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Galaxy groups and clusters

Galaxy groups and clusters are the largest known gravitationally bound objects to have arisen thus far in the process of cosmic structure formation. They form the densest part of the large-scale structure of the Universe. In models for the gravitational formation of structure with cold dark matter, the smallest structures collapse first and eventually build the largest structures, clusters of galaxies. Clusters are then formed relatively recently between 10 billion years ago and now. Groups and clusters may contain ten to thousands of individual galaxies. The clusters themselves are often associated with larger, non-gravitationally bound, groups called superclusters.

Groups of galaxies

Groups of galaxies are the smallest aggregates of galaxies. They typically contain no more than 50 galaxies in a diameter of 1 to 2 megaparsecs (Mpc)(see 1022 m for distance comparisons). Their mass is approximately 1013 solar masses. The spread of velocities for the individual galaxies is about 150 km/s. However, this definition should be used as a guide only, as larger and more massive galaxy systems are sometimes classified as galaxy groups. Groups are the most common structures of galaxies in the universe, comprising at least 50% of the galaxies in the local universe. Groups have a mass range between those of the very large elliptical galaxies and clusters of galaxies.

Our own galaxy, the Milky Way, is contained in the Local Group of more than 54 galaxies.

In July 2017 S. Paul, R. S. John et al. defined clear distinguishing parameters for classifying galaxy aggregations as ‘galaxy groups’ and ‘clusters’ on the basis of scaling laws that they followed. According to this paper, galaxy aggregations less massive than 8 × 1013 solar masses are classified as galaxy groups.

Clusters of galaxies

Clusters are larger than groups, although there is no sharp dividing line between the two. When observed visually, clusters appear to be collections of galaxies held together by mutual gravitational attraction. However, their velocities are too large for them to remain gravitationally bound by their mutual attractions, implying the presence of either an additional invisible mass component, or an additional attractive force besides gravity. X-ray studies have revealed the presence of large amounts of intergalactic gas known as the intracluster medium. This gas is very hot, between 107K and 108K, and hence emits X-rays in the form of bremsstrahlung and atomic line emission.

The total mass of the gas is greater than that of the galaxies by roughly a factor of two. However, this is still not enough mass to keep the galaxies in the cluster. Since this gas is in approximate hydrostatic equilibrium with the overall cluster gravitational field, the total mass distribution can be determined. It turns out the total mass deduced from this measurement is approximately six times larger than the mass of the galaxies or the hot gas. The missing component is known as dark matter and its nature is unknown. In a typical cluster perhaps only 5% of the total mass is in the form of galaxies, maybe 10% in the form of hot X-ray emitting gas and the remainder is dark matter. Brownstein and Moffat use a theory of modified gravity to explain X-ray cluster masses without dark matter. Observations of the Bullet Cluster are the strongest evidence for the existence of dark matter;  however, Brownstein and Moffat have shown that their modified gravity theory can also account for the properties of the cluster.

Observational methods

Clusters of galaxies have been found in surveys by a number of observational techniques and have been studied in detail using many methods:
 * Optical or infrared: The individual galaxies of clusters can be studied through optical or infrared imaging and spectroscopy. Galaxy clusters are found by optical or infrared telescopes by searching for overdensities, and then confirmed by finding several galaxies at a similar redshift. Infrared searches are more useful for finding more distant (higher redshift) clusters.
 * X-ray: The hot plasma emits X-rays that can be detected by X-ray telescopes. The cluster gas can be studied using both X-ray imaging and X-ray spectroscopy. Clusters are quite prominent in X-ray surveys and along with AGN are the brightest X-ray emitting extragalactic objects.
 * Radio: A number of diffuse structures emitting at radio frequencies have been found in clusters. Groups of radio sources (that may include diffuse structures or AGN) have been used as tracers of cluster location. At high redshift imaging around individual radio sources (in this case AGN) has been used to detect proto-clusters (clusters in the process of forming).
 * Sunyaev-Zel'dovich effect: The hot electrons in the intracluster medium scatter radiation from the cosmic microwave background through inverse Compton scattering. This produces a "shadow" in the observed cosmic microwave background at some radio frequencies.
 * Gravitational lensing: Clusters of galaxies contain enough matter to distort the observed orientations of galaxies behind them. The observed distortions can be used to model the distribution of dark matter in the cluster.

