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The Solar System consists of the Sun and the astronomical objects bound to it by gravity, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. Of the many objects that orbit the Sun, most of themass is contained within eight relatively solitary planets whose orbits are almost circular and lie within a nearly flat disc called the ecliptic plane. HP 586006-321 Battery

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,HP 586006-361 Battery

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 two regions populated by smaller objects. HP 586028-341 Battery

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 trans-Neptunian objects composed mostly of ices such as water, ammonia and methane. Within these two regions, five individual objects, Ceres, Pluto, Haumea, HP h588178-141 Battery

Makemake and Eris, are recognized to be large enough to have been rounded by their own gravity, and are thus termed dwarf planets.[e] In addition to thousands of small bodies[e] in those two regions, various other small body populations, such as comets, centaurs and interplanetary dust, freely travel between regions.HP 593553-001 Battery

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 hypothetical Oort cloud, which acts as the source for long-period comets, may also exist at a distance roughly a thousand times further than the heliosphere.HP 593554-001 Battery

Six of the planets and three of the dwarf planets are orbited by natural satellites,[b] usually termed "moons" after Earth's Moon. Each of the outer planets is encircled by planetary rings of dust and other particles.

Discovery and exploration

For many thousands of years, humanity, with a few notable exceptions, did not recognize the existence of the Solar System. HP HSTNN-CB0W Battery

People believed the Earth to be stationary at the center 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.HP HSTNN-CB0X Battery

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. HP HSTNN-I79C Battery

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.HP HSTNN-I81C Battery

Structure

The principal component of the Solar System is the Sun, a main sequence G2 star that contains 99.86 percent of the system's known mass and dominates it gravitationally. 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.HP HSTNN-IB0N Battery

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. 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).HP HSTNN-IB0X Battery

For exceptions, see retrograde motion.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 outer Kuiper belt of icy objects.HP HSTNN-LB0W Battery

Astronomers sometimes informally divide this structure into separate regions. The inner Solar System includes the four terrestrial planets and the main asteroid belt. The outer Solar System is beyond the asteroids, including the four gas giant planets. Since the discovery of the Kuiper belt, HP HSTNN-OB0X Battery

the outermost parts of the Solar System are considered a distinct region consisting of the objects beyond Neptune.

Kepler's laws of planetary motion describe the orbits of objects about the Sun. According to Kepler's laws, each object travels along an ellipse with the Sun at one focus. HP HSTNN-OB0Y Battery

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.HP HSTNN-Q61C Battery

The orbits of the planets are nearly circular, but many comets, asteroids and Kuiper belt objects follow highly elliptical orbits.

Due to the vast distances involved, many representations of the Solar System show orbits the same distance apart.HP HSTNN-Q62C Battery

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)  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. HP HSTNN-YB0X Battery

Attempts have been made to determine a relationship between these orbital distances (for example, the Titius–Bode law), but no such theory has been accepted.

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 planetMercury),HP NBP6A174B1 Battery

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.

The objects of the inner Solar System are composed mostly of rock,HP HSTNN-YB0X Battery

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 asmolecular hydrogen,HP NBP6A174 Battery

helium, and neon, which were always in the gaseous phase in the nebula. ces, like water, methane, ammonia, hydrogen sulfide and carbon dioxide, have melting points up to a few hundred kelvins, while their phase depends on the ambient pressure and temperature.HP NBP6A174B1 Battery

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.HP NBP6A175 Battery

Together, gases and ices are referred to as volatiles.

Sun

The Sun is the Solar System's star, and by far its chief component. Its large mass (332,900 Earth masses)  produces temperatures and densities in its core great enough to sustain nuclear fusion,  which releases enormous amounts of energy, mostly radiated into space as electromagnetic radiation, peaking in the 400–700 nm band we call visible light.HP NBP6A175B1 Battery

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. Stars are classified by the Hertzsprung–Russell diagram, a graph that plots the brightness of stars with their surface temperatures.HP WD548AA Battery

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. HP WD549AA Battery

It is believed 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.HP Envy 17 Notebook PC Battery

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. Elements heavier than hydrogen and helium were formed in the cores of ancient and exploding stars, HP Envy 17T Battery

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".HP HSTNN-Q61C Battery

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, creating a tenuous atmosphere (the heliosphere) that permeates the Solar System out to at least 100 AU (seeheliopause).HP GSTNN-Q62C Battery

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. 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.HP HSTNN-IB1E Battery

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.Coronal mass ejections and similar events blow a magnetic field and huge quantities of material from the surface of the Sun. HP HSTNN-YB0X Battery

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. HP 586006-361 Battery

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.HP NBP6A174 Battery

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.HP NBP6A174B1 Battery

The second extends from about 10 AU to about 40 AU, and was probably created by similar collisions within the Kuiper belt.

Inner Solar System

The inner Solar System is the traditional name for the region comprising the terrestrial planets and asteroids.HP 588178-141 Battery

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

The four inner or terrestrial planets have dense, rocky compositions, few or no moons, and no ring systems. HP Pavilion dv5 Adapter

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;Sony NP-F330 Battery

all have impact craters and tectonic surface features such as rift valleys andvolcanoes. 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).Asus Eee PC 904HA Adapter

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.Nikon D80  Battery
Mercury's almost negligible atmosphere consists of atoms blasted off its surface by the solar wind. 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.Sony PCGA-AC19V9 Adapter

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. Dell T555C Battery
It is the hottest planet, with surface temperatures over 400 °C, most likely due to the amount of greenhouse gases in the atmosphere. 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, HP Pavilion DV6-3013SL Battery
which suggests that its atmosphere is regularly replenished by volcanic eruptions.

