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The Solar SystemTemplate:Ref label consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun. Of the many objects that orbit the Sun, most of the mass is contained within eight relatively solitary planetsTemplate:Ref label whose orbits are almost circular and lie within a nearly flat disc called the ecliptic plane. The four smaller inner planets, Mercury, Venus, Earth and Mars, also called the terrestrial planets, are primarily composed of rock and metal. The four outer planets, the gas giants, are substantially more massive than the terrestrials. The two largest, Jupiter and Saturn, are composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are composed largely of ices, such as water, ammonia and methane, and are often referred to separately as "ice giants".

The Solar System is also home to a number of regions populated by smaller objects. The asteroid belt, which lies between Mars and Jupiter, is similar to the terrestrial planets as it is composed mainly of rock and metal. Beyond Neptune's orbit lie the Kuiper belt and scattered disc; linked populations of trans-Neptunian objects composed mostly of ices such as water, ammonia and methane. Within these populations, five individual objects, Ceres (1), Pluto (134340), Haumea (136108), Makemake (136472) and Eris (136199), are recognized to be large enough to have been rounded by their own gravity, and are thus termed dwarf planets.Template:Ref label In addition to thousands of small bodiesTemplate:Ref label in those two regions, several dozen of which are considered dwarf-planet candidates, various other small body populations including comets, centaurs and interplanetary dust freely travel between regions. Six of the planets and three of the dwarf planets are orbited by natural satellites,Template:Ref label usually termed "moons" after Earth's Moon. Each of the outer planets is encircled by planetary rings of dust and other particles.

The solar wind, a flow of plasma from the Sun, creates a bubble in the interstellar medium known as the heliosphere, which extends out to the edge of the scattered disc. The Oort cloud, which is believed to be the source for long-period comets, may also exist at a distance roughly 1000 times further than the heliosphere. The heliopause is the point at which pressure from the solar wind is equal to the opposing pressure of interstellar wind. The Solar System is located within one of the outer arms of Milky Way galaxy, which contains about 200 billion stars.

Discovery and exploration

For many thousands of years, humanity, with a few notable exceptions, did not recognize the existence of the Solar System. People believed the Earth to be stationary at the centre of the universe and categorically different from the divine or ethereal objects that moved through the sky. Although the Greek philosopher Aristarchus of Samos had speculated on a heliocentric reordering of the cosmos,[1] Nicolaus Copernicus was the first to develop a mathematically predictive heliocentric system.[2] His 17th-century successors, Galileo Galilei, Johannes Kepler and Isaac Newton, developed an understanding of physics that led to the gradual acceptance of the idea that the Earth moves around the Sun and that the planets are governed by the same physical laws that governed the Earth. Additionally, the invention of the telescope led to the discovery of further planets and moons. In more recent times, improvements in the telescope and the use of unmanned spacecraft have enabled the investigation of geological phenomena such as mountains and craters, and seasonal meteorological phenomena such as clouds, dust storms and ice caps on the other planets.

Structure

The principal component of the Solar System is the Sun, a G2 main-sequence star that contains 99.86 percent of the system's known mass and dominates it gravitationally.[3] The Sun's four largest orbiting bodies, the gas giants, account for 99 percent of the remaining mass, with Jupiter and Saturn together comprising more than 90 percent.Template:Ref label

Most large objects in orbit around the Sun lie near the plane of Earth's orbit, known as the ecliptic. The planets are very close to the ecliptic while comets and Kuiper belt objects are frequently at significantly greater angles to it.[4][5] All the planets and most other objects orbit the Sun in the same direction that the Sun is rotating (counter-clockwise, as viewed from above the Sun's north pole).[6] There are exceptions, such as Halley's Comet.

The overall structure of the charted regions of the Solar System consists of the Sun, four relatively small inner planets surrounded by a belt of rocky asteroids, and four gas giants surrounded by the Kuiper belt of icy objects. Astronomers sometimes informally divide this structure into separate regions. The inner Solar System includes the four terrestrial planets and the asteroid belt. The outer Solar System is beyond the asteroids, including the four gas giants.[7] Since the discovery of the Kuiper belt, the outermost parts of the Solar System are considered a distinct region consisting of the objects beyond Neptune.[8]

Most of the planets in the Solar System possess secondary systems of their own, being orbited by planetary objects called natural satellites, or moons (two of which are larger than the planet Mercury), or, in the case of the four gas giants, by planetary rings; thin bands of tiny particles that orbit them in unison. Most of the largest natural satellites are in synchronous rotation, with one face permanently turned toward their parent.

Kepler's laws of planetary motion describe the orbits of objects about the Sun. Following Kepler's laws, each object travels along an ellipse with the Sun at one focus. Objects closer to the Sun (with smaller semi-major axes) travel more quickly, as they are more affected by the Sun's gravity. On an elliptical orbit, a body's distance from the Sun varies over the course of its year. A body's closest approach to the Sun is called its perihelion, while its most distant point from the Sun is called its aphelion. The orbits of the planets are nearly circular, but many comets, asteroids and Kuiper belt objects follow highly elliptical orbits. The positions of the bodies in the Solar System can be predicted using numerical models.

Due to the vast distances involved, many representations of the Solar System show orbits the same distance apart. In reality, with a few exceptions, the farther a planet or belt is from the Sun, the larger the distance between it and the previous orbit. For example, Venus is approximately 0.33 astronomical units (AU)Template:Ref label farther out from the Sun than Mercury, while Saturn is 4.3 AU out from Jupiter, and Neptune lies 10.5 AU out from Uranus. Attempts have been made to determine a relationship between these orbital distances (for example, the Titius–Bode law),[9] but no such theory has been accepted.

A number of Solar System models on Earth attempt to convey the relative scales involved in the Solar System on human terms. Some models are mechanical — called orreries — while others extend across cities or regional areas.[10] The largest such scale model, the Sweden Solar System, uses the 110-metre Ericsson Globe in Stockholm as its substitute Sun, and, following the scale, Jupiter is a 7.5 metre sphere at Arlanda International Airport, 40 km away, while the farthest current object, Sedna, is a 10-cm sphere in Luleå, 912 km away.[11][12]

Range of selected bodies of the Solar System from the middle of the Sun. The left and right edges of each bar correspond to the perihelion and aphelion of the body, respectively. Long bars denote high orbital eccentricity.

Composition

The Sun, which comprises nearly all the matter in the Solar System, is composed of roughly 98% hydrogen and helium.[13] Jupiter and Saturn, which comprise nearly all the remaining matter, possess atmospheres composed of roughly 99% of those same elements.[14][15] A composition gradient exists in the Solar System, created by heat and light pressure from the Sun; those objects closer to the Sun, which are more affected by heat and light pressure, are composed of elements with high melting points. Objects farther from the Sun are composed largely of materials with lower melting points.[16] The boundary in the Solar System beyond which those volatile substances could condense is known as the frost line, and it lies at roughly 4 AU from the Sun.[17]

The objects of the inner Solar System are composed mostly of rock, the collective name for compounds with high melting points, such as silicates, iron or nickel, that remained solid under almost all conditions in the protoplanetary nebula. Jupiter and Saturn are composed mainly of gases, the astronomical term for materials with extremely low melting points and high vapor pressure such as molecular hydrogen, helium, and neon, which were always in the gaseous phase in the nebula. Ices, like water, methane, ammonia, hydrogen sulfide and carbon dioxide, They can be found as ices, liquids, or gases in various places in the Solar System, while in the nebula they were either in the solid or gaseous phase. Icy substances comprise the majority of the satellites of the giant planets, as well as most of Uranus and Neptune (the so-called "ice giants") and the numerous small objects that lie beyond Neptune's orbit. Together, gases and ices are referred to as volatiles.[18]

Sun

Main article: Sun

The Sun is the Solar System's star, and by far its chief component. Its large mass (332,900 Earth masses)[19] produces temperatures and densities in its core great enough to sustain nuclear fusion,[20] which releases enormous amounts of energy, mostly radiated into space as electromagnetic radiation, peaking in the 400–700 nm band of visible light.[21]

The Sun is classified as a type G2 yellow dwarf, but this name is misleading as, compared to the majority of stars in our galaxy, the Sun is rather large and bright.[22] Stars are classified by the Hertzsprung–Russell diagram, a graph that plots the brightness of stars with their surface temperatures. Generally, hotter stars are brighter. Stars following this pattern are said to be on the main sequence, and the Sun lies right in the middle of it. However, stars brighter and hotter than the Sun are rare, while substantially dimmer and cooler stars, known as red dwarfs, are common, making up 85 percent of the stars in the galaxy.[22][23]

Evidence suggests that the Sun's position on the main sequence puts it in the "prime of life" for a star, in that it has not yet exhausted its store of hydrogen for nuclear fusion. The Sun is growing brighter; early in its history it was 70 percent as bright as it is today.[24]

The Sun is a population I star; it was born in the later stages of the universe's evolution, and thus contains more elements heavier than hydrogen and helium ("metals" in astronomical parlance) than older population II stars.[25] Elements heavier than hydrogen and helium were formed in the cores of ancient and exploding stars, so the first generation of stars had to die before the universe could be enriched with these atoms. The oldest stars contain few metals, while stars born later have more. This high metallicity is thought to have been crucial to the Sun's developing a planetary system, because planets form from accretion of "metals".[26]

Interplanetary medium

Along with light, the Sun radiates a continuous stream of charged particles (a plasma) known as the solar wind. This stream of particles spreads outwards at roughly 1.5 million kilometres per hour,[27] creating a tenuous atmosphere (the heliosphere) that permeates the Solar System out to at least 100 AU (see heliopause).[28] This is known as the interplanetary medium. Activity on the Sun's surface, such as solar flares and coronal mass ejections, disturb the heliosphere, creating space weather and causing geomagnetic storms.[29] The largest structure within the heliosphere is the heliospheric current sheet, a spiral form created by the actions of the Sun's rotating magnetic field on the interplanetary medium.[30][31]

Earth's magnetic field stops its atmosphere from being stripped away by the solar wind. Venus and Mars do not have magnetic fields, and as a result, the solar wind causes their atmospheres to gradually bleed away into space.[32] Coronal mass ejections and similar events blow a magnetic field and huge quantities of material from the surface of the Sun. The interaction of this magnetic field and material with Earth's magnetic field funnels charged particles into the Earth's upper atmosphere, where its interactions create aurorae seen near the magnetic poles.

Cosmic rays originate outside the Solar System. The heliosphere partially shields the Solar System, and planetary magnetic fields (for those planets that have them) also provide some protection. The density of cosmic rays in the interstellar medium and the strength of the Sun's magnetic field change on very long timescales, so the level of cosmic radiation in the Solar System varies, though by how much is unknown.[33]

The interplanetary medium is home to at least two disc-like regions of cosmic dust. The first, the zodiacal dust cloud, lies in the inner Solar System and causes zodiacal light. It was likely formed by collisions within the asteroid belt brought on by interactions with the planets.[34] The second extends from about 10 AU to about 40 AU, and was probably created by similar collisions within the Kuiper belt.[35][36]

Inner Solar System

The inner Solar System is the traditional name for the region comprising the terrestrial planets and asteroids.[37] Composed mainly of silicates and metals, the objects of the inner Solar System are relatively close to the Sun; the radius of this entire region is shorter than the distance between Jupiter and Saturn.

Inner planets

Main article: Terrestrial planet

The four inner or terrestrial planets have dense, rocky compositions, few or no moons, and no ring systems. They are composed largely of refractory minerals, such as the silicates, which form their crusts and mantles, and metals such as iron and nickel, which form their cores. Three of the four inner planets (Venus, Earth and Mars) have atmospheres substantial enough to generate weather; all have impact craters and tectonic surface features such as rift valleys and volcanoes. The term inner planet should not be confused with inferior planet, which designates those planets that are closer to the Sun than Earth is (i.e. Mercury and Venus).

Mercury

Mercury (0.4 AU from the Sun) is the closest planet to the Sun and the smallest planet in the Solar System (0.055 Earth masses). Mercury has no natural satellites, and its only known geological features besides impact craters are lobed ridges or rupes, probably produced by a period of contraction early in its history.[38] Mercury's almost negligible atmosphere consists of atoms blasted off its surface by the solar wind.[39] Its relatively large iron core and thin mantle have not yet been adequately explained. Hypotheses include that its outer layers were stripped off by a giant impact, and that it was prevented from fully accreting by the young Sun's energy.[40][41]

Venus

Venus (0.7 AU from the Sun) is close in size to Earth (0.815 Earth masses), and, like Earth, has a thick silicate mantle around an iron core, a substantial atmosphere and evidence of internal geological activity. However, it is much drier than Earth and its atmosphere is ninety times as dense. Venus has no natural satellites. It is the hottest planet, with surface temperatures over 400 °C, most likely due to the amount of greenhouse gases in the atmosphere.[42] No definitive evidence of current geological activity has been detected on Venus, but it has no magnetic field that would prevent depletion of its substantial atmosphere, which suggests that its atmosphere is regularly replenished by volcanic eruptions.[43]

Earth

Earth (1 AU from the Sun) is the largest and densest of the inner planets, the only one known to have current geological activity, and is the only place in the Solar System where life is known to exist.[44] Its liquid hydrosphere is unique among the terrestrial planets, and it is also the only planet where plate tectonics has been observed. Earth's atmosphere is radically different from those of the other planets, having been altered by the presence of life to contain 21% free oxygen.[45] It has one natural satellite, the Moon, the only large satellite of a terrestrial planet in the Solar System.