Temperature and density

Clusters of galaxies are the most recent and most massive objects to have arisen in the hierarchical structure formation of the Universe and the study of clusters tells one about the way galaxies form and evolve. Clusters have two important properties: their masses are large enough to retain any energetic gas ejected from member galaxies and the thermal energy of the gas within the cluster is observable within the X-Ray bandpass. The observed state of gas within a cluster is determined by a combination of shock heating during accretion, radiative cooling, and thermal feedback triggered by that cooling. The density, temperature, and substructure of the intracluster X-Ray gas therefore represents the entire thermal history of cluster formation. To better understand this thermal history one needs to study the entropy of the gas because entropy is the quantity most directly changed by increasing or decreasing the thermal energy of intracluster gas.

title: Galaxy groups and clusters


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Grus (constellation)

Grus (, or colloquially ) is a constellation in the southern sky. Its name is Latin for the crane, a type of bird. It is one of twelve constellations conceived by Petrus Plancius from the observations of Pieter Dirkszoon Keyser and Frederick de Houtman. Grus first appeared on a 35 cm celestial globe published in 1598 in Amsterdam by Plancius and Jodocus Hondius and was depicted in Johann Bayer's star atlas Uranometria of 1603. French explorer and astronomer Nicolas-Louis de Lacaille gave Bayer designations to its stars in 1756, some of which had been previously considered part of the neighbouring constellation Piscis Austrinus. The constellations Grus, Pavo, Phoenix and Tucana are collectively known as the "Southern Birds".

The constellation's brightest star, Alpha Gruis, is also known as Alnair and appears as a 1.7-magnitude blue-white star. Beta Gruis is a red giant variable star with a minimum magnitude of 2.3 and a maximum magnitude of 2.0. Six star systems have been found to have planets: the red dwarf Gliese 832 is one of the closest stars to Earth to have a planetary system. Another—WASP-95—has a planet that orbits every two days. Deep-sky objects found in Grus include the planetary nebula IC 5148, also known as the Spare Tyre Nebula, and a group of four interacting galaxies known as the Grus Quartet.

History
The stars that form Grus were originally considered part of the neighbouring constellation Piscis Austrinus (the southern fish), with Gamma Gruis seen as part of the fish's tail. The stars were first defined as a separate constellation by the astronomer Petrus Plancius, who created twelve new constellations based on the observations of the southern sky by the Dutch explorers Pieter Dirkszoon Keyser and Frederick de Houtman, who had sailed on the first Dutch trading expedition, known as the Eerste Schipvaart, to the East Indies. Grus first appeared on a 35-centimetre-diameter celestial globe published in 1598 in Amsterdam by Plancius with Jodocus Hondius. Its first depiction in a celestial atlas was in the German cartographer Johann Bayer's Uranometria of 1603. De Houtman included it in his southern star catalogue the same year under the Dutch name Den Reygher, "The Heron", but Bayer followed Plancius and Hondius in using Grus.

An alternative name for the constellation, Phoenicopterus (Latin "flamingo"), was used briefly during the early 17th century, seen in the 1605 work Cosmographiae Generalis by Paul Merula of Leiden University and a c. 1625 globe by Dutch globe maker Pieter van den Keere. Astronomer Ian Ridpath has reported the symbolism likely came from Plancius originally, who had worked with both of these people. Grus and the nearby constellations Phoenix, Tucana and Pavo are collectively called the "Southern Birds".

The stars that correspond to Grus were generally too far south to be seen from China. In Chinese astronomy, Gamma and Lambda Gruis may have been included in the tub-shaped asterism Bàijiù, along with stars from Piscis Austrinus. In Central Australia, the Arrernte and Luritja people living on a mission in Hermannsburg viewed the sky as divided between them, east of the Milky Way representing Arrernte camps and west denoting Luritja camps. Alpha and Beta Gruis, along with Fomalhaut, Alpha Pavonis and the stars of Musca, were all claimed by the Arrernte.

Characteristics
Grus is bordered by Piscis Austrinus to the north, Sculptor to the northeast, Phoenix to the east, Tucana to the south, Indus to the southwest, and Microscopium to the west. Bayer straightened the tail of Piscis Austrinus to make way for Grus in his Uranometria. Covering 366 square degrees, it ranks 45th of the 88 modern constellations in size and covers 0.887% of the night sky. The three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is "Gru". The official constellation boundaries, as set by Belgian astronomer Eugène Delporte in 1930, are defined as a polygon of 6 segments. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 21:27.4:0 and 23:27.1:0, while the declination coordinates are between −36.31° and −56.39°. Grus is located too far south to be seen by observers in the British Isles and the northern United States, though it can easily be seen from Florida or San Diego; the whole constellation is visible to observers south of latitude 33°N.

Stars
Keyser and de Houtman assigned twelve stars to the constellation. Bayer depicted Grus on his chart, but did not assign its stars Bayer designations. French explorer and astronomer Nicolas-Louis de Lacaille labelled them Alpha to Phi in 1756 with some omissions. In 1879, American astronomer Benjamin Gould added Kappa, Nu, Omicron and Xi, which had all been catalogued by Lacaille but not given Bayer designations. Lacaille considered them too faint, while Gould thought otherwise. Xi Gruis had originally been placed in Microscopium. Conversely, Gould dropped Lacaille's Sigma as he thought it was too dim.

