MODEL · TIME AND MOTION
From clock time to planetary motion
Follow how Solar Time turns one instant into orbital positions, moon relationships, display scale, and camera projection.
One time value drives the scene
Real-time mode and manual playback are two ways of choosing the same input: an instant. Real time continually replaces that instant with the current clock. Manual playback advances it by the selected number of hours, days, or years per second. Pausing keeps the chosen instant fixed, allowing the camera to move without the bodies continuing along their orbits.
Returning a speed slider to zero therefore stops at the simulated date already reached. It does not jump back to the present. Returning to real time is a separate action because it changes the selected instant, not merely the playback rate.
Positions are calculated, not pre-rendered
Solar Time evaluates positions for the selected time. Modern-era planetary positions use established astronomical formulae; distant dates use bounded approximations that favor stable exploration over observatory precision. Elliptical motion also means a planet does not travel at a perfectly constant angular speed: it moves faster near perihelion and slower near aphelion.
The displayed orbit may be widened or compressed, but the time-dependent orbital phase remains the starting point. This separation lets the app offer a readable overview without claiming that every screen distance is a physical measurement.
Moons are solved relative to their parents
The Moon belongs to Earth's local system, Europa to Jupiter's, and Triton to Neptune's. Their local positions are combined with the parent planet's solar position. This hierarchy explains why changing a satellite orbit control should alter the local Earth–Moon, Jupiter–Europa, or Neptune–Triton separation without rearranging unrelated planets.
Mercury is different: it orbits the Sun as a planet. A local Sun–Mercury spacing control can prevent visual overlap, while the global orbit-spacing control still governs the planetary layout as a whole.
Triton makes orbital direction visible
Triton is Neptune's largest moon and moves around Neptune opposite to the planet's rotation: a retrograde orbit. NASA's Triton overview explains this unusual motion. Solar Time uses JPL NEP097 mean orbital elements with nodal precession rather than a full numerical ephemeris.
Open Neptune's card, enable Triton, then select the moon in the footer and follow it. Advance simulation time to compare its orbit with Neptune. Both normal and true-size views keep the satellite orbit tilted, while normal view enlarges its body and spacing for readability. Its initial displayed size is comparable to Pluto; true-size mode uses Triton's larger physical radius. These presentation choices do not change its orbital direction.
The surface texture completes gaps in the Voyager imagery artistically. It is useful for visual exploration, but the added terrain is not an observation; see the source and reconstruction credits.
Astronomical and displayed states stay separate
The default overview enlarges bodies and manages gaps so several objects remain selectable. Actual-size mode reduces those adjustments. At extreme distance, the browser still needs minimum visible points so tiny bodies do not disappear entirely. Those points are presentation aids; they do not change the stored planetary radius or orbit.
Try it in Solar Time
- Hold one instant: press 0, pause with Space, and rotate the camera. The viewpoint should change while every body remains tied to the paused time.
- Advance one variable: turn Real time off, select days, and raise the playback rate. Inner planets should cover more of their orbits than outer planets during the same simulated interval.
- Inspect a hierarchy: select Earth and then the Moon. Change only the Moon orbit control. Their local displayed separation should change without rearranging unrelated planets.
- Separate state from presentation: switch between normal and actual-size views. Orbital phase and parent relationships should remain; apparent size, spacing, and minimum visible points may change.
Sources and further reading
- NASA/JPL — Approximate Positions of the Planets
- NASA Science — Orbits and Kepler's Laws
- Solar Time Credits and model limitations