A lunar node is either of the two

orbital node 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. A non-inclined orbit, which is coplanarity, contained in the reference plane, has no nodes. P ...

s of the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

, that is, the two points at which the

orbit of the Moon The Moon orbits Earth in the prograde direction and completes one revolution relative to the Vernal Equinox and the stars in about 27.32 days (a tropical month and sidereal month) and one revolution relative to the Sun in about 29.53 days (a s ...

intersects the

ecliptic The ecliptic or ecliptic plane is the orbital plane of the Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic again ...

. The ''ascending'' (or ''north'') node is where the Moon moves into the northern ecliptic hemisphere, while the ''descending'' (or ''south'') node is where the Moon enters the southern ecliptic hemisphere.

Eclipses

lunar eclipse A lunar eclipse occurs when the Moon moves into the Earth's shadow. Such alignment occurs during an eclipse season, approximately every six months, during the full moon phase, when the Moon's orbital plane is closest to the plane of the Earth ...

can occur only when the

full Moon The full moon is the lunar phase when the Moon appears fully illuminated from Earth's perspective. This occurs when Earth is located between the Sun and the Moon (when the ecliptic coordinate system, ecliptic longitudes of the Sun and Moon opp ...

is near either lunar node (within 11° 38' ecliptic longitude), while a

solar eclipse A solar eclipse occurs when the Moon passes between Earth and the Sun, thereby obscuring the view of the Sun from a small part of the Earth, totally or partially. Such an alignment occurs during an eclipse season, approximately every six month ...

can occur only when the

new Moon In astronomy, the new moon is the first lunar phase, when the Moon and Sun have the same ecliptic longitude. At this phase, the lunar disk is not visible to the naked eye, except when it is silhouetted against the Sun during a solar eclipse. ...

is near either lunar node (within 17° 25'). Both solar eclipses of July 2000 (on the 1st and 31st days) occurred around the time when the Moon was at its ascending node. Ascending-node eclipses recur after one

draconic year A year or annus is the orbital period of a planetary body, for example, the Earth, moving in its orbit around the Sun. Due to the Earth's axial tilt, the course of a year sees the passing of the seasons, marked by change in weather, the hour ...

on average, which is about 0.94901

Gregorian year Gregorian may refer to: *The thought or ideology of Pope Gregory I or Pope Gregory VII (also called ''Gregorianism'') *Things named for Pope Gregory I: **Gregorian chant, the central tradition of Western plainchant, a form of monophonic, unaccompa ...

, as do descending-node eclipses.

Precession

Because the

orbital plane The orbital plane of a revolving body is the geometric plane in which its orbit lies. Three non-collinear points in space suffice to determine an orbital plane. A common example would be the positions of the centers of a massive body (host) an ...

of the Moon precesses in space, the lunar nodes also precess around the ecliptic, completing one revolution (called a ''draconic'' or ''

nodal period The nodal period (or draconic period) of a satellite is the time interval between successive passages of the satellite through either of its orbital nodes, typically the ascending node. This type of orbital period applies to artificial satellites, ...

'') in . (This is not the same length as a saros.) The same cycle measured against an inertial frame of reference, such as

International Celestial Reference System The International Celestial Reference System (ICRS) is the current standard celestial reference system adopted by the International Astronomical Union (IAU). Its origin is at the barycenter of the Solar System, with axes that are intended to "sh ...

(ICRS), a

coordinate system In geometry, a coordinate system is a system that uses one or more numbers, or coordinates, to uniquely determine the position of the points or other geometric elements on a manifold such as Euclidean space. The order of the coordinates is sig ...

relative to the

fixed stars In astronomy, fixed stars ( la, stellae fixae) is a term to name the full set of glowing points, astronomical objects actually and mainly stars, that appear not to move relative to one another against the darkness of the night sky in the backgro ...

, is 18.599525 years.

