Relative potential ($\Psi$)

In a bounded stellar system, a relative potential shifts the gravitational potential so that $\Psi$ vanishes at a chosen escape boundary. A common sign convention is $\Psi ={\Phi }_0-\Phi$.

Relative energy is the binding energy per unit mass measured from the chosen escape level, commonly $\mathcal{E}=\Psi -v^2/2$. Bound phase-space points have $\mathcal{E}>0$ in this convention.