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 universe where life is known to exist.HP Pavilion DV7-2085EL Battery
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.HP Pavilion DV9700 Battery
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).HP Mini 702EA Battery
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. Its red colour comes from iron oxide (rust) in its soil.Mars has two tiny natural satellites (Deimos and Phobos) thought to be captured asteroids.HP Pavilion DV7-1120EO Battery

Asteroid belt

Asteroids are mostly small Solar System bodies[e] composed mainly of refractory rocky and metallic minerals.

The main 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.HP Compaq 491278-001 Battery

Asteroids range in size from hundreds of kilometres across to microscopic. All asteroids save 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 achievedhydrostatic equilibrium.HP Pavilion DV6-1030US Battery

The asteroid belt contains tens of thousands, possibly millions, of objects over one kilometre in diameter. Despite this, the total mass of the main belt is unlikely to be more than a thousandth of that of the Earth. The main belt is very sparsely populated; spacecraft routinely pass through without incident.HP Compaq 490306-001 Battery

Asteroids with diameters between 10 and 10?4 m are called meteoroids.

Ceres

Ceres (2.77 AU) is the largest body in the asteroid belt and is classified as a dwarf planet. 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. HP Pavilion DV5-1211EM Battery

Ceres was considered a planet when it was discovered in the 19th century, but was reclassified as an asteroid in the 1850s as further observation revealed additional asteroids. It was again reclassified in 2006 as a dwarf planet.

Asteroid groups

Asteroids in the main belt are divided into asteroid groups and families based on their orbital characteristics.HP EliteBook 2530P Battery

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.HP Pavilion DV4385EA Battery

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.Compaq PP2100 Battery

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

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. HP Compaq KU532AA Battery

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.HP Pavilion DV6-1270EQ Battery

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. Jupiter and Saturn are each many tens of times the mass of the Earth and consist overwhelmingly of hydrogen and helium;HP Pavilion DV4385EA Battery

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.” All four gas giants have rings, although only Saturn's ring system is easily observed from Earth. HP Compaq Business  NC4400 Battery

The term outer planet should not be confused withsuperior 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. HP Pavilion ZD8227 Battery
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 63 known satellites. Nikon D200 Battery
The four largest, Ganymede, Callisto, Io, and Europa, show similarities to the terrestrial planets, such as volcanism and internal heating. 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. Acer PA-1650-02 Adapter
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; Sony CYBER-SHOT DSC-T10  Battery
two of which, Titan and Enceladus, show signs of geological activity, though they are largely made of ice.[56] 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.HP Compaq Business 6715b Battery

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.Kodak KLIC-7004 Battery
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.Acer Aspire 5920G Adapter
Neptune has 13 known satellites. The largest, Triton, is geologically active, with geysers of liquid nitrogen. 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.Canon Digital IXUS 90 IS Battery

Comets

Comets are small Solar System bodies,  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. HP 2133 Mini-Note PC Adapter

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.Toshiba PA3536U-1BRS Battery

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. Some comets with hyperbolic orbits may originate outside the Solar System, but determining their precise orbits is difficult.HP Compaq Business NX6110 Battery

Old comets that have had most of their volatiles driven out by solar warming are often categorised as asteroids.

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). HP Pavilion DV9000 Adapter

The largest known centaur, 10199 Chariklo, has a diameter of about 250 km.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.

Trans-Neptunian region

The area beyond Neptune, or the "trans-Neptunian region", is still largely unexplored. Dell Studio 1537 Battery

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.HP PPP009H Adapter

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. 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.Sony VGP-BPS8 Battery

However, 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.Dell PA-12 Adapter

Many Kuiper belt objects have multiple satellites, and most have orbits that take them outside the plane of the ecliptic.

The Kuiper belt can be roughly divided into the "classical" belt and the resonances. Resonances are orbits linked to that of Neptune (e.g. twice for every three Neptune orbits, or once for every two).Sony Cyber-shot DSC-T7/B  Battery

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. Members of the classical Kuiper belt are classified as cubewanos, after the first of their kind to be discovered, (15760) 1992 QB1, and are still in near primordial, low-eccentricity orbits.Dell LATITUDE M65 Battery

Pluto and Charon

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. HP Compaq 6720s Adapter
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"). Acer AS07B41 Battery
Beyond Charon, two much smaller moons,Nix and Hydra, 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.Dell Vostro 1310 Battery

Haumea and Makemake

Haumea (43.34 AU average), and Makemake (45.79 AU average), while smaller than Pluto, are the largest known objects in the classical Kuiper belt (that is, they are not in a confirmed resonance with Neptune). Haumea is an egg-shaped object with two moons.Sony VGP-BPL13 Battery
Makemake is the brightest object in the Kuiper belt after Pluto. Originally designated 2003 EL61 and 2005 FY9 respectively, they were given names and designated dwarf planets in 2008.[72] Their orbits are far more inclined than Pluto's, at 28° and 29°.Sony VGP-BPS13 Battery

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.Sony VGP-BPS13/B Battery

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."Sony VGP-BPS13/S Battery

Some astronomers also classify centaurs as inward-scattered Kuiper belt objects along with the outward-scattered residents of the scattered disc.

Eris

Eris (68 AU average) is the largest known scattered disc object, and caused a debate about what constitutes a planet, Sony VGP-BPS13A/B Battery

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.Sony VGP-BPS13A/S Battery

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;Sony VGP-BPS13AS Battery

this heliopause is considered the beginning of the interstellar medium. However, the Sun's Roche sphere, the effective range of its gravitational dominance, is believed to extend up to a thousand times farther.

