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Jupiter, in astronomy


(jo͞o`pətər), in astronomy, 5th planet from the sun and largest planet of the solar system.

Astronomical and Physical Characteristics

Jupiter's orbit lies beyond the asteroidasteroid,
or minor planet,
small body orbiting the sun. More than 300,000 asteroids have been identified and cataloged; more than a million are believed to exist in the main belt between Mars and Jupiter, with many more in the Kuiper belt
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 belt at a mean distance of 483.6 million mi (778.3 million km) from the sun; its period of revolution is 11.86 years. In order from the sun it is the first of the Jovian planets—Jupiter, SaturnSaturn,
in astronomy, 6th planet from the sun. Astronomical and Physical Characteristics of Saturn

Saturn's orbit lies between those of Jupiter and Uranus; its mean distance from the sun is c.886 million mi (1.
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, UranusUranus
, 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.
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, and NeptuneNeptune,
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.
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—very large, massive planets of relatively low density, having rapid rotation and a thick, opaque atmosphere. Jupiter has a diameter of 88,815 mi (142,984 km), more than 11 times that of the earth. Its mass is 318 times that of the earth and about 2 1-2 times the mass of all other planets combined.

The atmosphere of Jupiter is composed mainly of hydrogen, helium, methane, and ammonia. However, the concentration of nitrogen, carbon, sulfur, argon, xenon, and krypton—as measured by an instrument package dropped by the space probe Galileo during its 1995 flyby of the planet—is more than twice what was expected, raising questions about the accepted theory of Jupiter's formation. The atmosphere appears to be divided into a number of light and dark bands parallel to its equator and shows a range of complex features, including a storm called the Great Red Spot. Located in the southern hemisphere and varying from c.15,600 to 25,000 mi (25,000 to 40,000 km) in one direction and 7,500 to 10,000 mi (12,000 to 16,000 km) in the other, the storm rotates counterclockwise and has been observed ever since 1664, when Robert Hooke first noted it. Also in the southern hemisphere is the Little Red Spot, c.8,000 mi (13,000 km) across. It formed from three white-colored storms that developed in the 1940s, merged in 1998–2000, and became clearly red by 2006. Analysis of the data obtained when massive pieces of the comet Shoemaker Levy 9 plunged into Jupiter in 1994 has extended our knowledge of the Jovian atmosphere.

Jupiter has no solid rock surface. One theory pictures a gradual transition from the outer ammonia clouds to a thick layer of frozen gases and finally to a liquid or solid hydrogen mantle. Beneath that Jupiter probably has a core of rocky material with a mass 10–15 times that of the earth. The spot and other markings of the atmosphere also provide evidence for Jupiter's rapid rotation, which has a period of about 9 hr 55 min. This rotation causes a polar flattening of over 6%. The temperature ranges from about −190°F; (−124°C;) for the visible surface of the atmosphere, to 9°F; (−13°C;) at lower cloud levels; localized regions reach as high as 40°F; (4°C;) at still lower cloud levels near the equator. Jupiter radiates about four times as much heat energy as it receives from the sun, suggesting an internal heat source. This energy is thought to be due in part to a slow contraction of the planet. Jupiter is also characterized by intense nonthermal radio emission; in the 15-m range it is the strongest radio source in the sky. Jupiter has a huge asymetrical magnetic field, extending past the orbit of Saturn in one direction but far less in the direction of the sun. This magnetosphere traps high levels of energetic particles far more intense than those found within earth's Van Allen radiation beltsVan Allen radiation belts,
belts of radiation outside the earth's atmosphere, extending from c.400 to c.40,000 mi (c.650–c.65,000 km) above the earth. The existence of two belts, sometimes considered as a single belt of varying intensity, was confirmed from information
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. Six space probesspace probe,
space vehicle carrying sophisticated instrumentation but no crew, designed to explore various aspects of the solar system (see space exploration). Unlike an artificial satellite, which is placed in more or less permanent orbit around the earth, a space probe is
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 have encountered the Jovian system: Pioneers 10 and 11 (1973 and 1974), Voyagers 1 and 2 (both 1979), Ulysses (1992), and Galileo (1995–2003).

Its Moons and Rings

At least 63 natural satellites orbit Jupiter. They are conveniently divided into six main groups (in order of increasing distance from the planet): Amalthea, Galilean, Himalia, Ananke, Carme, and Pasiphae. The first group is comprised of the four innermost satellites—Metis, Adrastea, Amalthea, and Thebe. The red color of

Amalthea (diameter: 117 mi/189 km), a small, elongated satellite discovered (1892) by Edward BarnardBarnard, Edward Emerson,
1857–1923, American astronomer, b. Nashville, Tenn., grad. Vanderbilt Univ., 1887. From 1887 to 1895 he was astronomer at Lick Observatory in California, and from 1895 he was professor of practical astronomy at the Univ.
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, probably results from a coating of sulfur particles ejected from Io.

