## Derivation of Laplace's Equation for the Speed of Gravity from Newtonian Dynamics

Derivations of Laplace's formula for the change in period of the moon, that yielded a formula for the speed of gravity, has been derived by a number of authors. The key point is to consider the tangential force acting on the moon due to aberration due to the finite speed at which (supposedly) gravity propagates. To the central force, $\mu/a^2$, where $\mu$ is the gravitational parameter containing the mass of the earth, $GM$, and $a$ the semi-major axis, the aberration term $v/v_G$ is appended where $v_G$ is the speed at which gravity supposedly propagates.