Heliopause

The heliosphere is divided into two separate regions. Sony VGP-BPS13B/B Battery

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.Sony VGP-BPS13B/Q Battery

Here the wind slows dramatically, condenses and becomes more turbulent,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; Sony VGP-BPS13B/S Battery

but evidence from the Cassini andInterstellar Boundary Explorer spacecraft has suggested that it is in fact forced into a bubble shape by the constraining action of the interstellar magnetic field. 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.Sony VGP-BPS13Q Battery

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.

The shape and form of the outer edge of the heliosphere is likely affected by the fluid dynamics of interactions with the interstellar medium as well as solar magnetic fields prevailing to the south,Sony VGP-BPS13S Battery

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 theMilky Way.

No spacecraft have yet passed beyond the heliopause, so it is impossible to know for certain the conditions in local interstellar space.Sony VGP-BPL21 Battery

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. How well the heliosphere shields the Solar System from cosmic rays is poorly understood. Sony VGP-BPS21 Battery

A NASA-funded team has developed a concept of a "Vision Mission" dedicated to sending a probe to the heliosphere.

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)), Sony VGP-BPS21/S Battery

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, Sony VGP-BPS21A Battery

the gravitational effects of a passing star, or the galactic tide, the tidal force exerted by the Milky Way.

Sedna

90377 Sedna (525.86 AU average) is a large, reddish Pluto-like 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. Sony VGP-BPS21A/B Battery

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 2000 CR105,Sony VGP-BPS21B Battery

which has a perihelion of 45 AU, an aphelion of 415 AU, and an orbital period of 3,420 years. 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. Sedna is very likely a dwarf planet, though its shape has yet to be determined with certainty.Sony VGP-BPL8 Battery

Boundaries

Much of our 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.Sony VGP-BPL8A Battery

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.[91] Objects may yet be discovered in the Solar System's uncharted regions.Sony VGP-BPL8B Battery

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. Our Sun resides in one of the Milky Way's outer spiral arms, known as the Orion Arm or Local Spur.Sony VGP-BPS8 Battery

The Sun lies between 25,000 and 28,000 light years from the Galactic Centre, 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.Sony VGP-BPS8A Battery

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. The plane of the ecliptic lies at an angle of about 60° to thegalactic plane.

The Solar System's location in the galaxy is very likely a factor in the evolution of life on Earth.Sony VGP-BPS8B Battery

Its orbit is close to being circular and is at roughly the same speed as that of the spiral arms, which means it passes through them only rarely. Since spiral arms are home to a far larger concentration of potentially dangerous supernovae, this has given Earth long periods of interstellar stability for life to evolve.HP Compaq Business 6910p Battery

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. Panasonic LUMIX DMC-TZ4S Battery

The intense radiation of the galactic centre could also interfere with the development of complex life. 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.Sony NP-FH100 Battery

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. Toshiba Equium M50-192 Battery

The bubble is suffused with high-temperature plasma that suggests it is the product of several recent supernovae.

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. Apple MacBook Pro Battery

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). Apple PowerBook G4 Battery

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).Acer BATBL50L6 Battery

Our 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 its luminosity. 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. Acer Travelmate 2400 Battery

Its one confirmed planet, Epsilon Eridani b, is roughly 1.5 times Jupiter's mass and orbits its star every 6.9 years.

Formation and evolution

The Solar System formed from the gravitational collapse of a giant molecular cloud 4.568 billion years ago.  This initial cloud was likely several light-years across and probably birthed several stars.Dell Inspiron 1525 Adapter

As the region that would become the Solar System, known as the pre-solar nebula,collapsed, conservation of angular momentum made it rotate faster. The centre, where most of the mass collected, became increasingly hotter than the surrounding disc.Compaq Presario 2100 Adapter

As the contracting nebula rotated, it began to flatten into a spinning protoplanetary disc with a diameter of roughly 200 AU[104] and a hot, dense protostar at the centre. At this point in its evolution, the Sun is believed to have been a T Tauri star. Studies of T Tauri stars show that they are often accompanied by discs of pre-planetary matter with masses of 0.001–0.1 solar masses,Acer Aspire 1362 Battery

with the vast majority of the mass of the nebula in the star itself. The planets formed by accretion from this disk.

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.Toshiba Equium M50-192 Battery

The temperature, reaction rate, pressure, and density increased until hy

drostatic equilibrium was achieved, with the thermal energy countering the force of gravitational contraction. At this point the Sun became a full-fledged main sequencestar.Dell XPS M1330 Battery

The Solar System as we know it today will last until the Sun begins its evolution off of the main sequence of the Hertzsprung–Russell diagram. As the Sun burns through its supply of hydrogen fuel, the energy output supporting the core tends to decrease, causing it to collapse in on itself.Acer Travelmate 2200 Adapter

This increase in pressure heats the core, so it burns even faster. As a result, the Sun is growing brighter at a rate of roughly ten percent every 1.1 billion years.

Around 5.4 billion years from now, the hydrogen in the core of the Sun will have been entirely converted to helium, ending the main sequence phase.HP Compaq 6735b Adapter

As the hydrogen reactions shut down, the core will contract further, increasing pressure and temperature, causing fusion to commence via the helium process. Helium in the core burns at a much hotter temperature, and the energy output will be much greater than during the hydrogen process.Dell Vostro 1000 Battery

At this time, 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).HP Compaq nx7300 Adapter

Eventually, helium in the core will exhaust itself at a much faster rate than the hydrogen, and the Sun's helium burning phase will be but a fraction of the time compared to the hydrogen burning phase. The Sun is not massive enough to commence fusion of heavier elements, and nuclear reactions in the core will dwindle. Asus f82 Battery

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.[114] The ejected outer layers will form what is known as a planetary nebula, returning some of the material that formed the Sun to the interstellar medium.Dell XPS M1330 Battery

For many thousands of years, civilizations, with a few notable exceptions, did not recognize the existence of the Solar System. It was 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.HP Compaq Business 6910p Battery

While the Indian mathematician-astronomer Aryabhata and the Greek philosopherAristarchus of Samos had speculated on a heliocentric reordering of the cosmos, Nicolaus Copernicus first developed a mathematically predictive heliocentric system.Compaq PRESARIO R3000 Battery

His 17th-century successors Galileo Galilei,Johannes Kepler, and Isaac Newton developed an understanding of physics which led to the gradual acceptance of the idea that the Earth moves round the Sun and that the planets are governed by the same physical laws that governed the Earth. HP Compaq Business NX6110 Battery

In more recent times, this led to 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.