Mars

Mars (1.5 AU from the Sun) is smaller than Earth and Venus (0.107 Earth masses). It possesses an atmosphere of mostly carbon dioxide with a surface pressure of 6.1 millibars (roughly 0.6 percent that of the Earth's).[46] Its surface, peppered with vast volcanoes such as Olympus Mons and rift valleys such as Valles Marineris, shows geological activity that may have persisted until as recently as 2 million years ago.[47] Its red colour comes from iron oxide (rust) in its soil.[48] Mars has two tiny natural satellites (Deimos and Phobos) thought to be captured asteroids.[49]

Asteroid belt

Main article: Asteroid belt

Asteroids are small Solar System bodiesTemplate:Ref label composed mainly of refractory rocky and metallic minerals, with some ice.[50]

The asteroid belt occupies the orbit between Mars and Jupiter, between 2.3 and 3.3 AU from the Sun. It is thought to be remnants from the Solar System's formation that failed to coalesce because of the gravitational interference of Jupiter.[51]

Asteroids range in size from hundreds of kilometres across to microscopic. All asteroids except the largest, Ceres, are classified as small Solar System bodies, but some asteroids such as Vesta and Hygiea may be reclassed as dwarf planets if they are shown to have achieved hydrostatic equilibrium.[52]

The asteroid belt contains tens of thousands, possibly millions, of objects over one kilometre in diameter.[53] Despite this, the total mass of the asteroid belt is unlikely to be more than a thousandth of that of the Earth.[54] The asteroid belt is very sparsely populated; spacecraft routinely pass through without incident. Asteroids with diameters between 10 and 10−4 m are called meteoroids.[55]

Ceres

Ceres (2.77 AU) is the largest asteroid, a protoplanet, and a dwarf planet.Template:Ref label It has a diameter of slightly under 1000 km, and a mass large enough for its own gravity to pull it into a spherical shape. Ceres was considered a planet when it was discovered in the 19th century, but was reclassified as an asteroid in the 1850s as further observations revealed additional asteroids.[56] It was classified in 2006 as a dwarf planet.

Asteroid groups

Asteroids in the asteroid belt are divided into asteroid groups and families based on their orbital characteristics. Asteroid moons are asteroids that orbit larger asteroids. They are not as clearly distinguished as planetary moons, sometimes being almost as large as their partners. The asteroid belt also contains main-belt comets, which may have been the source of Earth's water.[57]

Trojan asteroids are located in either of Jupiter's L4 or L5 points (gravitationally stable regions leading and trailing a planet in its orbit); the term "Trojan" is also used for small bodies in any other planetary or satellite Lagrange point. Hilda asteroids are in a 2:3 resonance with Jupiter; that is, they go around the Sun three times for every two Jupiter orbits.[58]

The inner Solar System is also dusted with rogue asteroids, many of which cross the orbits of the inner planets.[59]

Outer Solar System

The outer region of the Solar System is home to the gas giants and their large moons. Many short-period comets, including the centaurs, also orbit in this region. Due to their greater distance from the Sun, the solid objects in the outer Solar System contain a higher proportion of volatiles such as water, ammonia and methane, than the rocky denizens of the inner Solar System, as the colder temperatures allow these compounds to remain solid.

Outer planets

The four outer planets, or gas giants (sometimes called Jovian planets), collectively make up 99 percent of the mass known to orbit the Sun.Template:Ref label Jupiter and Saturn are each many tens of times the mass of the Earth and consist overwhelmingly of hydrogen and helium; Uranus and Neptune are far less massive (<20 Earth masses) and possess more ices in their makeup. For these reasons, some astronomers suggest they belong in their own category, "ice giants".[60] All four gas giants have rings, although only Saturn's ring system is easily observed from Earth. The term outer planet should not be confused with superior planet, which designates planets outside Earth's orbit and thus includes both the outer planets and Mars.

Jupiter

Jupiter (5.2 AU), at 318 Earth masses, is 2.5 times the mass of all the other planets put together. It is composed largely of hydrogen and helium. Jupiter's strong internal heat creates a number of semi-permanent features in its atmosphere, such as cloud bands and the Great Red Spot.
Jupiter has 66 known satellites. The four largest, Ganymede, Callisto, Io, and Europa, show similarities to the terrestrial planets, such as volcanism and internal heating.[61] Ganymede, the largest satellite in the Solar System, is larger than Mercury.

Saturn

Saturn (9.5 AU), distinguished by its extensive ring system, has several similarities to Jupiter, such as its atmospheric composition and magnetosphere. Although Saturn has 60% of Jupiter's volume, it is less than a third as massive, at 95 Earth masses, making it the least dense planet in the Solar System. The rings of Saturn are made up of small ice and rock particles.
Saturn has 62 confirmed satellites; two of which, Titan and Enceladus, show signs of geological activity, though they are largely made of ice.[62] Titan, the second-largest moon in the Solar System, is larger than Mercury and the only satellite in the Solar System with a substantial atmosphere.

Uranus

Uranus (19.6 AU), at 14 Earth masses, is the lightest of the outer planets. Uniquely among the planets, it orbits the Sun on its side; its axial tilt is over ninety degrees to the ecliptic. It has a much colder core than the other gas giants, and radiates very little heat into space.[63]
Uranus has 27 known satellites, the largest ones being Titania, Oberon, Umbriel, Ariel and Miranda.

Neptune

Neptune (30 AU), though slightly smaller than Uranus, is more massive (equivalent to 17 Earths) and therefore more dense. It radiates more internal heat, but not as much as Jupiter or Saturn.[64]
Neptune has 13 known satellites. The largest, Triton, is geologically active, with geysers of liquid nitrogen.[65] Triton is the only large satellite with a retrograde orbit. Neptune is accompanied in its orbit by a number of minor planets, termed Neptune trojans, that are in 1:1 resonance with it.

Comets

Main article: Comet

Comets are small Solar System bodies,Template:Ref label typically only a few kilometres across, composed largely of volatile ices. They have highly eccentric orbits, generally a perihelion within the orbits of the inner planets and an aphelion far beyond Pluto. When a comet enters the inner Solar System, its proximity to the Sun causes its icy surface to sublimate and ionise, creating a coma: a long tail of gas and dust often visible to the naked eye.

Short-period comets have orbits lasting less than two hundred years. Long-period comets have orbits lasting thousands of years. Short-period comets are believed to originate in the Kuiper belt, while long-period comets, such as Hale–Bopp, are believed to originate in the Oort cloud. Many comet groups, such as the Kreutz Sungrazers, formed from the breakup of a single parent.[66] Some comets with hyperbolic orbits may originate outside the Solar System, but determining their precise orbits is difficult.[67] Old comets that have had most of their volatiles driven out by solar warming are often categorised as asteroids.[68]

Centaurs

The centaurs are icy comet-like bodies with a semi-major axis greater than Jupiter's (5.5 AU) and less than Neptune's (30 AU). The largest known centaur, 10199 Chariklo, has a diameter of about 250 km.[69] The first centaur discovered, 2060 Chiron, has also been classified as comet (95P) since it develops a coma just as comets do when they approach the Sun.[70]

Trans-Neptunian region

The area beyond Neptune, or the "trans-Neptunian region", is still largely unexplored. It appears to consist overwhelmingly of small worlds (the largest having a diameter only a fifth that of the Earth and a mass far smaller than that of the Moon) composed mainly of rock and ice. This region is sometimes known as the "outer Solar System", though others use that term to mean the region beyond the asteroid belt.

Kuiper belt

Main article: Kuiper belt

The Kuiper belt, the region's first formation, is a great ring of debris similar to the asteroid belt, but composed mainly of ice.[71] It extends between 30 and 50 AU from the Sun. Though it contains at least three dwarf planets, it is composed mainly of small Solar System bodies. Many of the largest Kuiper belt objects, such as Quaoar, Varuna, and Orcus, may be reclassified as dwarf planets. There are estimated to be over 100,000 Kuiper belt objects with a diameter greater than 50 km, but the total mass of the Kuiper belt is thought to be only a tenth or even a hundredth the mass of the Earth.[72] Many Kuiper belt objects have multiple satellites, and most have orbits that take them outside the plane of the ecliptic.[73]

The Kuiper belt can be roughly divided into the "classical" belt and the resonances.[71] Resonances are orbits linked to that of Neptune (e.g. twice for every three Neptune orbits, or once for every two). The first resonance begins within the orbit of Neptune itself. The classical belt consists of objects having no resonance with Neptune, and extends from roughly 39.4 AU to 47.7 AU.[74] Members of the classical Kuiper belt are classified as cubewanos, after the first of their kind to be discovered, Template:Mpl, and are still in near primordial, low-eccentricity orbits.[75]

Pluto and Charon

Template:TNO imagemap Pluto (39 AU average), a dwarf planet, is the largest known object in the Kuiper belt. When discovered in 1930, it was considered to be the ninth planet; this changed in 2006 with the adoption of a formal definition of planet. Pluto has a relatively eccentric orbit inclined 17 degrees to the ecliptic plane and ranging from 29.7 AU from the Sun at perihelion (within the orbit of Neptune) to 49.5 AU at aphelion.

Charon, Pluto's largest moon, is sometimes described as part of a binary system with Pluto, as the two bodies orbit a barycenter of gravity above their surfaces (i.e., they appear to "orbit each other"). Beyond Charon, more than two much smaller moons like Nix and Hydra are known to orbit within the system.

Pluto has a 3:2 resonance with Neptune, meaning that Pluto orbits twice round the Sun for every three Neptunian orbits. Kuiper belt objects whose orbits share this resonance are called plutinos.[76]

Haumea and Makemake

Makemake (45.79 AU average), while smaller than Pluto, is the largest known object in the classical Kuiper belt (that is, it is not in a confirmed resonance with Neptune). Makemake is the brightest object in the Kuiper belt after Pluto. It was named and designated a dwarf planet in 2008.[77] Its orbit is far more inclined than Pluto's, at 29°.[78]

Scattered disc

Main article: Scattered disc

The scattered disc, which overlaps the Kuiper belt but extends much further outwards, is thought to be the source of short-period comets. Scattered disc objects are believed to have been ejected into erratic orbits by the gravitational influence of Neptune's early outward migration. Most scattered disc objects (SDOs) have perihelia within the Kuiper belt but aphelia as far as 150 AU from the Sun. SDOs' orbits are also highly inclined to the ecliptic plane, and are often almost perpendicular to it. Some astronomers consider the scattered disc to be merely another region of the Kuiper belt, and describe scattered disc objects as "scattered Kuiper belt objects."[79] Some astronomers also classify centaurs as inward-scattered Kuiper belt objects along with the outward-scattered residents of the scattered disc.[80]

Eris

Eris (68 AU average) is the largest known scattered disc object, and caused a debate about what constitutes a planet, since it is 25% more massive than Pluto and about the same diameter. It is the most massive of the known dwarf planets. It has one moon, Dysnomia. Like Pluto, its orbit is highly eccentric, with a perihelion of 38.2 AU (roughly Pluto's distance from the Sun) and an aphelion of 97.6 AU, and steeply inclined to the ecliptic plane.

Farthest regions

The point at which the Solar System ends and interstellar space begins is not precisely defined, since its outer boundaries are shaped by two separate forces: the solar wind and the Sun's gravity. The outer limit of the solar wind's influence is roughly four times Pluto's distance from the Sun; this heliopause is considered the beginning of the interstellar medium.[28] However, the Sun's Hill sphere, the effective range of its gravitational dominance, is believed to extend up to a thousand times farther.[81]

Heliopause

The heliosphere is divided into two separate regions. The solar wind travels at roughly 400 km/s until it collides with the interstellar wind; the flow of plasma in the interstellar medium. The collision occurs at the termination shock, which is roughly 80–100 AU from the Sun upwind of the interstellar medium and roughly 200 AU from the Sun downwind.[82] Here the wind slows dramatically, condenses and becomes more turbulent,[82] forming a great oval structure known as the heliosheath. This structure is believed to look and behave very much like a comet's tail, extending outward for a further 40 AU on the upwind side but tailing many times that distance downwind; but evidence from the Cassini and Interstellar Boundary Explorer spacecraft has suggested that it is in fact forced into a bubble shape by the constraining action of the interstellar magnetic field.[83] Both Voyager 1 and Voyager 2 are reported to have passed the termination shock and entered the heliosheath, at 94 and 84 AU from the Sun, respectively.[84][85] The outer boundary of the heliosphere, the heliopause, is the point at which the solar wind finally terminates and is the beginning of interstellar space.[28]

The shape and form of the outer edge of the heliosphere is likely affected by the fluid dynamics of interactions with the interstellar medium[82] as well as solar magnetic fields prevailing to the south, e.g. it is bluntly shaped with the northern hemisphere extending 9 AU farther than the southern hemisphere. Beyond the heliopause, at around 230 AU, lies the bow shock, a plasma "wake" left by the Sun as it travels through the Milky Way.[86]

No spacecraft have yet passed beyond the heliopause, so it is impossible to know for certain the conditions in local interstellar space. It is expected that NASA's Voyager spacecraft will pass the heliopause some time in the next decade and transmit valuable data on radiation levels and solar wind back to the Earth.[87] How well the heliosphere shields the Solar System from cosmic rays is poorly understood. A NASA-funded team has developed a concept of a "Vision Mission" dedicated to sending a probe to the heliosphere.[88][89]

Oort cloud

Main article: Oort cloud

The hypothetical Oort cloud is a spherical cloud of up to a trillion icy objects that is believed to be the source for all long-period comets and to surround the Solar System at roughly 50,000 AU (around 1 light-year (ly)), and possibly to as far as 100,000 AU (1.87 ly). It is believed to be composed of comets that were ejected from the inner Solar System by gravitational interactions with the outer planets. Oort cloud objects move very slowly, and can be perturbed by infrequent events such as collisions, the gravitational effects of a passing star, or the galactic tide, the tidal force exerted by the Milky Way.[90][91]

Sedna

90377 Sedna (525.86 AU average) is a large, reddish object with a gigantic, highly elliptical orbit that takes it from about 76 AU at perihelion to 928 AU at aphelion and takes 12,050 years to complete. Mike Brown, who discovered the object in 2003, asserts that it cannot be part of the scattered disc or the Kuiper belt as its perihelion is too distant to have been affected by Neptune's migration. He and other astronomers consider it to be the first in an entirely new population, which also may include the object Template:Mpl-, which has a perihelion of 45 AU, an aphelion of 415 AU, and an orbital period of 3,420 years.[92] Brown terms this population the "inner Oort cloud", as it may have formed through a similar process, although it is far closer to the Sun.[93] Sedna is very likely a dwarf planet, though its shape has yet to be determined with certainty.

