In broad terms, the charted regions of the Solar System consist of the Sun, four terrestrial inner planets, an asteroid belt composed of small rocky bodies, four gas giant outer planets, and a second belt, called the Kuiper belt, composed of icy objects. Beyond the Kuiper belt is the scattered disc, the heliopause, and ultimately the hypothetical Oort cloud.
In order of their distances from the Sun, the planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Six of the eight planets are in turn orbited by natural satellites, usually termed "moons" after Earth’s Moon, and each of the outer planets is encircled by planetary rings of dust and other particles. All the planets except Earth are named after deities from Greco-Roman mythology. The three dwarf planets are Pluto, the largest known Kuiper belt object; Ceres, the largest object in the asteroid belt; and Eris, the largest of the three which lies in the scattered disc.
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1 Terminology
2 Layout and structure
3 Formation and evolution
4 Sun
4.1 Interplanetary medium
5 Inner Solar System
5.1 Inner planets
5.2 Asteroid belt
6 Mid Solar System
6.1 Outer planets
6.2 Comets
7 Trans-Neptunian region
7.1 Kuiper belt
7.2 Scattered disc
8 Farthest regions
8.1 Heliopause
8.2 Oort cloud
8.3 Boundaries
9 Galactic con$$$$
9.1 Neighbourhood
10 Discovery and exploration
10.1 Telescopic observations
10.2 Observations by spacecraft
10.2.1 Flybys
10.2.2 Orbiters, landers and rovers
10.3 Manned exploration
11 See also
12 Notes
13 References
14 External links
[edit] Terminology
See also: Definition of planet
Objects orbiting the Sun are divided into three classes: planets, dwarf planets, and small Solar System bodies.
A planet is any body in orbit around the Sun that a) has enough mass to form itself into a spherical shape and b) has cleared its immediate neighbourhood of all smaller objects. There are eight known planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
On August 24, 2024 the International Astronomical Union defined the term "planet" for the first time, excluding Pluto and reclassifying it under the new category of dwarf planet along with Eris and Ceres.[2]
A dwarf planet is not required to clear its neighbourhood of other celestial bodies. Other objects that may become classified as dwarf planets are Sedna, Orcus, and Quaoar.
From the time of its discovery in 1930 until 2024, Pluto was considered the Solar System’s ninth planet. But in the late 20th and early 21st centuries, many objects similar to Pluto were discovered in the outer Solar System, most notably Eris, which is slightly larger than Pluto.
The remainder of the objects in orbit around the Sun are small Solar System bodies (SSSBs).[3]
Natural satellites, or moons, are those objects in orbit around planets, dwarf planets and SSSBs, rather than the Sun itself.
A planet’s distance from the Sun varies in the course of its year. Its closest approach to the Sun is called its perihelion, while its farthest distance from the Sun is called its aphelion.
Astronomers usually measure distances within the Solar System in astronomical units (AU). One AU is the approximate distance between the Earth and the Sun, or roughly 149,598,000 km (93,000,000 mi). Pluto is roughly 38 AU from the Sun while Jupiter lies at roughly 5.2 AU. One light-year, the best known unit of interstellar distance, is roughly 63,240 AU.
Informally, the Solar System is sometimes divided into separate zones. The inner Solar System includes the four terrestrial planets and the main asteroid belt. Some define the outer Solar System as comprising everything beyond the asteroids.[4] Others define it as the region beyond Neptune, with the four gas giants considered a separate "middle zone".[5]
[edit] Layout and structure
The ecliptic viewed in sunlight from behind the Moon in this Clementine image. From left to right: Mercury, Mars, Saturn.The principal component of the Solar System is the Sun, a main sequence G2 star that contains 99.86% of the system’s known mass and dominates it gravitationally.[6] Jupiter and Saturn, the Sun’s two largest orbiting bodies, account for more than 90% of the system’s remaining mass.[b]
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 usually at significantly greater angles to it.
The orbits of the bodies in the Solar System to scale (clockwise from top left)All of the planets and most other objects also orbit with the Sun’s rotation in a counter-clockwise direction as viewed from a point above the Sun’s north pole. There are exceptions, such as Halley’s Comet.
