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Encyclopedia of Astrobiology pp 1502Cite as

Semi Major Axis

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Synonyms

Half-major axis

Definition

The semimajor axis of an ellipse is one-half of the major axis, that is, of the longest axis. This is one of the basic parameters when describing the orbit of two bodies in gravitational interaction. It is equivalent to the radius in the case of a circular orbit.

See also

Keplerian Orbits

Orbit

Semi Minor Axis

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Author information

Authors and Affiliations

  1. LESIA, Observatoire Paris-Site de Meudon, 5 Pl Jules Janssen, 92195, Meudon, France

    Daniel Rouan (Professor)

Authors
  1. Daniel Rouan
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Corresponding author

Correspondence to Daniel Rouan .

Editor information

Editors and Affiliations

  1. Astrophysicist, Laboratoire d’Astrophysique de Bordeaux, BP 89, 33270, Floirac, France

    Muriel Gargaud

  2. Departamento de Planetología y Habitabilidad Centro de Astrobiología (CSIC-INTA), Universidad Autónoma de Madrid Campus Cantoblanco, Torrejón de Ardoz, 28049, Madrid, Spain

    Ricardo Amils

  3. Department of Astrophysics, Centro de Astrobiología (INTA-CSIC) Ctra de Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain

    José Cernicharo Quintanilla

  4. Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd. NW, Washington, DC, 20015, USA

    Henderson James (Jim) Cleaves II

  5. Department of Astronomy, University of Massachusetts Lederle Graduate Research, 710 North Pleasant Street, Amherst, MA, 01003-9305, USA

    William M. Irvine

  6. GEOTOP & Départment des Sciences de la Terre et de l’Atmosphère, Université du Québec à Montréal, CP 8888, succ. Centre-Ville, Montréal, QC, H3C 3P8, Canada

    Daniele L. Pinti

  7. Astrobiology, CNES/DSP/EU, 2 place Maurice-Quentin, 75039, Paris, France

    Michel Viso

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© 2011 Springer-Verlag Berlin Heidelberg

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Rouan, D. (2011). Semi Major Axis. In: Gargaud, M., et al. Encyclopedia of Astrobiology. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-11274-4_1424

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