Metis (diameter: 25 mi/40 km),

Adrastea (diameter: 12 mi/20 km), and

Thebe (diameter: 62 mi/100 km) are all oddly shaped and were discovered in 1979 in photographs returned to earth by the Voyager 1 space probe. Metis and Adrastea orbit close to Jupiter's thin ring system; material ejected from these moons helps maintain the ring.

The four largest satellites—Io, Europa, Ganymede, and Callisto—were discovered by Galileo in 1610, shortly after he invented the telescope, and are known as the Galilean satellite group.

Io (diameter: 2,255 mi/3,630 km), the closest to Jupiter of the four, is the most active geologically, with 30 active volcanoes that are probably energized by the tidal effects of Jupiter's enormous mass.

Europa (diameter: 1,960 mi/3,130 km) is a white, highly reflecting body whose smooth surface is covered with dark streaks up to 43 mi/70 km in width and from several hundred to several thousand miles in length.

Ganymede (diameter: 3,268 mi/5,262 km), second most distant of the four and the largest satellite in the solar system, has heavily cratered regions, tens of miles across, that are surrounded by younger, grooved terrain.

Callisto (diameter: 3,000 mi/4,806 km), the most distant and the least active geologically of the four, has a heavily cratered surface.

Themisto (diameter: 5 mi/8 km) orbits Jupiter midway between the Galilean and next main group of satellites, the Himalias. The Himalia group consists of five tightly clustered satellites with orbits outside that of Callisto—

Leda (diameter: 6 mi/10 km),

Himalia (diameter: 106 mi/170 km),

Lysithea (diameter: 15 mi/24 km),

Elara (diameter: 50 mi/80 km), and

S/2000 J11 (diameter: 2.5 mi/4 km). These 14 inner satellites are regular, that is, their orbits are relatively circular, near equatorial, and prograde, i.e., moving in the same orbital direction as the planet. Almost all of the remainder are irregular in that their orbits are large, elliptical, inclined to that of the planet, and usually retrograde, i.e., motion opposite to that of the planet's rotation. (Jupiter's irregular satellites are distinguished from the regular by the spelling of their names, which all end in the letter "e".)

Situated between the Himalia and Ananke groups is Carpo (diameter: 2 mi/3 km), which like Thermisto doesn't seem to fit into any of the main groups. The Ananke group comprises 17 satellites, which share similar orbits and range from 1.2 to 2.5 mi (2–4 km) in diameter except for two:

S/2003 J12,








Praxidike (diameter: 4.5 mi/7 km),



Ananke (diameter: 12.5 mi/20 km),

S/2003 J16,

S/2003 J3,

S/2003 J18,

Helike, and

S/2003 J15.

Like the Ananke group, the Carme group is remarkably homogeneous. It comprises 17 satellites, which share similar orbits and, except for one, range from 1.2 to 3 mi (2–5 km) in diameter:









Carme (diameter: 28 mi/46 km),




S/2003 J17,

S/2003 J10,

S/2003 J9,

S/2003 J5, and

S/2003 J19. The most distant of the groups from the planet is the Pasiphae, which comprises 14 widely dispersed satellites that, except for two, range from 1.2 to 4.5 mi (2–7 km) in diameter:

S/2000 J12,




Pasiphae (diameter: 36 mi/58 km),


Sinope (diameter: 23 mi/38 km),





S/2000 J23,

S/2000 J4, and

S/2000 J14. The odd orbits of the irregular satellites indicate that they were captured after Jupiter's formation. Because they are small, irregularly shaped, and clustered into groups, it is believed that they originated as parts of a larger body that either shattered due to Jupiter's enormous gravity or broke apart in a collision with another body.

Jupiter has three ringsring,
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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Main, and

Gossamer—similar to those of Saturn but much smaller and fainter. An intense radiation belt lies between the rings and Jupiter's uppermost atmospheric layers.

