Three-Body Orbits

An interactive gallery of periodic solutions of the planar Newtonian three-body problem, rendered as glowing trails in the browser — plus a braid view that unrolls each orbit along a time axis.

It plays three published catalogues:

Collection	Orbits	Source
Classic	20 famous orbits: figure-eight, Lagrange, Šuvakov–Dmitrašinović butterflies & moths, Broucke	Moore 1993; Chenciner & Montgomery 2000; Šuvakov & Dmitrašinović, PRL 110, 114301 (2013); Broucke 1975
Li & Liao	2,044 zero-angular-momentum orbits (695 equal-mass, 1,349 with m₃ ∈ {0.5 … 10})	Li & Liao, Sci. China PMA 60, 129511 (2017); Li, Jing & Liao, PASJ 70, 64 (2018) — sjtu-liao/three-body
Free-fall	24,582 initial conditions = 12,409 distinct collisionless free-fall orbits (236 self-dual)	Hristov, Hristova, Dmitrašinović & Tanikawa, Celest. Mech. Dyn. Astron. 136, 7 (2024), arXiv:2308.16159 — data

Run it

No build step and no dependencies — open app/index.html in a browser (works from file://), or serve the folder:

python3 -m http.server -d app 8000   # then open http://localhost:8000

Deploy: it's a static site. On Vercel, import the repo as-is — vercel.json serves the app/ folder with no build step. On GitHub Pages, publish from main and open /app/.

Features

• Grid of live orbits — any rows × columns, paging/shuffling through each catalogue, filters (mass ratio, symmetry class, self-dual, T* range) and sorting (T*, word length, Lyapunov exponent, random).
• Braid view (B) — each body becomes a world-line: position projected on an adjustable axis (→) against time (↑). The bodies ride a "now" line while their history scrolls down; at every crossing the strand nearer the viewer passes over, as in a braid diagram. The time window is in scale-invariant time t* so every cell scrolls at the same rate.
• Braid lab (L): a census of the braid of every catalogued orbit (14,473 in all). Plot braid entropy log λ against T*, crossings, syzygies, word length or the Lyapunov exponent, with correlation and Nielsen–Thurston type tables. The census is validated against the published topology: 2,043/2,044 Li & Liao free-group words (the remaining entry is an error in the published table) and 236/236 self-dual syzygy sequences. Click a point to open that orbit. A second mode, Form lifetimes, tests how long forms survive. Each orbit is nudged by ε = 10⁻³ … 10⁻¹³ and run until its syzygy sequence first deviates. The measured lifetimes follow τ ≈ ln(δ/ε)/λ_p, with λ_p from the monodromy matrix: median λ_fit/λ_p = 0.995 for unstable Li & Liao orbits, and λ_p matches the published free-fall Lyapunov exponents to within 1%.
• Clouds (C): objects at finite resolution. A cloud of 200 nearby states evolves, in the Chirikov standard map (a KAM island or the chaotic sea; click the portrait to place a cloud) or around a three-body orbit. Two members are one object at resolution ε if they have stayed within ε of each other so far. The view shows the cloud coloured by object, the count N(ε, t), and the dendrogram, which only gains branches as time runs. The first split matches the prediction from the stretching of the cloud's centre, δ₀Λ*(t) = ε, to within a few percent.
• Inspector (click a cell) — full-precision initial conditions, period, T* = T|E|³ᐟ², energy, Lyapunov exponent, dual i.c.; braid topology: the braid word (e.g. the figure-eight is (σ₁σ₂⁻¹)³), Nielsen–Thurston type, dilatation, free-group word and syzygy sequence; form lifetime: lifetime against perturbation size, from the census or computed live; an Agekyan–Anosova domain map of all 24,582 free-fall i.c.s (click to load the nearest, or simulate any point); a stability test that nudges a body by 10⁻ⁿ and integrates several periods; and a custom initial-conditions editor (masses, positions, velocities).
• Look — palettes (incl. custom), trail length/width, glow, body size (scaled by m¹ᐟ³), ghost path, equal-duration or T*-proportional loops.
• Export — PNG snapshot or a WebM/MP4 recording of one full loop.

Keys: Space pause · S settings · B braids · L braid lab · C clouds · ←/→ page · Esc back.

How it works

Integrator (app/physics.js). The orbits are extremely unstable (the free-fall catalogue reports Lyapunov multipliers up to e³⁰ per period) and pass through near-collisions down to ~10⁻⁸, so a plain Runge–Kutta drifts or stalls. The app uses algorithmic regularization (Mikkola & Tanikawa 1999): a logarithmic-Hamiltonian leapfrog — exact for Kepler motion — in chain coordinates (relative vectors along the two shortest edges, so a close pair keeps full double precision), driven by Gragg–Bulirsch–Stoer extrapolation with adaptive step and exact landing on a target time.

• Free-fall orbits start at rest and come to rest again at T/2, after which the motion retraces itself. Only [0, T/2] is integrated and the second half is the mirror image — the loop is exactly periodic. Typical residual speed at T/2: ~10⁻⁷.
• Li & Liao orbits are integrated to their published T (10 digits); all 2,044 return to their initial state within 6·10⁻⁵.
• Classic orbits (initial conditions given to fewer digits) have their period refined to the closest phase-space return, and the tiny residual is removed linearly so the loop is seamless.

Each orbit takes ~1–10 ms to compute; cells are filled a few per frame.

This is the beginning of the README. Read the rest at the original. Read the full README ↗