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in astronomy, 8th planet from the sun at a mean distance of about 2.8 billion mi (4.5 billion km) with an orbit lying between those of Uranus and the dwarf planet Pluto; its period of revolution is about 165 years. (Pluto has such a highly elliptical orbit that from 1979 to 1999 it was closer to the sun than Neptune; it will remain farther from the sun for 220 years, when it will again pass inside Neptune's orbit.) Neptune was discovered as the result of observed irregularities in the motion of Uranus and was the first planet to be discovered on the basis of theoretical calculations. J. C. Adams of Britain and U. J. Le Verrier of France independently predicted the position of Neptune, and it was discovered by J. C. Galle in 1846, the day after he received Le Verrier's prediction. Neptune has an equatorial diameter of about 30,700 mi (49,400 km), nearly four times that of the earth, and a mass about 17 times the earth's mass. It is much like Uranus and the other giant planets, with a thick atmosphere of hydrogen, helium, methane, and ammonia, a relatively low density, and a rapid period of rotation. On Aug. 24–25, 1989, the U.S. spacecraft Voyager 2 observed Neptune and its moons. It discovered that Neptune's atmosphere has zones like Jupiter's as well as giant storm systems as dark spots on its surface. Although Neptune receives a much smaller fraction of the sun's radiation than does Uranus, its surface temperature is similar: −350°F; (−212°C;).This may indicate a possible internal heat source. Neptune's largest moon, Triton, was discovered in 1846, a month after the discovery of the planet itself. Triton has a diameter of about 1,700 mi (2,700 km), and its motion is retrograde (see retrograde motionretrograde motion,
in astronomy, real or apparent movement of a planet, dwarf planet, moon, asteroid, or comet from east to west relative to the fixed stars. The most common direction of motion in the solar system, both for orbital revolution and axial rotation, is from west to
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), i.e., opposite to that of the planet's rotation. Its surface temperature is −400°F; (−240°C;), making it one of the coldest objects in the solar system. Nereid, discovered in 1949, has a diameter of about 210 mi (338 km), is very faint, and has a highly elliptic orbit; it may be of asteroid origin. Voyager discovered six smaller dark moons orbiting between the planet and Triton: Naiad, Thalassa, Despina, Galatea, Larissa, and Proteus—all irregularly shaped, ranging from 35 to 260 mi (58–418 km) in diameter. Five additional moons 25–39 mi (40–62 km) in diameter, named Halimede, Psamathe, Sao, Laomadela, and Neso, were discovered using earth-based telescopes in 2002 and 2003, and an unnamed 14th moon was identified in images taken (2004–9) by the Hubble Space Telescope. Since Neptune was named for the Roman god of the sea, its moons have been named for various lesser sea gods and nymphs in Greek mythology. Voyager also found a faint ringring,
in astronomy, relatively thin band of rocks and dust and ice particles that orbit around a planet in the planet's equatorial plane. All four of the giant planets in the solar system—Jupiter, Saturn, Uranus, and Neptune— have rings, although only those of Saturn
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 system with three bands. These are named Adams, Le Verrier, and Galle in honor of the planet's discoverers. Composed of small rocks and dust, the rings are not uniform in thickness or density. Adams, the outermost, contains three prominent arcs named Liberty, Equality, and Fraternity.


See P. Moore, Planet Neptune (1989); E. Burgess, Far Encounter: The Neptune System (1992); G. E. Hunt et al., Atlas of Neptune (1994).


in Roman religion and mythology, god of water. He was presumably an indigenous god of fertility, but in later times he was identified with the Greek PoseidonPoseidon
, in Greek religion and mythology, god of the sea, protector of all waters. After the fall of the Titans, Poseidon was allotted the sea. He was worshiped especially in connection with navigation; but as the god of fresh waters he also was worshiped as a fertility god.
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, god of the sea. At his festival, the Neptunalia (July 23), arbors were dedicated to him.


(nep -tewn) The eighth planet of the Solar System, orbiting the Sun every 164.79 years at an almost constant distance of 30.06 AU. It is the most distant giant planet. It has a diameter of 50 538 km, a mass of 17.2 Earth-masses, and a density of 1.76 times that of water. Neptune has 13 known satellites; Triton and Nereid were detected from Earth and the rest were discovered as a result of the Voyager 2 flyby in Aug. 1989, during which Neptune's rings were also confirmed and photographed. Orbital and physical characteristics are given in Tables 1 and 2, backmatter.

Neptune was discovered in 1846 by Johann Gottfried Galle at the Berlin Observatory on the basis of predictions supplied by the Frenchman Urbain Leverrier, who had analyzed observed perturbations in the motion of Uranus. Similar predictions had been made by the English mathematician John Couch Adams.

