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{{Short description|Where the orbit of the Moon intersects the ecliptic}}
{{more footnotes|date=January 2018}}
[[File:Lunar eclipse diagram-en.svg|320px|thumb|The lunar nodes are the two points where the [[orbit of the Moon|Moon's orbital path]] crosses the [[ecliptic]], the Sun's apparent yearly path on the [[celestial sphere]].]]

A '''lunar node''' is either of the two [[orbital node]]s of the [[Moon]], that is, the two points at which the [[orbit of the Moon]] [[intersection (Euclidean geometry)|intersects]] the [[ecliptic]]. The ''ascending'' (or ''north'') node is where the Moon moves into the northern [[ecliptic coordinate system|ecliptic hemisphere]], while the ''descending'' (or ''south'') node is where the Moon enters the southern ecliptic hemisphere.

A [[lunar eclipse]] can occur only when the [[full moon|full Moon]] is near either lunar node (within 11° 38' ecliptic longitude), while a [[solar eclipse]] can occur only when the [[new moon|new Moon]] is near either lunar node (within 17° 25').

Because the [[orbital plane]] of the Moon [[lunar precession|precesses]] in space, the lunar nodes [[nodal precession|also precess]] around the ecliptic, completing one revolution (called a ''draconic'' or ''[[nodal period]]'') in {{convert|18.612958|year|day|abbr=off}}. (This is not the same length as a [[saros (astronomy)|saros]].) The same cycle measured against an inertial frame of reference, such as [[International Celestial Reference System]] (ICRS), a [[coordinate system]] relative to the [[fixed stars]], is 18.599525 years.

Both solar eclipses of July 2000 (on the [[solar eclipse of July 1, 2000|1st]] and [[solar eclipse of July 31, 2000|31st]] days) occurred around the time when the Moon was at its ascending node. Ascending-node eclipses recur after one [[draconic year]] on average, which is about 0.94901 [[Gregorian year]], as do descending-node eclipses.

==Names and symbols==

[[File:Astronomicum Caesareum (1540).f18.jpg|thumb|upright=0.7|The dragon in [[Petrus Apianus|Peter Apian]]'s ''Astronomicum Caesareum'', 1540.]]

The nodes are called by different names in different cultures of the world.

In [[Hindu astronomy]], the nodes are considered with the [[Classical planet#Indian astrology|seven planets]] among the nine [[Navagrahas]]; the ascending node ☊ is called ''[[Rahu]]'' and the descending node ☋ is called ''[[Ketu (mythology)|Ketu]]''.<ref>{{ Citation | last = Hartner | first = Willy | author-link = Willy Hartner | date = 1938 | title = The Pseudoplanetary Nodes of the Moon's Orbit in Hindu and Islamic Iconographies: A Contribution to the History of Ancient and Medieval Astrology | journal = Ars Islamica | volume = 5 | issue = 2 | pages = 112–154 | jstor = 4520926 }}</ref> In [[Tibetan astrology]] (partially based on the [[Kalachakra#Astrology|Kalachakra Tantra]]) these nodes are respectively named ''Rahu'' and ''[[Kalagni Rudra Upanishad#Name|Kalagni]]''.<ref>{{ Citation |last = Berzin | first = Alexander | author-link = Alexander Berzin (scholar) | date = 1987 | title = An Introduction to Tibetan Astronomy and Astrology | journal = The Tibet Journal | volume = 12 | issue = 1 | pages = 17–28 | jstor = 43300228 }}</ref>

In medieval texts, the nodes are referred to as ''ras wa dhanav al-tinnîn'' in [[Arabic (language)|Arabic]]. ''rosh ha-tely u-zenavo'' in [[Hebrew language|Hebrew]], and ''caput draconis'' (head of the dragon) or ''cauda draconis'' (tail of the dragon) in [[Latin (language)|Latin]].<ref>{{ Citation | last = Sela | first = Shlomo | date = 2003 | title = Abraham Ibn Ezra and the Rise of Medieval Hebrew Science | series = Brill's Series in Jewish Studies | volume = 32 | publisher = Brill | place = Leiden / Boston | pages = 124–126, 244–245 | isbn = 9789004129733 }}</ref> The ascending node is referred to as the '''dragon's head''' with the [[astronomy|astronomical]] or [[astrology|astrological]] symbol of ☊ and the descending node is known as the '''dragon's tail''' with the symbol ☋.

