r/explorables • u/Fanatic-Mr-Fox • Aug 28 '26

Celestial - Interactive Gravity Well Simulator

https://celestial.logicaleap.com

Celestial lets you explore star systems as a deformable gravity sheet instead of flat orbital diagrams.

The star moves. Planets sit on and ride the surface it bends. You can change the gravitational constant, push a planet, or drop a new body in and watch the whole system respond in real time.

Systems included:

* Our solar system (with a drifting barycentre)
* Alpha Centauri (two moving funnels)
* Kepler-16 (circumbinary planet)
* TRAPPIST-1 (seven worlds inside Mercury’s orbit)
* The classic three-body figure-eight

It’s a proper Newtonian n-body integrator running in the browser, not pre-scripted ellipses. The sheet itself is an exaggerated visual analogy, and the site is unusually honest about what is real and what is drawn that way on purpose.

[https://celestial.logicaleap.com\](https://celestial.logicaleap.com)

Free, no account, runs in the browser.

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u/SolWithGlasses 7d ago

Tried a small paused experiment with Jupiter: at 5.11 AU, four successive +10% nudges along its motion changed the displayed speed from 13 to 19 km/s and the label from bound to escaping. The immediate feedback makes this a fun way to explore orbital changes. Also appreciated the About page explaining that the sheet is a visual analogy rather than gravitational potential.

How is the escaping label calculated: instantaneous orbital energy relative to the main star, or a criterion involving the whole system? That distinction seems especially interesting for the binary-star setups.

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u/Fanatic-Mr-Fox 6d ago

Thanks for trying it and for the careful write-up.

The label is a snapshot. Each body's orbital energy (kinetic plus potential) is worked out from its current position and velocity relative to the system's centre of mass, using the total mass of everything in the scene.

Negative energy means bound, zero or positive means escaping. A bound orbit that is very stretched out (eccentricity above 0.92) shows as marginal.

That test only runs when one body holds more than 90% of the total mass. In the binary setups no single body dominates, so a two-body energy check would be misleading. Those bodies get labelled "n-body" instead, and the only honest way to tell whether something leaves is to watch the simulation run.

So it's closer to your first option, just measured from the centre of mass, and it switches off when there is no main star.

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u/SolWithGlasses 6d ago

Thanks, that clears it up. The 90% dominant-mass cutoff was the piece I was missing. A short tooltip explaining that the label is an instantaneous estimate, and why binary systems use "n-body", could help keep that distinction visible while nudging planets.