A LITTLE CONTEXT ✕
A model for curiosity. Orbit Explorer is an original PopFun tool for exploring the Sun, eight planets, and 22 selected moons. Drag the map to change its angle, scroll or use +/− to zoom, and select a world to see its details. On the focused map, arrow keys rotate, Shift-arrows pan, +/− zoom, and Home resets to the Sun.
Camera: choose the Sun, a planet, or a moon as the center. The camera follows that entity as time changes. Tilt ranges continuously from +90° (above the J2000 ecliptic plane), through 0° (edge-on), to −90° (below). Turn changes azimuth. Drag empty space to rotate; Shift-drag, middle/right-drag, or Pan mode pans the view. Recenter clears the pan; the home button resets to the Sun. Fit system frames a planet and its moons. Arrow keys rotate, Shift-arrows pan, +/− zoom, and Home resets. Camera settings are preserved in share links. Zooming uses a finite viewing depth so distant foreground bodies do not cover a close-up system.
On mobile, Center and Drag action stay visible. Tap Camera settings to reveal tilt, turn, presets, Recenter and Fit system; tap again to collapse them. The map’s zoom and home controls stay available.
Explore: open Explore or the map’s expand button for a full-window map with Center and UTC date/time always available. More controls includes drag mode, label density, Fit system and date recovery. Done or Escape returns to the page. Date/time is UTC, including in the Explore picker.
Undo: Undo drag restores the time before the latest successful planet drag, for up to 20 drags in this session. Intermediate solutions within one drag count as one step. Rotation, panning and zooming do not add undo steps. Entering a date manually or starting playback clears drag history. Undo cancels pending drag solutions before restoring the whole system.
Labels: Off hides names, Focused names the selected and centered bodies, Few prioritizes up to six, Balanced adjusts the budget to the map area, and All attempts every visible name. Collision avoidance can omit labels even in All. Changing label density never hides celestial bodies or alters their positions. The setting is saved in this browser and shared links.
Touch controls: use one finger on empty space to rotate, or drag a planet along its orbit to change UTC time. Move two fingers together to pan; spread or pinch them to zoom around their midpoint. Two-finger gestures never change the date. Lift all fingers before starting another one-finger drag. Choose Pan screen for one-finger panning, or use the zoom and tilt buttons. Scroll the page outside the map.
Planet dragging: grab a planet on the Orbits map and move it along its numerical track. The service solves its heliocentric longitude against JPL ephemerides and selects a corresponding supported date near the drag’s starting time. All bodies and their orientations then update to that UTC instant. Pending cursor rings are interaction guides, not alternate celestial positions. At edge-on angles, depth is ambiguous; the closest time branch is used. Dragging changes time rather than changing the underlying orbit.
Planet and moon positions use JPL numerical ephemerides , evaluated with NAIF SPICE on the PopFun servers. The installed kernels are DE440, MAR099, JUP365, SAT441, URA182 and NEP098, with NAIF PCK00011 for body orientation. Dates cover 1800–2050. UTC is converted to dynamical time by SPICE. All vectors use the same J2000 ecliptic frame; moons are relative to their parent planet centers. The selected UTC time is shown beside the date and preserved in shared links.
Planet dragging and newly selected times can use small exact SPICE position/orientation snapshots. Daily interpolation grids and paths load separately; only data for the selected instant is used. At fast playback speeds, the scene waits for the next exact snapshot when a grid is unavailable. Heavy daily preparation runs independently so it does not block these updates. Surface images are reused only when their orientation, lighting and texture match exactly; hidden inspector artwork redraws when visible again.
Positions move smoothly between dated JPL position and velocity samples. Independent checks against Horizons at three dates for all 22 moons differed by at most about 3 meters; interpolation checks at withheld times across six dates differed from direct SPICE by at most 0.6 meters. These are measured checks, not a universal bound on physical ephemeris uncertainty. Positions are geometric at the selected instant, without light-travel or observer corrections. This is a spatial explorer rather than an apparent sky chart for a telescope.
Planet and moon tracks are sampled from the same numerical ephemerides. Moon tracks span roughly one orbital period around the selected UTC date; planet tracks span roughly one orbit within the supported range. Perturbations and precession are included in the source ephemerides. These sampled tracks may not close into perfect ellipses.
Axis and rotation: known body-fixed orientations come from dated NAIF/IAU PCK models. Position, spin and pole direction use the same selected instant. The displayed north-axis line and zero-longitude meridian follow that model. Smooth orientation follows the dated rotation and rotation-rate data; withheld checks across six dates agreed with direct SPICE within 0.009 arcsecond. The IAU models have their own physical uncertainty; Earth and Moon use the standard IAU models rather than specialized Earth-orientation or high-precision lunar binary kernels. Gas-giant and solar rotation grids are standard reference systems, not reconstructions of moving clouds or solar features. Hyperion and Nereid have no supported orientation model in these data: their spin and axes are marked unavailable and no surface orientation is invented.
The Sun is the only star modeled here. The decorative star field was removed; the optional background is a reference grid. Surface art is schematic except the static Earth map from NASA/Goddard Space Flight Center Scientific Visualization Studio’s Blue Marble , courtesy of Reto Stockli (NASA/GSFC) and NASA’s Earth Observatory. This historical composite is geographic artwork, not weather for the selected date.
On the Orbits map, enabled moons appear alongside planets. The default uses true orbital distances. To inspect small moon orbits, choose a planet as the camera center and use Fit system. Optional Magnified diagram spacing uniformly enlarges local distances within each planet’s system to make moons visible while preserving directions and distance ratios. Magnified diagram is explicitly a display scale, not a different ephemeris. Choose Moons → True distance to return to the shared distance scale. Compact planet spacing uses a separate scale per planetary system. The focused Moons view has its own true/compact spacing. Measurements always use the unscaled JPL vectors. Body sizes, surface artwork and rings are illustrative. Planet size comparison uses common-scale equatorial diameters; moon facts use twice the mean radius.
The catalog includes 22 selected moons, not every known satellite. Diameters and other mean facts come from the NASA Planetary Fact Sheet and JPL satellite physical parameters . Published mean periods are used for fact displays and track-window lengths, not to propagate moon positions.
Use Visible items to toggle every included body and display layer independently. Inspecting an item does not enable it. The region filter also applies to moons on the Orbits map; their visibility is independent of their parent’s switch. Your choices are saved locally and in share links. Loading or unavailable ephemeris data is clearly indicated; positions and distances are not replaced with an illustrative fallback. Playback waits when the next date needs data.
Inspired by the idea of exploring space in a browser, including Solar System Scope . Interface and code are original; no assets or code from Solar System Scope are used. Earth artwork is credited above. Share view copies the date, selection, view, and distance endpoints into a link.