Jupiter, in Roman religion and mythology


in Roman religion and mythology, the supreme god, also called Jove. Originally a sky deity associated with rain and agriculture, he developed into the great father god, prime protector of the state, concerned, like the Greek ZeusZeus
, in Greek religion and mythology, son and successor of Kronos as supreme god. His mother, Rhea, immediately after his birth concealed him from Kronos, who, because he was fated to be overthrown by one of his children, ate all his offspring.
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 (with whom he is identified), with all aspects of life. At his temple on the Capitol, triumphant generals honored him with their spoils and magistrates paid homage to him with sacrifices. Jupiter was the son of SaturnSaturn,
in Roman religion and mythology, god of harvests, later identified with the Greek Kronos. Little is known of the origins of his cult. His reign was regarded as the Golden Age. He was the husband of Ops and the father of Jupiter, Juno, Ceres, Pluto, and Neptune.
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 and OpsOps
, in Roman religion, goddess of harvests. She was the wife of Saturn, by whom she bore Jupiter and Juno. At her festivals, the Opiconsivia and the Opalia, held in August and December, respectively, she was worshiped as a goddess of sowing and reaping and was associated with
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 and the brother and husband of JunoJuno,
in Roman religion and mythology, wife and sister of Jupiter. In early Roman times she, like the Greek Hera (with whom she was later identified), was goddess and protector of women, concerned especially with their sexual life.
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(joo -pă-ter) The largest planet in the Solar System, orbiting the Sun at a mean distance of 5.2 AU once every 11.86 years. It has an equatorial diameter of 142 994 km (11 times that of the Earth) and a polar diameter of 133 708 km. This oblateness results from a rotation period of less than 10 hours, shorter than that of any other planet. Jupiter has a mass more than twice that of all the other planets combined but its average density, only 1.3 times that of water, suggests that it contains a high proportion of the lightest elements, hydrogen and helium. Orbital and physical characteristics are given in Table 1, backmatter.

Oppositions recur at 13 month intervals; the planet then has, on average, an apparent diameter of 47 arc seconds and shines at about magnitude –2.5, brighter than every other night-time object apart from the Moon, Venus, and (rarely) Mars. Jupiter has 63 known satellites, including the four Galilean satellites visible with a minimum of optical aid, and also a ring system (see Jupiter's rings). Telescopes show the disk to be crossed by bands of light and dark clouds, called zones and belts respectively, running parallel to the equator. Irregular spots and streaks are seen, their motion across the disk indicating planetary rotation periods varying between about 9 hours 51 minutes in equatorial regions and 9 hours 56 minutes at high latitudes. Except for the Great Red Spot and the white ovals, most of the markings are temporary, lasting for days or months.

Models for Jupiter's atmospheric and internal structure have been refined following the flybys of the spaceprobes Pioneer 10 and 11 in 1973 and 1974, the Voyager probes in 1979, and Ulysses in 1992, and the detailed investigation of the Jovian system made by the Galileo spacecraft between 1996 and 2003; earlier spectroscopic work had, however, detected the presence of hydrogen, ammonia, and methane, and also water vapor, ethane, acetylene, phosphine, germanium tetrahydride, and carbon monoxide. It appears that the white or yellowish zones are areas of higher clouds supported by upward convection of warm gases; the reddish-brown belts have descending gas flows and lower clouds. With a rapidly rotating planet the weather systems are primarily zonal, and it is this that produces the banded colorful cloud systems superimposed with spots of a variety of different shades of colors; the spots are anticyclonically rotating systems. Huge convective storms are found in the equatorial region of Jupiter, and cyclonic storms, called barges, are seen in the northern latitudes. Eddies may give rise to the spots. At latitudes greater than about 45°, the belt/zone system gives way to a mottled surface appearance corresponding to ascending and descending convection cells (gas columns). The higher cloud zones appear to comprise ammonia crystals while the lower cloud belts may contain sulfur compounds, hydrogen and ammonium hydrosulfide, or complex organic compounds, possibly formed in photochemical reactions energized by ultraviolet radiation and by lightning discharges in the atmosphere. The highest cloud features, such as the Great Red Spot, may be colored red by traces of phosphorus brought up by convection from the lower atmosphere.

Jupiter radiates, as heat, about twice as much energy as it receives from the Sun, indicating that there is an internal reservoir of thermal energy left over from its creation 4.6 thousand million years ago. This internal energy source aids in driving Jupiter's weather system. In addition to the rapid rotation of Jupiter, the outflow of energy from the planet and a greenhouse effect ensure that there is little variation in temperature between the equator and poles, or between the day and night hemispheres. Atmospheric temperatures increase from -130°C at the cloud tops to about 30°C at the base of a lower cloud layer of water droplets and ice-crystals believed to lie about 70 km below the ammonia clouds. Over this same range the pressure rises from 0.5 to 4.5 (Earth) atmospheres. All Jupiter's weather occurs in this upper skin of its 1000-km deep gaseous atmosphere. At first sight the Jovian weather system appears quite different from that of the Earth. The analyses of the Voyager data have shown, however, that Jupiter (and also Saturn) and the Earth drive their meteorological systems in the same way, with energy being transported from the small-scale features into the main flow. The depth of the motions are unknown. However, they appear more stable than the specific cloud elements whose lifetimes vary from months to years to decades.

