Celestial Mechanics is the application of Mechanics
to celestial objects, e.g., planets, galaxies, Moons,
etc. Mechanics, in turn is the branch of physics dealing
with forces and motion. More specifically, Dynamics is the
study of forces and resulting motions, e.g., orbits and
Statics is the study of forces in the absence of motion,
e.g., why the inside of the Moon doesn't collapse to allow
it to grow smaller, and Kinematics is the study of motion
without relation to the forces.
For example, Kepler's Laws , which describe orbits
(Keplerian Orbit) fall under the heading of Kinematics,
whereas Newton's Laws, which describe the way forces
effect on orbits fall under Dynamics.