Orbital node

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Orbital node

An orbital node is one of the two points where an orbit

ORBit

ORBit is a Common Object Request Broker Architecture 2.4 compliant Object Request Broker . It features mature C , C++ and Python bindings, and less developed bindings for Perl, Lisp , Pascal , Ruby , and Tcl....
crosses a plane of reference

Plane of reference

A term used in celestial mechanics, the plane of reference is the plane by means of which orbital elements are defined. The two main orbital elements that are measured with respect to the plane of reference are the inclination and the longitude of the ascending node....
which it is inclined to. An orbit which is contained in the plane of reference (called non-inclined) has no nodes. Common planes of reference include: The line of nodes is the intersection of the object's orbital plane with the plane of reference. It passes through the two nodes.

If a reference direction from one side of the plane of reference to the other is defined, the two nodes can be distinguished.

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An orbital node is one of the two points where an orbit

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Plane of reference

For a geocentric orbit
Geocentric orbit

A geocentric orbit is an orbit of any object orbital revolution the Earth, such as the Moon or artificial satellites. Currently there are approximately 2465 artificial satellites orbiting the Earth and 6216 pieces of space debris as tracked by the Goddard Space Flight Center....
, the Earth
Earth

Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...
's equator
Equator

The equator is the intersection of the Earth's surface with the Plane perpendicular to the Earth's rotation and containing the Earth's center of mass....
ial plane. In this case, non-inclined orbits are called equatorial.
For a heliocentric orbit
Heliocentric orbit

A heliocentric orbit is an orbit around the Sun. In our Solar System, all planets, comets, and asteroids are in such orbits, as are many artificial Space probe and pieces of Space debris....
, the ecliptic
Ecliptic

The ecliptic is the apparent path that the Sun traces out in the sky during the year. As it appears to move in the sky in relation to the stars, the apparent path aligns with the planets throughout the course of the year....
. In this case, non-inclined orbits are called ecliptic.
For an orbit outside the Solar System
Solar System

The Solar System consists of the Sun and those Astronomical object bound to it by gravity: the eight planets and five dwarf planets, their 173 known Natural satellite, and billions of Small Solar System body....
, the plane through the primary perpendicular to a line through the observer and the primary (called the plane of the sky).^{, chap. 17.}

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

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. 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.^{, p. 137.}

The symbol of the ascending node is

(Unicode

Unicode

Unicode is a computing industry standard allowing computers to consistently represent and manipulate Character expressed in most of the world's writing systems....
: U+260A, ?), and the symbol of the descending node is

(Unicode

Unicode

Latin

Latin is an Italic language, historically spoken in Latium and Ancient Rome. Through the Military history of the Roman Empire, Latin spread throughout the Mediterranean and a large part of Europe....
: caput draconis, Arabic: ra's al-jauzahar) and dragon's tail , respectively.^{, p. 141;}^{, p. 245.} 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.^{, pp. 196–197;}^{, p. 65;}^{, pp. 95–96.} The Greek

Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
terms a?aß?ß???? and ?ataß?ß???? were also used for the ascending and descending nodes, giving rise to the English

English language

English is a West Germanic language that originated in Anglo-Saxon England and has lingua franca status in many parts of the world as a result of the military, economic, scientific, political and cultural influence of the British Empire in the 18th, 19th and early 20th centuries and that of the United States from the mid 20th century onwa...
words anabibazon and catabibazon.^;^{, ¶27.}

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

Longitude of the ascending node

The longitude of the ascending node is one of the orbital elements used to specify the orbit of an object in space. It is the angle from a reference direction, called the origin of longitude, to the direction of the ascending node, measured in a reference plane....
(or, sometimes, the longitude of the node.)

Lunar nodes

For the orbit of the Moon

Moon

The Moon is Earth's only natural satellite and the List of natural satellites by diameter satellite in the Solar System. The average centre-to-centre distance from the Earth to the Moon is km, about thirty times the diameter of the Earth....
around the Earth

Earth

Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...
, the reference plane is taken to be the ecliptic

Ecliptic

The ecliptic is the apparent path that the Sun traces out in the sky during the year. As it appears to move in the sky in relation to the stars, the apparent path aligns with the planets throughout the course of the year....
, not the equatorial plane. The gravitational pull

Gravitation

Gravitation is a natural phenomenon that gives weight to objects. In everyday life, attraction due to gravity is the result of the presence of relatively large bodies, such as the Earth and the Moon....
of the Sun

Sun

The Sun , a G V star, is the star at the center of the Solar System. The Earth and other matter orbit the Sun, which by itself accounts for about 98.6% of the Solar System's mass....
upon the Moon

Moon

Lunar precession

There are two important precessional motions in the Orbit of the Moon.The long axis of the moon's elliptical orbit precessiones about once in just under 9 years....
gradually westward, performing a complete circle in approximately 18.6 years.

Orbital node

Lunar nodes

See also