The first exploration of the Solar System was conducted by telescope, when astronomers first began to map those objects too faint to be seen with the naked eye.Dell Latitude D610 Adapter

Galileo Galilei was the first to discover physical details about the individual bodies of the Solar System. He discovered that the Moon was cratered, that the Sun was marked with sunspots, and that Jupiter had four satellites in orbit around it. Christiaan Huygens followed on from Galileo's discoveries by discovering Saturn's moon Titan and the shape of the rings of Saturn.Asus Eee PC 701 Adapter

Giovanni Domenico Cassini later discovered four more moons of Saturn, the Cassini division in Saturn's rings.[3]

Edmond Halley realised in 1705 that repeated sightings of a comet were recording the same object, returning regularly once every 75–76 years. This was the first evidence that anything other than the planets orbited the Sun. HP Compaq Business NX6325 Battery

Around this time (1704), the term "Solar System" first appeared in English.

In 1781, William Herschel was looking for binary stars in the constellation of Taurus when he observed what he thought was a new comet. Its orbit revealed that it was a new planet, Uranus, the first ever discovered.Dell Studio XPS 16 Battery

Giuseppe Piazzi discovered Ceres in 1801, a small world between Mars and Jupiter that initially was considered a new planet. However, subsequent discoveries of thousands of other small worlds in the same region led to their eventual reclassification as asteroids.Acer Aspire 5520 Battery

By 1846, discrepancies in the orbit of Uranus led many to suspect a large planet must be tugging at it from farther out. Urbain Le Verrier's calculations eventually led to the discovery of Neptune.[8] The excess perihelion precession of Mercury's orbit led Le Verrier to postulate the intra-Mercurian planet Vulcan in 1859, but that would turn out to be an irrelevant thesis.Acer TravelMate 5720 Adapter

While it is debatable when the Solar System was truly "discovered," three 19th century observations determined its nature and place in the universe beyond reasonable doubt. First, in 1838, Friedrich Bessel successfully measured a stellar parallax, an apparent shift in the position of a star created by the Earth's motion around the Sun.HP Compaq 6735s Adapter

This was not only the first direct, experimental proof of heliocentrism, but also revealed, for the first time, the vast distance between our Solar System and the stars. Then, in 1859, Robert Bunsen and Gustav Kirchhoff, using the newly invented spectroscope,Dell XPS M1330 Battery

examined the spectral signature of the Sun and discovered that it was composed of the same elements as existed on Earth, establishing for the first time a physical link between the Earth and the heavens.[9] Then, Father Angelo Secchi compared the spectral signature of the Sun with those of other stars, and found them virtually identical. HP Compaq nc6230 Adapter

The realisation that the Sun was a star led to the hypothesis that other stars could have systems of their own, though this was not to be proven for nearly 140 years.

Further apparent discrepancies in the orbits of the outer planets led Percival Lowell to conclude that yet another planet, "Planet X", must lie beyond Neptune. Dell T117C Battery

After his death, his Lowell Observatoryconducted a search which ultimately led to Clyde Tombaugh's discovery of Pluto in 1930. Pluto was, however, found to be too small to have disrupted the orbits of the outer planets, and its discovery was therefore coincidental.Asus x5dij-sx039c Battery

Like Ceres, it was initially considered to be a planet, but after the discovery of many other similarly sized objects in its vicinity it was reclassified in 2006 as a dwarf planet by the IAU.

In 1992, the first evidence of a planetary system other than our own was discovered, orbiting the pulsar PSR B1257+12. Dell Inspiron 1464 Battery

Three years later, 51 Pegasi b, the first extrasolar planet around a Sunlike star, was discovered. As of 2008, 221 extrasolar systems have been found.

Also in 1992, astronomers David C. Jewitt of the University of Hawaii and Jane Luu of the Massachusetts Institute of Technology discovered (15760) 1992 QB1. HP Compaq 6720s Adapter

This object proved to be the first of a new population, which became known as the Kuiper belt; an icy analogue to the asteroid belt of which such objects as Pluto and Charon were deemed a part.

Mike Brown, Chad Trujillo and David Rabinowitz announced the discovery of Eris in 2005, a scattered disc object larger than Pluto and the largest object discovered in orbit round the Sun since Neptune.Dell Latitude D630 Adapter

Observations by spacecraft

Since the start of the Space Age, a great deal of exploration has been performed by robotic spacecraft missions that have been organized and executed by various space agencies.

All planets in the Solar System have now been visited to varying degrees by spacecraft launched from Earth. HP Pavilion dm4 Battery

Through these unmanned missions, humans have been able to get close-up photographs of all the planets and, in the case of landers, perform tests of the soils and atmospheres of some.

The first artificial object sent into space was the Soviet satellite Sputnik 1, launched in 1957, which successfully orbited the Earth until January 4 the following year. Sony NP-FS11 Battery

The American probe Explorer 6, launched in 1959, was the first satellite to image the Earth from space.

