English: A diagram of the polar form of an ellipse. When applied to orbits, with the object orbiting the focus F₁, this ellipse has the following properties:

• ${\displaystyle {\overrightarrow {AF_{1}}}=d_{1}}$ is the periapsis
• ${\displaystyle {\overrightarrow {BF_{1}}}=d_{2}}$ is the apoapsis