Names and symbols

The nodes are called by different names in different cultures of the world. In medieval texts, the nodes are referred to as ''ras wa dhanav al-tinnîn'' in

Arabic Arabic (, ' ; , ' or ) is a Semitic languages, Semitic language spoken primarily across the Arab world.Semitic languages: an international handbook / edited by Stefan Weninger; in collaboration with Geoffrey Khan, Michael P. Streck, Janet C ...

. ''rosh ha-teli u-zenavo'' (ראש ה תלי וזנבו) in

Hebrew Hebrew (; ; ) is a Northwest Semitic language of the Afroasiatic language family. Historically, it is one of the spoken languages of the Israelites and their longest-surviving descendants, the Jews and Samaritans. It was largely preserved ...

, and ''caput draconis'' (head of the dragon) or ''cauda draconis'' (tail of the dragon) in

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

. The ascending node is referred to as the dragon's head with the

astronomical Astronomy () is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution. Objects of interest include planets, moons, stars, nebulae, galaxies ...

astrological Astrology is a range of divinatory practices, recognized as pseudoscientific since the 18th century, that claim to discern information about human affairs and terrestrial events by studying the apparent positions of celestial objects. Dif ...

symbol of ☊ and the descending node is known as the dragon's tail with the symbol ☋. In

Hindu astronomy Astronomy has long history in Indian subcontinent stretching from pre-historic to modern times. Some of the earliest roots of Indian astronomy can be dated to the period of Indus Valley civilisation or earlier. Astronomy later developed as a dis ...

, the nodes are considered with the

seven planets 7 is a number, numeral, and glyph. 7 or seven may also refer to: * AD 7, the seventh year of the AD era * 7 BC, the seventh year before the AD era * The month of July Music Artists * Seven (Swiss singer) (born 1978), a Swiss recording artist * ...

among the nine

Navagrahas Navagraha are nine heavenly bodies and deities that influence human life on Earth according to Hinduism and Hindu astrology. The term is derived from ''nava'' ( sa, नव "nine") and ''graha'' ( sa, ग्रह "planet, seizing, laying hold of, ...

; the ascending node ☊ is called ''

Rahu Rāhu (Sanskrit: राहु, 16px, ☊) is one of the nine major celestial bodies (navagraha) in Hindu texts and the king of meteors. It represents the ascension of the moon in its precessional orbit around the earth, also referred as the ...

'' and the descending node ☋ is called ''

Ketu KETU (1120 AM) is a radio station licensed to serve Catoosa, Oklahoma. The station is owned by Antonio Perez, through licensee Radio Las Americas Arkansas, LLC. The station was licensed originally to Atoka, Oklahoma, and operated for many years ...

''. In

Tibetan astrology Tibetan astrology () is a traditional discipline of the Tibetan peoples that has influence from both Chinese astrology and Indian astrology. Tibetan astrology is one of the 'Ten Sciences' (Wylie: rig-pa'i gnas bcu; Sanskrit: daśavidyā) in the en ...

(partially based on the

Kalachakra Tantra ''Kālacakra'' () is a polysemic term in Vajrayana Buddhism that means "wheel of time" or "time cycles". "''Kālacakra''" is also the name of a series of Buddhist texts and a major practice lineage in Indian Buddhism and Tibetan Buddhism. The ta ...

) these nodes are respectively named ''Rahu'' and '' Kalagni''.

Declination extremes

The Moon's orbit is inclined about 5.14° to the

; 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 The celestial equator is the great circle of the imaginary celestial sphere on the same plane as the equator of Earth. This plane of reference bases the equatorial coordinate system. In other words, the celestial equator is an abstract projectio ...

, whose plane is

perpendicular In elementary geometry, two geometric objects are perpendicular if they intersect at a right angle (90 degrees or π/2 radians). The condition of perpendicularity may be represented graphically using the ''perpendicular symbol'', ⟂. It can ...