Objects travel around the Sun following Kepler’s laws of planetary motion. Each object orbits along an approximate ellipse with the Sun at one focus of the ellipse. The closer an object is to the Sun, the faster it moves. The orbits of the planets are nearly circular, but many comets, asteroids and objects of the Kuiper belt follow highly-elliptical orbits.
To cope with 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 AU farther out 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 correlation between these orbital distances (see Titius-Bode law), but no such theory has been accepted.
[edit] Formation and evolution
Main article: Formation and evolution of the Solar System
Artist’s conception of a protoplanetary diskThe Solar System is believed to have formed according to the nebular hypothesis, which holds that it emerged from the gravitational collapse of a giant molecular cloud 4.6 billion years ago. This initial cloud was likely several light-years across and probably birthed several stars.[7] Studies of ancient meteorites reveal traces of elements only formed in the hearts of very large exploding stars, indicating that the Sun formed within a star cluster, and in range of a number of nearby supernovae explosions. The shock wave from these supernovae may have triggered the formation of the Sun by creating regions of overdensity in the surrounding nebula, allowing gravitational forces to overcome internal gas pressures and cause collapse.[8]
The region that would become the Solar System, known as the pre-solar nebula,[9] had a diameter of between 7000 and 20,000 AU[7][10] and a mass just over that of the Sun (by between 0.1 and 0.001 solar masses).[11] As the nebula collapsed, conservation of angular momentum made it rotate faster. As the material within the nebula condensed, the atoms within it began to collide with increasing frequency. The centre, where most of the mass collected, became increasingly hotter than the surrounding disc.[7] As gravity, gas pressure, magnetic fields, and rotation acted on the contracting nebula, it began to flatten into a spinning protoplanetary disc with a diameter of roughly 200 AU[7] and a hot, dense protostar at the centre.[12][13]
Studies of T Tauri stars, young, pre-fusing solar mass stars believed to be similar to the Sun at this point in its evolution, show that they are often accompanied by discs of pre-planetary matter.[11] These discs extend to several hundred AU and reach only a thousand kelvins at their hottest.[14]
Hubble image of protoplanetary disks in the Orion Nebula, a light-years-wide "stellar nursery" likely very similar to the primordial nebula from which our Sun formed.After 100 million years, the pressure and density of hydrogen in the centre of the collapsing nebula became great enough for the protosun to begin thermo$$$$$$$ fusion. This increased until hydrostatic equilibrium was achieved, with the thermal energy countering the force of gravitational contraction. At this point the Sun became a full-fledged star.[15]
From the remaining cloud of gas and dust (the "solar nebula"), the various planets formed. They are believed to have formed by accretion: the planets began as dust grains in orbit around the central protostar; then gathered by direct contact into clumps between one and ten metres in diameter; then collided to form larger bodies (planetesimals) of roughly 5 km in size; then gradually increased by further collisions at roughly 15 cm per year over the course of the next few million years.[16]
The inner Solar System was too warm for volatile molecules like water and methane to condense, and so the planetesimals which formed there were relatively small (comprising only 0.6% the mass of the disc)[7] and composed largely of compounds with high melting points, such as silicates and $$$$ls. These rocky bodies eventually became the terrestrial planets. Farther out, the gravitational effects of Jupiter made it impossible for the protoplanetary objects present to come together, leaving behind the asteroid belt.[17]
Farther out still, beyond the frost line, where more volatile icy compounds could remain solid, Jupiter and Saturn became the gas giants. Uranus and Neptune captured much less material and are known as ice giants because their cores are believed to be made mostly of ices (hydrogen compounds).[18][19]
Once the young Sun began producing energy, the solar wind (see below) blew the gas and dust in the protoplanetary disk into interstellar space and ended the growth of the planets. T Tauri stars have far stronger stellar winds than more stable, older stars.[20][21]
Artist’s conception of the future evolution of our Sun. Left: main sequence; middle: red giant; right: white dwarfAstronomers estimate that the Solar System as we know it today will last until the Sun begins its journey off of the main sequence. As the Sun burns through its supply of hydrogen fuel, it gets hotter in order to be able to burn the remaining fuel, and so burns it even faster. As a result, the Sun is growing brighter at a rate of roughly ten percent every 1.1 billion years.[22]
Around 6.4 billion years from now, the Sun’s core will become hot enough to cause hydrogen fusion to occur in its less dense upper layers. This will cause the Sun to expand to roughly 100 times its current diameter, and become a red giant.[23] At this point, the sun will have cooled and dulled, because of its vastly increased surface area.