The atmosphere of Jupiter consists primarily of hydrogen and helium in the ratio 89.8 to 10.2 (by mass). The hydrogen becomes liquid at a depth of 1000 km; this marks the interface between atmosphere and planetary interior. At a depth of about 25 000 to 30 000 km, under an estimated two to three megabars of pressure, the hydrogen becomes metallic: the molecules dissociate into protons and a sea of unattached electrons. Temperatures may increase from 2000 K at 1000 km to some 20 000 K at the planet's center where there may be a rocky core 10 to 20 times more massive than the Earth. The bulk of Jupiter's interior is thus composed of liquid hydrogen, most of which is in metallic form.

A magnetic field, probably arising from a dynamo action within Jupiter's conductive metallic hydrogen, has a total strength about 19 000 times that of the Earth's magnetic field. Jupiter's field is tilted by 11° relative to its rotation axis and is reversed in polarity relative to that of the Earth. It supports a magnetosphere, about 15 million km across, in which the eight inner satellites orbit. The magnetosphere contains radiation belts possibly 10 000 times more intense than the Earth's Van Allen radiation belts.

Jupiter emits radio waves by three mechanisms: high-frequency thermal radio noise comes from the atmosphere along with infrared radiation; high-frequency nonthermal synchrotron emission is generated by electrons in Jupiter's magnetic field; intense bursts of decametric radio waves are believed to arise from electrical discharges along Jovian magnetic field lines when Io, with its conductive ionosphere, moves across them. A small fraction of the sulfur and sulfur dioxide erupting from volcanoes on Io manages to escape Io's gravity and becomes part of Jupiter's magnetosphere. High temperatures ionize the material giving rise to the Io torus , a huge doughnut-shaped ring of plasma. The Io torus lies in the plane of Jupiter's magnetic equator, inclined by 11° to the plane of Io's orbit.

Enlarge picture
An engraving from the seventeenth century of Jupiter with his thunderbolt and eagle. Reproduced by permission of Fortean Picture Library.


(religion, spiritualism, and occult)

Jupiter, the fifth planet from the Sun, is the largest body in the solar system, containing two-thirds the mass of the entire solar system outside the Sun. It is like a miniature planetary system all by itself. Since 2000, Jupiter is now known to have 28 moons of varying sizes. The four largest of them are easily visible with even a small telescope. Galileo discovered these larger moons in 1610. They are called Galilean satellites. Copernicus’s model of the heliocentric solar system was supported by the fact that these bodies were noticed to be orbiting another planet.

Jupiter begins a grouping of planets that have a different composition from the four terrestrial planets. These are referred to as the Jovian planets because of their giant sizes. (Jove was the chief Roman deity.) Jupiter’s gassy composition is a combination of 90 percent hydrogen and 10 percent helium. It has no solid surface at all. Jupiter rotates once every 10 hours. It orbits the Sun every 11.86 years. Its most distinguishing feature is the giant red spot. Observations from the 1979 Voyager mission identified the red spot as the vortex of a violent, long-lasting anticyclonic storm, similar to big storms on earth. Superbolts of giant-sized lightning and giant polar aurorae were also Voyager discoveries about Jupiter.

Early Greek mythology called Jupiter Zeus, and the Romans called him Jove. Jupiter was the son of Saturn (Kronos.) Just as the Oracle of Delphi predicted to Saturn, Zeus was the son to dethrone him, as he had overpowered his own father, Ouranos. Zeus and his brothers drew lots for their share of the universe. Zeus, Lord of the Sky, became chief of the Gods. His power was greater than all the others combined. He was righteous and demanded right action from men, not sacrifices. Jupiter is associated with the idea of justice. His low side made him out of control with his anger and his incalculable use of lightning bolts. He was never a faithful husband. He often acted like a storm cloud, building things up to turbulence. His high side can make things glorious. He gives hope and honors and bestows great gifts. Zeus was known for his great highs and lows.