Flybys

The first successful probe to fly by another Solar System body was Luna 1, which sped past the Moon in 1959. Originally meant to impact with the Moon, it instead missed its target and became the first artificial object to orbit the Sun.Dell Inspiron 1520 Adapter

Mariner 2 was the first probe to fly by another planet, Venus, in 1962. The first successful flyby of Mars was made by Mariner 4 in 1965. Mariner 10 first passed Mercury in 1974.

The first probe to explore the outer planets was Pioneer 10, which flew by Jupiter in 1973. Pioneer 11 was the first to visit Saturn, in 1979. Toshiba PA3399U-1BRS Battery

The Voyager probes performed a grand tour of the outer planets following their launch in 1977, with both probes passing Jupiter in 1979 and Saturn in 1980 – 1981. Voyager 2 then went on to make close approaches to Uranus in 1986 and Neptune in 1989.Acer Aspire 5920G Adapter

The Voyager probes are now far beyond Neptune's orbit, and are on course to find and study the termination shock, heliosheath, and heliopause. According to NASA, bothVoyager probes have encountered the termination shock at a distance of approximately 93 AU from the Sun.Acer Aspire 5920 Battery

The first flyby of a comet occurred in 1985, when the International Cometary Explorer (ICE) passed by the cometGiacobini-Zinner,  while the first flybys of asteroids were conducted by the Galileo space probe, which imaged both 951 Gaspra (in 1991) and 243 Ida (in 1993) on its way to Jupiter.IBM Thinkpad T40 Adapter

No Kuiper belt object has yet been visited by a spacecraft. Launched on January 19, 2006, the New Horizons probe is currently en route to becoming the first man-made spacecraft to explore this area. This unmanned mission is scheduled to fly by Pluto in July 2015. Nikon COOLPIX 4300 Battery

Should it prove feasible, the mission will then be extended to observe a number of other Kuiper belt objects.

Orbiters, rovers and landers

In 1966, the Moon became the first Solar System body beyond Earth to be orbited by an artificial satellite (Luna 10), followed by Mars in 1971 (Mariner 9),Apple MB771 Battery

Venus in 1975 (Venera 9), Jupiter in 1995 (Galileo), the asteroid 433 Eros in 2000 (NEAR Shoemaker), Saturn in 2004 (Cassini–Huygens), and Mercury in 2011 (MESSENGER). The Dawn spacecraft is currently set to orbit the asteroid Vesta in 2011 and the dwarf planet Ceres in 2015.Sony DSC-P5 Battery

The first probe to land on another Solar System body was the Soviet Luna 2 probe, which impacted the Moon in 1959. Since then, increasingly distant planets have been reached, with probes landing on or impacting the surfaces of Venus in 1966 (Venera 3), Mars in 1971 (Mars 3, although a fully successful landing didn't occur until Viking 1 in 1976),Dell Inspiron 6400 Adapter

the asteroid 433 Eros in 2001 (NEAR Shoemaker), and Saturn's moon Titan (Huygens) and the comet Tempel 1 (Deep Impact) in 2005. The Galileo orbiter also dropped a probe into Jupiter's atmosphere in 1995; since Jupiter has no physical surface, it was destroyed by increasing temperature and pressure as it descended.Toshiba PA3534U-1BRS Battery

To date, only two worlds in the Solar System, the Moon and Mars, have been visited by mobile rovers. The first rover to visit another celestial body was the Soviet Lunokhod 1, which landed on the Moon in 1970. The first to visit another planet was Sojourner, which travelled 500 metres across the surface of Mars in 1997. Sony NP-FP50 Battery

The only manned rover to visit another world was NASA's Lunar rover, which travelled with Apollos 15, 16 and 17 between 1971 and 1972.

Manned exploration

Manned exploration of the Solar System is currently confined to Earth's immediate environs. HP Compaq nx7300 Adapter

The first human being to reach space (defined as an altitude of over 100 km) and to orbit the Earth was Yuri Gagarin, a Soviet cosmonaut who was launched in Vostok 1 on April 12, 1961. The first man to walk on the surface of another Solar System body was Neil Armstrong, who stepped onto the Moon on July 21, 1969 during the Apollo 11 mission;Dell Latitude D820 Adapter

five more Moon landings occurred through 1972. The United States' Space Shuttle, which debuted in 1981, is the only reusable spacecraft to successfully make multiple orbital flights. The five shuttles that have been built have flown a total of 121 missions, with two of the craft destroyed in accidents. Toshiba PA3399U-1BRS Battery

The first orbital space station to host more than one crew was NASA's Skylab, which successfully held three crews from 1973 to 1974. The first true human settlement in space was the Soviet space station Mir, which was continuously occupied for close to ten years, from 1989 to 1999.Dell Studio XPS 1640 Battery

It was decommissioned in 2001, and its successor, the International Space Station, has maintained a continuous human presence in space since then. In 2004,SpaceShipOne became the first privately funded vehicle to reach space on a suborbital flight. That year, U.S. President George W. Dell Latitude D830 Battery

Bush announced the Vision for Space Exploration, which called for a replacement for the aging Shuttle, a return to the Moon and, ultimately, a manned mission to Mars.

