Introductory remarks on chaoticity in dynamics and orbit mechanics

Deterministic dynamical systems are considered where chaoticity is associated with high sensitivity to small changes in the initial conditions. It is shown that, if the initial conditions, the equations of motion, and their solutions are not known for regions of the phase space where instablity is considerable, the motion becomes unpredictable and chaotic. The extent of chaoticity is evaluated by Liapunov's characteristic numbers, Poincare's surface of sections, Fourier power spectra, and, for undamped systems, by the measure of irreversibility.