Editing Orbital node

{{Short description|Point where an orbit crosses a plane of reference to which it is inclined}}
[[File:Orbit1.svg|thumb|upright=1.20|The ascending node is one of several [[orbital elements]].]]
{{Astrodynamics}}
An '''orbital node''' is either of the two points where an [[orbit]] [[intersection (Euclidean geometry)|intersects]] a [[plane of reference]] to which it is inclined.<ref name="col">{{cite encyclopedia |url=http://www.bartleby.com/65/no/node.html |title=node |encyclopedia=[[Columbia Encyclopedia]] |edition=6th |location=New York |publisher=[[Columbia University Press]] |year=2004 |access-date=May 17, 2007 |url-status=dead |archive-url=https://web.archive.org/web/20070309221338/http://www.bartleby.com/65/no/node.html |archive-date=March 9, 2007 }}</ref> A [[non-inclined orbit]], which is [[coplanarity|contained]] in the reference plane, has no nodes.

==Planes of reference==
Common [[plane of reference|planes of reference]] include the following:
* For a [[geocentric orbit]], [[Earth]]'s [[equatorial plane]]. In this case, non-inclined orbits are called ''equatorial''.<ref name="darlinglon">{{cite encyclopedia |url=http://www.daviddarling.info/encyclopedia/L/line_of_nodes.html |title=line of nodes |encyclopedia=The Encyclopedia of Astrobiology, Astronomy, and Spaceflight |first=David |last=Darling |access-date=May 17, 2007}}</ref>
* For a [[heliocentric orbit]], the [[ecliptic]] or [[invariable plane]]. In this case, non-inclined orbits are called ''ecliptic''.<ref name="darlinglon" />
* For an orbit outside the [[Solar System]], the plane through the [[primary (astronomy)|primary]] perpendicular to a line through the observer and the primary (called the ''[[plane of the sky]]'').<ref>{{cite web |url=http://astrowww.phys.uvic.ca/~tatum/celmechs.html |title=Chapter 17 |work=Celestial Mechanics |first=Jeremy B. |last=Tatum |author-link=Jeremy B. Tatum |access-date=May 17, 2007}}</ref>

== Node distinction ==
[[File:Planet orbit nodes 2 animation.gif|thumb|upright=1.1|Animation about nodes of two elliptic trajectories. (Click on 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.<ref name="darlingasc">[http://www.daviddarling.info/encyclopedia/A/ascending_node.html ascending node], entry in ''The Encyclopedia of Astrobiology, Astronomy, and Spaceflight'', David Darling, on line, accessed May 17, 2007.</ref> 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.<ref>''The Binary Stars'', R. G. Aitken, New York: Semi-Centennial Publications of the University of California, 1918.</ref><sup>, p.&nbsp;137.</sup>

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 straight line resulting from the intersection of the object's orbital plane with the plane of reference; it passes through the two nodes.<ref name="darlinglon" />

== Symbols and nomenclature ==
{{wiktionary|anabibazon}}{{wiktionary|catabibazon}}
The symbol of the ascending node is [[Image:Ascending node (bold).svg|16px]] ([[Unicode]]: U+260A, ☊), and the symbol of the descending node is [[Image:Descending node (bold).svg|16px]] ([[Unicode]]: U+260B, ☋).

In medieval and early modern times, the ascending and descending nodes of the Moon in the ecliptic plane were called the "dragon's head" ({{langx|la|caput draconis}}, {{langx|ar|[[Gochihr (Zoroastrianism)|رأس الجوزهر]]}}) and "dragon's tail" ({{langx|la|cauda draconis}}), respectively.<ref>{{cite journal | url=https://www.jstor.org/stable/1005726 | jstor=1005726 | title=A Survey of Islamic Astronomical Tables | last1=Kennedy | first1=E. S. | journal=Transactions of the American Philosophical Society | date=1956 | volume=46 | issue=2 | pages=123–177 | doi=10.2307/1005726 | url-access=subscription }}</ref>{{rp|p.141;}}<ref>[http://digital.library.wisc.edu/1711.dl/HistSciTech.Cyclopaedia01 Cyclopædia, or, An universal dictionary of arts and sciences] {{Webarchive|url=https://web.archive.org/web/20081202061430/http://digital.library.wisc.edu/1711.dl/HistSciTech.Cyclopaedia01 |date=2008-12-02 }}, Ephraim Chambers, London: Printed for J. and J. Knapton [and 18 others], 1728, vol. 1.</ref>{{rp|p.245}} These terms originally referred to the times when the [[Moon]] crossed the apparent path of the sun in the sky (as in a [[solar eclipse]]). 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.<ref>{{cite journal | url=https://www.jstor.org/stable/230070 | jstor=230070 | title=Planetary Latitudes, the Theorica Gerardi, and Regiomontanus | last1=Kren | first1=Claudia | journal=Isis | date=1977 | volume=68 | issue=2 | pages=194–205 | doi=10.1086/351767 | url-access=subscription }}</ref>{{rp|pp.196&ndash;197;}}<ref>{{cite journal | url=https://www.jstor.org/stable/229000 | jstor=229000 | title=Prophatius Judaeus and the Medieval Astronomical Tables | last1=Harper | first1=Richard I. | journal=Isis | date=1971 | volume=62 | issue=1 | pages=61–68 | doi=10.1086/350708 | url-access=subscription }}</ref>{{rp|p.65;}}<ref>{{cite journal | url=https://www.jstor.org/stable/2935702 | jstor=2935702 | title=Lexicographical Gleanings from the Philobiblon of Richard de Bury | last1=West | first1=Andrew F. | journal=Transactions of the American Philological Association | date=1891 | volume=22 | pages=93–104 | doi=10.2307/2935702 | url-access=subscription }}</ref>{{rp|pp.95&ndash;96}}

