(redirected from 7th planet)
Also found in: Dictionary, Thesaurus.


, in astronomy

Uranus (yo͝orāˈnəs, yo͝orˈə–), in astronomy, 7th planet from the sun, at a mean distance of 1.78 billion mi (2.87 billion km), with an orbit lying between those of Saturn and Neptune; its period of revolution is slightly more than 84 years. The first planet discovered in modern times with the aid of a telescope, Uranus was detected in 1781 by Sir William Herschel, who originally thought it to be a comet. Because the calculated orbit of Uranus did not compare accurately with the observed orbit, astronomers concluded that a disturbing influence was present. A study of this irregularity led to the discovery of Neptune in 1846. Uranus has a diameter of c.31,760 mi (46,700 km), roughly 4 times that of the earth, and a mass of about 14.5 times that of the earth. Like the other ice giant, Neptune, Uranus has a relatively thick atmosphere of hydrogen, helium, and methane; a relatively low density; and a rapid period of rotation of about 17.9 hr, which causes a polar flattening of over 6%. However, its axis of rotation is tilted 98° to the plane of its orbit. The Voyager 2 space probe found that Uranus has the most inclined magnetic field in the solar system, and some astronomers interpret this as evidence that the magnetic field is reversing its polarity. Viewed through a telescope, Uranus appears as a greenish disk, slightly elliptical because of its rapid rotation. Its temperature is estimated to be about −330℉ (−200℃), and at this temperature ammonia, the main constituent of the visible cloud cover, would exist in the form of ice crystals. Uranus has 27 known natural satellites with diameters ranging in size from 7 mi (11 km) to 986 mi (1,578 km).

Prior to 1986, only five of Uranus's natural satellites were known: Titania, the largest, and Oberon were discovered by Herschel in 1787; Ariel and Umbriel, by William Lassell in 1851; and Miranda, by Gerard Kuiper in 1948. When Voyager 2 flew by Uranus in 1986, it discovered 10 more natural satellites—Cordelia, Ophelia, Bianca, Cressida, Desdemona, Juliet, Portia, Rosalind, Belinda, and Puck—and confirmed the existence of 11 rings. Two additional satellites, Caliban and Sycorax, were discovered in 1997, and three more, Prospero, Setebos, and Stephano, were found in 1999. Trinculo, a small irregular satellite, was discovered in 2002; eight other small satellites are also irregular, that is, their motion around Uranus is retrograde (motion opposite to that of the planet's rotation). The moons of Uranus are named after characters found in the works of William Shakespeare and Alexander Pope.

Titania along with Oberon and Umbriel appear geologically to be relatively quiet. Ariel has surface features that indicate past seismic activity. Miranda shows the most dramatic surface of all, with fracture patterns and sudden landscape changes that indicate that the moon fell apart and then reassembled after a collision in its early history. In 1977, during an occultation by Uranus of a star, astronomers detected a system of nine narrow rings of small, dark particles orbiting around the planet; two more rings, many tiny ringlets, and arcs of rings were later found by Voyager 2. Uranus's rings are distinctly different from those of Jupiter and Saturn. For example, Saturn's rings are very bright and easily seen but Uranus's are very dark, with only 5% of the sunlight being reflected back. Uranus's rings also are very narrow and flat. The widest part of Uranus's outermost ring, the epsilon ring, is 60 mi (97 km) across. The others are only 1 to 2 mi (1.5–3.2 km) wide and barely half a mile (0.8 km) deep.


, in Greek religion and mythology
Uranus, in Greek religion and mythology, the heaven, first ruler of the universe, son of Gaea (the earth). He was the father of Gaea's children, the Titans, the Cyclopes, and the Hundred-handed Ones (the Hecatoncheires). Fearing that his children would rebel against him, he imprisoned them, but Kronos, a Titan, with the help of Gaea, castrated him, thereby taking away his power. From the blood of Uranus that fell on Earth sprang the three Furies (the Erinyes), the goddesses of revenge. According to Hesiod, Aphrodite was born of Uranus' discarded flesh and the foaming sea.
The Columbia Electronic Encyclopedia™ Copyright © 2022, Columbia University Press. Licensed from Columbia University Press. All rights reserved.