In Mesopotamian astrology, Jupiter was linked to Marduk, ruler of the gods. Marduk was associated with wisdom, justice, water, and vegetation. Jupiter, known as the Greater Benefic, is the planet of hope, possibilities, expansion, and plenty. It is the most diurnal planet, next to the Sun. Jupiter has beneficial qualities in a nocturnal chart, as well. Jupiter rules the fire triplicity at night. It rules the masculine fire sign, Sagittarius. It is adventurous and robust in a diurnal chart. Jupiter is also the traditional ruler of the feminine water sign, Pisces. It is exalted in Cancer. Jupiter’s affinity with water signs makes it more compassionate and generous. In a nocturnal chart, Jupiter is more subdued and moderate. Jupiter is in its fall in Capricorn and its detriment in Virgo, both earth signs. This shows how unhappy Jupiter is when forced to conform and fit into rigid forms.

Jupiter is a social planet. Its influence is open, expansive, and temperate. When in sect, it confirms and radifies what the Sun selects. When contrary to sect, it creates obstacles to stabilization because too much is included. In the hellenistic system, the star Jupiter is assigned the special essence of reputation and crowns of office and expectations.

When Jupiter is dignified its influence is magnanimous, mild tempered, just, wise, and religious. When not dignified its influence can be scattered, over done, shallow, indifferent, and easily led astray. Its real character is good-natured, freedom loving, confident, and conscious of right and wrong, wanting to do what is best. Its optimistic outlook often brings good fortune and opportunity. There is ease to life that allows for luck and happiness.

Jupiter is traditionally associated with begetting children, desire, knowledge, friendships with great men, abundance, great gifts, freedom, trust, possessions, justice, reputation, preferments of priests, government, inheritances, benefaction, confirmation of good things, and deliverance from bad things. It represents officials, administrators, advisors, counselors, aristocrats, aristocracy, and foreign ministry. It rules law, courts, judges, lawyers, and the judicial system, as well as clergy, priests, ministers, and religious leaders. In business, Jupiter rules bankers, brokers, bondsmen, cashiers, clerks, magistrates, managers, merchants, stockbrokers, stocks, treasuries, trusts, and taxes. It is associated with celebrations, coronations, commemorations, grandeur, graduations, inaugurations, monuments, pageants, parades, regalia, rituals, salutes, and winning.

Jupiter gives affluence, amplification, applause, betterment, benevolence, bonuses, charity, chivalry, compensation, credentials, dignity, distinction, elite position, eminence, endowments, enhancement, extravagance, good fortune, gain, generosity, increases, endorsement, inheritance, integrity, joviality, luck, magnanimity, magnificence, opulence, philanthropy, prestige, pride, proclamation, promotion, protocol, protection, purity, recommendation, redemption, reputation, remuneration, restitution, reverence, self-esteem, sincerity, spirituality, splendor, success, superiority, temperance, title, tributes, verification, vindication, wealth, wisdom, worthiness, and worship.

Classical diseases and health problems associated with Jupiter are abscesses, accumulations, arteries, assimilation of food, blood in general and blood pressure, boils, the formation of red blood cells, diabetes, diseases from excess, enlargements, fatty degeneration, glands, growths, hepatic system, liver, upper legs and thighs, obesity, pleurisy, and tumors.

Modern astrology links Jupiter with the level of intelligence that perceives the world around us and puts things into a context that creates our beliefs and our world-views. It develops the rational thinking processes that lead to conclusion and understanding, bringing opinion and wisdom. Jupiter is the storyteller and is responsible for the dissemination of information on a broad scale. It is influential and inspirational in its delivery of ideas. In modern times it is associated with advertising, sales, and propaganda. Jupiter relates to higher levels of thought: education, philosophy, psychology and religion.

In Relating: An Astrological Guide to Living with Others on a Small Planet, Liz Greene identifies Jupiter as the planet symbolizing the myth-making principle:

Jupiter is thus connected with the urge within the psyche to create symbols, and this takes us into profound depths when we consider the creative power that has shaped the great myths, legends, and religions of the world. It is no less a creative power that shapes the symbolism of our dreams, so that each dream is a masterpiece of meaning and could not be altered in any way for improvement. In this way Jupiter is truly a god of the gateway, for he forms a link between conscious and unconscious through the creation and intuitive understanding of symbols. As we have seen, symbols are the primordial language of life; and Jupiter symbolizes the function which both creates them within man and intuits their meaning.

In Jyotish astrology, Jupiter is associated with the elephant-headed god Ganesh, and the king of the gods, Indra. The myths call Jupiter either Guru, which means “teacher,” or Brhaspati, which means “lord of sacred speech.” Jupiter is the guru to the gods.

