system.

Lon/Lat on all bodies is planetographic. Lon/Lat are defined in the standard fixed-body reference frames (IAU2000), which is System III for Jupiter/Saturn/Uranus/Neptune.

NB: Some bodies (such as some small satellites, comets and asteroids) indicate lon/lat positions even though their pole positions may not be known. In these cases a rotation vector has been assumed, which may well be incorrect! For these bodies, the lon/lat values on the body are printed in red to indicate that they are provisional and to be used with caution.

If the Close bodies only option is checked, then solar system bodies are tabulated only for the closest planet, plus its satellites, plus the Earth and Sun.

If the Target body only option is checked, then solar system bodies are tabulated only for the named target body.

Each data table is accompanied by a downloadable text file with the same information in the same format at the table. The format of this text file is one header line, plus one data line for each entry of the table. Fields are separated by commas (i.e., CSV). The CSV tables are always generated and may be downloaded regardless of whether the HTML table is displayed or not.

Invalid values (e.g., missing stellar magnitudes, or longitudes for satellites with no defined longitude system) are indicated as -999. -999 is never a valid data value.

Downtrack Error

[Optional] If set, this specifies the uncertainty in the observer's position, in seconds along its track. The uncertainty is plotted by outlining each body with an ellipse which shows its position at each end of the uncertainty. Blue + signs indicate the body centers at each end. Value is the halfwidth; i.e., error ellipse corresponds to t-dt .. t+dt.

Using downtrack error requires Surface Style = Albedo.

For New Horizons Pluto encounter planning, the recommended 1σ value to use is 50 seconds halfwidth, as per Leslie Young.

Groundtrack t/2

[Optional] If specified, the spacecraft groundtrack on the target body is plotted. For instance, 500 plots the sub-spacecraft groundtrack position 500 seconds before and after the current time, for 1000 seconds total.

Currently available only for LRO, but can be enabled for other missions if requested.

Impact Sites

[LRO-GV and Earth-GV only] This option allows plotting of the location of the GRAIL or LCROSS impacts, or any other arbitrary location on the Moon. Up to two sites can be plotted.

Impact Sites Input Parameters
Longitude	Site position, in degrees E.
Latitude	Site position, in degrees N.
Label	[Optional] Text for label.
Radius	[Optional] Size of the circle plotted, in km.

The pull-down selector may be used to automatically fill in the Lon/Lat values for GRAIL and LCROSS. If None is selected, then no sites will be plotted.

Ref Frame

Specifies whether the plot should be generated in J2000 celestial coordinates (RA/Dec), or ecliptic coordinates (Lon/Lat, i.e., ECLIPJ2000). The coordinates of the plot need not be the same as the coordinates of the center position, although they may be. If they are not (for instance, celestial RA/Dec specified for the center position, and the plot generated in ecliptic Lon/Lat), then the proper conversions applied between the two coordinate systems.

Plot Size [pixels]

Change the width of the returned plot. Default is 700 pixels. Height = width + 70.

Plot Title

[Optional] A title for the plot. Printed on the top line, preceding the UTC range.

Flip RA?

By default, RA is plotted such that values decrease along the X axis. If checked, RA values will be inverted such that they increase along the X axis.

White sky?

Default is black sky with white stars (better for web). If checked, plot is made with black stars on a white sky (better for printing).

This option does not simply invert the entire plot; for instance, albedo maps are displayed properly regardless of this setting.

List kernel info?

If checked, prints a list of the kernel files passed to SPICE to generate the ephemeris. As per the SPICE convention, if a body is listed in multiple files for the same time range, then the last one listed is used.

A few notes on GV's kernel handling:

Following the SPICE convention, GV's kernel files are ordered such that the last-loaded ones have priority. GV lists files in the order loaded.

GV uses an initial skeleton set of kernels to initialize itself, and then subsequently loads the selected kernel set. This will occasionally cause confusion when using an incomplete kernel set: for instance, if you request an observation of body B, and your kernel set has no position for B, but GV's skeleton kernel does, then GV will not generate an error message. Note that when List Kernel Info is selected, the both the skeleton kernel set and the user kernel set are listed.

GV's User-Uploaded Kernels are flexible and powerful. There are several limitations:

Occasionally users have a problem uploading large .zip files (> 10 MB) through GV's web interface. If this happens to you, contact me and I will install them manually.
Uploading a kernel file which makes large internal changes to SPICE -- such as flipping Pluto's pole direction (pck00010.tpc) -- may give unpredictable results.

Pluto RHR

If checked, the Pluto system will be plotted using right-handed (RHR) coordinates, by using NAIF planetary constants file pck00010.tpc. If unchecked, then the pole position specified in the selected kernel file will be used.

Be aware of unintended consequences of this selection. For instance, Charon's radius also changes between pck00008.tpc and pck00009.tpc. When chosen, GV adopts all of the values in pck000010.tpc, not just that for the Pluto system pole location.