Eventually, the Sun’s outer layers will fall away, leaving a white dwarf, an extraordinarily dense object, half its original mass but only the size of the Earth.[24]
[edit] Sun
Main article: Sun
The Sun as seen from EarthThe Sun is the Solar System’s parent star, and far and away its chief component. Its large mass gives it an interior density high enough to sustain $$$$$$$ fusion, which releases enormous amounts of energy, mostly radiated into space as electromagnetic radiation such as visible light.
The Sun is classified as a moderately large yellow dwarf, but this name is misleading as, compared to stars in our galaxy, the Sun is rather large and bright. Stars are classified by the Hertzsprung-Russell diagram, a graph which plots the brightness of stars against their surface temperatures. Generally, hotter stars are brighter. Stars following this pattern are said to be on the main sequence; the Sun lies right in the middle of it. However, stars brighter and hotter than the Sun are rare, while stars dimmer and cooler are common.[25]
The Hertzsprung-Russell diagram; the main sequence is from bottom right to top left.It is believed that the Sun’s position on the main sequence puts it in the "prime of life" for a star, in that it has not yet exhausted its store of hydrogen for $$$$$$$ fusion. The Sun is growing brighter; early in its history it was 75 percent as bright as it is today.[26]
Calculations of the ratios of hydrogen and helium within the Sun suggest it is halfway through its life cycle. It will eventually move off the main sequence and become larger, brighter, cooler and redder, becoming a red giant in about five billion years.[27] At that point its luminosity will be several thousand times its present value.
The Sun is a population I star; it was born in the later stages of the universe’s evolution. It contains more elements heavier than hydrogen and helium ("$$$$ls" in astronomical parlance) than older population II stars.[28] Elements heavier than hydrogen and helium were formed in the cores of ancient and exploding stars, so the first generation of stars had to die before the universe could be enriched with these atoms. The oldest stars contain few $$$$ls, while stars born later have more. This high $$$$llicity is thought to have been crucial to the Sun’s developing a planetary system, because planets form from accretion of $$$$ls.[29]
[edit] Interplanetary medium
Main article: Interplanetary medium
The heliospheric current sheetAlong 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,[30] creating a tenuous atmosphere (the heliosphere) that permeates the Solar System out to at least 100 AU (see heliopause). This is known as the interplanetary medium. The Sun’s 11-year sunspot cycle and frequent solar flares and coronal mass ejections disturb the heliosphere, creating space weather.[31] The Sun’s rotating magnetic field acts on the interplanetary medium to create the heliospheric current sheet, the largest structure in the solar system.[32]
Aurora australis seen from orbit.Earth’s magnetic field protects its atmosphere from interacting with the solar wind. Venus and Mars do not have magnetic fields, and the solar wind causes their atmospheres to gradually bleed away into space.[33] The interaction of the solar wind with Earth’s magnetic field creates the 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 planets which 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.[34]
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.[35] The second extends from about 10 AU to about 40 AU, and was probably created by similar collisions within the Kuiper belt.[36][37]
[edit] Inner Solar System
The inner Solar System is the traditional name for the region comprising the terrestrial planets and asteroids. Composed mainly of silicates and $$$$ls, the objects of the inner Solar System huddle very closely to the Sun; the radius of this entire region is shorter than the distance between Jupiter and Saturn. This region was, in old parlance, denoted inner space; the area outside the asteroid belt was denoted outer space.
