Definition of semimajor axis in English:

semimajor axis


  • Either of the halves of the major axis of an ellipse.

    • ‘To the extent that the parent star's mass is known from its spectrum and luminosity, the periodicity of the Doppler signal yields the planetary orbit's semimajor axis a.’
    • ‘The speed of the satellite is inversely proportional to the square root of the radius of the orbit (or more strictly the semimajor axis of the orbit).’
    • ‘The semimajor axes of an ellipse are the longest lines crossing the area covered by the ellipse, and including the two foci.’
    • ‘The initial covariance matrices of each lander were set to correspond to a 15 by 8 kilometer landing ellipse with a semimajor axis in the East-West direction.’
    • ‘Kepler's third law of planetary motion says that the square of the planet's orbital period is proportional to the cube of its semimajor axis.’