\begin{definition}[Definition:Kepler's Equation]
Consider a system consisting of two bodies $B_1$ and $B_2$ in elliptical orbit around each other.
Let $e$ denote the eccentricity of that orbit.
'''Kepler's equation''' is the equation that describes the relation between the mean anomaly and eccentric anomaly of $B_1$ with respect to $B_2$:
:$M = E - e \sin E$
where:
:$M$ is the mean anomaly
:$E$ is the eccentric anomaly.
{{NamedforDef|Johannes Kepler|cat = Kepler}}
\end{definition}