The Hénon-Heiles system (1964) models galactic stellar dynamics. Below E≈1/12, orbits are regular KAM tori (closed curves in the Poincaré section). Near E≈1/6, chaos appears — tori break into cantori and scattered points. The KAM theorem (Kolmogorov-Arnold-Moser) guarantees persistence of many tori under small perturbations, but chaos invades at higher energy.