Boundaries

Much of the Solar System is still unknown. The Sun's gravitational field is estimated to dominate the gravitational forces of surrounding stars out to about two light years (125,000 AU). Lower estimates for the radius of the Oort cloud, by contrast, do not place it farther than 50,000 AU.[94] Despite discoveries such as Sedna, the region between the Kuiper belt and the Oort cloud, an area tens of thousands of AU in radius, is still virtually unmapped. There are also ongoing studies of the region between Mercury and the Sun.[95] Objects may yet be discovered in the Solar System's uncharted regions.

Galactic context

The Solar System is located in the Milky Way galaxy, a barred spiral galaxy with a diameter of about 100,000 light-years containing about 200 billion stars. The Sun resides in one of the Milky Way's outer spiral arms, known as the Orion–Cygnus Arm or Local Spur.[96] The Sun lies between 25,000 and 28,000 light years from the Galactic Centre,[97] and its speed within the galaxy is about 220 kilometres per second, so that it completes one revolution every 225–250 million years. This revolution is known as the Solar System's galactic year.[98] The solar apex, the direction of the Sun's path through interstellar space, is near the constellation of Hercules in the direction of the current location of the bright star Vega.[99] The plane of the ecliptic lies at an angle of about 60° to the galactic plane.Template:Ref label

The Solar System's location in the galaxy is a factor in the evolution of life on Earth. Its orbit is close to circular, and orbits near the Sun are at roughly the same speed as that of the spiral arms. Therefore, the Sun passes through arms only rarely. Since spiral arms are home to a far larger concentration of supernovae, gravitational instabilities, and radiation which could disrupt the Solar System, this has given Earth long periods of stability for life to evolve.[100] The Solar System also lies well outside the star-crowded environs of the galactic centre. Near the centre, gravitational tugs from nearby stars could perturb bodies in the Oort Cloud and send many comets into the inner Solar System, producing collisions with potentially catastrophic implications for life on Earth. The intense radiation of the galactic centre could also interfere with the development of complex life.[100] Even at the Solar System's current location, some scientists have hypothesised that recent supernovae may have adversely affected life in the last 35,000 years by flinging pieces of expelled stellar core towards the Sun as radioactive dust grains and larger, comet-like bodies.[101]

Neighbourhood

The immediate galactic neighbourhood of the Solar System is known as the Local Interstellar Cloud or Local Fluff, an area of denser cloud in an otherwise sparse region known as the Local Bubble, an hourglass-shaped cavity in the interstellar medium roughly 300 light years across. The bubble is suffused with high-temperature plasma that suggests it is the product of several recent supernovae.[102]

There are relatively few stars within ten light years (95 trillion km) of the Sun. The closest is the triple star system Alpha Centauri, which is about 4.4 light years away. Alpha Centauri A and B are a closely tied pair of Sun-like stars, while the small red dwarf Alpha Centauri C (also known as Proxima Centauri) orbits the pair at a distance of 0.2 light years. The stars next closest to the Sun are the red dwarfs Barnard's Star (at 5.9 light years), Wolf 359 (7.8 light years) and Lalande 21185 (8.3 light years). The largest star within ten light years is Sirius, a bright main-sequence star roughly twice the Sun's mass and orbited by a white dwarf called Sirius B. It lies 8.6 light years away. The remaining systems within ten light years are the binary red dwarf system Luyten 726-8 (8.7 light years) and the solitary red dwarf Ross 154 (9.7 light years).[103] The Solar System's closest solitary sun-like star is Tau Ceti, which lies 11.9 light years away. It has roughly 80 percent the Sun's mass, but only 60 percent of its luminosity.[104] The closest known extrasolar planet to the Sun lies around the star Epsilon Eridani, a star slightly dimmer and redder than the Sun, which lies 10.5 light years away. Its one confirmed planet, Epsilon Eridani b, is roughly 1.5 times Jupiter's mass and orbits its star every 6.9 years.[105]

A diagram of our location in the observable Universe. (Click here for an alternate image.)

Formation and evolution

The Solar System formed from the gravitational collapse of a giant molecular cloud 4.568 billion years ago.[106] This initial cloud was likely several light-years across and probably birthed several stars.[107] As the region that would become the Solar System, known as the pre-solar nebula,[108] collapsed, conservation of angular momentum made it rotate faster. The centre, where most of the mass collected, became increasingly hotter than the surrounding disc.[107] As the contracting nebula rotated, it began to flatten into a spinning protoplanetary disc with a diameter of roughly 200 AU[107] and a hot, dense protostar at the centre.[109][110] The planets formed by accretion from this disk.[111]

Within 50 million years, the pressure and density of hydrogen in the centre of the protostar became great enough for it to begin thermonuclear fusion.[112] The temperature, reaction rate, pressure, and density increased until hydrostatic equilibrium was achieved: the thermal pressure equaled the force of gravity. At this point the Sun became a main-sequence star.[113]

The Nice model explains many otherwise puzzling features of the history and structure of the Solar System. In this model, the four giant planets (Jupiter, Saturn, Uranus and Neptune) originally formed in orbits between ~5.5 and ~17 astronomical units (AU) from the Sun, (inside the current orbit of Uranus). A disk of planetesimals, of ~35 Earth masses, extended beyond this to ~35 AU. Gravitational interactions between these planets and the planetismal disc caused changes to the planets' orbits. Over a period of several hundred million years, Saturn, Uranus and Neptune migrated outwards, Neptune passing Uranus, while Jupiter migrated a small distance inwards.

The Solar System will remain roughly as we know it today until the hydrogen in the core of the Sun has been entirely converted to helium, which will occur roughly 5.4 billion years from now. This will mark the end of the Sun's main-sequence life. At this time, the core of the Sun will collapse, and the energy output will be much greater than at present. The outer layers of the Sun will expand to roughly up to 260 times its current diameter; the Sun will become a red giant. Because of its vastly increased surface area, the surface of the Sun will be considerably cooler than it is on the main sequence (2600 K at the coolest).[114] Eventually, the core will be hot enough for helium fusion to begin in the core; the Sun will burn helium for a fraction of the time it burned hydrogen in the core. The Sun is not massive enough to commence fusion of heavier elements, and nuclear reactions in the core will dwindle. Its outer layers will fall away into space, leaving a white dwarf, an extraordinarily dense object, half the original mass of the Sun but only the size of the Earth.[115] The ejected outer layers will form what is known as a planetary nebula, returning some of the material that formed the Sun—but now enriched with heavier elements like carbon—to the interstellar medium.

Visual summary

A sampling of closely imaged Solar System bodies, selected for size and detail and sorted by volume. The Sun is approximately 10,000 times larger than, and 41 trillion times the volume of, the smallest object shown. Other lists include: List of Solar System objects by size, List of natural satellites, List of minor planets, and Lists of comets.

 Sun Jupiter Saturn Uranus Neptune Earth Venus Mars Ganymede Titan Mercury Callisto Io Moon Europa Triton Eris Pluto Titania Rhea Oberon Iapetus Charon Umbriel Ariel Dione Tethys 1 Ceres 4 Vesta Enceladus Miranda Proteus Mimas Hyperion Phoebe 253 Mathilde 243 Ida Phobos Deimos 951 Gaspra Ranging order by size. (Data table: Wikipedia)

Notes

1. Template:Note labelCapitalization of the name varies. The IAU, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects (Solar System). However, the name is commonly rendered in lower case (solar system) – as, for example, in the Oxford English Dictionary and Merriam-Webster's 11th Collegiate Dictionary
2. Template:Note labelSee List of natural satellites for the full list of natural satellites of the eight planets and five dwarf planets.
3. Template:Note labelThe mass of the Solar System excluding the Sun, Jupiter and Saturn can be determined by adding together all the calculated masses for its largest objects and using rough calculations for the masses of the Oort cloud (estimated at roughly 3 Earth masses), the Kuiper belt (estimated at roughly 0.1 Earth mass)[72] and the asteroid belt (estimated to be 0.0005 Earth mass)[54] for a total, rounded upwards, of ~37 Earth masses, or 8.1 percent the mass in orbit around the Sun. With the combined masses of Uranus and Neptune (~31 Earth masses) subtracted, the remaining ~6 Earth masses of material comprise 1.3 percent of the total.
4. Template:Note labelAstronomers measure distances within the Solar System in astronomical units (AU). One AU equals the average distance between the centers of Earth and the Sun, or 149,598,000 km. Pluto is about 38 AU from the Sun and Jupiter is about 5.2 AU from the Sun. One light-year is 63,240 AU.
5. Template:Note labelAccording to current definitions, objects in orbit around the Sun are classed dynamically and physically into three categories: planets, dwarf planets and small Solar System bodies. A planet is any body in orbit around the Sun that has enough mass to form itself into a spherical shape and has cleared its immediate neighbourhood of all smaller objects. By this definition, the Solar System has eight known planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Pluto does not fit this definition, as it has not cleared its orbit of surrounding Kuiper belt objects.[116] A dwarf planet is a celestial body orbiting the Sun that is massive enough to be rounded by its own gravity but has not cleared its neighbouring region of planetesimals and is not a satellite.[116] By this definition, the Solar System has five known dwarf planets: Ceres, Pluto, Haumea, Makemake, and Eris.[77] Other objects may be classified in the future as dwarf planets, such as Sedna, Orcus, and Quaoar.[117] Dwarf planets that orbit in the trans-Neptunian region are called "plutoids".[118] The remainder of the objects in orbit around the Sun are small Solar System bodies.[116]
6. Template:Note labelIf ψ is the angle between the north pole of the ecliptic and the north galactic pole then:
$\cos\psi=\cos(\beta_g)\cos(\beta_e)\cos(\alpha_g-\alpha_e)+\sin(\beta_g)\sin(\beta_e)$,where $\beta_g=$27° 07′ 42.01″ and $\alpha_g=$12h 51m 26.282 are the declination and right ascension of the north galactic pole,[119] while $\beta_e=$66° 33′ 38.6″ and $\alpha_e=$18h 0m 00 are those for the north pole of the ecliptic. (Both pairs of coordinates are for J2000 epoch.) The result of the calculation is 60.19°.

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Formation of the Solar System

[[The origin of our Solar System is not fully understood, but meteorites have revealed the date of it birth. Because meteorites contains the oldest rocks in the Solar System, careful analysis of them tells us that they have formed about 4.6 thousand million years ago. Most astronomers that the Sun and the Solar System were born when a huge cloud of gas and dust collapsed under the pull of its own gravity. While no one knows for certain how the collapse began, it has been suggested that a nearby supernova explosion was the cause. How it formed? Billions of years ago, perhaps as a result of a supernova explosion, a large cloud of gas and dust began to fall together. The central part became the Sun and the remainder settled into a spinning disc. Rocky particles formed in the hotter inner parts of the disc, and rocky and icy particles formed in its cooler outer zones. The inner planets, including the Earth formed from rocky particles and the giant planets also pulled in a lot of gas.

Possible way of formation: 1)Supernova Shock Wave A supernova explosion sent a shock wave hurtling through space. When the shock reached a gas cloud, it squeezed the cloud, which then started to colapse.

2)The Solar Nebula As the cloud collapsed, it began to spin, and formed a swirling disc of gas and dust called the solar nebula. The center of the solar nebula grew hotter and denser than the surrounding disc, which was hot near the centre but cool at the edge.

3)Building the planets Small particles began to stick together to from larger clumps, which grew eventually to kilometres across in size. Collisions between these bodies built up the terrestrial planets and the cores of the giant planets.

4)The nebula disperses As the young Sun became hotter and brighter it blew away the remaining gas and dust. It also blew away the original atmospheres that had formed around terrestrial planets. Farther from the Sun, the giant planets were able to hold on to deep envelops of gas.

5)The Solar System today The Solar System is now 4.6 thousand million years old. The Sun is a middle-aged star, and the planets have their familiar features.

As the centre of the cloud continued to shrink it becomes globe-shaped and it got heated up. Eventually it became so hot that it started to shine as a star, now known as the Sun. Within the rest of the cloud, over a period of about 100 million years, more and more particles gradually stuck together until the planets and their moons were formed. The giant planets, which formed in the outer part of the cloud, contained icy materials as well as rocky materials. Uranus and Neptune, especially, contained a lot of ice. Each of the giants attracted huge envelopes of gas. Jupiter and Saturn ended up with deep oceans of liquid hydrogen and helium around their cores.

During the formation of the planets and their moons, many rocky bits were left over. Thousands of them, the asteroids, circle the Sun between the orbits of Mars and Jupiter. Many other bits of rock, ice and dust drift far beyond the planets at the very edge of the Solar System, these pieces form comets. Comets probably contain origianl icy and dusty materials that dates back to the birth of the Solar System.