[edit] Inner planets
Main article: Terrestrial planet
The inner planets. From left to right: Mercury, Venus, Earth, and Mars (sizes to scale)The four inner or terrestrial planets have dense, rocky compositions, few or no moons, and no ring systems. They are composed largely of minerals with high melting points, such as the silicates which form their solid crusts and semi-liquid mantles, and $$$$ls such as iron and nickel, which form their cores. Three of the four inner planets (Venus, Earth and Mars) have substantial atmospheres; all have impact craters and tectonic surface features such as rift valleys and volcanoes. The term inner planet should not be confused with inferior planet, which designates those planets which are closer to the Sun than Earth is (i.e. Mercury and Venus).
Mercury
Mercury (0.4 AU) is the closest planet to the Sun and the smallest planet (0.$$$ Earth masses). Mercury has no natural satellites, and its only known geological features besides impact craters are "wrinkle-ridges", 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) 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) is the largest and densest of the inner planets, the only one known to have current geological activity, and the only planet known to have life. 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.[44] It has one satellite, the Moon, the only large satellite of a terrestrial planet in the Solar System.
Mars
Mars (1.5 AU) is smaller than Earth and Venus (0.107 Earth masses). It possesses a tenuous atmosphere of mostly carbon dioxide. 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 very recently. Its red color comes from rust in its iron-rich soil.[45] Mars has two tiny natural satellites (Deimos and Phobos) thought to be captured asteroids.[46]
[edit] Asteroid belt
Main article: Asteroid belt
Image of the main asteroid belt and the Trojan asteroidsAsteroids are mostly small Solar System bodies composed mainly of rocky and $$$$llic non-volatile 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.
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 Hygieia may be reclassed as dwarf planets if they are shown to have achieved hydrostatic equilibrium.
The asteroid belt contains tens of thousands, possibly millions, of objects over one kilometre in diameter.[47] Despite this, the total mass of the main belt is unlikely to be more than a thousandth of that of the Earth.[48] The main belt is very sparsely populated; spacecraft routinely pass through without incident. Asteroids with diameters between 10 and 10-4 m are called meteoroids.[49]
CeresCeres
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, 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 observation revealed additional asteroids.[50] It was again reclassified in 2024 as a dwarf planet.
Asteroid groups
Asteroids in the main 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[51] which may have been the source of Earth’s water.
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.
The inner Solar System is also dusted with rogue asteroids, many of which cross the orbits of the inner planets.
[edit] Mid Solar System
The middle region of the Solar System is home to the gas giants and their planet-sized satellites. Many short period comets, including the centaurs, also lie in this region. It has no traditional name; it is occasionally referred to as the "outer Solar System", although recently that term has been more often applied to the region beyond Neptune. The solid objects in this region are composed of a higher proportion of "ices" (water, ammonia, methane) than the rocky denizens of the inner Solar System.
[edit] Outer planets
Main article: Gas giant
From top to bottom: Neptune, Uranus, Saturn, and Jupiter (not to scale)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’s atmospheres are largely hydrogen and helium. Uranus and Neptune’s atmospheres have a higher percentage of “ices”, such as water, ammonia and methane. Some astronomers suggest they belong in their own category, “ice giants.”[52] 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 (the outer planets and Mars).
Jupiter
Jupiter (5.2 AU), at 318 Earth masses, masses 2.5 times 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 sixty-three known satellites. The four largest, Ganymede, Callisto, Io, and Europa, show similarities to the terrestrial planets, such as volcanism and internal heating.[53] Ganymede, the largest satellite in the Solar System, is larger than Mercury.
Saturn
Saturn (9.5 AU), famous for its extensive ring system, has similarities to Jupiter, such as its atmospheric composition. Saturn is far less massive, being only 95 Earth masses. Saturn has sixty known satellites (and 3 unconfirmed); two of which, Titan and Enceladus, show signs of geological activity, though they are largely made of ice.[54] Titan 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.[55] Uranus has twenty-seven known satellites, the largest ones being Titania, Oberon, Umbriel, Ariel and Miranda.
