Limitations

The position of the small body relative to the Earth is obtained from the most precise orbit data available from the Horizons ephemeris system. The orbits of the planets and the Moon are approximations using the two-body model.

The orbit viewer is limited to dates between the close approach and a few weeks into the past and the future.

Orbit Paths

Orbit paths are rendered such that the portion of the orbit above the ecliptic plane is shown with a heavy line weight and the portion below is shown with a light line weight.

When zoomed in extremely close to a planet or moon, it may appear slightly off its orbit path. This is due to the fact that the orbit path is approximated using a series of straight-line segments.

View Selection

The default view is an oblique perspective of the ecliptic plane. You can select a pre-defined view from the "Look from:" menu.

• +90 degrees ecliptic latitude - view from directly "above" the ecliptic plane
• Ecliptic - view from the edge of the ecliptic plane

The view is initially centered on the Earth. It can also be centered on the Moon or the small body being displayed.

Zoom

To zoom in or out, use the mouse wheel or the appropriate zoom "gesture" on your trackpad or mobile device.

Rotation

To rotate the view around the axis normal to the ecliptic plane, drag the mouse left or right within the window or use the keyboard's left/right arrows. To rotate around the screen's horizontal axis, drag the mouse up or down within the window or use the keyboard's up/down arrows.

Customizing the Display

There are several controls within the "Settings" menu that allow you to customize the display. The top few controls are general (not specific to any particular object).

• Planet Labels - display the orbits of all objects
• Date Label - display the selected date in the upper right corner
• Ecliptic Grid - display the grid lines representing the ecliptic J2000 reference plane
• Sun-Earth Rotating Axes - display the heliocentric radial-tangential-normal (RTN) frame attached to the Earth. The R-axis is aligned with the Sun-Earth direction and the N-axis is normal to the ecliptic J2000 reference plane. The positive direction is represented with a thicker line. The Sun is in the negative direction along the R-axis. The T-axis, which completes the orthogonal dextral reference frame, is not shown
• Distance Display - display the nominal distance between the selected small-body and Earth (and Sun)
• Viewer Controls - show the primary animation controls in the upper right corner

The next group of controls is for customizing the display of specific objects. There is a top-level checkbox for each object which controls all content related to that object. Then there are the following sub-level controls:

• Orbit - display the object's orbit
• Label - display the object's name
• Moon - (Earth only) display the Moon and its orbit
• Geostationary - (Earth only) display the geostationary ring: equatorial circular orbit with 24-hour period and geocentric radius approximately equal to 42,160 km
• Drop Lines - (small-body only) display lines that connect the small body's orbit to the ecliptic plane, perpendicular to the ecliptic plane (only for the small body)

Additional controls are available by right-clicking on a body.

Full Screen

To enter full-screen mode, click on the expansion icon . To exit full-screen, press the ESC key.

Viewer Controls

The viewer controls are presented in four rows: "motion controls", "step size", "date selector", and "extra controls".

motion controls

• run animation backward in time
• single-step animation backward in time
• stop the running animation
• single-step the animation forward in time
• run the animation forward in time

step size

Select from various time-step intervals from 1-hour to 1-year.

date selector

Select the button to display a calendar-date picker. Or, use the date/time input box to manually enter a specific date/time.

extra controls

• full-screen selector (use ESC-key to exit)
• capture a snapshot of the screen, without menus or controls

Coordinate System

The coordinate system uses the J2000 ecliptic as the reference plane and places the origin at the solar system barycenter. The horizontal axis is directed toward the J2000 vernal equinox, while the vertical axis is normal to the J2000 ecliptic plane. A brighter line indicates the positive direction of each axis.

This orbit viewer was written and developed at JPL by Kevin Gill with contributions from Paul Chodas, Javier Roa, and Alan Chamberlin. Written in JavaScript, it makes use of WebGL via the open-source three.js package.

The representation of the small body trajectory uses the most precise data available via the Horizons system.

Version 2.0

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