(yû-ray -nŭs, yoor -ă-nŭs) The seventh planet of the Solar System and the first to be discovered telescopically – by William Herschel in 1781. The third largest of the giant planets, it has an equatorial diameter of about 51 119 km, a mass 14.5 times that of the Earth, and a density 1.3 times that of water. Uranus orbits the Sun every 84.01 years, varying in distance between 18.31 and 20.07 AU. At oppositions, which recur four days later each year, it has a mean angular diameter of 3.7 arc seconds and a magnitude of 5.6, near the limit of naked eye visibility. Telescopically Uranus shows a featureless greenish disk making visual determination of its rotation period impossible. The period is about 16 hours and retrograde. Orbital and physical characteristics are given in Table 1, backmatter.

Uranus' equator is tilted by 98° with respect to its orbit, making it unique in having its rotation axis close to its orbital plane. This means that the north and south poles alternately point toward the Sun, giving highly exaggerated seasonal changes on the planet.

Voyager 2 flew by Uranus in 1986, and at this time its south pole was pointing almost directly at the Sun. Images of the planet show a remarkably featureless surface. Faint cloud markings determine that winds on Uranus blow at 40–160 m s–1 in the same direction as the planet rotates. These Uranian winds arrange the planet's cloud features into east-west bands.

The outer layers of Uranus are predominantly hydrogen and helium in gaseous state and with low density. The temperature in the upper atmosphere is around 60 K so methane and hydrogen condense to form clouds of ice crystals. The methane forms at higher altitudes, giving Uranus its blue-green color. Uranus' outer atmosphere rotates differentially between 16.2 and 16.9 hours at cloud-surface level, depending on latitude. Its internal rotation rate is about 17.23 hours. It is thought it has a rocky core, primarily iron and silicon, about the size of the Earth.

The equatorial region of Uranus receives little sunlight, but its effective temperature is almost the same as the sunlit pole. This implies that heat is efficiently transported between the poles and the equator.

Auroral activity noted before the Voyager probes gave indications that Uranus has a magnetosphere. It is now known that Uranus has a magnetic field about the same as the Earth's. The magnetic axis is inclined by nearly 60° from its axis of rotation and, like the other Jovian planets, is opposite in polarity to the Earth's.

Uranus has 27 known satellites and a ring system. See Uranus' rings; Uranus' satellites.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006


(religion, spiritualism, and occult)

Uranus is our solar system’s seventh planet, orbiting between Saturn and Neptune at an average distance of about 1.75 billion miles from the Sun. Since it is 20 times further away from the Sun than Earth, it takes Uranus 84 Earth years to travel around the Sun. The blue-green planet also has a day of a little more than 17 hours, 7 hours shorter than an Earth day. The way in which this planet travels is unusual and even eccentric. Rather than rotating on an axis that is perpendicular to the plane of its orbit, Uranus spins on its side with its south pole facing the sun. It also rotates from east to west, the opposite direction of Earth and most other planets.

The third largest planet in our solar system, Uranus is about four times the size of Earth. It is 30,000 miles in diameter, compared to Jupiter’s 85,000-mile diameter. As with all gas planets, Uranus has very faint rings around it made up of large chunks of rocky material. Since the rocks are dark in color, the rings cannot be viewed well from Earth. Uranus also has more than 20 moons. The five largest were named for characters in the plays of William Shakespeare and Alexander Pope: Miranda, Ariel, Umbriel, Titania, and Oberon.

Uranus was the first planet to be discovered by an astronomer. Earlier sightings had been made—John Flamsteed first recorded it in 1690—but it had been cataloged as a star. William Herschel spotted Uranus on March 13, 1781, and named the planet Georgium Sidus for George III, the king of England at that time. Many simply called the planet Herschel, after its discoverer. By the mid-1800s the agreed-upon name of Uranus came into common usage, which Bode had proposed as more consistent with the mythological names of the other planets.

The Greek god of the heavens, Uranus was an early supreme god who was the son and mate of Gaia, the creation goddess. An unpredictable, creative, and tyrannical god, he ate his children so they could not usurp his power in the future. He was father of the Titans, of which Cronus (Saturn) was one, and predecessor to the Olympian gods. On Gaia’s bequest Cronus castrated Uranus and forced him to release the other children from his stomach, thus usurping his father’s power after all.

As the first known planet beyond Saturn, the discovery of Uranus caused something of an upheaval in traditional astronomy and astrology circles. In addition, the timing of Uranus’s discovery coincided with the independence revolutions of America and France and the industrial revolution in England. These disruptions of intellectual and political circles gave astrologers reason to believe that Uranus represented rebelliousness, disruptive influences, breaking away from traditional patterns or rules, as well as concern for humanity and brotherhood, progress, and inventiveness. Hence, it was suggested that Uranus ruled or coruled the zodiac sign of Aquarius.