Our Solar System

The Solar System is like a small oasis in space. At its centre is the Sun, whose gravitational pull keeps the planets in their orbits. These orbits, except for that of Pluto, lie in nearly the same plane; so if you were to make a model of the Solar System, all the planetary orbits would be contained within the thickness of a disc like phonograph record. All the planets orbit the Sun in the same direction; looked at from a position above the Solar System, they move counter-clockwise. The speed at which each planet travels depends on its distance from the Sun, those closer moving faster than those farther out. Thus Mercury, the planet closest to the Sun, moves at a speed of 47.87 km/sec (29.75 mls/sec), whereas Pluto, the outermost of the planets, travels at only 4.74 km/sec (2.95mls/sec). So while Mercury takes only 88 Earth days to complete one orbit of the Sun, Pluto takes 248.5 Earth years - more than a thousand times longer.

Another feature common to all the planets is that they rotate about their axes as they orbit the Sun. One complete axial rotation is a day, but this period is highly variable. On Venus, for example, axial rotation takes approximately 243 Earth days, while on Jupiter a complete rotation takes a little less than ten hours. Also varying is the degree of axial inclination of the planets. For example, the Earth's polar axis is inclined at an angle of 23*27' to the vertical (the vertical being measured with respect to the plane of the Earth's orbit). For Venus, however, the axis is inclined at 178*C while the axial inclination of Jupiter is a mere 3*05'.

As well as these larger, named plantes, none of which has a diameter smaller than one-quarter of the Earth's, the Solar System contains a host of other bodies. Concentrated mainly between Mars and Jupiter, there are tens of thousands of asteroids that orbit the Sun, the largest of which is Ceres, with a diameter of 974 km (605mls).

Also in the Solar System are meteors and comets. Comets have elongated elliptical orbits which lie at quite wide angles to the plane of the Solar System. If the size of the Solar System is taken as being the distance these comets travel from the Sun before starting to return, then the solar System extends some two light-years out into space.

Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. Uranus is similar in composition to Neptune, and both are of different chemical composition than the larger gas giants Jupiter and Saturn. For this reason, astronomers sometimes place them in a separate category called "ice giants". Uranus's atmosphere, although similar to Jupiter's and Saturn's in its primary composition of hydrogen and helium, contains more "ices" such as water, ammonia, and methane, along with traces of hydrocarbons.[12] It is the coldest planetary atmosphere in the Solar System, with a minimum temperature of 49 K (−224 °C). It has a complex, layered cloud structure, with water thought to make up the lowest clouds, and methane thought to make up the uppermost layer of clouds.[12] In contrast, the interior of Uranus is mainly composed of ices and rock.[11]

Like the other gas giants, Uranus has a ring system, a magnetosphere, and numerous moons. The Uranian system has a unique configuration among the planets because its axis of rotation is tilted sideways, nearly into the plane of its revolution about the Sun. Its north and south poles therefore lie where most other planets have their equators.[16] In 1986, images from Voyager 2 showed Uranus as a virtually featureless planet in visible light without the cloud bands or storms associated with the other giants.[16] Terrestrial observers have seen signs of seasonal change and increased weather activity in recent years as Uranus approached its equinox. The wind speeds on Uranus can reach 250 meters per second (900 km/h, 560 mph).[17]

History

Though it is visible to the naked eye like the five classical planets, it was never recognized as a planet by ancient observers because of its dimness and slow orbit.[18] Sir William Herschel announced its discovery on March 13, 1781, expanding the known boundaries of the Solar System for the first time in history. Uranus was also the first planet discovered with a telescope.

Discovery

Uranus had been observed on many occasions before its recognition as a planet, but it was generally mistaken for a star. The earliest recorded sighting was in 1690 when John Flamsteed observed the planet at least six times, cataloging it as 34 Tauri. The French astronomer Pierre Lemonnier observed Uranus at least twelve times between 1750 and 1769,[19] including on four consecutive nights.

Sir William Herschel observed the planet on March 13, 1781 while in the garden of his house at 19 New King Street in the town of Bath, Somerset, England (now the Herschel Museum of Astronomy),[20] but initially reported it (on April 26, 1781) as a "comet".[21] Herschel "engaged in a series of observations on the parallax of the fixed stars",[22] using a telescope of his own design.

He recorded in his journal "In the quartile near ζ Tauri ... either [a] Nebulous star or perhaps a comet".[23] On March 17, he noted, "I looked for the Comet or Nebulous Star and found that it is a Comet, for it has changed its place".[24] When he presented his discovery to the Royal Society, he continued to assert that he had found a comet while also implicitly comparing it to a planet:[25] The power I had on when I first saw the comet was 227. From experience I know that the diameters of the fixed stars are not proportionally magnified with higher powers, as planets are; therefore I now put the powers at 460 and 932, and found that the diameter of the comet increased in proportion to the power, as it ought to be, on the supposition of its not being a fixed star, while the diameters of the stars to which I compared it were not increased in the same ratio. Moreover, the comet being magnified much beyond what its light would admit of, appeared hazy and ill-defined with these great powers, while the stars preserved that lustre and distinctness which from many thousand observations I knew they would retain. The sequel has shown that my surmises were well-founded, this proving to be the Comet we have lately observed. [1][2]Replica of the telescope used by Herschel to discover Uranus (William Herschel Museum, Bath)Herschel notified the Astronomer Royal, Nevil Maskelyne, of his discovery and received this flummoxed reply from him on April 23: "I don't know what to call it. It is as likely to be a regular planet moving in an orbit nearly circular to the sun as a Comet moving in a very eccentric ellipsis. I have not yet seen any coma or tail to it".[26]

While Herschel continued to cautiously describe his new object as a comet, other astronomers had already begun to suspect otherwise. Russian astronomer Anders Johan Lexell was the first to compute the orbit of the new object[27] and its nearly circular orbit led him to a conclusion that it was a planet rather than a comet. Berlin astronomer Johann Elert Bode described Herschel's discovery as "a moving star that can be deemed a hitherto unknown planet-like object circulating beyond the orbit of Saturn".[28] Bode concluded that its near-circular orbit was more like a planet than a comet.[29]

The object was soon universally accepted as a new planet. By 1783, Herschel himself acknowledged this fact to Royal Society president Joseph Banks: "By the observation of the most eminent Astronomers in Europe it appears that the new star, which I had the honour of pointing out to them in March 1781, is a Primary Planet of our Solar System."[30] In recognition of his achievement, King George III gave Herschel an annual stipend of £200 on the condition that he move to Windsor so that the Royal Family could have a chance to look through his telescopes.[31]

Naming

Maskelyne asked Herschel to "do the astronomical world the faver [sic] to give a name to your planet, which is entirely your own, [and] which we are so much obliged to you for the discovery of."[32] In response to Maskelyne's request, Herschel decided to name the object Georgium Sidus (George's Star), or the "Georgian Planet" in honour of his new patron, King George III.[33] He explained this decision in a letter to Joseph Banks:[30] In the fabulous ages of ancient times the appellations of Mercury, Venus, Mars, Jupiter and Saturn were given to the Planets, as being the names of their principal heroes and divinities. In the present more philosophical era it would hardly be allowable to have recourse to the same method and call it Juno, Pallas, Apollo or Minerva, for a name to our new heavenly body. The first consideration of any particular event, or remarkable incident, seems to be its chronology: if in any future age it should be asked, when this last-found Planet was discovered? It would be a very satisfactory answer to say, 'In the reign of King George the Third'. [3][4]William Herschel, discoverer of UranusHerschel's proposed name was not popular outside of Britain, and alternatives were soon proposed. Astronomer Jérôme Lalande proposed the planet be named Herschel in honour of its discoverer.[34] Swedish astronomer Erik Prosperin proposed the name Neptune which was supported by other astronomers who liked the idea to commemorate the victories of the British Royal Naval fleet in the course of the American Revolutionary War by calling the new planet even Neptune George III or Neptune Great Britain.[27] Bode opted for Uranus, the Latinized version of the Greek god of the sky, Ouranos. Bode argued that just as Saturn was the father of Jupiter, the new planet should be named after the father of Saturn.[31][35][36] In 1789, Bode's Royal Academy colleague Martin Klaproth named his newly discovered element "uranium" in support of Bode's choice.[37] Ultimately, Bode's suggestion became the most widely used, and became universal in 1850 when HM Nautical Almanac Office, the final holdout, switched from using Georgium Sidus to Uranus.[35]

Name

Uranus is named after the ancient Greek deity of the sky Uranus (Ancient Greek: Οὐρανός), the father of Cronus (Saturn) and grandfather of Zeus (Jupiter), which in Latin became "Ūranus".[1] It is the only planet whose name is derived from a figure from Greek mythology rather than Roman mythology. The adjective of Uranus is "Uranian".[38] The pronunciation of the name Uranus preferred among astronomers is /ˈjʊərənəs/ EWR-ə-nəs,[2] with stress on the first syllable as in Latin Ūranus, in contrast to the colloquial /jʊˈrnəs/ ew-RAY-nəs, with stress on the second syllable and a long a, though both are considered acceptable.[e]

Uranus has two astronomical symbols. The first to be proposed, ♅,[f] was suggested by Lalande in 1784. In a letter to Herschel, Lalande described it as "un globe surmonté par la première lettre de votre nom" ("a globe surmounted by the first letter of your surname").[34] A later proposal, ⛢,[g] is a hybrid of the symbols for Mars and the Sun because Uranus was the Sky in Greek mythology, which was thought to be dominated by the combined powers of the Sun and Mars.[40] In the Chinese, Japanese, Korean, and Vietnamese languages, the planet's name is literally translated as the sky king star (天王星).[41][42]

Orbit and rotation

[5][6]Uranus revolves around the Sun once every 84 Earth years. Its average distance from the Sun is roughly 3 billion km (about 20 AU)[7][8]A 1998 false-colour near-infrared image of Uranus showing cloud bands, rings, and moons obtained by the Hubble Space Telescope's NICMOS camera.Uranus revolves around the Sun once every 84 Earth years. Its average distance from the Sun is roughly 3 billion km (about 20 AU). The intensity of sunlight on Uranus is about 1/400 that on Earth.[43] Its orbital elements were first calculated in 1783 by Pierre-Simon Laplace.[44] With time, discrepancies began to appear between the predicted and observed orbits, and in 1841, John Couch Adams first proposed that the differences might be due to the gravitational tug of an unseen planet. In 1845, Urbain Le Verrier began his own independent research into Uranus's orbit. On September 23, 1846, Johann Gottfried Galle located a new planet, later named Neptune, at nearly the position predicted by Le Verrier.[45]

The rotational period of the interior of Uranus is 17 hours, 14 minutes, clockwise (retrograde). As on all giant planets, its upper atmosphere experiences very strong winds in the direction of rotation. At some latitudes, such as about two-thirds of the way from the equator to the south pole, visible features of the atmosphere move much faster, making a full rotation in as little as 14 hours.[46]

Axial tilt

Uranus has an axial tilt of 97.77 degrees, so its axis of rotation is approximately parallel with the plane of the Solar System. This gives it seasonal changes completely unlike those of the other major planets. Other planets can be visualized to rotate like tilted spinning tops on the plane of the Solar System, while Uranus rotates more like a tilted rolling ball. Near the time of Uranian solstices, one pole faces the Sun continuously while the other pole faces away. Only a narrow strip around the equator experiences a rapid day-night cycle, but with the Sun very low over the horizon as in the Earth's polar regions. At the other side of Uranus's orbit the orientation of the poles towards the Sun is reversed. Each pole gets around 42 years of continuous sunlight, followed by 42 years of darkness.[47] Near the time of the equinoxes, the Sun faces the equator of Uranus giving a period of day-night cycles similar to those seen on most of the other planets. Uranus reached its most recent equinox on December 7, 2007.[48][49]

Northern hemisphere Year Southern hemisphere
Winter solstice 1902, 1986 Summer solstice
Vernal equinox 1923, 2007 Autumnal equinox
Summer solstice 1944, 2028 Winter solstice
Autumnal equinox 1965, 2049 Vernal equinox

One result of this axis orientation is that, on average during the year, the polar regions of Uranus receive a greater energy input from the Sun than its equatorial regions. Nevertheless, Uranus is hotter at its equator than at its poles. The underlying mechanism which causes this is unknown. The reason for Uranus's unusual axial tilt is also not known with certainty, but the usual speculation is that during the formation of the Solar System, an Earth-sized protoplanet collided with Uranus, causing the skewed orientation.[50] Uranus's south pole was pointed almost directly at the Sun at the time of Voyager 2's flyby in 1986. The labeling of this pole as "south" uses the definition currently endorsed by the International Astronomical Union, namely that the north pole of a planet or satellite shall be the pole which points above the invariable plane of the Solar System, regardless of the direction the planet is spinning.[51][52] A different convention is sometimes used, in which a body's north and south poles are defined according to the right-hand rule in relation to the direction of rotation.[53] In terms of this latter coordinate system it was Uranus's north pole which was in sunlight in 1986.