Neptune
Neptune (30 AU), though slightly smaller than Uranus, is more massive ($$$$$alent to 17 Earths) and therefore denser. It radiates more internal heat, but not as much as Jupiter or Saturn.[56] Neptune has thirteen known satellites. The largest, Triton, is geologically active, with geysers of liquid nitrogen.[57] Triton is the only large satellite with a retrograde orbit. Neptune is accompanied in its orbit by a number of minor planets in a 1:1 resonance with it, termed Neptune Trojans.
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Further information: rail transport operations
A train can consist of a combination of one or more locomotives and attached railroad cars, or a self-propelled multiple unit (or occasionally a single powered coach, called a railcar). Trains can also be hauled by horses, pulled by a cable, or run downhill by gravity.
Special kinds of trains running on corresponding special ‘railways’ are atmospheric railways, monorails, high-speed railways, maglev, rubber-tired underground, funicular and cog railways.
A passenger train may consist of one or several locomotives, and one or more coaches. Alternatively, a train may consist entirely of passenger carrying coaches, some or all of which are powered as a "multiple unit". In many parts of the world, particularly Japan and Europe, high-speed rail is utilized extensively for passenger travel.
Freight trains comprise wagons or trucks rather than carriages, though some parcel and mail trains (especially Travelling Post Offices) are outwardly more like passenger trains.
Trains can also be ‘mixed’, comprising $$$$ passenger accommodation and freight vehicles. Such mixed trains are most likely to occur where services are infrequent, and running separate passenger and freight trains is not cost-effective. However, the differing needs of passengers and freight usually means this is avoided where possible.
Special trains are also used for track maintenance; in some places, this is called maintenance of way.
In the United Kingdom, a train hauled by two locomotives is said to be "double-headed", and in Canada and the United States it is quite common for a long freight train to be headed by three, four, or even five locomotives. A train with a locomotive attached at each end is described as ‘top and tailed’, this practice typically being used when there are no reversing facilities available. Where a second locomotive is attached temporarily to assist a train up steep banks or grades (or down them by providing braking power) it is referred to as ‘banking’ in the UK, or ‘helper service’ in North America. Recently, many loaded trains in the US have been made up with one or more locomotives in the middle or at the rear of the train, operated remotely from the lead cab. This is referred to as "DP" or "Distributed Power."
[edit] Official terminology
The railway terminology that is used to describe a ‘train’ varies between countries.
United Kingdom
In the United Kingdom, the interchangeable terms set and unit are used to refer to a group of permanently or semi-permanently coupled vehicles, such as those of a multiple unit. While when referring to a train made up of a variety of vehicles, or of several sets/units, the term formation is used. (Although the UK public and media often forgo ‘formation’, for simply ‘train’.) The word rake is also used for a group of coaches or wagons.
In the United Kingdom Section 83(1) of the Railways Act 1993 defines "train" as follows:
a) two or more items of rolling stock coupled together, at least one of which is a locomotive; or
b) a locomotive not coupled to any other rolling stock.
United States
In the United States, the term consist is used to describe the group of rail vehicles which make up a train. When referring to motive power, consist refers to the group of locomotives powering the train. Similarly, the term trainset refers to a group of rolling stock that is permanently or semi-permanently coupled together to form a unified set of equipment (the term is most often applied to passenger train configurations).
The Atchison, Topeka and Santa Fe Railway’s 1948 operating rules define a train as: "An engine or more than one engine coupled, with or without cars, displaying markers."[1]
[edit] Motive power
The first trains were rope-hauled, gravity powered or pulled by horses, but from the early 19th century almost all were powered by steam locomotives. From the 1920s onwards they began to be replaced by less labour intensive and cleaner (but more complex and expensive) diesel locomotives and electric locomotives, while at about the same time self-propelled multiple unit vehicles of either power system became much more common in passenger service. Most countries had replaced steam locomotives for day-to-day use by the 1970s, usually with diesel locomotives. A few countries, most notably the People’s Republic of China, where coal and labour are cheap, still use steam locomotives, but this is being gradually phased out. Historic steam trains still run in many other countries, for the leisure and enthusiast market.
