• Semi-major axis


  • It is the measure of the radius of an orbit taken from the points of that same orbit's two most distant points.[1]

Semi-major axis in astronomyEdit

  • Basicly, is the distance from which a planet is separated from its star.
    • An exemple of a semi-major axis; Earth's semi-major axis = 1 astronomical unit, Earth is then 1 astronomical unit away from the Sun.
  • The semi-major axis is one of the most important orbital elements of an orbit, along with its orbital period.
  • For solar system objects, the semi-major axis is related to the period of the orbit.[1]
  • The astronomical unit is the unit used to measure the semi-major axis of a planet.[1]
  • It is one of the data used to identify if an exoplanet is located within the habitable zone of its planetary system.



  1. 1.0 1.1 1.2