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 vernal equinox), the Moon's

declination In astronomy, declination (abbreviated dec; symbol ''δ'') is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declination's angle is measured north or south of the ...

reaches a maximum and minimum (northern and southern extremes): about 28.6° from the celestial equator. Therefore, the moonrise or moonset

azimuth An azimuth (; from ar, اَلسُّمُوت, as-sumūt, the directions) is an angular measurement in a spherical coordinate system. More specifically, it is the horizontal angle from a cardinal direction, most commonly north. Mathematicall ...

has its northern- and southernmost points on the horizon; the Moon at

culmination In observational astronomy, culmination is the passage of a celestial object (such as the Sun, the Moon, a planet, a star, constellation or a deep-sky object) across the observer's local meridian. These events were also known as meridian transits ...

has its lowest and highest

altitude Altitude or height (also sometimes known as depth) is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context ...

(when the body transits the

meridian Meridian or a meridian line (from Latin ''meridies'' via Old French ''meridiane'', meaning “midday”) may refer to Science * Meridian (astronomy), imaginary circle in a plane perpendicular to the planes of the celestial equator and horizon * ...

); and first sightings of the

new moon In astronomy, the new moon is the first lunar phase, when the Moon and Sun have the same ecliptic longitude. At this phase, the lunar disk is not visible to the naked eye, except when it is silhouetted against the Sun during a solar eclipse. ...

potentially have their latest times. Furthermore,

occultation An occultation is an event that occurs when one object is hidden from the observer by another object that passes between them. The term is often used in astronomy, but can also refer to any situation in which an object in the foreground blocks ...

s by the Moon of the

Pleiades The Pleiades (), also known as The Seven Sisters, Messier 45 and other names by different cultures, is an asterism and an open star cluster containing middle-aged, hot B-type stars in the north-west of the constellation Taurus. At a distance of ...

star cluster, which is over 4° north of the ecliptic, occur during a comparatively brief period once every nodal period.

Effect on tides

The

precession Precession is a change in the orientation of the rotational axis of a rotating body. In an appropriate reference frame it can be defined as a change in the first Euler angle, whereas the third Euler angle defines the rotation itself. In othe ...

of the lunar nodes has a small effect on Earth's

tides Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables can ...

–

atmospheric An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...

oceanic Oceanic may refer to: *Of or relating to the ocean *Of or relating to Oceania **Oceanic climate **Oceanic languages **Oceanic person or people, also called "Pacific Islander(s)" Places * Oceanic, British Columbia, a settlement on Smith Island, ...

, or crustal. The U.S.

National Oceanic and Atmospheric Administration The National Oceanic and Atmospheric Administration (abbreviated as NOAA ) is an United States scientific and regulatory agency within the United States Department of Commerce that forecasts weather, monitors oceanic and atmospheric conditio ...

(NOAA) determines

mean lower low water A chart datum is the water level surface serving as origin of depths displayed on a nautical chart. A chart datum is generally derived from some tidal phase, in which case it is also known as a tidal datum. Common chart datums are ''lowest as ...

(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. The 19-year recording period is the nearest full-year count to the 18.6-year cycle of the lunar nodes. In conjunction with

sea level rise Globally, sea levels are rising due to human-caused climate change. Between 1901 and 2018, the globally averaged sea level rose by , or 1–2 mm per year on average.IPCC, 2019Summary for Policymakers InIPCC Special Report on the Ocean and Cry ...

caused by

global warming In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...

, lunar nodal precession is predicted to contribute to a rapid rise in the frequency of

coastal flooding Coastal flooding normally occurs when dry and low-lying land is submerged by seawater. The range of a coastal flooding is a result of the elevation of floodwater that penetrates the inland which is controlled by the topography of the coastal land ...

throughout the 2030s.

References

External links

Sun and Moon Polar Applet
showing moonrise/moonset azimuths

What are the standstills of the Moon? Retrieved 2016-08-26.

about inertial frame of reference for measuring movements of celestial bodies.

{{DEFAULTSORT:Lunar Node Orbit of the Moon Technical factors of Western astrology Technical factors of Hindu astrology