However, these laws are not sufficient to describe exactly where in an orbit a planet is, or how that orbit is oriented. Instead, we have to specify the values of the orbital elements. Note that several of these elements are redundant, as they can be used to derive other orbital elements.
|Type of orbital parameter||Name||Symbol|
|These orbital elements tell us information about the shape of an orbit:||Semi-major axis||a|
|These orbital elements tell us the orientation of an orbit:||Orbital inclination||i|
|Argument of perihelion||ω|
|These orbital elements tell us the position and speed of a planet in its orbit:||Orbital velocity||v|
|Mean daily motion||d|
Finally, we need to specify the epoch (t0), or reference date of the coordinate system. This is usually given as the time when the planet is at its closest approach to the Sun.