Why does this orbit do that?

A gravitational sandbox. Place stars, planets and black holes. Watch the field, drop test particles, and read why the motion is what it is — Gauss's law on a probing ring, Kepler's closed orbits, the two-frequency resonance counter, and what changes when relativity flicks on near a black hole.

Space

select a body type, then click to place
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mass 10 GR 0.00
star (source) planet (light) black hole (strong, GR) traced particle drag a body to move · drag empty space to pan · scroll to zoom
Flux through ring
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Enclosed mass
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ω_r / ω_φ
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predicted precession
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Why — local analysis at the cursor

Place a body, then move the cursor over a ring to probe Gauss's law, or drop a test particle to watch its orbit.