The period of an orbit, usually denoted $T$, is the total time taken for an object to complete one full revolution on its orbit.
The planets orbit the sun in ellipses, with the sun at one focus.
The radius of a planet sweeps out a constant area per unit time.
\begin{equation} T^2 = \frac{4\pi^2a^3}{GM} \end{equation} where $T$ is the period, $G$ is the gravitational constant, and $M$ is the mass of the sun.
The eccentricity is a measure of the elongation of an ellipse. It is defined as: \begin{equation} \epsilon = \sqrt{1 - \frac{b^2}{a^2}} \end{equation} where $a$ and $b$ are the semimajor and semiminor axis lengths respectively.
The point of a planet's furthest distance from the sun on its orbit.
Is the point of a planet's closest approach to the sun.
For an earth orbit, the furthest distance from the earth.
For an earth orbit, the closest distance to the earth.