Orbital node

From Wikipedia, the free encyclopedia
  (Redirected from Ascending node)
The ascending node is one of several orbital elements.

An orbital node is either of the two points where an orbit intersects a plane of reference to which it is inclined.[1] A non-inclined orbit, which is contained in the reference plane, has no nodes.

Planes of reference

Common planes of reference include the following:

Node distinction

Animation about nodes of two elliptic trajectories. (Click onto image.)

If a reference direction from one side of the plane of reference to the other is defined, the two nodes can be distinguished. For geocentric and heliocentric orbits, the ascending node (or north node) is where the orbiting object moves north through the plane of reference, and the descending node (or south node) is where it moves south through the plane.[4] In the case of objects outside the Solar System, the ascending node is the node where the orbiting secondary passes away from the observer, and the descending node is the node where it moves towards the observer.[5], p. 137.

The position of the node may be used as one of a set of parameters, called orbital elements, which describe the orbit. This is done by specifying the longitude of the ascending node (or, sometimes, the longitude of the node.)

The line of nodes is the intersection of the object's orbital plane with the plane of reference. It passes through the two nodes.[2]

Symbols and nomenclature

The symbol of the ascending node is Northnode-symbol.png (Unicode: U+260A, ☊), and the symbol of the descending node is Southnode-symbol.png (Unicode: U+260B, ☋). In medieval and early modern times the ascending and descending nodes were called the dragon's head (Latin: caput draconis, Arabic: ra's al-jauzahar) and dragon's tail (Latin: cauda draconis), respectively.[6], p. 141; [7], p. 245. These terms originally referred to the times when the Moon crossed the apparent path of the sun in the sky. Also, corruptions of the Arabic term such as ganzaar, genzahar, geuzaar and zeuzahar were used in the medieval West to denote either of the nodes.[8], pp. 196–197; [9], p. 65; [10], pp. 95–96. The Greek terms αναβιβάζων and καταβιβάζων were also used for the ascending and descending nodes, giving rise to the English words anabibazon and catabibazon.[11][12], ¶27.

Lunar nodes

For the orbit of the Moon around Earth, the plane is taken to be the ecliptic, not the equatorial plane. The gravitational pull of the Sun upon the Moon causes its nodes to gradually precess westward, completing a cycle in approximately 18.6 years.[1][13]

See also


  1. ^ a b "node". Columbia Encyclopedia (6th ed.). New York: Columbia University Press. 2004. Retrieved May 17, 2007.  Archived 2007-03-09 at the Wayback Machine.
  2. ^ a b c Darling, David. "line of nodes". The Encyclopedia of Astrobiology, Astronomy, and Spaceflight. Retrieved May 17, 2007. 
  3. ^ Tatum, Jeremy B. "Chapter 17". Celestial Mechanics. Retrieved May 17, 2007. 
  4. ^ ascending node, entry in The Encyclopedia of Astrobiology, Astronomy, and Spaceflight, David Darling, on line, accessed May 17, 2007.
  5. ^ The Binary Stars, R. G. Aitken, New York: Semi-Centennial Publications of the University of California, 1918.
  6. ^ Survey of Islamic Astronomical Tables, E. S. Kennedy , Transactions of the American Philosophical Society, new series, 46, #2 (1956), pp. 123–177.
  7. ^ Cyclopædia, or, An universal dictionary of arts and sciences, Ephraim Chambers, London: Printed for J. and J. Knapton [and 18 others], 1728, vol. 1.
  8. ^ Planetary Latitudes, the Theorica Gerardi, and Regiomontanus, Claudia Kren, Isis, 68, #2 (June 1977), pp. 194–205.
  9. ^ Prophatius Judaeus and the Medieval Astronomical Tables, Richard I. Harper, Isis 62, #1 (Spring, 1971), pp. 61–68.
  10. ^ Lexicographical Gleanings from the Philobiblon of Richard de Bury, Andrew F. West, Transactions of the American Philological Association (1869-1896), 22 (1891), pp. 93–104.
  11. ^ anabibazon, entry in Webster's third new international dictionary of the English language unabridged: with seven language dictionary, Chicago: Encyclopædia Britannica, 1986. ISBN 0-85229-503-0.
  12. ^ New thoughts on the genesis of the mysteries of Mithras[permanent dead link], Roger Beck, Topoi 11, #1 (2001), pp. 59–76.
  13. ^ Marcia Rieke. "Introduction: Coordinates, Seasons, Eclipses (lecture notes)". Astronomy 250. University of Arizona. Retrieved May 17, 2007. 
Retrieved from "https://en.wikipedia.org/w/index.php?title=Orbital_node&oldid=822683372#Node_distinction"
This content was retrieved from Wikipedia : http://en.wikipedia.org/wiki/Ascending_node
This page is based on the copyrighted Wikipedia article "Orbital node"; it is used under the Creative Commons Attribution-ShareAlike 3.0 Unported License (CC-BY-SA). You may redistribute it, verbatim or modified, providing that you comply with the terms of the CC-BY-SA