The planet returns to opposition two days later each year, appearing as a magnitude 7.7 object visible in binoculars. When viewed by Earthbound telescopes, Neptune appears as a featureless greenish disk only 2.2 arc seconds across. As with Uranus, Neptune's color arises from the methane within its atmosphere, which is predominantly hydrogen and helium with a mixture of methane, water, and ammonia.

Voyager 2 was able to return excellent information and pictures from Neptune in 1989. The most conspicuous feature seen in Neptune's atmosphere is the Great Dark Spot. There are also whitish cirruslike clouds of methane ice crystals. These clouds are at about 50–70 km above the main cloud deck. Neptune has belts and zones similar to Jupiter, but they are much fainter. The most prominent is a broad darkish band high in southern latitude. Embedded in this band is a smaller dark spot, about half the size of the Great Dark Spot.

Neptune's core is thought to be rocky, primarily iron and silicon; it rotates in about 16 hours. Neptune's atmosphere revolves more slowly. Some cloud features take as long as 18 hours to complete one revolution of the planet. This is contrary to the clouds of the other Jovian planets, implying Neptune's atmospheric circulation is retrograde.

Neptune radiates more energy than it receives from the Sun, which implies it has an internal heat source. Temperatures in the upper atmosphere vary from around 60 K at the equator and poles to 50 K at mid-latitudes. The planet has a magnetic field, slightly weaker than the other giant planets. It is inclined at 47° to its axis of rotation and orientated opposite to that of the Earth's.

Enlarge picture
An image from the sixteenth century of Neptune, Roman god of the sea, riding a whale. Reproduced by permission of Fortean Picture Library.


(religion, spiritualism, and occult)

Neptune is a cold planet located between Uranus and Pluto. Visible only with the aid of a telescope, it is a large, gaseous planet with a turbulent atmosphere consisting of hydrogen, helium, and methane. This violent environment is caused by a storm the size of Earth, called the Great Dark Spot, which circles Neptune every 18.3 hours.

The unusual events surrounding the discovery of Neptune, an astrological symbol for illusion, are quite fitting for this elusive planet. Neptune was first sighted by Galileo in December 1612. Instead of identifying Neptune as a planet, Galileo believed it was a moon of Jupiter and did not research it further. It was not until 1845, more than two centuries later, that a British astronomer and mathematician, John Couch Adams, theorized that the growing discrepancy between the predicted and observed positions of Uranus’s orbit was the result of an unknown planetary body. He immediately began to analyze Uranus’s deviations using Newton’s Mechanics. In September of the same year, Adams presented his calculations for the positions of the hypothetical planet to James Challis, director of Cambridge Observatory. However, Challis refused to examine Adams’s work, probably considering the likelihood of a young graduate student solving such a complex matter to be ludicrous. As such, Adams’s theory was given neither consideration nor observation time by an observatory until after a similar hypothesis with nearly identical placements for the new planet was published by French astronomer and mathematician Urbain Leverrier.

Leverrier independently began researching the same theory—the possibility of another planet influencing Uranus’s orbit—approximately one year after Adams’s calculations were complete and turned away by Challis. After submitting his third letter to the Académie des Sciences regarding this breakthrough, Leverrier became frustrated at the disinterest of astronomers to actually observe the heavens for this new planet. In September 1846 Leverrier sent his predictions to a German astronomer and acquaintance, Johann Galle, at the Berlin Observatory. Within a few hours on or about September 24, Galle found Neptune with the aid of detailed star maps not far from Leverrier’s predicted position. Despite the initial dispute between authorities in England and France about who would receive credit due for the discovery of Neptune, Adams and Leverrier became friends.

After its discovery in 1846, it was suggested that Neptune be named after the Roman god of the sea. In the early 20th century, this name was confirmed after astronomers learned of Neptune’s watery interior. Poseidon, the Greek counterpart of Neptune, who is pictured as a bearded and majestic male holding a trident, was the brother of Zeus (Jupiter) and Hades (Pluto). After defeating their father Cronos (Saturn) in the Trojan War, the brothers divided the world into three parts. Zeus took command of the sky, Hades the underworld, and Poseidon rulership of the sea. Poseidon built a grand palace under the sea, yet spent as much time on land in Olympus as in his palace. This accounts for his importance on dry land as well as the sea. He came to rule not only the oceans and seas that lap at the shore, but also the rivers that moisten the land. Mythology reveals Poseidon as having a violent temper as well as a savage and unpredictable nature. When angered, his rage often displayed itself through storms and earthquakes on land and at sea, making them much feared especially by seafarers. Floods and droughts were also common results of his wrath. Yet, he also brought tranquility and stillness to the waters as he skimmed over the waves on his chariot.