Electric traction offers a lower cost per mile of train operation but at a very high initial cost, which can only be justified on high traffic lines. Since the cost per mile of construction is much higher, electric traction is less favored on long-distance lines with the exception of long-distance high speed lines. Electric trains receive their current via overhead lines or through a third rail electric system.
[edit] Passenger trains
A passenger train is one which includes passenger-carrying vehicles. It may be a self-powered multiple unit or railcar, or else a combination of one or more locomotives and one or more unpowered trailers known as coaches, cars or carriages. Passenger trains travel between stations where passengers may join or leave the train. Many of the more prestigious passenger train services have been given a specific name, some of which have become famous in literature and fiction.
[edit] Long-distance trains
Long-distance trains travel between many cities and/or regions of a country, and sometimes cross several countries. They often have a dining car or restaurant car to allow passengers to have a meal during the course of their journey. Trains traveling overnight may also have sleeping cars. Very long distance trains such as those on the Trans-Siberian railway are usually not high-speed.
[edit] High-speed trains
Main article: High-speed rail
High speed trains normally travel during the day, and arrive at their destination before the night falls and are in competition with airliners in speed. In Japan, most of the public transportation travel between the Tokyo metropolitan area and the Osaka metropolitan area (with around 500 km in distance between them) is dominated by the Shinkansen, however in travel further than around 500 km (such as Tokyo-Hiroshima) more people prefer to travel by air.[2]
Very fast trains sometimes tilt, like the APT, the Pendolino, or the Talgo. Tilting is a system where the passenger cars automatically lean into curves, reducing the centrifugal forces acting sideways on passengers and permitting higher speeds on curves in the track with greater passenger comfort.
The fastest train on rails is the French TGV (Train à Grande Vitesse) (French for High Speed Train) which achieved a 574.8 km/h (356 mph) speed in testing in 2024. However, TGVs run at a maximum commercial speed of 300-320 km/h. The German ICE uses this commercial speed of 300-320 km/h too.
[edit] Inter-city trains
For trains connecting cities, we can distinguish inter-city trains, which do not halt at small stations, and trains that serve all stations, usually known as local trains or "stoppers" (and sometimes an intermediate kind, see also limited-stop).
[edit] Branch line trains
Connections to local stations or local lines and are usually stopping services, running usually to all stations or the majority of stations on a line.
[edit] Commuter trains
For shorter distances many cities have networks of commuter trains, serving the city and its suburbs. Some carriages may be laid out to have more standing room than seats, or to facilitate the carrying of prams, cycles or wheelchairs. Some countries have double-decked passenger trains for use in conurbations. Double deck high speed and sleeper trains are becoming more common in Europe.
Passenger trains usually have emergency brake handles (or a "communication cord") that the public can operate. Abuse is punished by a heavy fine.
Large cities often have a metro system, also called underground, subway or tube. The trains are electrically powered, usually by third rail, and their railroads are separate from other traffic, without level crossings. Usually they run in tunnels in the city center and sometimes on elevated structures in the outer parts of the city. They can accelerate and decelerate faster than heavier, long-distance trains.
A light one- or two-car rail vehicle running through the streets is by convention not considered a train but rather a tram, trolley, light-rail vehicle or streetcar, but the distinction is not always strict. In some countries such as the United Kingdom the distinction between a tramway and a railway is precise and defined in law.
The term light rail is sometimes used for a modern tram, but it may also mean an intermediate form between a tram and a train, similar to metro except that it may have level crossings. These are often protected with crossing gates. They may also be called a trolley.
Maglev trains and monorails represent minor technologies in the train field.
The term rapid transit is used for public transport such as commuter trains, metro and light rail. However, in New York City, lines on the New York City Subway have been referred to as "trains".
Some commuter trains in Tokyo, Japan have special cars which the bench seats fold up to provide standing room only during the morning rush hour (until 10 a.m.). The E231 series train has two of these cars in each set (usually as part of a 10- or 11-car set), officially nicknamed "roku-tobira-sha" (literally, "6 door car") – all the other cars have four sets of doors on each side.