An orrery is a mechanical device that illustrates the relative positions and motions of the planets and moons in the solar system in a heliocentric model. Dell Inspiron E1505 Adapter

Though the Greeks had working planetaria, the first orrery was a planetarium of the modern era was produced in 1704, and one was presented to the Earl of Orrery — whence the name came. They are typically driven by a clockwork mechanism with a globe representing the Sun at the centre, and with a planet at the end of each of the arms.Asus Eee PC 1201PN Battery

History

The first modern orrery was built circa 1704 by George Graham and Thomas Tompion. Graham gave the first model (or its design) to the celebrated instrument maker John Rowley of London to make a copy for Prince Eugene of Savoy. Rowley was commissioned to make another copy for his patronCharles Boyle, 4th Earl of Orrery, from which the device took its name.Asus Eee PC 701 Adapter

This model was presented to Charles' son John, later the 5th Earl. Its importance was partially in that mechanical models of the universe, correctly named planeteriums gained the name Orrery,

There were planetary machines before 1704, indeed according to Cicero, the Greek philosopher who was writing in the first century BC, Posidoniusconstructed an planetary model.Dell XPS M1330 Battery

The Antikythera mechanism, discovered in 1904 in 42m of water off the Greek island of Antikythera and extensively studied, exhibited the diurnal motions of the sun, moon, and the five known planets. The Antikythera mechanism is now considered one of the first orreries but for many decades was ignored as it thought to be far too complex to be genuine,fujifilm np95 Battery

and was not mentioned in the 1967 Science Museum booklet. It was heliocentric and used as a mechanical calculator designed to calculate astronomical positions.

Copernicus in De Revolutionibus Orbium Coelestium published in Nuremberg in 1543 challenged the Western religious teaching of a geocentric universe where the sun rotated around the earth. Asus Eee PC 900 Adapter

He found that some Greek philosophers had proposed a heliocentric universe. This simplified the apparent epicyclic motions of the planets, making it feasible to represent the planets path as a simple circle. This could be modelled by the use of gears. Sony VAIO PCG-713 Battery

Tycho Brahe'simproved instruments made precise observations of the skys (1576-1601), and from these Johannes Kepler (1621) deduced that planets orbited the sun in ellipses. In 1687 Isaac Newton explained the cause of this motion in his theory of gravitation.Dell Latitude D830 Adapter

Christian Huygens published details of a heliocentric planetary machine in 1703, which he built while resident in Paris between 1665 and 1681. He calculated the gear trains that were need to represent a year length of 365.242 days, and using that to produce the cycles of the principal planets. As lated as 1650, P. Dell Studio XPS 1640 Battery

Schirleus has produced a Geocentric planetarium showing the sun as a planet with Mercury and Venus moving around it as moons.

Joseph Wright's picture "A Philosopher giving a Lecture on the Orrery in which a lamp is put in place of the Sun" (ca. 1766) which hangs in Derby Museum and Art Gallery,Panasonic LUMIX DMC-TZ4S  Battery

features a group (three men, three children, and a lone woman) listening to a lecture by a 'natural philosopher'—the only light in the otherwise darkened room is from the "sun" in the brass orrery, which, in this case, has rings that cause it to appear to be similar to an armillary sphere. The demonstration was thereby able to cover eclipses.HP Compaq Business NX6320 Battery

To put this in context, it was in 1762 that John Harrison's Chronometer allowed longitude to be accurately measured and also in 1766 that the astronomerTitius first demonstrated that the mean distance of the planets could be represented by the progression.Canon POWERSHOT G2 Battery

That is, 0.4, 0.7, 1.0, 1.6, 2.8, 5.2 ... The numbers refer to astronomical units, that is 1.496 x 10? km (93 x 10? miles). The Derby Orrery does not show mean distance, but demonstrated the relative planetary movements: all part of a process understanding contemporary cutting edge scientific thinking.Dell Latitude E6500 Battery

Eisinga's "Planetarium" was built from 1774 to 1781 by Eise Eisinga in his home in Franeker, in the Netherlands. It displays the planets across the width of a room's ceiling, and has been in operation almost continually since it was created. This orrery, was a planetarium in both senses of the word- firstly a complex planetary machine, Dell LATITUDE D630 Battery

and secondly it was displayed in a special room, that was a sort of theatre for the observers. Eisinga house was bought by the Dutch Royal family who gave him a pension.

In 1764, Benjamin Martin devised a new type of planetary model, where the planets were carried on brass arms leading from a series of concentric or coaxial tubes. Asus R33030 Adapter

With this construction it was difficult to make the planets revolve, and to get the moons to turn around the planets. Martin suggested that the conventional orrery should be consist of three parts: The planetarium where the planets revolved around the sum, the tellurian which showed the inclined axis of the earth and how it revolved around the sun,Dell Mini 1011 Battery

and the lunarium which showed the eccentric rotations of the moon around the earth. In one orrery, these three motions could be mounted on a common table, separately using the central spindle as a prime mover.

Explanation

All orreries are planetariums or planetaria (alternative plural). The term orrery has only existed since 1714. toshiba pa3332u-1brs Battery

A grand orrery is one that includes the outer planets known at the time of its construction. The word planetarium, (plural always planetariums) has been captured and now usually refers to hemispherical theatres in which images of the night sky are projected onto an overhead surface. HP Compaq 6710b Adapter

Planetariums (orreries) can range widely in size from hand-held to room-sized. An orrery is used to demonstrate the motion of the planets, while a mechanical device used to predict eclipses and transits is called an Astrarium.

An orrery should properly include the sun, earth and the (earth's) moon (plus optionally other planets.) HP Compaq nx6325 Adapter

A model that only includes the earth, its moon and the sun is called a tellurion, and one which only includes the earth and moon a lunarium. A jovilabe is a model of Jupiter and its moons.