Neptune’s correlation with the sea is quite symbolic when working with this planet in the natal chart. His association with the sign of Pisces was made by the poet Manilius in the first century c.e., who believed Neptune, as god of the ocean, most likely had a bond with the sign of the Fish. This connection was adopted by many modern astrologers, who consider Neptune the ruler of Pisces. As a seafaring god, Neptune’s role in mythology connects him with all maritime matters and liquids. As such, boats, sailing, fish, sea creatures, bodies of water, fog, and floods all fall under his domain. Psychologically speaking, the sea symbolizes the collective and personal unconscious as well as all that is part of the subtle, intangible side of human existence. Thus, Neptune speaks to the intuitive mind, inspiration and imagination, dreams and psychic receptivity. Yet, the depth of water often distorts vision causing illusion or disillusionment, and bringing states of confusion, escapism, and suffering.

In the birth chart, Neptune indicates the ability to see beyond the finite self and world in order to experience unity with a greater whole. It seeks to dissolve the limitations and boundaries of the physical world by beautifying life or raising it to a higher level through displays of compassion, service, and creative force. This inner desire is often sought through artistic or spiritual experience. These activities allow one to escape the bonds of the mundane reality for a time. Through suffering, the wisdom of Neptune helps to flow through difficulties, leading towards levels of consciousness beyond the ego and providing the capacity to see the unity in all. Hence, Neptune teaches empathy and the highest form of love. Neptune is the higher expression or octave of the planet Venus. Venus symbolizes personal love and harmonization with others, while Neptune represents universal love and unity with the cosmos. Neptune refines and sensitizes everything it touches such that one steps beyond the crudeness and coarseness within and embraces the capacity for unselfish devotion and giving.

Individuals with this planet prominent in their horoscope often feel a need to merge or submerge themselves in a group, even to the point of sacrificing their own interests for a collective belief (such as a religious or political movement). It is also possible such individuals are susceptible to victimization or an attitude of being the victim. Neptunian people are extremely sensitive to others in their environment as well as to other realms. They can be clear channels for information from other planes of consciousness. However, this sensitivity also makes them susceptible to becoming a psychic sponge, absorbing and identifying with everyone else’s feelings and suffering.

Boundaries, then, become paramount in working with the energy of Neptune. A true Neptunian feels connected with everything. They are naturally kind and caring towards others and display a great love of animals and all helpless creatures. Often individuals with a strong Neptune care for the problems of others as if they were their own and can get so tangled with others’ vibrations that they require some degree of solitude in order to revitalize themselves and separate their thoughts and feelings from those of others. Otherwise, it is quite easy for these individuals to become lost in the clouds, unable to separate reality from illusion. This sensitivity supports Neptune’s connection with addiction, alcohol, intoxicants, and hallucinogenic drugs as a means of escaping the difficulties of the world and the fear of connecting or merging with a higher source.

Neptune is also the embodiment of imagination and artistic sensitivity. Its gifts include artistic and musical talents, imagination, inspiration, and visionary abilities. Its artistic capacities include film, photography, dance, and painting. This planet is also associated with mysticism and spiritual enlightenment. Thus, matters of religion connect Neptune with saints, nuns, monks, priests, churches, alters, and other dimensions.

Neptune moves very slowly in the sky, completing an orbit of the Sun every 164.79 years, meaning it stays almost 14 years in each sign of the zodiac. Because of its slow movement, its significance in a zodiacal sign is often considered more generational than individual, describing shifts of ideology within society. However, its house placement in the birth chart shows in what area of life it is easiest to delude one’s self or where one has and can make use of intuitive sensitivity and creativity in order to fulfill one’s highest ideals. There is often a deep sense of mission and a willingness to sacrifice personal interest, rising above the demands of the ego, for the larger good in the attainment of this ideal. Its placement is also where one is most attuned with the higher realms. Negative manifestations of Neptune can include escapism (including addictions), deception (including self-deception), confusion, depression, guilt, and vagueness. Planets in aspect with Neptune are inclined towards fantasy, dreaminess, and a vulnerable nature, making its expression susceptible to disillusionment.

Neptune’s glyph, or symbol, resembles the trident that the god Poseidon or Neptune is often shown holding. The crescent is pointing upwards, indicating spiritual receptivity, and is descending to the cross of mater which it rests upon.

—Tishelle Betterman


Bloch, Douglas, and Demetra George. Astrology for Yourself: A Workbook for Personal Transformation. Oakland, CA: Wingbow Press, 1987.
Burk, Kevin. Astrology: Understanding the Birth Chart. St. Paul, MN: Llewellyn Publications, 2001.
Campion, Nicholas. The Practical Astrologer. New York: Harry N. Abrams, 1987.
Campion, Nicholas, and Steve Eddy. The New Astrology: The Art and Science of the Stars. North Pomfret, VT: Trafalgar Square Publishing, 1999.
George, Llewellyn. The New A to Z Horoscope Maker and Delineator. 13th ed. Edited by Marylee Bytheriver. St. Paul, MN: Llewellyn Publications, 1986.
Hamilton, Edith. Mythology. New York: Little, Brown, 1942.