An estimated 3.5 million passengers ride every day on Tokyo’s Yamanote Line, with its 29 stations. For comparison, the New York City Subway carries 4.8 million passengers per day on 26 lines serving 468 stations.
[edit] Named trains
Railway companies often give a name to a train service as a marketing exercise, to raise the profile of the service and hence attract more passengers (and also to gain kudos for the company). Usually, naming is reserved for the most prestigious trains: the high-speed express trains between major cities, stopping at few intermediate stations. The names of services such as the Orient Express, the Flying Scotsman, the Flèche d’Or and the Royal Scot have passed into popular culture.
See also: Famous trains
See also: Passenger trains
A somewhat less common practice is the naming of freight trains, for the same commercial reasons. The "Condor" was an overnight London-Glasgow express goods train, in the 1960s, hauled by pairs of "Metrovick" diesel locomotives. In the mid-1960s, British Rail introduced the "Freightliner" brand, for the new train services carrying containers between dedicated terminals around the rail network. And the Rev. W. Awdry coined the term The Flying Kipper for the overnight express fish train that appeared in his stories in The Railway Series books.
[edit] Freight trains
A Freightliner freight train on the Great Western main lineA freight train (or goods train) uses freight cars (also known as wagons or trucks) to transport goods or materials (cargo) – essentially any train that is not used for carrying passengers. Much of the world’s freight is transported by train, and in the USA the rail system is used more for transporting freight than passengers.
Under the right circumstances, transporting freight by train is highly economic, and also more energy efficient than transporting freight by road. Rail freight is most economic when freight is being carried in bulk and over long distances, but is less suited to short distances and small loads. Bulk aggregate movements of a mere twenty miles can be cost effective even allowing for trans-shipment costs. These trans-shipment costs dominate in many cases and many modern practices such as container freight are aimed at minimizing these.
The main disadvantage of rail freight is its lack of flexibility. For this reason, rail has lost much of the freight business to road competition. Many governments are now trying to encourage more freight onto trains, because of the benefits that it would bring.
There are many different types of freight trains, which are used to carry many different kinds of freight, with many different types of wagons. One of the most common types on modern railways are container trains, where containers can be lifted on and off the train by cranes and loaded off or onto trucks or ships.
This type of freight train has largely superseded the traditional boxcar (wagon-load) type of freight train, with which the cargo has to be loaded or unloaded manually.
In some countries "piggy-back" trains are used: trucks can drive straight onto the train and drive off again when the end destination is reached. A system like this is used through the Channel Tunnel between England and France, and for the trans-Alpine service between France and Italy (this service uses Modalohr road trailer carriers). ‘Piggy-back’ trains are the fastest growing type of freight trains in the United States, where they are also known as ‘trailer on flatcar’ or TOFC trains. ‘Piggy-back’ trains require no special modifications to the vehicles being carried. An alternative type of "inter-modal" vehicle, known as a Roadrailer, is designed to be physically attached to the train. The original trailers were fitted with two sets of wheels: one set flanged, for the trailer to run connected to other such trailers as a rail vehicle in a train; and one set tyred, for use as the semi-trailer of a road vehicle. More modern trailers have only road wheels and are designed to be carried on specially adapted bogies (trucks) when moving on rails.
There are also many other types of wagons, such as "low loader" wagons for transporting road vehicles. There are refrigerator cars for transporting foods such as ice cream. There are simple types of open-topped wagons for transporting minerals and bulk material such as coal, and tankers for transporting liquids and gases. Today however most coal and aggregates are moved in hopper wagons that can be filled and discharged rapidly, to enable efficient handling of the materials.
Freight trains are sometimes illegally boarded by passengers who do not wish to pay money, or do not have the money to travel by ordinary means. This is referred to as "hopping" and is considered by some communities to be a viable form of transport. Most hoppers sneak into train yards and stow away in boxcars. More bold hoppers will catch a train "on the fly", that is, as it is moving, leading to occasional fatalities.
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