The [[Koine Greek]] terms {{lang|grc|αναβιβάζων}} and {{lang|grc|καταβιβάζων}} were also used for the ascending and descending nodes, giving rise to the English terms ''anabibazon'' and ''catabibazon''.<ref>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}}.</ref><ref>[https://www.persee.fr/doc/topoi_1161-9473_2001_num_11_1_1928 New thoughts on the genesis of the mysteries of Mithras], Roger Beck, ''Topoi'' '''11''', #1 (2001), pp. 59&ndash;76.</ref>{{rp|&nbsp;¶27}}

==Lunar nodes==
{{main article|Lunar node}}
[[File:Lunar eclipse diagram-en.svg|thumb|Nodes of the Moon]]
For the [[orbit of the Moon]] around [[Earth]], the [[plane of reference|plane]] is taken to be the [[ecliptic]], not the [[celestial equator|equatorial plane]]. The [[gravity|gravitational]] pull of the [[Sun]] upon the Moon causes [[lunar node|its nodes]] to gradually [[lunar precession|precess]] westward, completing a cycle in approximately 18.6 years.<ref name="col" /><ref>{{cite web |url=http://ircamera.as.arizona.edu/astr_250/Lectures/LECTURE_01.HTM |title=Introduction: Coordinates, Seasons, Eclipses (lecture notes) |work=Astronomy 250 |author=Marcia Rieke |publisher=[[University of Arizona]] |access-date=May 17, 2007 |archive-date=August 26, 2016 |archive-url=https://web.archive.org/web/20160826192421/http://ircamera.as.arizona.edu/astr_250/Lectures/LECTURE_01.HTM |url-status=dead }}</ref>

===Use in astrology===

The image of the ascending and descending orbital nodes as the head and tail of a dragon, 180 degrees apart in the sky, goes back to the Chaldeans; it was used by the Zoroastrians, and then by Arabic astronomers and astrologers. In Middle Persian, its head and tail were respectively called {{lang|pal|gōzihr&thinsp;sar}} and {{lang|pal|gōzihr&thinsp;dumb}}; in Arabic, {{lang|ar|al-ra's al-jawzihr}} and {{lang|ar|al-dhanab al-jawzihr}} — or in the case of the Moon, ___&nbsp;{{lang|ar|al-tennin}}.<ref>{{cite encyclopedia |title=Gōzihr |encyclopedia=Encyclopædia Iranica (iranicaonline.org) |date=February 17, 2012 |at=Vol. XI, Fasc. 2, p. 184 |url=https://iranicaonline.org/articles/gozihr |access-date=March 28, 2023}}<br>Cf. [[Gochihr (Zoroastrianism)]].</ref> Among the arguments against astrologers made by [[Ibn Qayyim al-Jawziyya]] (1292–1350), in his ''Miftah Dar al-SaCadah:'' "Why is it that you have given an influence to {{lang|ar|al-Ra's}} [the head] and {{lang|ar|al-Dhanab}} [the tail], which are two imaginary points [ascending and descending nodes]?"<ref name=Livingston>{{Cite journal | title=Ibn Qayyim al-Jawziyyah: A Fourteenth Century Defense against Astrological Divination and Alchemical Transmutation | first=John W. | last=Livingston | journal=Journal of the American Oriental Society | volume=91 | issue=1 | year=1971 | pages=96–103 | doi=10.2307/600445| jstor=600445}}</ref>

==See also==
* [[Eclipse]]
* [[Euler angles]]
* [[Longitude of the ascending node]]

== References ==
{{reflist|30em}}

{{DEFAULTSORT:Orbital Node}}
[[Category:Technical factors of astrology]]
[[Category:Orbits]]
[[Category:Point (geometry)]]