Visibility

From 1995 to 2006, Uranus's apparent magnitude fluctuated between +5.6 and +5.9, placing it just within the limit of naked eye visibility at +6.5.[10] Its angular diameter is between 3.4 and 3.7 arcseconds, compared with 16 to 20 arcseconds for Saturn and 32 to 45 arcseconds for Jupiter.[10] At opposition, Uranus is visible to the naked eye in dark skies, and becomes an easy target even in urban conditions with binoculars.[54] In larger amateur telescopes with an objective diameter of between 15 and 23 cm, the planet appears as a pale cyan disk with distinct limb darkening. With a large telescope of 25 cm or wider, cloud patterns, as well as some of the larger satellites, such as Titania and Oberon, may be visible.[55]

Internal structure

[9][10]Size comparison of Earth and Uranus[11][12]Diagram of the interior of UranusUranus's mass is roughly 14.5 times that of the Earth, making it the least massive of the giant planets. Its diameter is slightly larger than Neptune's at roughly four times Earth's. A resulting density of 1.27 g/cm3 makes Uranus the second least dense planet, after Saturn.[7][9] This value indicates that it is made primarily of various ices, such as water, ammonia, and methane.[11] The total mass of ice in Uranus's interior is not precisely known, as different figures emerge depending on the model chosen; it must be between 9.3 and 13.5 Earth masses.[11][56] Hydrogen and helium constitute only a small part of the total, with between 0.5 and 1.5 Earth masses.[11] The remainder of the non-ice mass (0.5 to 3.7 Earth masses) is accounted for by rocky material.[11]

The standard model of Uranus's structure is that it consists of three layers: a rocky (silicate/iron-nickel) core in the center, an icy mantle in the middle and an outer gaseous hydrogen/helium envelope.[11][57] The core is relatively small, with a mass of only 0.55 Earth masses and a radius less than 20% of Uranus's; the mantle comprises the bulk of the planet, with around 13.4 Earth masses, while the upper atmosphere is relatively insubstantial, weighing about 0.5 Earth masses and extending for the last 20% of Uranus's radius.[11][57] Uranus's core density is around 9 g/cm3, with a pressure in the center of 8 million bars (800 GPa) and a temperature of about 5000 K.[56][57] The ice mantle is not in fact composed of ice in the conventional sense, but of a hot and dense fluid consisting of water, ammonia and other volatiles.[11][57] This fluid, which has a high electrical conductivity, is sometimes called a water–ammonia ocean.[58] The bulk compositions of Uranus and Neptune are very different from those of Jupiter and Saturn, with ice dominating over gases, hence justifying their separate classification as ice giants. There may be a layer of ionic water where the water molecules break down into a soup of hydrogen and oxygen ions, and deeper down superionic water in which the oxygen crystallises but the hydrogen ions move freely within the oxygen lattice.[59]

While the model considered above is reasonably standard, it is not unique; other models also satisfy observations. For instance, if substantial amounts of hydrogen and rocky material are mixed in the ice mantle, the total mass of ices in the interior will be lower, and, correspondingly, the total mass of rocks and hydrogen will be higher. Presently available data does not allow science to determine which model is correct.[56] The fluid interior structure of Uranus means that it has no solid surface. The gaseous atmosphere gradually transitions into the internal liquid layers.[11] For the sake of convenience, a revolving oblate spheroid set at the point at which atmospheric pressure equals 1 bar (100 kPa) is conditionally designated as a "surface". It has equatorial and polar radii of 25 559 ± 4 and 24 973 ± 20 km, respectively.[7] This surface will be used throughout this article as a zero point for altitudes.

Internal heat

Uranus's internal heat appears markedly lower than that of the other giant planets; in astronomical terms, it has a low thermal flux.[17][60] Why Uranus's internal temperature is so low is still not understood. Neptune, which is Uranus's near twin in size and composition, radiates 2.61 times as much energy into space as it receives from the Sun.[17] Uranus, by contrast, radiates hardly any excess heat at all. The total power radiated by Uranus in the far infrared (i.e. heat) part of the spectrum is 1.06 ± 0.08 times the solar energy absorbed in its atmosphere.[12][61] In fact, Uranus's heat flux is only 0.042 ± 0.047 W/m2, which is lower than the internal heat flux of Earth of about 0.075 W/m2.[61] The lowest temperature recorded in Uranus's tropopause is 49 K (−224 °C), making Uranus the coldest planet in the Solar System.[12][61]

One of the hypotheses for this discrepancy suggests that when Uranus was hit by a supermassive impactor, which caused it to expel most of its primordial heat, it was left with a depleted core temperature.[62] Another hypothesis is that some form of barrier exists in Uranus's upper layers which prevents the core's heat from reaching the surface.[11] For example, convection may take place in a set of compositionally different layers, which may inhibit the upward heat transport;[12][61] it is possible that double diffusive convection is a limiting factor.[11]

Atmosphere

Main article: Atmosphere of UranusAlthough there is no well-defined solid surface within Uranus's interior, the outermost part of Uranus's gaseous envelope that is accessible to remote sensing is called its atmosphere.[12] Remote sensing capability extends down to roughly 300 km below the 1 bar (100 kPa) level, with a corresponding pressure around 100 bar (10 MPa) and temperature of 320 K.[63] The tenuous corona of the atmosphere extends remarkably over two planetary radii from the nominal surface at 1 bar pressure.[64] The Uranian atmosphere can be divided into three layers: the troposphere, between altitudes of −300 and 50 km and pressures from 100 to 0.1 bar; (10 MPa to 10 kPa), the stratosphere, spanning altitudes between 50 and 4000 km and pressures of between 0.1 and 10−10 bar (10 kPa to 10 µPa), and the thermosphere/corona extending from 4,000 km to as high as 50,000 km from the surface.[12] There is no mesosphere.

Composition

The composition of the Uranian atmosphere is different from the rest of the planet, consisting as it does mainly of molecular hydrogen and helium.[12] The helium molar fraction, i.e. the number of helium atoms per molecule of gas, is 0.15 ± 0.03[15] in the upper troposphere, which corresponds to a mass fraction 0.26 ± 0.05.[12][61] This value is very close to the protosolar helium mass fraction of 0.275 ± 0.01,[65] indicating that helium has not settled in the center of the planet as it has in the gas giants.[12] The third most abundant constituent of the Uranian atmosphere is methane (CH4).[12] Methane possesses prominent absorption bands in the visible and near-infrared (IR) making Uranus aquamarine or cyan in color.[12] Methane molecules account for 2.3% of the atmosphere by molar fraction below the methane cloud deck at the pressure level of 1.3 bar (130 kPa); this represents about 20 to 30 times the carbon abundance found in the Sun.[12][14][66] The mixing ratio[h] is much lower in the upper atmosphere owing to its extremely low temperature, which lowers the saturation level and causes excess methane to freeze out.[67] The abundances of less volatile compounds such as ammonia, water and hydrogen sulfide in the deep atmosphere are poorly known. They are probably also higher than solar values.[12][68] Along with methane, trace amounts of various hydrocarbons are found in the stratosphere of Uranus, which are thought to be produced from methane by photolysis induced by the solar ultraviolet (UV) radiation.[69] They include ethane (C2H6), acetylene (C2H2), methylacetylene (CH3C2H), and diacetylene (C2HC2H).[67][70][71] Spectroscopy has also uncovered traces of water vapor, carbon monoxide and carbon dioxide in the upper atmosphere, which can only originate from an external source such as infalling dust and comets.[70][71][72]

Troposphere

The troposphere is the lowest and densest part of the atmosphere and is characterized by a decrease in temperature with altitude.[12] The temperature falls from about 320 K at the base of the nominal troposphere at −300 km to 53 K at 50 km.[63][66] The temperatures in the coldest upper region of the troposphere (the tropopause) actually vary in the range between 49 and 57 K depending on planetary latitude.[12][60] The tropopause region is responsible for the vast majority of the planet’s thermal far infrared emissions, thus determining its effective temperature of 59.1 ± 0.3 K.[60][61]

The troposphere is believed to possess a highly complex cloud structure; water clouds are hypothesised to lie in the pressure range of 50 to 100 bar (5 to 10 MPa), ammonium hydrosulfide clouds in the range of 20 to 40 bar (2 to 4 MPa), ammonia or hydrogen sulfide clouds at between 3 and 10 bar (0.3 to 1 MPa) and finally directly detected thin methane clouds at 1 to 2 bar (0.1 to 0.2 MPa).[12][14][63][73] The troposphere is a very dynamic part of the atmosphere, exhibiting strong winds, bright clouds and seasonal changes, which will be discussed below.[17]

Upper atmosphere

The middle layer of the Uranian atmosphere is the stratosphere, where temperature generally increases with altitude from 53 K in the tropopause to between 800 and 850 K at the base of the thermosphere.[64] The heating of the stratosphere is caused by absorption of solar UV and IR radiation by methane and other hydrocarbons,[74] which form in this part of the atmosphere as a result of methane photolysis.[69] Heat is also conducted from the hot thermosphere.[74] The hydrocarbons occupy a relatively narrow layer at altitudes of between 100 and 300 km corresponding to a pressure range of 10 to 0.1 mbar (1000 to 10 kPa) and temperatures of between 75 and 170 K.[67][70] The most abundant hydrocarbons are methane, acetylene and ethane with mixing ratios of around 10−7 relative to hydrogen. The mixing ratio of carbon monoxide is similar at these altitudes.[67][70][72] Heavier hydrocarbons and carbon dioxide have mixing ratios three orders of magnitude lower.[70] The abundance ratio of water is around 7×10−9.[71] Ethane and acetylene tend to condense in the colder lower part of stratosphere and tropopause (below 10 mBar level) forming haze layers,[69] which may be partly responsible for the bland appearance of Uranus. The concentration of hydrocarbons in the Uranian stratosphere above the haze is significantly lower than in the stratospheres of the other giant planets.[67][75]

The outermost layer of the Uranian atmosphere is the thermosphere and corona, which has a uniform temperature around 800 to 850 K.[12][75] The heat sources necessary to sustain such a high value are not understood, since neither solar far UV and extreme UV radiation nor auroral activity can provide the necessary energy. The weak cooling efficiency due to the lack of hydrocarbons in the stratosphere above 0.1 mBar pressure level may contribute too.[64][75] In addition to molecular hydrogen, the thermosphere-corona contains many free hydrogen atoms. Their small mass together with the high temperatures explain why the corona extends as far as 50 000 km or two Uranian radii from the planet.[64][75] This extended corona is a unique feature of Uranus.[75] Its effects include a drag on small particles orbiting Uranus, causing a general depletion of dust in the Uranian rings.[64] The Uranian thermosphere, together with the upper part of the stratosphere, corresponds to the ionosphere of Uranus.[66] Observations show that the ionosphere occupies altitudes from 2 000 to 10 000 km.[66] The Uranian ionosphere is denser than that of either Saturn or Neptune, which may arise from the low concentration of hydrocarbons in the stratosphere.[75][76] The ionosphere is mainly sustained by solar UV radiation and its density depends on the solar activity.[77] Auroral activity is insignificant as compared to Jupiter and Saturn.[75][78]

• Uranus's Atmosphere
• [13]Temperature profile of the Uranian troposphere and lower stratosphere. Cloud and haze layers are also indicated.
• [14]Zonal wind speeds on Uranus. Shaded areas show the southern collar and its future northern counterpart. The red curve is a symmetrical fit to the data.

Planetary rings

Main article: Rings of UranusThe rings are composed of extremely dark particles, which vary in size from micrometers to a fraction of a meter.[16] Thirteen distinct rings are presently known, the brightest being the ε ring. All except two rings of Uranus are extremely narrow—they are usually a few kilometres wide. The rings are probably quite young; the dynamics considerations indicate that they did not form with Uranus. The matter in the rings may once have been part of a moon (or moons) that was shattered by high-speed impacts. From numerous pieces of debris that formed as result of those impacts only few particles survived in a limited number of stable zones corresponding to present rings.[79][80]

William Herschel described a possible ring around Uranus in 1789. This sighting is generally considered doubtful, as the rings are quite faint, and in the two following centuries none were noted by other observers. Still, Herschel made an accurate description of the epsilon ring's size, its angle relative to the Earth, its red color, and its apparent changes as Uranus traveled around the Sun.[81][82] The ring system was definitively discovered on March 10, 1977 by James L. Elliot, Edward W. Dunham, and Douglas J. Mink using the Kuiper Airborne Observatory. The discovery was serendipitous; they planned to use the occultation of the star SAO 158687 by Uranus to study the planet's atmosphere. When their observations were analyzed, they found that the star had disappeared briefly from view five times both before and after it disappeared behind the planet. They concluded that there must be a ring system around the planet.[83] Later they detected four additional rings.[83] The rings were directly imaged when Voyager 2 passed Uranus in 1986.[16] Voyager 2 also discovered two additional faint rings bringing the total number to eleven.[16]

In December 2005, the Hubble Space Telescope detected a pair of previously unknown rings. The largest is located at twice the distance from the planet of the previously known rings. These new rings are so far from the planet that they are called the "outer" ring system. Hubble also spotted two small satellites, one of which, Mab, shares its orbit with the outermost newly discovered ring. The new rings bring the total number of Uranian rings to 13.[84] In April 2006, images of the new rings with the Keck Observatory yielded the colours of the outer rings: the outermost is blue and the other red.[85][86] One hypothesis concerning the outer ring's blue colour is that it is composed of minute particles of water ice from the surface of Mab that are small enough to scatter blue light.[85][87] In contrast, the planet's inner rings appear grey.[85]

• Uranus's Rings
• [15]Animation about the discovering occultation in 1977. (Click on it to start)
• [16]Uranus has a complicated planetary ring system, which was the second such system to be discovered in the Solar System after Saturn's.[79]
• Uranus's aurorae against its equatorial rings, imaged by the Hubble telescope. Unlike the aurorae of Earth and Jupiter, they are not in line with the planet's poles, due to its lopsided magnetic field.

