semi = [Latin] half; maior = [Latin] great; axis = [Latin] axis The semimajor axis is one of the orbital elements that determine the shape and orientation of a simple orbit in space It is a measure for the size of the orbit of a celestial object For an ellipse, it is equal to one half of the length of the longest axis of the ellipse For a circle, it is equal to the radius of the circle For an object orbiting around a much heavier object (such as a planet or spacecraft around the Sun, or a moon or spacecraft around a planet), the semimajor axis of the orbit is equal to the average of the smallest and the largest distance between the light and the heavy objects
semi = [Latin] half The semimajor axis is one of the orbital elements that determine the shape and orientation of a simple orbit in space It is a measure for the size of the orbit of a celestial object For an ellipse, it is equal to one half of the length of the longest axis of the ellipse For a circle, it is equal to the radius of the circle For an object orbiting around a much heavier object (such as a planet or spacecraft around the Sun, or a moon or spacecraft around a planet), the semimajor axis of the orbit is equal to the average of the smallest and the largest distance between the light and the heavy objects
a property of an ellipse, giving its width measured along the line connecting its two foci The semi-major axis of an orbital ellipse is one of the "orbital elements" characterizing it, and is directly related to the energy of the motion
a property of an ellipse, equal to half its greatest width, as measured along the line connecting its two foci The semi-major axis of an orbital ellipse is one of the "orbital elements" characterizing it, and is directly related to the energy of the motion