McEvers, Joan. Planets: The Astrological Tools. Saint Paul, MN: Llewellyn Publications, 1989.

Valentine, Christine. Images of the Psyche: Exploring the Planets through Psychology and Myth. Shaftesbury, Dorset, UK: Element Books, 1991.



a principal planet of our solar system, the eighth in distance from the sun. It has the astronomical sign ψ. Neptune was discovered in 1846. Its mean distance from the sun (semimajor axis of the orbit) is 30.06 astronomical units, or 4.5 billion km. The eccentricity of Neptune’s orbit is 0.0086, and the inclination to the plane of the ecliptic is 1° 46.4’. Neptune makes a complete revolution around the sun (sidereal period of revolution) in 164.79 years with an average orbital velocity of 5.4 km/sec. In the sky, the planet (which cannot be seen by the unaided eye) looks like a star of 7.8 magnitude with an angular diameter varying from 2.2“ to 2.4”. With powerful magnification, it appears as a greenish disk without any details. Neptune’s diameter is 49,500 km, which is 3.88 times the equatorial diameter of the earth. The oblateness of the planet is estimated to be 1/60. Neptune’s volume is 57 times greater than the earth’s volume. Its mass is 17.28 times that of the earth (1.03 × 1026 kg), and its mean density is 1.84 g/cm3. The acceleration of the force of gravity on the surface of Neptune is about 11 m/sec2 (15 percent more than on the earth). The second critical spacecraft velocity (escape velocity) at the surface of Neptune is 23 km/sec. Neptune’s period of rotation about its axis is 15.8 hr. Neptune’s equator is inclined at an angle of 29° to the plane of its orbit.

The planet has two satellites. Triton, discovered by W. Lassell in 1846, is comparatively large, with a diameter of about 4,000 km, and revolves around Neptune in the retrograde direction with a period of about 5.9 days. The second satellite, Nereid, was discovered in 1949 by the American astronomer G. P. Kuiper. A small body, with a diameter of 300 km, it revolves around the planet with a period of about one year (360 days).

Neptune receives very little light and heat because of its remoteness from the sun and because the atmosphere of Neptune scatters into space up to 83 percent of the incident radiation. Strong absorption bands of methane (CH4) are observed in the spectrum of Neptune; these bands are particularly intense at the red end of the spectrum, which causes the planet to have a greenish color. Neptune’s equilibrium temperature is —220°C. Radio measurements yield a temperature of about —160°; this latter temperature evidently refers to a layer under the clouds and indicates that the planet does have its own heat. Traces of molecular hydrogen H2 have also been detected in the spectrum of Neptune; however, the predominant element in the atmosphere and interior of Neptune is probably helium; evidence for this is the comparatively high mean density of the planet.

The discovery of Neptune was one of the most remarkable achievements of astronomy. In 1783, just two years after the discovery of the planet Uranus, A. J. Lexell, who had studied the motion of Uranus and was the first to compute its orbital elements, expressed the hypothesis that the irregularities detected in the motion of Uranus were caused by the gravitational attraction of an unknown planet revolving about the sun beyond the orbit of Uranus. J. C. Adams and U. Leverrier, completely unknown to one another, proceeded in a similar way in the search for this planet in the mid-19th century. In September 1845, Adams reported the results of his computations, which contained all the orbital elements and the position of the planet in the sky, to G. Airy, director (astronomer royal) of the Royal Greenwich Observatory. Airy did not familiarize himself with Adams’ work until nine months after he had received it. Meanwhile, Leverrier had computed the orbital elements of the new planet and its position in the sky and reported his results to the Berlin Astronomical Observatory on Sept. 18, 1846. The planet was discovered by J. Galle on Sept. 23, 1846, the first evening after the letter was received. The planet was found just 52’ from the computed position.




in ancient Roman mythology, the god of springs and rivers. Later identified with the ancient Greek god Poseidon, Neptune was worshiped as the god of the seas, who agitated and calmed them with his trident. In Rome, a temple to Neptune was erected in the Circus Flaminius; a holiday honoring him (Neptunalia) was celebrated on July 23.

In a figurative sense Neptune means the element of the sea.


The outermost of the four giant planets, and the next to last planet, from the sun; it is 30 astronomical units from the sun, and the sidereal revolution period is 164.8 years.


in allegories of the elements, personification of water. [Art: Hall, 128]
See: Water


the Roman god of the sea


the eighth planet from the sun, having eight satellites, the largest being Triton and Nereid, and a faint planar system of rings or ring fragments. Mean distance from sun: 4497 million km; period of revolution around sun: 164.8 years; period of rotation: 14 to 16 hours; diameter and mass: 4.0 and 17.2 times that of earth respectively


A hypertext system for computer assisted software engineering, developed at Tektronix.
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