A lunar node is either of the two orbital nodes of the Moon, that is, the two points at which the orbit of the Moon intersects the ecliptic. 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 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 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 of the Moon precesses in space, the lunar nodes also precess around the ecliptic, completing one revolution (called a ''draconic'' or '' nodal period'') 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 (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. ''rosh ha-teli u-zenavo'' (ראש ה תלי וזנבו) in Hebrew, and ''caput draconis'' (head of the dragon) or ''cauda draconis'' (tail of the dragon) in Latin. The ascending node is referred to as the dragon's head with the astronomical or astrological symbol of ☊ and the descending node is known as the dragon's tail with the symbol ☋. In Hindu astronomy, the nodes are considered with the seven planets 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'' and the descending node ☋ is called '' Ketu''. In Tibetan astrology (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 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

vernal equinox Spring equinox or vernal equinox or variations may refer to: * March equinox, the spring equinox in the Northern Hemisphere * September equinox, the spring equinox in the Southern Hemisphere Other uses * Nowruz, Persian/Iranian new year which be ...

), 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 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 (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, occultations 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 precession 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, or crustal. 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. 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 caused by global warming, lunar nodal precession is predicted to contribute to a rapid rise in the frequency of coastal flooding 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