A planetarium will show the orbital period of each planet and the rotation rate, as shown in the table above. Acer Aspire 5720 Adapter

A tellurian will show the earth with the moon revolving around the sun. It will use the angle ofinclination of the equator from the table above to show how it rotates around its own axis. It was show the earths moon, rotating around the earth. A lunarium is designed to show the complex motions of the moon as it revolves around the earth.Toshiba Equium A110-252 Battery

Orreries are usually not built to scale. Some fixed solar system scale models have been built and are often many kilometres in size. A normal mechanical clock could be used to produce an extremely simple orrery with the Sun in the centre, Earth on the minute hand and Jupiter on the hour hand; Acer Aspire 5052ANWXMi Battery

Earth would make 12 revolutions around the Sun for every 1 revolution of Jupiter. Note however that Jupiter's actual year is 11.86 Earth years long, so this particular example would lose accuracy rapidly. A real orrery would be more accurate and include more planets, and would perhaps make the planets rotate as well.Dell Mini 1011v Battery

Projection orreries

Many planetariums (buildings) have a projection orrery, which projects onto the dome of the planetarium a Sun with either dots or small images of the planets. These usually are limited to the planets from Mercury to Saturn, although some include Uranus. HP Compaq nx7300 Adapter

The light sources for the planets are projected onto mirrors which are geared to a motor which drives the images on the dome. Typically the Earth will circle the Sun in one minute, while the other planets will complete an orbit in time periods proportional to their actual motion. Dell Vostro 1510 Battery

Thus Venus, which takes 224.7 days to orbit the Sun, will take 42 seconds to complete an orbit on an orrery, and Jupiter will take 11.86 minutes.

Some planetariums have taken advantage of this to use orreries to simulate planets and their moons. Toshiba PA3534U-1BRS Battery

Thus Mercury orbits the Sun in 0.24 of an Earth year, while Phobos and Deimos orbit Mars in a similar 4:1 time ratio. Planetarium operators wishing to show this have placed a red cap on the Sun (to make it resemble Mars) and turned off all the planets but Mercury and Earth. Similar tricks can be used to show Pluto and its three moons.Asus M50 Battery

Notable orreries

Shoemaker John Fulton of Fenwick, Ayrshire, built three between 1823 and 1833 - the last is in Glasgow's Kelvingrove Art Gallery and Museum.

The Franeker Planetarium built by a wool carder called Eise Eisinger in his own living room, in the small city of Franeker in Friesland, is in fact an orrery. Asus Eee PC 901 Battery

It was constructed between 1774 to 1781. The "face" of the model looks down from the ceiling of a room, with most of the mechanical works in the space above the ceiling. It is driven by a pendulum clock, which has 9 weights or ponds. The planets move around the model in real time.Dell Inspiron 6400 Battery

An innovative concept is to have people play the role of the moving planets and other Solar system objects. Such a model, called a human orrery, has been laid out with precision at the Armagh Observatory.HP Compaq Business NC6220 Battery

Meccano Planetaria

The first Meccano Orrery was described in June 1918 Meccano Manual, though it is the last quarter of the 20th Century that Alan Partridge, John Nuttall, Pat Briggs and Michael Whiting have experimented with the limitations and possibilty of this medium. There are six methods of building orreries:Sony VGP-BPS9 Battery

  • Telescopic concentric tubing, though the tubing is not a Meccano part. For a full 9 planet system, 18 concentric tubes and 19 geared motions are needed
  • Nested hollow turntables with internal gearing. A 1984 Jovilabe showing Jupiter and the 14 then known moons required 14 tuntables and 324 gears; it is accurate to within 0.01% .Sony VGP-BPS13 Battery
  • Fixed central rod, with top drive and sun and planet gearing. In this method, the sun drives the first planet and this then drives the second and so on. The errors are thus cummulative, but non Meccano gearing can keep this with in 0.02%
  • Fixed central tube, with bottom drive and sun and planet gearing. This removes the need for an overhead gantry- improving the appearance.HP Compaq nx7300 Adapter
  • Two component epicyclic gearing.
  • Fixed Central Rod, Epicyclic gearing, top drive by 'by-pass gearing' from below. HP Compaq 2510p Adapter

Solar System models, especially mechanical models, called orreries, that illustrate the relative positions and motions of the planets and moons in the Solar System have been built for centuries. While they often showed relative sizes, these models were usually not built to scale. Dell Studio PP39L Battery

The enormous ratio of interplanetary distances to planetary diameters makes constructing a scale model of the Solar System a challenging task. As one example of the difficulty, the distance between the Earth and the Sun is almost 12 000 times the diameter of the Earth.Nikon COOLPIX 5700  Battery

If the smaller planets are to be easily visible to the naked eye, large outdoor spaces are generally necessary, as is some means for highlighting objects that might otherwise not be noticed from a distance. The objects in such models do not move. Traditional orreries often did move and some used clockworks to make the relative speeds of objects accurate.Dell Studio XPS 16 Battery

These can be thought of as being correctly scaled in time instead of distance.

One 1:6 300 000 000 scale model, designed to be easily replicated, is called The Thousand-Yard Model and spans about a kilometre. In it, the Earth is represented by a peppercorn. HP Compaq nx7400 Adapter

A school class building this model might tape the peppercorn to an index card to make it more visible. Another scale model is the 1:10 000 000 000 model, in which 100 000 km is represented by 1 cm. In this model, the Sun is 600m from the Kuiper belt and dwarf planet Pluto. The largest scale model in the world is the Sweden Solar System.HP Pavilion DV6500 Adapter

In July 2005 the Austrian art group monochrom placed the planets true to scale (sun, 4 meters in diameter at Machine Gallery, Alvarado Street, near Echo Park) throughout the Los Angeles cityscape. Then they conducted an 'illegal space car race' through the Solar System.Dell T117C Battery

In regional Australia, in the area surrounding Coonabarabran (Australia's Astronomy Capital) there is a model Solar System that reaches from the Observatory (The Sun) to surrounding towns and localities.