Magnetosphere

[17][18]The magnetic field of Uranus as observed by Voyager 2 in 1986. S and N are magnetic south and north poles.Before the arrival of Voyager 2, no measurements of the Uranian magnetosphere had been taken, so its nature remained a mystery. Before 1986, astronomers had expected the magnetic field of Uranus to be in line with the solar wind, since it would then align with the planet's poles that lie in the ecliptic.[88]

Voyager's observations revealed that the magnetic field is peculiar, both because it does not originate from the planet's geometric center, and because it is tilted at 59° from the axis of rotation.[88][89] In fact the magnetic dipole is shifted from the center of the planet towards the south rotational pole by as much as one third of the planetary radius.[88] This unusual geometry results in a highly asymmetric magnetosphere, where the magnetic field strength on the surface in the southern hemisphere can be as low as 0.1 gauss (10 µT), whereas in the northern hemisphere it can be as high as 1.1 gauss (110 µT).[88] The average field at the surface is 0.23 gauss (23 µT).[88] In comparison, the magnetic field of Earth is roughly as strong at either pole, and its "magnetic equator" is roughly parallel with its geographical equator.[89] The dipole moment of Uranus is 50 times that of Earth.[88][89] Neptune has a similarly displaced and tilted magnetic field, suggesting that this may be a common feature of ice giants.[89] One hypothesis is that, unlike the magnetic fields of the terrestrial and gas giants, which are generated within their cores, the ice giants' magnetic fields are generated by motion at relatively shallow depths, for instance, in the water–ammonia ocean.[58][90]

Despite its curious alignment, in other respects the Uranian magnetosphere is like those of other planets: it has a bow shock located at about 23 Uranian radii ahead of it, a magnetopause at 18 Uranian radii, a fully developed magnetotail and radiation belts.[88][89][91] Overall, the structure of Uranus's magnetosphere is different from Jupiter's and more similar to Saturn's.[88][89] Uranus's magnetotail trails behind the planet into space for millions of kilometers and is twisted by the planet's sideways rotation into a long corkscrew.[88][92]

Uranus's magnetosphere contains charged particles: protons and electrons with small amount of H2+ ions.[89][91] No heavier ions have been detected. Many of these particles probably derive from the hot atmospheric corona.[91] The ion and electron energies can be as high as 4 and 1.2 megaelectronvolts, respectively.[91] The density of low energy (below 1 kiloelectronvolt) ions in the inner magnetosphere is about 2 cm−3.[93] The particle population is strongly affected by the Uranian moons that sweep through the magnetosphere leaving noticeable gaps.[91] The particle flux is high enough to cause darkening or space weathering of the moon’s surfaces on an astronomically rapid timescale of 100,000 years.[91] This may be the cause of the uniformly dark colouration of the moons and rings.[80] Uranus has relatively well developed aurorae, which are seen as bright arcs around both magnetic poles.[75] Unlike Jupiter's, Uranus's aurorae seem to be insignificant for the energy balance of the planetary thermosphere.[78]

Climate

Main article: Climate of UranusUranus's southern hemisphere in approximate natural colour (left) and in shorter wavelengths (right), showing its faint cloud bands and atmospheric "hood" as seen by Voyager 2At ultraviolet and visible wavelengths, Uranus's atmosphere is remarkably bland in comparison to the other gas giants, even to Neptune, which it otherwise closely resembles.[17] When Voyager 2 flew by Uranus in 1986, it observed a total of ten cloud features across the entire planet.[16][94] One proposed explanation for this dearth of features is that Uranus's internal heat appears markedly lower than that of the other giant planets. The lowest temperature recorded in Uranus's tropopause is 49 K, making Uranus the coldest planet in the Solar System, colder than Neptune.[12][61]

Banded structure, winds and clouds

In 1986 Voyager 2 found that the visible southern hemisphere of Uranus can be subdivided into two regions: a bright polar cap and dark equatorial bands (see figure on the right).[16] Their boundary is located at about −45 degrees of latitude. A narrow band straddling the latitudinal range from −45 to −50 degrees is the brightest large feature on the visible surface of the planet.[16][95] It is called a southern "collar". The cap and collar are thought to be a dense region of methane clouds located within the pressure range of 1.3 to 2 bar (see above).[96] Besides the large-scale banded structure, Voyager 2 observed ten small bright clouds, most lying several degrees to the north from the collar.[16] In all other respects Uranus looked like a dynamically dead planet in 1986. Unfortunately Voyager 2 arrived during the height of the planet's southern summer and could not observe the northern hemisphere. At the beginning of the 21st century, when the northern polar region came into view, the Hubble Space Telescope (HST) and Keck telescope initially observed neither a collar nor a polar cap in the northern hemisphere.[95] So Uranus appeared to be asymmetric: bright near the south pole and uniformly dark in the region north of the southern collar.[95] In 2007, when Uranus passed its equinox, the southern collar almost disappeared, while a faint northern collar emerged near 45 degrees of latitude.[97] The first dark spot observed on Uranus. Image obtained by the HST ACS in 2006.In the 1990s, the number of the observed bright cloud features grew considerably partly because new high resolution imaging techniques became available.[17] Most were found in the northern hemisphere as it started to become visible.[17] An early explanation—that bright clouds are easier to identify in the dark part of the planet, whereas in the southern hemisphere the bright collar masks them—was shown to be incorrect: the actual number of features has indeed increased considerably.[98][99] Nevertheless there are differences between the clouds of each hemisphere. The northern clouds are smaller, sharper and brighter.[99] They appear to lie at a higher altitude.[99] The lifetime of clouds spans several orders of magnitude. Some small clouds live for hours, while at least one southern cloud may have persisted since Voyager flyby.[17][94] Recent observation also discovered that cloud features on Uranus have a lot in common with those on Neptune.[17] For example, the dark spots common on Neptune had never been observed on Uranus before 2006, when the first such feature dubbed Uranus Dark Spot was imaged.[100] The speculation is that Uranus is becoming more Neptune-like during its equinoctial season.[101]

The tracking of numerous cloud features allowed determination of zonal winds blowing in the upper troposphere of Uranus.[17] At the equator winds are retrograde, which means that they blow in the reverse direction to the planetary rotation. Their speeds are from −100 to −50 m/s.[17][95] Wind speeds increase with the distance from the equator, reaching zero values near ±20° latitude, where the troposphere's temperature minimum is located.[17][60] Closer to the poles, the winds shift to a prograde direction, flowing with the planet's rotation. Windspeeds continue to increase reaching maxima at ±60° latitude before falling to zero at the poles.[17] Windspeeds at −40° latitude range from 150 to 200 m/s. Since the collar obscures all clouds below that parallel, speeds between it and the southern pole are impossible to measure.[17] In contrast, in the northern hemisphere maximum speeds as high as 240 m/s are observed near +50 degrees of latitude.[17][95][102]

Seasonal variation

[19][20]Uranus in 2005. Rings, southern collar and a bright cloud in the northern hemisphere are visible (HST ACS image).For a short period from March to May 2004, a number of large clouds appeared in the Uranian atmosphere, giving it a Neptune-like appearance.[99][103] Observations included record-breaking wind speeds of 229 m/s (824 km/h) and a persistent thunderstorm referred to as "Fourth of July fireworks".[94] On August 23, 2006, researchers at the Space Science Institute (Boulder, CO) and the University of Wisconsin observed a dark spot on Uranus's surface, giving astronomers more insight into the planet's atmospheric activity.[100] Why this sudden upsurge in activity should be occurring is not fully known, but it appears that Uranus's extreme axial tilt results in extreme seasonal variations in its weather.[49][101] Determining the nature of this seasonal variation is difficult because good data on Uranus's atmosphere have existed for less than 84 years, or one full Uranian year. A number of discoveries have been made. Photometry over the course of half a Uranian year (beginning in the 1950s) has shown regular variation in the brightness in two spectral bands, with maxima occurring at the solstices and minima occurring at the equinoxes.[104] A similar periodic variation, with maxima at the solstices, has been noted in microwave measurements of the deep troposphere begun in the 1960s.[105] Stratospheric temperature measurements beginning in the 1970s also showed maximum values near the 1986 solstice.[74] The majority of this variability is believed to occur owing to changes in the viewing geometry.[98]

There are some reasons to believe that physical seasonal changes are happening in Uranus. While the planet is known to have a bright south polar region, the north pole is fairly dim, which is incompatible with the model of the seasonal change outlined above.[101] During its previous northern solstice in 1944, Uranus displayed elevated levels of brightness, which suggests that the north pole was not always so dim.[104] This information implies that the visible pole brightens some time before the solstice and darkens after the equinox.[101] Detailed analysis of the visible and microwave data revealed that the periodical changes of brightness are not completely symmetrical around the solstices, which also indicates a change in the meridional albedo patterns.[101] Finally in the 1990s, as Uranus moved away from its solstice, Hubble and ground based telescopes revealed that the south polar cap darkened noticeably (except the southern collar, which remained bright),[96] while the northern hemisphere demonstrated increasing activity,[94] such as cloud formations and stronger winds, bolstering expectations that it should brighten soon.[99] This indeed happened in 2007 when the planet passed an equinox: a faint northern polar collar arose, while the southern collar became nearly invisible, although the zonal wind profile remained slightly asymmetric, with northern winds being somewhat slower than southern.[97]

The mechanism of physical changes is still not clear.[101] Near the summer and winter solstices, Uranus's hemispheres lie alternately either in full glare of the Sun's rays or facing deep space. The brightening of the sunlit hemisphere is thought to result from the local thickening of the methane clouds and haze layers located in the troposphere.[96] The bright collar at −45° latitude is also connected with methane clouds.[96] Other changes in the southern polar region can be explained by changes in the lower cloud layers.[96] The variation of the microwave emission from the planet is probably caused by a changes in the deep tropospheric circulation, because thick polar clouds and haze may inhibit convection.[106] Now that the spring and autumn equinoxes are arriving on Uranus, the dynamics are changing and convection can occur again.[94][106]

Formation

Main article: Formation and evolution of the Solar SystemFor details of the evolution of Uranus's orbit, see Nice model.Many[who?] argue that the differences between the ice giants and the gas giants extend to their formation.[107][108] The Solar System is believed[by whom?] to have formed from a giant rotating ball of gas and dust known as the presolar nebula. Much of the nebula's gas, primarily hydrogen and helium, formed the Sun, while the dust grains collected together to form the first protoplanets. As the planets grew, some of them eventually accreted enough matter for their gravity to hold onto the nebula's leftover gas.[107][108] The more gas they held onto, the larger they became; the larger they became, the more gas they held onto until a critical point was reached, and their size began to increase exponentially. The ice giants, with only a few Earth masses of nebular gas, never reached that critical point.[107][108][109] Recent simulations of planetary migration have suggested that both ice giants formed closer to the Sun than their present positions, and moved outwards after formation, a hypothesis which is detailed in the Nice model.[107]

Moons

Main article: Moons of UranusSee also: Timeline of discovery of Solar System planets and their natural satellitesMajor moons of Uranus in order of increasing distance (left to right), at their proper relative sizes and albedos (collage of Voyager 2 photographs)[21][22]The Uranus System (NACO/VLT image)Uranus has 27 known natural satellites.[109] The names for these satellites are chosen from characters from the works of Shakespeare and Alexander Pope.[57][110] The five main satellites are Miranda, Ariel, Umbriel, Titania and Oberon.[57] The Uranian satellite system is the least massive among the gas giants; indeed, the combined mass of the five major satellites would be less than half that of Triton alone.[9] The largest of the satellites, Titania, has a radius of only 788.9 km, or less than half that of the Moon, but slightly more than Rhea, the second largest moon of Saturn, making Titania the eighth largest moon in the Solar System. The moons have relatively low albedos; ranging from 0.20 for Umbriel to 0.35 for Ariel (in green light).[16] The moons are ice-rock conglomerates composed of roughly fifty percent ice and fifty percent rock. The ice may include ammonia and carbon dioxide.[80][111]

Among the satellites, Ariel appears to have the youngest surface with the fewest impact craters, while Umbriel's appears oldest.[16][80] Miranda possesses fault canyons 20 kilometers deep, terraced layers, and a chaotic variation in surface ages and features.[16] Miranda's past geologic activity is believed to have been driven by tidal heating at a time when its orbit was more eccentric than currently, probably as a result of a formerly present 3:1 orbital resonance with Umbriel.[112] Extensional processes associated with upwelling diapirs are the likely origin of the moon's 'racetrack'-like coronae.[113][114] Similarly, Ariel is believed to have once been held in a 4:1 resonance with Titania.[115]

Uranus possesses at least one horseshoe orbiter occupying the Sun-Uranus L3 Lagrangian point— a gravitationally unstable region at 180º in its orbit, 83982 Crantor.[116][117] Crantor currently moves inside Uranus' co-orbital region on a complex, temporary horseshoe orbit. 2010 EU65 is also a promising Uranus horseshoe librator candidate.[117]

Exploration

[23][24]Crescent Uranus as imaged by Voyager 2 while departing for NeptuneMain article: Exploration of UranusIn 1986, NASA's Voyager 2 interplanetary probe encountered Uranus. This flyby remains the only investigation of the planet carried out from a short distance, and no other visits are currently planned. Launched in 1977, Voyager 2 made its closest approach to Uranus on January 24, 1986, coming within 81,500 kilometers of the planet's cloudtops, before continuing its journey to Neptune. Voyager 2 studied the structure and chemical composition of Uranus's atmosphere,[66] including the planet's unique weather, caused by its axial tilt of 97.77°. It made the first detailed investigations of its five largest moons, and discovered 10 new moons. It examined all nine of the system's known rings and discovered two new ones.[16][80][118] It also studied the magnetic field, its irregular structure, its tilt and its unique corkscrew magnetotail caused by Uranus's sideways orientation.[88]

The possibility of sending the Cassini spacecraft to Uranus was evaluated during a mission extension planning phase in 2009.[119] It would take about twenty years to get to the Uranian system after departing Saturn.[119] A Uranus orbiter and probe was recommended by the 2013–2022 Planetary Science Decadal Survey published in 2011; the proposal envisages launch during 2020–2023 and a 13-year cruise to Uranus.[120] A Uranus entry probe could use Pioneer Venus Multiprobe heritage and descend to 1–5 atmospheres.[120] The ESA evaluated a "medium-class" mission called Uranus Pathfinder.[121] A New Frontiers Uranus Orbiter has been evaluated and recommended in the study, The Case for a Uranus Orbiter.[122] Such a mission is aided by the ease with which a relatively big mass can be sent to the system—over 1500 kg with an Atlas 521 and 12-year journey.[123] For more concepts see Proposed Uranus missions.