==Declination extremes==
{{see also|Lunar standstill}}

The Moon's orbit is inclined about 5.14° to the [[ecliptic]]; hence, the Moon can be up to about 5° north or south of the ecliptic. The ecliptic is inclined about 23.44° to the [[celestial equator]], whose plane is [[perpendicular]] to the rotational axis of Earth. As a result, once during the 18.6-year nodal period (when the ascending node of the Moon's orbit coincides with the [[Equinox (celestial coordinates)|vernal equinox]]), the Moon's [[declination]] reaches a maximum and minimum (northern and southern extremes): about 28.6° from the celestial equator. Therefore, the moonrise or moonset [[azimuth]] has its northern- and southernmost points on the horizon; the Moon at [[culmination]] has its lowest and highest [[altitude]] (when the body transits the [[meridian (astronomy)|meridian]]); and first sightings of the [[new moon]] potentially have their latest times. Furthermore, [[occultation]]s by the Moon of the [[Pleiades]] star cluster, which is over 4° north of the ecliptic, occur during a comparatively brief period once every nodal period.

==Effect on tides==
The [[lunar precession|precession]] of the lunar nodes has a small effect on Earth's [[Theory of tides|tides]] – [[Atmospheric tide|atmospheric]], [[Ocean tide|oceanic]], or [[Crustal tide|crustal]].<ref>Godin, G. (2015). The Use of Nodal Corrections in the Calculation of Harmonic Constants. The International Hydrographic Review, 63(2). Retrieved from https://journals.lib.unb.ca/index.php/ihr/article/view/23428</ref><ref name="KayeStuckey1973">{{cite journal|last1=Kaye|first1=Clifford A.|last2=Stuckey|first2=Gary W.|title=Nodal Tidal Cycle of 18.6 Yr.: Its Importance in Sea-Level Curves of the East Coast of the United States and Its Value in Explaining Long-Term Sea-Level Changes|journal=Geology|volume=1|issue=3|year=1973|pages=141|issn=0091-7613|doi=10.1130/0091-7613(1973)1<141:NTCOYI>2.0.CO;2}}</ref>
The U.S. [[National Oceanic and Atmospheric Administration]] (NOAA) determines [[mean lower low water]] (MLLW) at a location by averaging the height of the lowest tide recorded at that location each day during a 19-year recording period, known as the National Tidal Datum Epoch.<ref>{{cite web |url=http://tidesandcurrents.noaa.gov/datum_options.html |title=Tidal Datums |work=Tides and Currents |publisher=[[NOAA]]}}</ref> The 19-year recording period is the nearest full-year count to the 18.6-year cycle of the lunar nodes.<ref>{{cite web |url=https://tidesandcurrents.noaa.gov/publications/tidal_datums_and_their_applications.pdf |title=Tidal Datums and Their Applications |work=Tides and Currents |publisher=[[NOAA]] (Special Publication NOS CO-OPS 1) |location=[[Silver Spring, MD]] |date=June 2000}}</ref>

In conjunction with [[sea level rise]] caused by [[Climate change|global warming]], lunar nodal precession is predicted to contribute to a rapid rise in the frequency of [[coastal flooding]] throughout the 2030s.<ref>{{Cite journal|last=Thompson|first=Philip R.|last2=Widlansky|first2=Matthew J.|last3=Hamlington|first3=Benjamin D.|last4=Merrifield|first4=Mark A.|last5=Marra|first5=John J.|last6=Mitchum|first6=Gary T.|last7=Sweet|first7=William|date=July 2021|title=Rapid increases and extreme months in projections of United States high-tide flooding|url=http://www.nature.com/articles/s41558-021-01077-8|journal=Nature Climate Change|language=en|volume=11|issue=7|pages=584–590|doi=10.1038/s41558-021-01077-8|issn=1758-678X}}</ref>

==See also==
* [[Astrology]]
* [[Eclipse]]
* [[Horoscope]]
* [[Lunar standstill]]
* [[Orbit of the Moon]]
* [[Natal chart]]

== References ==
<references/>

==External links==
* [http://www.jgiesen.de/sunmoonpolar/ Sun and Moon Polar Applet], showing moonrise/moonset azimuths
* [https://web.archive.org/web/20110614150005/http://www.astro.uu.nl/~strous/AA/en/antwoorden/hemel.html#v320 Astronomy Answers]: What are the standstills of the Moon? Retrieved 2016-08-26.
* [http://www.jqjacobs.net/astro/eclipse.html Eclipses, Cosmic Clockwork of the Ancients]
* [http://www.iol.ie/~geniet/eng/moonfluct.htm Lunar and solar periods], about inertial frame of reference for measuring movements of celestial bodies.
* [http://www.iol.ie/~geniet/eng/moonfluct.htm Mean lunar and solar periods]

{{DEFAULTSORT:Lunar Node}}
[[Category:Orbit of the Moon]]
[[Category:Technical factors of Western astrology]]
[[Category:Technical factors of Hindu astrology]]

Lunar node - Revision history

imported>Whiteguru at 12:18, 31 July 2021