In the US, a precedent-setting model Solar System project the Voyage National Program began with installation of Voyage on the National Mall in Washington, DC, in front of the Smithsonian museums.Acer PA-1650-02 Adapter

It is a 1:10 000 000 000 scale model approved by the US Commission of Fine Arts and National Capital Planning Commission. It was designed for replication and permanent installation in communities across the nation. It was also designed as a center-piece for sustained community-wide science education, Acer Aspire 5920G Adapter

embracing a "Learning Community Model" of programming for students, teachers, families, and the public. Grade K-12 lessons available for download enhance the exhibition experience. Voyage is now permanently installed in Kansas City, Houston, and Corpus Christi.Asus S1 Adapter

It is approved for installation in Des Moines, Orlando, and Baltimore, and a dozen other sites are exploring it as a site feature in their community. For the International Year of Astronomy 2009, Voyage has now become available worldwide as "the Voyage International Program" with storyboard translation into any language. HP Pavilion dv6000 Battery

The Voyage National Program also has a Facebook page with photoalbums for all the Voyage communities.

In 2009, to celebrate International Year of Astronomy, the Scottish Solar System project created an approximate scale model of the Solar System, with correctly scaled objects representing the major planets sited temporarily, Ibm Thinkpad T30 Battery

for Autumn Moonwatch week (Oct 24th - Nov 1st 2009) at the locations of a number of Scottish amateur astronomy groups and societies. In this model the Sun was represented by the main building of Glasgow Science Centre. The Scottish Solar System project was coordinated by Dr Martin Hendry, astronomer at the University of Glasgow,Dell Studio PP39L Battery

and Glasgow Science Centre. Although the model did not include Pluto (which on the same scale would be located roughly in the Faroe Islands), its scale of 1:8 200 000 was smaller than any other model listed in the table below. On the same scale the nearest star beyond the Solar System, Proxima Centauri, would still lie nearly 5 million km from Glasgow Science Centre.HP Pavilion dv5 Adapter

A model based on a classroom globe

Relating the size of the Solar System to familiar objects can make it easier for students to grasp the relative distances. Most classroom globes are 41 cm (16 inches) in diameter. If the Earth were reduced to this size, the Moon would be a 10 cm (4 in) baseball floating 12 metres (40 feet) away.HP Compaq Business NC6400 Battery

The Sun would be abeach ball 14 stories tall (somewhat smaller than the Spaceship Earth ride at Epcot) floating 5 kilometres (3 miles) away. While a complete model to this scale has never been built, a Solar System built centered in Washington DC, London, or Sydney, to that scale (approximately 1:31 000 000) would look like this:HP Compaq 490306-001 Battery

If the scale of the above model is increased to 1:310 000 000, i.e. all distances and sizes reduced by a factor of 10, then the Earth and Venus can be modeled by ping pong balls, the Moon and smaller planets by various size marbles or lumps of modeling clay, the gas giants by balloons or larger playing balls, Compaq Presario CQ35-100 Battery

and a circle the diameter of the Sun can be drawn on the floor of most classrooms. The scale distance to ? Centauri would be 1/3 of the way to the Moon.

A model based on a sports field

Relating the size of the Solar System to familiar objects can make it easier for students to grasp the relative distances.HP Compaq HSTNN-LB51 Battery

Most American schools have a football field associated with the high school (100 yards or 92 meters long). Other schools may have a soccer field nearby (90 to 120 m long). If the Sun was reduced to slightly less than one inch (21 mm), Pluto would be a 0.002 inch (0.05 mm) speck floating 100 yards (91.4 meters) away.HP Pavilion ZE4500 Battery

Jupiter would be less than three-thirty-secondths of an inch (2.38 mm) in diameter and would sit on the 13 yd (11.88 m) line. Uranus would be less than one-thirty-secondth of an inch (0.79 mm) sitting nearly on the 50 yd (45.72 m) line. At that scale, the speed of light would be about 1 inch every 5 seconds (5 mm per second). HP G62-100EB Battery

Light takes about 5.5 hours to go from the Sun to Pluto. Here is what the Solar System built to that scale would look like. This complete model would be simple to make with scale planets taped to wood stakes or metal rods. The scale is approximately 1:64 700 000 000.HP Pavilion DV6-1211AX Battery

A model for primary school children

Relating the size of objects to the planets can be difficult for children, particularly if the objects are so small that they cannot be seen. The Scale below is 10 x (times) the scale above, which is a convenient size, virtually all of the objects can be seen. At this scale the distance from the sun to Pluto is just under 1 km (metric units only). HP Pavilion DV6-1220SO Battery

At this scale, the speed of light would be about 50 mm per second. Light takes about 5.5 hours to go from the Sun to Pluto. The scale is approximately 1:6 470 000 000. At this scale the Sun could be represented by a children's soccer ball, and ? Centauri A is about the size of an adult soccer ball. HP EliteBook 6930P Battery

The smaller planets are about the size of "ice cream sprinkles" (which vary in size from less than 1mm to close to 2mm). Even at this scale ? Centauri A is on another continent or at the centre of the earth, a distance of about 6,300km.HP Pavilion DV6-1210SA Battery

Children can have some fun with this model, for example Mercury could be a small red sprinkle while Earth might be a larger blue sprinkle. Venus might be smaller. Children can look for two small red spirnkles for Mercury and Mars. To maintain relativities Mercury should be slightly smaller than Mars etc. Compaq Presario CQ71 Battery

The objects can be assembled in the classroom and then taken outside to a large park.

Misleading models

The models sketched here are an eye opener to many people interested in, but not knowing much about astronomy. HP Pavilion DV7-1290EO Battery

They are far cry from the drawings of the Solar System one usually sees in books or on the internet, such as the one to the right. Even if it is stated in the text that the layout is not to scale, it is often difficult for the reader to fully comprehend how discrepant the scale of the distances in the image is compared to the sizes of the objects depicted.HP G6000 Battery,HP HDX X18-1005EA Battery

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