In culture

In astrology, the planet Uranus ([25]) is the ruling planet of Aquarius. Since Uranus is colored cyan and Uranus is associated with electricity, the color electric blue, a color close to cyan, is associated with the sign Aquarius.[124] (See Uranus in astrology)

The chemical element uranium, discovered in 1789 by the German chemist Martin Heinrich Klaproth, was named after the newly discovered planet Uranus.[125] Uranus, the Magician is a movement in Gustav Holst's The Planets, written between 1914 and 1916. Operation Uranus was the successful military operation in World War II by the Soviet army to take back Stalingrad and marked the turning point in the land war against the Wehrmacht.

The line, Then felt I like some watcher of the skies/When a new planet swims into his ken, from John Keats's On First Looking Into Chapman's Homer is a reference to Herschel's discovery of Uranus.[126]

Uranus is frequently a subject of Crude humor due to the colloquial pronunciation of its name. However, these jokes do not reflect the pronunciation preferred by astronomers, which is "you-ranus", with stress on the first syllable.[127]

{ { Infobox televisión | Show_name = La Patrulla de Zula | Imagen = [ [Archivo: Zula Patrol.png | La Patrulla de Zula ] ] | Creador = Deb M. Manchester | Escritor = Cydne Clark
[ [ Nicole Dubuc ] ]
[ [ Simon Jowett ] ] | Director = Cerebro Kindregan el Kent Butterwoth | Format = [ [ ciencia ] ]
[ [ teatro musical | Musical ] ] | Voces = [ [ Cam Clarke ] ]
[ [ Nancy Cartwright ] ]
[ [ Tress MacNeille ] ]
[ [ Frank Welker ] ]
Kurt Kelly | Compositor = [ [ Jeff Danna ] ]
[ [ Fletcher Beasley ] ] | País = [ [Estados Unidos] ] | Language = [ [Idioma Inglés | Inglés ] ] | Num_seasons = 4 | Num_episodes = 52 | Executive_producer = Deb M. Manchester a Bet Hubbard
[ [ Margaret Loesch ] ] | Empresa = [ [ El criadero ( empresa ) | El criadero ] ]
Zula EE.UU.
[ [ América Televisión Pública ] ]
Marvista Entretenimiento | Red = [ [ PBS ] ] (2005-2007)
[ [ Qubo ] ] ( 2007 -presente) | First_aired = { { Fecha de inicio | 2005 | Septiembre | 5 } } | Last_aired = { { Fecha de finalización | 2010 | Junio ​​| 18 } } | Sitio web = http://zulaworld.com/ | Production_website = http://www.zula.com/ } } ' ' La Patrulla de Zula es una serie animada de televisión distribuida por [ [ American Public Television ] ] a [ [ servicio público de radiodifusión | PBS ]] estaciones en los Estados Unidos. Actualmente se está transmitiendo en [[ ] ] y Qubo WGBX niños. Algunas adaptaciones de la Patrulla de Zula también incluyen espectáculos del planetario .

La serie trata de la ciencia como los personajes del título viajan al espacio en viñetas que enseñan a los espectadores sobre el espacio, nuestra galaxia , y la amistad. Los temas científicos se basan en la tierra y de la ciencia solar.

Personajes

La Patrulla de Zula === ===

• ' Bula ' ( [ [ Cam Clarke ] ]) es el capitán de la Patrulla de Zula . Se ve a sí mismo como el líder maduro de la fuerza , sin embargo , aun a menudo se mete en problemas . Su lema principal es " Este es un trabajo de la Patrulla de Zula ! " En la primera temporada, que constantemente se preocupa por su Zeeter pareja, y cuando se pone con frecuencia en problemas. Algunos episodios , como el "Partido de Bula Girar" , " pasando por una fase " , y " Forget -me- Naut " , se centran en él, porque sus travesuras a veces salen mal . Él y Zeeter recientemente comenzó a aparecer en el momento Multo en la tercera temporada . Él es de color verde con el pelo corto de color rojo brillante en la parte superior . En " pasando por una fase " , se convierte en un weremouse Zulean como una tradición de Zula le debe elegir un Zulabane [ [ flor ] ] con pétalos de color azul alrededor de él que libera polen mágico. Como se transforma de nuevo con el [ [ fase de la luna ] ] s que cambia , se vuelve gris y ganancias de los oídos, nariz, bigotes y la cola de un ratón. Cuando la luna está llena , se convierte desnudo , peludo y grande con un vientre rojo-naranja .
• ' Zeeter ' ( [ [ Nancy Cartwright ] ]) es el piloto Zula Patrol con un [ [ error ] ] como la cabeza y el único miembro del grupo para tener un [ [ Belt ( prendas de vestir) | Cinturón ] ] y [ [ guantes] ] s . Ella cree que el hacer es la mejor manera de aprender , que a menudo le pone en el borde con Multo , que prefiere investigar antes de hacerlo . Sin embargo, ella sigue siendo amigo de él , a pesar de su tendencia a servir recetas repugnantes . Ella ha sido el mejor amigo y compañero de Bula durante mucho tiempo, ya que estaban en Zula Scouts ( parodia de [ [ Boy Scouts of America | Boy Scouts ] ] y [ [ Girl Scouts de los EE.UU. | Girl Scouts ] ] ) . Ella es de color púrpura , con los párpados de color azul claro muestran cuando ellos o parpadea cierra . A veces se usa botas cohete para ir en la velocidad.
• ' Multo ( Cam Clarke) es el científico del grupo , dando datos útiles acerca de las cosas de la Patrulla de Zula pueda necesitar para completar su misión. A veces , sin darse cuenta, hace que algunas de las misiones . Él tiene un libro llamado Multopedia , que el equipo utiliza cuando se necesita una respuesta a sus preguntas. Aunque a menudo distraído, Multo es respetado por todos. Multo es también el anfitrión del Momento Multo , donde se revisa el tema que se trata en ese episodio , y es el presentador de varios eventos diferentes . Aunque ninguno de los episodios de la serie se centran en él, la mayoría de las aventuras , al igual que la película Under The Weather, se centran principalmente en la investigación. Él también tiene una tendencia a servir la comida asquerosa que le gusta , pero los otros no lo hacen. Él tiene una relación mentor- estudiante con Wizzy y Wigg , que alojan el Momento Multo con él . Es de color amarillo con tres ojos . La voz de ' Multo es una basada en la voz del legendario comediante [ [ Ed Wynn ] ] .
• ' Wizzy y Wigg ' ( [ [ BJ Ward (actriz ) | BJ Ward ] ] y [ [ Nika Futterman ] ] ) son los Patrulleros Zula más pequeños con alas en la espalda . Son dos hermanos gemelos , y aunque se discuten como la mayoría de los hermanos hacen, son fundamentalmente inseparables. Wizzy tiene un cuerpo azul y Wigg tiene un morado . También parecen mariposas. Algunos episodios se centran en ellos, ya que reúnen información para responder a sus preguntas. Son buenos amigos con Multo pesar de sus tendencias para servirles sus recetas. En los nuevos episodios, Multo les complementa con el eslogan : "Tú piensas como los científicos ! " Sus nombres son una referencia a la expresión [ [ WYSIWYG ] ] .
• ' Gorga ' ( [ [ Frank Welker ] ]) es el espacio doméstico de la Patrulla de Zula . Fue rescatado por Bula, y ha sido su compañero desde entonces. A pesar de que actúa como un perro, la nariz tiene muchas funciones como [ [ de aspiración ] ] proyección y video.

Los villanos === ===

• 'Dark Truder ' ( [ [ Kurt Kelly ] ]) es el villano principal. A menudo se trata de controlar el espacio , pero rara vez tiene éxito . Esto se debe a que nunca se toma el tiempo para realmente sentarse y mirar sus hechos. En un episodio que dicen que tiene un punto débil , y finalmente se llama " blando grande " en ese episodio . También hace una serie de [ [ disfraz ] ] s incluyendo [ [ travestismo ] ] como Madame Luna .
• ' Traxie ' (Nancy Cartwright ) es profunda animado oscuro peluca roja de Truder , que desaprueba sus malvados planes . También viene en diferentes estilos y colores. Ella a veces se coloca en la cabeza. Además, ella tiene un tío llamado Fred que aparece al final de " Las entradas y salidas de los planetas " .
• ' Deliria ' ( [ [ Tress MacNeille ] ]) es el otro villano principal , sobre todo en la segunda y tercera temporada. Ella es el dueño de una fábrica de basura en los artículos , aunque la mitad de las veces , son fundamentalmente defectuoso. Ella camadas a través del espacio , así como velocidades , por lo que a menudo recibe una gran cantidad de billetes de la Patrulla de Zula . Su cuerpo es de goma, lo que le permite cambiar de forma , pero siempre termina mostrando una parte de su cara cuando ella lo hace. Aunque ninguno de los demás patrulleros puede decir a sus disfraces , Zeeter algo puede distinguir la forma .
• ' Cloid ' ( [ [ de Dave Wittenberg ] ]) es robot sirviente de Deliria . Él tiene un acento británico y es un worrywart . La mayoría de las veces , se trata de compartir un poco de su conocimiento del espacio con Deliria pero ella no le hace caso . A menudo, cuando lo que necesita para alejarse de la Patrulla de Zula , deja Cloid cargar con la culpa . También conduce su limusina espacio.

Objetos Espacio

• ' La [ [ planetas ] ]' son los planetas del sistema solar , que orbitan alrededor del sol. Hay 9 ( los ocho actuales y el planeta enano [ [ Plutón ] ] ) que se ven en la mayoría de los episodios. Los planetas tienen rostros , personalidades y ciertas voces y les encanta la Patrulla de Zula . Sin embargo, son sólo caracteres principales en los que aparecen y hablan en , como " Partido de Bula Girar" , " The Outsider ", " Lo pequeño es hermoso ", "A Tale of Two Planets ", " Caza de la Tierra ", " El Ins y salidas de los planetas "," club de Marte " , " Young at Heart " , y el " Caso de los anillos que faltan " . [ [ Mercurio ( planeta ) | Mercurio ] ] (dios de la marcha) tiene un poco de color marrón oscuro. [ [ Venus ] ] ( diosa del amor ) habla con un [ [ Mid-Atlantic Inglés | Mid-Atlantic ] ] accent . Nuestro planeta [ [ Tierra ] ] aparece en " Family Feud ", donde inicialmente se seca con tristeza a causa de la [ [ hidrógeno ] ] y [ [ oxígeno ] ] elementos se separan, pero al final , ya que están juntos de nuevo, ella está felizmente restaurada con todo el [ [ agua ] ] . [ [ Marte ] ] ( dios de la guerra ) castiga Truder Oscuro y Traxie al soplar a la basura con el viento de arena para insultarlo como " de segunda clase " . El planeta más grande [ [ Júpiter ] ] (el rey de los dioses) que hace un cameo de primer plano en el principio de " Family Feud " . [ [ Saturno ] ] ( dios de la agricultura , la agricultura y la cosecha ) tiene sus anillos que revolotean a su alrededor cuando se vuelve . [ [ Urano ] ] (dios de la vejez ) es mucho más como un tipo genial , porque de él vistiendo un negro [ [ boina ] ] . [ [ Neptuno ] ] ( dios del mar ) es un poco triste sus anillos se han ido en el "Caso de los anillos que faltan " episodio. Plutón ( dios de los muertos ) tiene un compañero luna llamado [ [ Caronte ( la luna ) | Caronte ] ] que tiene un rostro femenino y una personalidad amable. En el episodio llamado " The Outsider " , trata de levantarle el ánimo cuando es insultado por algunos otros planetas.
• ' La [ [Estrellas ] ] s ' aparecer en diferentes colores. Algunos son femeninos y otros son masculinos. [ [ Polaris ] ] es una estrella amarilla que habla con un acento británico . Ella sólo aparece en la "Noche de los Fweeebs " . El [ [ Sun ] ] , que es nuestra fuente de luz , tiene un rostro femenino . Cuando [ [ agujero Negro | Hoyo Negro ] ] habla , ella tiene una voz con eco . Protie aparece en la Patrulla de Zula [ [ tira de película ] ] y es inicialmente un [ [ protoestrella ] ] hasta que se convierte en una estrella adulta con una brillante [ [ aqua (color ) | aqua color] ] . Byron , Buck Starburst y todas las otras protoestrellas se pide a convertirse en estrellas ya mayores del mismo color , para encender el buque Zulean .
• ' La [ [Luna ] ] ': Este personaje también se conoce como la luna de nuestro planeta , que es también la luna de la Tierra. En "Tres de anillos Gorga " , que es secuestrada en un gran [ [Net ( dispositivo) | net ] ] , pero luego decide escapar de la [ [ circo ] ] con Gorga para ir de aventuras gratis .
• ' La [ [ cometa ] ] s ' aparecer en diferentes episodios . Conrad sólo aparece en " A Tale Comet " donde conoce Zeeter , Wizzy y Wigg . Carlos sólo aparece en "Los Juegos de la galaxia Milky - Way " que cumplan ellas y el resto de la Patrulla de Zula .

