SUN–VENUS ENGINE

NASA Horizons · 3D Orbit · Light-Delayed Gravity · Elastic Collision

Mission Clock

Y:0000 M:00 D:00

Warp 1× → 1 week / real-sec Clock = actual sim time

Sim elapsed: 0.000 yr Week 0

NASA Horizons API

Epoch Date YYYY-MM-DD

e.g. 2026-01-01 · min 1900-01-01

Ready. Fetches Sun + Venus from JPL Horizons.

Time Warp1.0×

Zoom1.0

Live Telemetry

Reference Ephemeris

Horizons daily + Kepler

Where bodies should be per JPL Horizons actual data (when in range 1900–2100) and analytic Kepler propagation. Drift vs sim reveals light-delay and integration error.

          ● Horizons = real NASA ephemeris

          ● Kepler = analytic two-body solution

Physics Guide

Light-Delayed Gravity▸

In Newtonian gravity, force is instantaneous — the Sun would "know" Venus's position right now. This simulation instead propagates gravity at the speed of light (c = 299,792 km/s).

When computing the gravitational pull of the Sun on Venus at time t, we look up where the Sun was at the light-delay time t_ret = t − d/c, where d is the current Sun–Venus distance. The force direction points from Venus toward that past position of the Sun.

For Sun–Venus the light delay is ~360 seconds (~6 minutes). The orbital effect is tiny but physically correct — this is the same principle behind gravitational wave propagation.

Symplectic Leapfrog▸

The simulation uses Verlet/leapfrog integration, a symplectic method that conserves orbital energy over long timescales far better than Euler integration.

Each timestep: v += a·(dt/2), then x += v·dt, forces are recomputed, then v += a·(dt/2) again (kick-drift-kick). The substep size is 3,600 sim-seconds (1 hour) for accuracy despite the week-per-second tick rate.

Elastic Soft-Body Collision▸

When the centre-to-centre distance falls below the sum of physical radii (Sun r = 695,700 km, Venus r = 6,052 km), an elastic collision is triggered.

The impulse along the collision normal conserves both momentum and kinetic energy (coefficient of restitution = 1). Bodies are also displaced apart to prevent interpenetration. There is no softening on the gravitational potential — the only floor is the physical surface collision itself.

Time Scale & Units▸

All physics runs in km · km/s · seconds — real SI-adjacent units.

Tick rate: at Warp 1×, 1 real second advances 604,800 sim-seconds (1 week). At Warp 10×, 1 real second advances 10 sim-weeks, and so on.
Mission Clock: shows the actual simulated calendar time elapsed (Y/M/D), derived directly from simTime. It speeds up and slows down with the time warp slider — there is no separate clock rate.

G = 6.674 × 10⁻²⁰ km³/(kg·s²)
c = 299,792.458 km/s

NASA Horizons Data▸

Position and velocity are fetched from JPL Horizons (ssd.jpl.nasa.gov/api/horizons.api), NASA's high-precision ephemeris service used for real mission planning.

We request state vectors — Cartesian position (km) and velocity (km/s) — for the Sun and Venus relative to the Solar System Barycenter at your chosen epoch.

Coordinate frame: Horizons defaults to ICRF (equatorial), whose x-y plane is Earth's equatorial plane — not the orbital plane. We request REF_PLANE=ECLIPTIC so the output is rotated to the J2000 mean ecliptic. In that frame, x-y is the ecliptic plane and z captures Venus's 3.39° inclination. All three axes are used — the simulation is fully 3D.

The built-in J2000 fallback stores values in ICRF (for source transparency) and applies the same ecliptic rotation via icrfToEcliptic() — a rotation by the obliquity ε = 23.439° about the x-axis — before passing data to the sim.

Source Built-in J2000

Light Delay — s

Distance — AU

Collision None

NASA Updated —

— AU