An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

1) Classical mechanics: A variable X whose total rate of change dX/dt along the path of a → dynamical system is zero. In other words, a function of an object's position, velocity, or both that does not change even as the object moves. For example, the total energy of a → simple harmonic oscillator is a constant of the motion.
2) Quantum mechanics: An → observable that remains constant in time. As an example, the energy is a constant of the motion of all systems whose → Hamiltonian does not depend explicitly upon time.

→ constant; → motion.