In The Myths and Gods of India, Alain Danielou notes that Indra represents the power of the thunderbolt, the all-pervading electric energy, which is the nature of cosmic as well as animal life. He is the deity of the sphere of space, and the ruler of the storm. Indra embodies the qualities of all the gods, hence becoming the greatest. Ever young, Indra embodies all the virtues of youth: heroism, generosity, and exuberance. He stands for action and service but also for the need of force, which leads to power, to victory, and booty. He leads warriors and protects them with his thunderbolt and his bow, the rainbow. Indra loves intoxicants and pleasure. As the embodiment of virility, Indra is represented in the bull, the perfect male. He has numerous love affairs, including the wives of sages. He is given many names. Today, Indra is not the object of direct veneration, but he receives incidental worship and there is a festival in his honor called the “Raising of the Standard of Indra.”

—Norma Jean Ream


Bills, Rex. The Rulership Book, A Directory of Astrological Correspondences. Richmond, VA: Macoy Publishing & Masonic Supply Co., 1971.
Crane, Joseph. A Practical Guide to Traditional Astrology. Orleans, MA: Archive for the Retrieval of Historical Astrological Texts, 1997.
Danielou, Alain. The Myths and Gods of India. Rochester, VT: Inner Traditions International, 1991.
Greene, Liz. Relating: An Astrological Guide to Living with Others on a Small Planet. 2d ed. York Beach, ME: Samuel Weiser, 1978.
Hamilton, Edith. Mythology. Boston: Little, Brown, 1942.
Pasachoff, Jay M. Contemporary Astronomy. 4th ed. Philadelphia: Saunders College Publishing, 1989.
Schmidt, Robert, translator. Vettius Valens, Book I, Chapter I. Original Source Texts and Auxiliary Materials for the Study of Hellenistic Astrology and Project Hindsight, Phaser Foundation, 2002.
Wilson, James. A Complete Dictionary of Astrology. London: W. Hughes, 1819.



the fifth planet from the sun in our solar system; astronomical symbol, Jupiter.

General information. Jupiter, the largest of the Jovian planets, has been known since antiquity. It revolves around the sun at a mean distance of 5.203 astronomical units (778 million km). Its orbit has an eccentricity of 0.048, and the inclination of its orbital plane to the plane of the ecliptic is 1.3°. Jupiter completes one revolution around the sun in 11,862 years, traveling at an average velocity of 13.06 km/sec. The mean synodic period of revolution is 399 days. In 12 years Jupiter traverses the entire sky along the ecliptic and can be seen at opposition as a pale yellowish star of stellar magnitude – 2.6; at favorable opposition it is surpassed only by Venus and Mars in brightness. Its visible disk has the form of an ellipse, whose axes at mean opposition can be seen at an angle of 46.5″ and 43.7″. At conjunction with the sun, Jupiter’s angular dimensions are one-third smaller and its brightness is 0.84 stellar magnitude fainter than at oppositions. The visual albedo is 0.67.

Jupiter’s equatorial diameter is 142,600 km, and its polar diameter, 134,140 km; the planet’s oblateness (1/15.9) is due to its rapid axial rotation. The rotation period is 9 hr 50 min 30 sec near the equator (System I) and 9 hr 55 min 40 sec at middle latitudes (System II). Jupiter’s volume exceeds the volume of the earth by a factor of 1,315, while its mass exceeds the earth’s mass by a factor of 318. Jupiter’s mass is 1/1047.39 the mass of the sun. Its mean density (1.33 g/cm3) differs little from the solar density. The acceleration of gravity is 27.90 m/sec2 at the poles and 25.90 m/sec2 at the equator; the centrifugal acceleration at the equator is 2.25 m/sec2. The escape velocity from Jupiter’s surface is 61 km/sec. (All the geometrical, mechanical, and physical characteristics are from 1974 data.) Information on Jupiter and its satellites was greatly enriched by the measurements and observations made by the American space probes Pioneer 10 (1973) and Pioneer 11 (1974).

Atmosphere. Jupiter’s observable surface consists of clouds and other atmospheric formations and is crossed by numerous dark bands (belts) separated by light zones running parallel to the equator, which is inclined only 3°04′ to Jupiter’s orbital plane. The bands display a variety of colors and have a complex structure that is constantly changing. The appearance of the north and south equatorial bands, which disappear and reappear with an established cyclicity of about four years, is especially variable. The very narrow equatorial band also sometimes becomes invisible. By contrast, the circumpolar regions are comparatively stable.

