Linked from
The 15 pages that link to Semimajor axis, each with the reason it gives.
Kepler's laws of planetary motionRelated: It is the precise orbital size used in the third law.
Orbital periodRelated: For a given central mass, a larger semimajor axis means a longer period.
Vis-viva equationRelated: It determines the orbital energy and therefore the speed scale.
Orbital perturbationBroader topic: Changes in this element often indicate energy gain or loss.
Planetary orbitBroader topic: It measures an orbit’s overall scale and helps determine its period.
Kepler orbitRelated: For bound Kepler orbits, it sets orbital size and period.
Kepler's first lawRelated: It sets the characteristic size of the orbital ellipse.