In twentieth-century western astrology Uranus was given rulership of Aquarius, though traditionally and that role belonged to Saturn. Uranus is classified as an outer planet (outside of Saturn’s orbit) and stays in each sign of the zodiac for seven years, and is thus considered to have a generational effect. Therefore, assigning rulership of a sign exclusively to an outer planet, including Uranus, is not as simple or appropriate as twentieth-century astrologers had hoped it might be. In light of discoveries from cross-cultural astrological studies and ancient texts, recently translated into English, which make apparent the logic behind Saturn’s rulership of Aquarius, it appears more reasonable to continue using the traditional seven planet rulerships of the zodiac signs. However, it can be generally agreed upon that the newly discovered planets can add additional meaning as corulers of signs. Hence, Uranus is the coruler of Aquarius, along with Saturn as its main indicator.

In the Saturn world of the material and the structured, Uranus represents the rejection of rules that no longer serve us and the installation of a new paradigm that sees through the illusion of Saturn’s limits. It is the crack in the cosmic view and it is the leap forward into the unknown led by intuition and inspired ideas. Uranus brings the sudden force that tears down unneeded walls so that something newer and better can be built from its foundations. Uranus is associated with humanity, ideals, eccentricity, philanthropy, originality, creative inspiration and genius, but also with chaos, accidents, disasters, antisocial behavior and radical individualism. It is a planet of personal and global transformation, but the way it brings this about is through sudden, swift, unexpected change. Uranus is like lightning—it seemingly comes from nowhere and illuminates with a brilliant flash. It is said to rule astrology, science, electricity, and technology, and is symbolized by inventors, scientists, humanitarians and revolutionaries.

Although the various planets are connected with a wide range of activities and objects, they also, when found in a natal chart, represent different parts of the psyche. Uranus represents the creative, innovative, freedom-seeking part of the self and its placement by sign and house shows much about how and where a person can best express his creative genius and originality, as well as where to anticipate sudden, dramatic change. If the natal chart shows that Uranus was retrograde at birth, and Uranus retrogrades every year for five months, then the urge for freedom may be directed internally, leading to progressive ideas and advanced thinking. A retrograde Uranus afflicted by house placement or hard aspect, however, may indicate a native that is merely erratic or eccentric. In either case, interest in the occult may occur as well. A natal Uranus that is stationary points to a native that is very concerned with humanitarian issues, who may become an instrument of change.

Physically, Uranus is connected to the body’s nervous system because of its association with electricity and electrical impulses. Those natives with a prominent Uranus in their chart, particularly if the planet is connected to the first house, can be high strung, oversensitive, and prone to nervous tension and exhaustion. Uranus-type illnesses come on suddenly and disappear just as mysteriously.

—Linda R. Birch


Arnett, Bill. The Nine Planets. www.seds.org/nineplanets/nineplanets/.
Astronomy for Kids. www.dustbunny.com/afk.
Bloch, Douglas, and Demetra George. Astrology for Yourself. 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.
Lineman, Rose, and Jan Popelka. Compendium of Astrology. Atglen, PA: Whitford Press, 1984.
The Astrology Book, Second Edition © 2003 Visible Ink Press®. All rights reserved.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



the seventh major planet from the sun in the solar system; its astronomical symbol is Uranus or ♅. One of the giant planets, Uranus was discovered by W. Herschel in 1781. The planet had been observed accidentally even earlier but remained unrecognized among the stars.

Uranus revolves around the sun at a mean distance of 19.19 astronomical units in a nearly circular orbit. The orbital eccentricity is 0.047, and the inclination of the orbit to the ecliptic is only 0.77°. Uranus completes one revolution around the sun in 84.015 years, or 30,685 earth days. The synodic period, during which the oppositions and conjunctions are repeated, is 369.7 days. Since Uranus is a sufficiently bright object of about sixth magnitude, it is easily observed through binoculars, but a telescope with a magnification of not less than 60 × is required to resolve the disk. The planet is barely distinguishable with the naked eye. The apparent diameter of Uranus ranges from 3.4″ to 4.3″. The true equatorial diameter of the planet is 50,700 km, or 3.98 times the diameter of the earth. The volume of Uranus is 61 times that of the earth, but its mass is 14.56 times that of the earth because the mean density of the planet is low and equal to 1.32 g/cm3, which is characteristic of the giant planets. The acceleration gravity at the planet’s equator is 1,040 cm/sec2 minus 60 cm/sec2 due to centrifugal acceleration, and the escape velocity is 22 km/sec.