The amount of solar heat incident per unit area of Jupiter is 51.0 W/m2, that is, it is smaller by a factor of 27 than the amount of heat incident on the earth. It is capable of heating the surface of Jupiter to an equilibrium temperature of 110°K. However, direct measurements by both ground-based equipment and space probes indicate a temperature of up to 145°K from measurements in the infrared radiation of Jupiter and even higher values, up to 170°K, in the microwave region. In some parts of the dark bands, infrared radiation at very long waves implies temperatures of 200°–270°K. A record high temperature of 310°K was detected in one dark spot (6,000 × 12,000 km) near the equator. Such a temperature can result only from a flow of heat from the planet’s interior that exceeds the heat coming from the sun by a factor of 2.

Jupiter’s cloud structure contains more or less constant formations, such as the Great Red Spot, located at a latitude of about 22° in the southern tropical zone. The Great Red Spot is oval in shape, with a length of about 40,000 km and a width of about 13,000 km. Although its color is red, there are years when it can be distinguished only with difficulty against the white background of the zone. Rotational effects and vertical movements in the atmosphere, combined with different cloud levels, are responsible for the complex dependence of the visible systematic motions at various distances from the equator. The rotation periods System I and System II describe only the average rotation of Jupiter’s atmosphere. In fact, systematically directed winds, acting in a given belt or zone, lead to markedly different values of the period of rotation.

The chemical composition of Jupiter’s atmosphere has been determined spectroscopically. Methane (CH4) and ammonia (NH3) were the first compounds detected in Jupiter’s atmosphere on the basis of the strong absorption bands. Subsequently, molecular hydrogen (H2), water vapor (H2O), and the molecules of acetylene (C2H2), ethane (C2H6), phosphene (PH3), and finally carbon monoxide (CO) were detected from weak absorption bands in the infrared region of the spectrum.

The dark bands of Jupiter are aerosol-like, consisting of particles measuring 0.2–0.3 ptm. Ammonia crystals have been detected above the level where the atmospheric pressure is 1 atmosphere (the geometrical dimensions of Jupiter given above correspond to this level). Solid polysulfide particles are located somewhat below this level, ice crystals are found still lower, and finally, 60 km below this level, suspended drops of an ammonia-water solution are found.

Internal structure. There are several models of Jupiter’s structure based on different assumptions regarding its chemical composition. Because of Jupiter’s strong gravity, the gas pressure increases very rapidly with depth, and even at a distance of 10,000 km from the surface it becomes so great that the predominant gas, hydrogen, undergoes a change of state, from the normal molecular phase to the metallic. The temperature increases as the center of the planet is approached, and consequently the metallic hydrogen melts (the temperature near the center of Jupiter approaches 20,000°K at a pressure of the order of 100 million atmospheres and a density of 20–30 g/cm3). Some models of Jupiter assume the existence of an ice layer (H2O) of significant thickness, but only near the surface, where the temperature is low.

Apparently, Jupiter has a solid shell comparatively close to the surface. The assumption that such a shell exists could explain the magnetic field, which rigidly rotates together with the planet, and the inhomogeneities of the heat fluxes, which are manifested in numerous details of the bands and especially in the long-existing Great Red Spot, which rotates with nearly the same period as Jupiter’s magnetic field.

Magnetic field. Jupiter’s magnetic field has been detected from strong radio-frequency radiation, which is especially intense at decimeter and decameter wavelengths. Decimeter waves originate from near-planetary space and are synchrotron radiation of electrons trapped by Jupiter’s magnetosphere in radiation belts similar to those of the earth. The decameter radiation (at a 7.5-m wavelength) is in the form of noise storms, lasting from a few hours to a few minutes. The radiation is directed and originates from certain small areas on Jupiter’s surface. It follows from the periodic recurrence of the radio outbursts that their sources rotate with a period of 9 hr 55 min 30 sec (System III). The decimeter radiation also changes with this period. It is this period that is ascribed to the rotation of the solid layer that actually forms the surface of Jupiter. The nature of Jupiter’s solid layer remains unknown (as of the 1970’s). Its upper boundary should be located near the visible surface, and its lower boundary may be located where the metallic hydrogen changes from the solid phase to the liquid. Electrical currents that are responsible for Jupiter’s magnetic field arise at this boundary and within the liquid core. The strength of Jupiter’s magnetic field is 4 oersteds. The direction of its magnetic axis forms an angle of about 10° with its axis of rotation.