Otros personajes secundarios

• ' La Familia Zlorg ' y su color azul- y - verde mascota ' Gloop ' son los personajes gigantes de la serie. Toda esta familia aparece en algunos episodios . También cuentan con un vehículo de su propio tamaño y todos ellos son más grandes que la Patrulla de Zula , Truder Oscuro, Traxie y todos los demás extranjeros . En el episodio llamado " Blubglub " , sólo Chester y Lilly aparecen en el parque de atracciones de agua . Tienen un padre llamado Charles y una madre llamada Madge que lleva un collar de perlas de color púrpura.
• ' La [ [ Cloud] ] s ' aparecerá en un par de episodios . [ [ Cumulus ] ] es una nube blanca masculina con acento occidental. [ [ Stratus ] ] es un pequeño masculina gris con el dialecto de un agente cool. [ [ Cumulonimbus cloud | Cumulonimbus ] ] es una nube femenino gris oscuro con un acento británico y [ [ Cirrus ] ] es un ser femenino gris claro con un acento francés .
• ' Testy y ' Beakini está hablando [[ ]] de vidrio envases de Multo . Tienen caras, brazos y piernas. Testy es un [ [ tubo de ensayo ] ] y se dice a veces las respuestas incorrectas a las preguntas de Multo . Beakini es un [ [ matraz ] ] y tiene un poco de acento japonés .
• ' Voop ' es un Zulean [ [ volcán ] ] con una cara femenina. Con su pico , se libera vapor blanco.
• 'Wilson ' es un espacio gigante [ [ gusano ] ] que vive en un colorido [ [ agujero de gusano ] ] . Él es muy amable con la Patrulla de Zula .
• 'Iris Bloodshot ' es un extranjero sin boca de color rosa con un solo gigante azul [ [ ojo ] ] y diminutos tentáculos. En varios episodios se parece tener un agolpamiento en Bula , llamándolo ' querida ' que el resto de los patrulleros .
• ' Buzzy ' es un [ [ hurón ] ], que es amigo de la Patrulla de Zula . Con su collar traductor , él habla humana. Él aparece en dos episodios titulada " Lléveme a su hurón " y "Estás Calambres My Space " .
• ' La Polkadotians ' sólo aparecerá en el episodio llamado " lo que sube tiene que bajar " . Ellos viven en un planeta llamado Polkadotia , que es menor que Zula , que es pesado para ellos cuando están en ella. Moeb es el azul con una nariz de conmutación de idioma que se parece a la nariz de un cerdo . Larmee es el púrpura con un traje rosa y Quilee es el verde con patas de pollo y los lunares amarillos. Ellos pueden ser una referencia a [ [ Los Tres Chiflados ] ] , cuyos nombres eran Moe , Larry y Curly. Además, Quilee hace uno de los sonidos de firma de Curly .
• ' Profesor Autofocus ' es un amigo cercano de la Patrulla de Zula y uno de los muchos amigos de Multo . Posee un museo telescopio en Zulaopolis , y en el episodio " Telescooped ! " él llama a la Patrulla de Zula para ayudar a encontrar a su telescopio, junto con los otros que desaparecieron . Él sólo aparece durante ese episodio.
• 'Francis (apodado ' Frankie ) es una conversación [ [ Linterna ] ], que sólo aparece en " Wigg y Luz Wizzy el Camino" . Su rostro es de [ [ la luz ] ] cuando se enciende .
• ' La Chromilians ' vivir en la Villa del Arco Iris. Uno de ellos se llama ' Roy G. Biv y la otra se llama ' Ray N. Beau . Lleva una camisa arco iris horizontal y el propietario actual del Rainbow Inn. Todos los Chromilians tienen sentimientos dependiendo de un color como el amarillo de la felicidad y el azul para la tristeza .
• ' Profesor Precipito ' es un profesor que vive en las montañas Zulean donde hay una gran cantidad de nieve y es un buen amigo de Multo . Ella lo " poco espolvorear " llama porque le gusta su donas con poco dulces rocía. Ella habla con un acento escocés.
• ' Flo ' es una flor silenciosa Zulean con una base de pétalos con forma de corazón y de color azul cielo . Ella tiene un cuerpo de color púrpura con pétalos de color azul alrededor de la base del pétalo. Cuando se sale de la tierra , ella camina en dos pies y cuando se bebe agua, ella misma se duplica .
• ' Dr. Paranecium ' es un ciudadano de Itty - bittyopolis que parece Multo solamente con pequeños puntos . Trabaja como científico.
• 'Long John Jupiter ' es un pirata, una parodia extranjero de [ [ Long John Silver .]] Su primera aparición fue en un [ [ mapa del tesoro .]]
• ' La [ [ agua ] ] Átomos ': El [ [ hidrógeno ] ] Los átomos en este programa son de color azul claro y todos sus nombres comienzan con "H". Los [ [ oxígeno ]] Los átomos son el rojo y el único cuyo nombre es revelado es Ollie cuya madre es Ma oxígeno . Todos estos átomos tienen un [ [ Sur de América Inglés | Sur acento americano ] ] , pero la diferencia es que hay más hidrógenos que oxígenos .
• ' La [ [ viento ] ] Hermanos ' se nombran Ventoso , Gusty y Gale. A diferencia de sus hermanos , ella es la más suave a pesar de que le intimidan , pero más tarde el comportamiento de los hermanos cambiado.
• ' Beethoven ' es un [ [ escarabajo ] ], cuyo casco se ve como el pelo humano . Él lleva el nombre del compositor de música clásica [ [ Ludwig Von Beethoven ] ] .
• ' Wilhemina ' es un hablador [ [ flor ] ] con pétalos de color púrpura y rosa. Ella es parte de la Zulean [ [ jardín ] ] .
• 'Chip ' es un hablador [ [ glaciar ] ] que prefiere lugares fríos .

Episodios == ==

# ! Lista de los episodios! ! Fecha de Publicación - | La Historia de un cometa / Esto parece un trabajo para el Dudes Zula | | 05 de septiembre 2005 - | La sonda que vino a cenar / Forget- Me- Naut | | 13 de septiembre 2005 - | Corto es bella / La caja de los anillos Desaparecidos | | 27 de septiembre 2005 - | Litterbugs gigantes del espacio / RV de los Gigantes | | 18 de octubre 2005 - | Star Crossed / noche de los Fweebs | | 23 de noviembre 2005 - | La materia, la materia pelea de todas partes / Familiar | | 04 de noviembre 2005 - | Round and Round We Go / El Go'er movimiento lento | | 09 de diciembre 2005 - | Club de Marte / The Outsider | | 26 de diciembre 2005 - | Blue Moon / pasando por una fase | | 27 de diciembre 2005 - | Vuela con nosotros a la Luna / Castaway Asteroid | | 27 de diciembre 2005 - | Blubgub / Flower Power | | 28 de diciembre 2005 - | Las cosas de la Anillos / ¿Cómo Rust fue ganado | | 09 de junio 2006 - | Estaciones espaciales Duelo / Don 't Look ahora | | 07 de noviembre 2006 - | Roca y Seguridad / Support Your Neighborhood Volcano | | 05 de diciembre 2006 - | Hide 'n Seek en Júpiter / A Tale of Two Planets | | 12 de diciembre 2006 - | El sonido de la Multo / Ojos en el cielo | | 30 de marzo 2007 - | Birds of a Feather / Bula ' s Heroes : El gran golpe de camuflaje | | 10 de abril 2007 - | explosiva con el pasado de la Tierra / La Gran Climb | | 05 de junio 2007 - | Si se parece a una planta / Splitsville | | 05 de julio 2007 - | Larva or Leave Me / caza del huevo | | 06 de noviembre 2007 - | Hey Kids! Increíble Space Monkeys / The Blorp | | 11 de enero 2008 - | Los elementos / Viaje al centro de la Gorga Desaparecidos | | 11 de febrero 2008 - | Choosing Sides / Campamento Gusano | | 04 de abril 2008 - | There Goes the Neighborhood | | 16 de junio 2008 - | La gran raza del río / Cuando usted desea sobre una estrella de mar | | 27 de junio 2008 - | El show debe Float On / The Crown Affair Truder | | 14 de julio 2008 - | Mine Shaft | | 15 de julio 2008 - | Ey niños , monos espaciales increíbles! | | 30 de agosto 2008 - | Cook-Off/Treasure Chili en las nubes | | 08 de septiembre 2008 - | Creature Features | | 14 de octubre 2008 - | Dog Gone Gorga / The Milky Way Galaxy Games | | 15 de octubre 2008 - | Down Under | | 20 de diciembre 2008 - | Ice Station Zula | | 08 de febrero 2009 - | Me, Myself and Io | | 21 de abril 2009 - | Mine Shaft / The Cavern Crystal | | 29 de mayo 2009 - | Round and Round We Go | | 15 de diciembre 2005 - | Shadow Play / La Luna Celosa | | 18 de septiembre 2005 - | Spin Control : El efecto / Cráter Raters Venus : Viaje a Mercurio | | 03 de junio 2008 - | Día de Sun / Time Out | | 27 de septiembre 2009 - | The Big Mess / Telescooped | | 26 de diciembre 2005 - | Las entradas y salidas de los planetas / Jóvenes de Corazón | | 18 de diciembre 2005 - | El lagarto que vino a cenar / La isla de los endotermos | | 17 de junio 2008 - | Three Ring Gorga / Luna Mayhem | | 12 de febrero 2006 - | Vanishing Cream / There Goes the Neighborhood | | 05 de junio 2008 - | Villano del Año / uno es el número lonliest | | 18 de junio 2008 - | ¿Dónde fue a parar todo el agua / The Dew Drops | ? | 16 de enero 2010 - | Wigg y Luz Wizzy el Camino / Look To The Rainbow | | 05 de febrero 2006 }

Premios == == 2006 : Nominada al premio Annie a la mejor música en un Animated Television Production : Jeff Danna , Para el " Caso de los Anillos desaparecidas" episodio.

Elenco Voz

- Carácter ! Actor / actriz - | [ [ Cam Clarke ] ] - | [ [ Nancy Cartwright ] ] - | [ [ Tress MacNeille ] ] - | [ [ Frank Welker ] ] - | [ [ Kurt Kelly ] ] - | [ [ Nika Futterman ] ] - | [ [ Catalina Thompson ] ] - | [ [ David Wittenberg ] ] - | [ [ Abby Pollock ] ] }

Enlaces externos

• { {Website oficial | http://www.zula.com/ } }
• [ Http://www.qubo.com/index.php?path=show&id=8 página Qubo ]
• { { IMDb título | 0478960 } }
• [ Http://www.kidscreen.com/articles/daily/20080227/zula.html Zula llega a los cines la película para mostrar una sola vez ] (27 de febrero de 2008) en Kidscreen
• [ Http://articles.latimes.com/2009/may/10/business/fi-himi10 " Patrulla de Zula creador priorizada diversión "] Los Angeles Times 10 de mayo 2009

{ { } } Muestra PBSKids

{ { DEFAULTSORT : Patrulla de Zula } } [ [ Categoría : Serie animada de televisión de 2000 ] ] [ [ Categoría: 2005 serie de televisión estadounidense debuta ] ] [ [ Categoría: serie de televisión de los niños de América ] ] [ [ Categoría: muestra la red PBS ] ] [ [ Categoría : PBS Kids ] ] [ [ Categoría: Qubo ] ] [ [ Categoría: Telemundo muestra ] ] [ [ Categoría: muestra NBC ] ]

Nuestro Sistema Solar

El Sistema Solar es como un pequeño oasis en el espacio. En su centro se encuentra el Sol, cuya fuerza de gravedad mantiene a los planetas en sus órbitas . Estas órbitas , a excepción de la de Plutón , se encuentran casi en el mismo plano , por lo que si usted fuera a hacer un modelo del Sistema Solar, las órbitas de los planetas se encuentran en el espesor de un disco como disco fonográfico . Todos los planetas giran alrededor del Sol en la misma dirección ; miraban desde una posición por encima de la Sistema Solar , se mueven hacia la izquierda. La velocidad a la que viaja cada planeta depende de su distancia al Sol , los más cercanos a moverse más rápido que los más alejados . Así, Mercurio, el planeta más cercano al Sol , se mueve a una velocidad de 47,87 kilometros / segundo ( 29,75 ml / seg ), mientras que Plutón, el más exterior de los planetas , viaja a sólo 4,74 kilometros / segundo ( 2.95mls/sec ) . Así, mientras que Mercurio tiene sólo 88 días terrestres en completar una órbita del Sol, Plutón tarda 248,5 años la Tierra - más de mil veces más.

Otra característica común a todos los planetas es que giran alrededor de sus ejes en sus órbitas alrededor del sol. Una rotación axial completa es un día , pero este período es muy variable . En Venus , por ejemplo , la rotación axial tarda aproximadamente 243 días de la Tierra , mientras que en Júpiter una rotación completa tarda un poco menos de diez horas . También es variable el grado de inclinación axial de los planetas . Por ejemplo , el eje polar de la Tierra está inclinado en un ángulo de 23 * 27 ' a la vertical ( el ser vertical medida con respecto al plano de la órbita de la Tierra ) . Para Venus, sin embargo, el eje está inclinado 178 * C , mientras que la inclinación axial de Júpiter es un mero 3 * 05 ' .

Además de estos grandes, plantes con nombre, ninguno de los cuales tiene un diámetro menor que una cuarta parte de la de la Tierra , el Sistema Solar contiene una gran cantidad de otros cuerpos. Concentra principalmente entre Marte y Júpiter , hay decenas de miles de asteroides que orbitan alrededor del Sol, la más grande de las cuales es Ceres , con un diámetro de 974 kilometros ( 605mls ) .

También en el Sistema Solar son meteoros y cometas. Los cometas tienen órbitas elípticas alargadas que se encuentran en ángulos muy amplios con respecto al plano del Sistema Solar. Si el tamaño del Sistema Solar se toma como la distancia de estos cometas viajan desde el Sol antes de empezar a devolver y el sistema solar se extiende unos dos años luz en el espacio.