The figure of Uranus is highly flattened at the poles, the oblate-ness being about 1:33. The flattening reflects the rapid rotation of the planet about its axis; the rotation period is 10.8 hours. Because no features are observable on the disk of Uranus, the fact that the planet rotates cannot be established from direct observations. The rotation period was determined on the basis of periodic changes in the planet’s brightness with an amplitude of up to 0.15 magnitude and on the basis of the Doppler shift of the planet’s spectral lines, which makes it possible to obtain the equatorial linear rotation velocity. Most of the planets, if viewed from their north poles, rotate counterclockwise, that is, in the same direction as they revolve around the sun. In contrast, Uranus—like Venus—rotates in the retrograde direction. The axis of rotation of Uranus lies nearly in the orbital plane, forming an angle of 98° with a line perpendicular to the orbit.

Because of its great distance from the sun, Uranus receives very little light and heat from the sun, nearly 370 times less than that received by the earth. However, the reflectivity of Uranus is very great, the highest among the planets. The spherical albedo of Uranus is 0.93, and its geometric albedo is 0.57. If Uranus reflects all of the sun’s thermal radiation with such effectiveness, the planet’s surface temperature should be very low, less than 90°K (–180°C). Such a low surface temperature is confirmed by measurements in the infrared region, where the mean temperature was found to be only 55±3°K. At the same time, the temperature measured in the centimeter wavelength range is considerably greater than 100°K, which indicates the existence of a heat flux from the interior of the planet. The high albedo of Uranus indicates the presence of a thick atmosphere. Spectroscopy has revealed the presence of molecular hydrogen (H2) in the amount of 100 kilometer-atmospheres (km-atm) above the cloud layer and of methane (CH4) in the amount of 3 to 150 km-atm, according to various estimates. The atmospheric pressure at the level of the clouds is estimated as 3 atm. Theoretical studies of the internal structure of Uranus have yielded the following results: (1) the outer gaseous envelope consists of H2, He, and CH4; (2) the total mass of the three gases is about 10 percent of the mass of the planet; (3) the thickness of the envelope is 27 percent of the radius of the planet; and (4) a liquid core, consisting mostly of water, lies beneath the gaseous envelope.

Uranus has five satellites, which move in the planet’s equatorial plane and in the direction of the planet’s rotation. All five satellites are faint and can be observed only with large telescopes. Herschel discovered the two outermost and brightest satellites, Titania and Oberon, in 1787. W. Lassell discovered Ariel and Umbriel, which are not as bright, in 1851. Miranda, the innermost satellite, was discovered through photography by the American astronomer J. Kuiper in 1948; the magnitude of Miranda is 16.5. The size of the satellites can only be roughly estimated on the basis of their brightness. The largest, Titania, has a diameter of between 500 and 1,300 km; the smallest, Miranda, has a diameter of 150 to 500 km.

Rings around Uranus were discovered in 1977.


Moroz, V. I. Fizika planet. Moscow, 1967.
Martynov, D. Ia. Planety: Reshennye i nereshennye problemy. Moscow, 1970.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


[′yu̇r·ə·nəs or yu̇′rā·nəs]
A planet, seventh in the order of distance from the sun; it has five known satellites, and its equatorial diameter is about four times that of the earth.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


Greek myth the personification of the sky, who, as a god, ruled the universe and fathered the Titans and Cyclopes on his wife and mother Gaea (earth). He was overthrown by his son Cronus


one of the giant planets, the seventh planet from the sun, sometimes visible to the naked eye. It has about 15 satellites, a ring system, and an axis of rotation almost lying in the plane of the orbit. Mean distance from sun: 2870 million km; period of revolution around sun: 84 years; period of axial rotation: 17.23 hours; diameter and mass: 4 and 14.5 times that of earth respectively
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005


Hideyuki Nakashima <nakashim@el.go.jp>, 1993. A logic-based knowledge representation language. An extension of Prolog written in Common Lisp, with Lisp-like syntax. Extends Prolog with a multiple world mechanism, plus term descriptions to provide functional programming.

This article is provided by FOLDOC - Free Online Dictionary of Computing (foldoc.org)