Jupiter’s magnetosphere is very large. In the regions closest to the planet (up to 20 radii from the planet), it has a marked dipole character and includes radiation belts, containing field-trapped electrons with energies above 6 megaelectron volts. The interaction of the electrons with the field gives rise to decimeter synchrotron radiation. In more distant regions, the central magnetosphere extends to a distance of 60 Jupiter radii and is deformed by rotation. Plasma emissions and oscillations that emit in the decameter band are possible here. The outer magnetosphere, which extends to the magnetopause, whose size is variable, is located still farther out, up to 90–100 Jupiter radii from the planet. On the far side it extends beyond Saturn’s orbit. All five of the satellites closest to Jupiter lie within the central magnetosphere. The closest large satellite—Io—apparently has its own magnetic field and significantly influences the frequency of Jupiter’s radio outbursts.

Satellites. Thirteen satellites of Jupiter are known. Satellite XIII (JXIII) was the last to be discovered (1974). The first four satellites, which are also the largest, were discovered by Galileo in 1610. The fifth satellite—JV, discovered in 1892, nearly three centuries later—is the closest to the planet, only 2.54 Jupiter equatorial radii from the planet. All of these five satellites move essentially in circular orbits, whose planes coincide with the plane of Jupiter’s equator. Their periods of revolution range from 12 hr for JV to 16.8 days for JIV. The remaining satellites of Jupiter, all of which have been discovered in the 20th century, lie at greater distances from the planet.

In 1976 the names of all the satellites were officially confirmed. Nearly all are named after mythological figures in one way or another associated with Jupiter (the first four satellites were named

Table 1. Jupiter’s satellites1
SatelliteRadius (km)Stellar magnitude at opposition
11976 data
Io(JI) ...............1,82049
Europa (JII) ...............1,5305.3
Ganymede (JIII) ...............2,61046
Callista (JIV) ...............2,4505.6
Amalthea (JV) ...............12013
Himalia (JVI) ...............~80142
Elara(JVII) ...............~5017
Pasiphae(JVIII) ...............~1218
Sinope(JIX) ...............~1018.6
Lysithea (JX) ...............~8188
Carme (JXI) ...............~9186
Ananke(JXII) ...............~818.7
Leda (JXIII) ...............~520

by Galileo). Table 1 lists Jupiter’s satellites, along with a number of their characteristics.

The four Galilean satellites are the sizes of planets (Ganymede and Callisto are larger than Mercury). Their periods of axial rotation and revolution around Jupiter coincide. Their average densities are higher than the density of Jupiter: 2.89, 3.20, 2.07, and 1.54 g/cm3. They all have low temperatures, close to the equilibrium temperature. Their albedos are quite high but lower than Jupiter’s albedo, implying the presence of surface features rather than the presence of a thick atmosphere. Indeed, radar and infrared observations have established that their surfaces consist of ice or an ice-rock mixture, since sizable irregularities have been observed. Pioneer 10 and Pioneer 11 photographed Ganymede from nearby, revealing stable dark and light formations. Io has been found to have an atmosphere and a significant ionosphere. It may be assumed from the close coincidence of the planes of the first five satellites with Jupiter’s equatorial plane that the satellites were formed at the same time as the planet from one cluster of primary material. As far as the other satellites are concerned, they most probably were asteroids at one time in the past and were captured by Jupiter.


Moroz, V. I. Fizika planet. Moscow, 1967.
Fizicheskie kharakteristiki planet-giganlov. Alma-Ata, 1971.
Zharkov. V. N. Vnutrennee stroenie Zemli, Luny i planet. Moscow, 1973.
Dolginov, Sh. Sh. Magnetizmplanet. Moscow, 1974.
Martynov, D. Ia. Planety: Reshennye i nereshennye problemy. Moscow, 1970.
Zemlia i Vselennaia. (Articles and comments on Jupiter for the period 1974–77.)



The largest planet in the solar system, and the fifth in order of distance from the sun; semimajor axis = 485 × 106 miles (780 × 106 kilometers); sidereal revolution period = 11.86 years; mean orbital velocity = 8.2 miles per second (13.2 kilometers per second); inclination of orbital plane to ecliptic = 1.03; equatorial diameter = 88,700 miles (142,700 kilometers); polar diameter = 82,800 miles (133,300 kilometers); mass = about 318.4 (earth = 1).


(in Roman tradition) the king and ruler of the Olympian gods


the largest of the planets and the fifth from the sun. It has 16 satellites and is surrounded by a transient planar ring system consisting of dust particles. Mean distance from sun: 778 million km; period of revolution around sun: 11.86 years; period of axial rotation: 9.83 hours; diameter and mass: 11.2 and 317.9 times that of earth respectively


To kill an IRC robot or user and then take its place by adopting its nick so that it cannot reconnect. Named after a particular IRC user who did this to NickServ, the robot in charge of preventing people from inadvertently using a nick claimed by another user.