Explore / live simulation
Explore the solar system.
Choose a world. Watch its motion. Follow your curiosity.
Downloading simulator…
Waiting for simulation state.
Time elapsed: —
Illustrative mode enlarges bodies and moon spacing; Real scale uses physical sizes and distances. This model is not the sky on a particular date.
Keyboard shortcuts and playback help
Space pause · N step · R reset · C cycle all bodies · 1–9 / 0 select first ten · V view · F frame system · B frame body · A camera rotation · T trail frame · X vectors · E export · Mouse wheel to zoom. Shortcuts require canvas focus; Tab continues through the page.
Restart restores time zero and fresh trails while keeping selection, speed, pause state, and view settings. Hidden-tab time is excluded. Touch users can use the buttons above; no keyboard is needed.
All controls and camera help →Selected object: physical measurements
Measurements come from the C simulation in physical units. Distance and speed are relative to the selected body's parent, independent of illustrative size and moon spacing.
Published model estimates are labeled. Unknown masses use test particles that feel gravity without exerting it. Unknown radii use wire markers in both views; their drawn size is not a physical measurement.
- Parent body
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- Distance from parent
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- Speed relative to parent
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- Mass
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- Physical radius
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- Parent-relative acceleration
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- Parent-relative specific energy
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- Absolute position (X, Y, Z)
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- Absolute velocity (X, Y, Z)
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- Visual radius magnification
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- Camera target / distance (visual)
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Show this system fits a planet and its moons; selecting a moon frames its parent and siblings. Show whole system selects the scene's first body (the Sun in the core demonstration) and restores its family view. Center on this object zooms to just that body or its unknown-size marker. Use framing again after motion or zoom to refit the view.
Numerical diagnostics
- Active scene
- Waiting for C runtime…
- History sample spacing
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- Achieved speed
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- Pending simulation time
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- Integrator / step / ticks
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- Total massive-body energy
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- Normalized energy change
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- Linear momentum magnitude
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- Angular momentum magnitude
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Energy change uses initial kinetic energy plus the absolute potential energy, keeping the escape-threshold comparison meaningful when total energy is near zero. Massless tracers do not contribute to totals. A fixed Sun constrains linear momentum; use the free Earth–Moon lesson to study its conservation. Parent-relative specific energy is an instantaneous two-body diagnostic, not an invariant of the perturbed full scene.
Optional vectors show parent-relative velocity in green and acceleration in orange. Their direction is physical; their length is illustrative. Parent-relative trails move historical parent/child pairs to the parent's present position. Both views leave recorded SI state unchanged.
Where does the gravity come from?
Top six source contributions, sampled at —. Percentages use the sum of source magnitudes, not net acceleration; vectors can cancel. Fixed bodies can have computed gravity while their positions remain constrained.
| Source | Acceleration | Magnitude share | X, Y, Z (m/s²) |
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How to read the model
Read the scale.
Illustrative mode enlarges bodies and separates close moons. Real-scale mode uses physical radii and distances, so small bodies can become nearly invisible. Camera-relative drawing preserves local detail at large distances. Each grid cell spans 0.1 AU within a bounded local patch.
Read the history.
Trails show recorded motion, not complete predicted orbits. Bounded history uses uniform sampling across the full run; spacing increases as time passes. Lesson cadence rounds the initial 300 seconds up to whole configured ticks. Fine satellite loops become less resolved during long runs.
Read the numbers.
The core/catalog 15-second physics steps are checked against 100-day orbital-phase and convergence tests. Lessons can vary their fixed step and method to study numerical error. Requested orbital playback speeds range from one hour to 15 days per real second; the collision lesson uses 1/5/10/25/50 simulated seconds per real second. Bounded work per frame keeps controls responsive; slower hardware retains pending time and reports achieved speed. Speed presets never enlarge the integration step. This is an educational model, not a dated ephemeris.