Grus has several bright stars. Marking the left wing is Alpha Gruis, a blue-white star of spectral type B6V and apparent magnitude 1.7, around 101 light-years from Earth. Its traditional name, Alnair, means "the bright one" and refers to its status as the brightest star in Grus (although the Arabians saw it as the brightest star in the Fish's tail, as Grus was then depicted).Alnair Alnair is around 380 times as luminous and has over 3 times the diameter of the Sun. Lying 5 degrees west of Alnair, denoting the Crane's heart is Beta Gruis (the proper name is Tiaki ), a red giant of spectral type M5III. It has a diameter of 0.8 astronomical units (AU) (if placed in the Solar System it would extend to the orbit of Venus) located around 170 light-years from Earth. It is a variable star with a minimum magnitude of 2.3 and a maximum magnitude of 2.0. An imaginary line drawn from the Great Square of Pegasus through Fomalhaut will lead to Alnair and Beta Gruis.

Lying in the northwest corner of the constellation and marking the crane's eye is Gamma Gruis, a blue-white subgiant of spectral type B8III and magnitude 3.0 lying around 211 light-years from Earth. Also known as Al Dhanab, it has finished fusing its core hydrogen and has begun cooling and expanding, which will see it transform into a red giant.

There are several double stars visible to the naked eye in Grus. Forming a triangle with Alnair and Beta, Delta Gruis is an optical double whose components—Delta1 and Delta2—are separated by 45 arcseconds. Delta1 is a yellow giant of spectral type G7III and magnitude 4.0, 309 light-years from Earth, and may have its own magnitude 12 orange dwarf companion. Delta2 is a red giant of spectral type M4.5III and semiregular variable that ranges between magnitudes 3.99 and 4.2, located 325 light-years from Earth. It has around 3 times the mass and 135 times the diameter of the Sun. Mu Gruis, composed of Mu1 and Mu2, is also an optical double—both stars are yellow giants of spectral type G8III around 2.5 times as massive as the Sun with surface temperatures of around 4900 K. Mu1 is the brighter of the two at magnitude 4.8 located around 275 light-years from Earth, while Mu2 the dimmer at magnitude 5.11 lies 265 light-years distant from Earth. Pi Gruis, an optical double with a variable component, is composed of Pi1 Gruis and Pi2. Pi1 is a semi-regular red giant of spectral type S5, ranging from magnitude 5.31 to 7.01 over a period of 191 days, and is around 532 light-years from Earth. One of the brightest S-class stars to Earth viewers, it has a companion star of apparent magnitude 10.9 with sunlike properties, being a yellow main sequence star of spectral type G0V. The pair make up a likely binary system. Pi2 is a giant star of spectral type F3III-IV located around 130 light-years from Earth, and is often brighter than its companion at magnitude 5.6. Marking the right wing is Theta Gruis, yet another double star, lying 5 degrees east of Delta1 and Delta2.

RZ Gruis is a binary system of apparent magnitude 12.3 with occasional dimming to 13.4, whose components—a white dwarf and main sequence star—are thought to orbit each other roughly every 8.5 to 10 hours. It belongs to the UX Ursae Majoris subgroup of cataclysmic variable star systems, where material from the donor star is drawn to the white dwarf where it forms an accretion disc that remains bright and outshines the two component stars. The system is poorly understood, though the donor star has been calculated to be of spectral type F5V. These stars have spectra very similar to novae that have returned to quiescence after outbursts, yet they have not been observed to have erupted themselves. The American Association of Variable Star Observers recommends watching them for future events. CE Gruis (also known as Grus V-1) is a faint (magnitude 18–21) star system also composed of a white dwarf and donor star; in this case the two are so close they are tidally locked. Known as polars, material from the donor star does not form an accretion disc around the white dwarf, but rather streams directly onto it.

Six star systems are thought to have planetary systems. Tau1 Gruis is a yellow star of magnitude 6.0 located around 106 light-years away. It may be a main sequence star or be just beginning to depart from the sequence as it expands and cools. In 2002 the star was found to have a planetary companion. HD 215456, HD 213240 and WASP-95 are yellow sunlike stars discovered to have two planets, a planet and a remote red dwarf, and a hot Jupiter, respectively; this last—WASP-95b—completes an orbit round its sun in a mere two days. Gliese 832 is a red dwarf of spectral type M1.5V and apparent magnitude 8.66 located only 16.1 light-years distant; hence it is one of the nearest stars to the Solar System. A Jupiter-like planet—Gliese 832 b—orbiting the red dwarf over a period of 9.4±0.4 years was discovered in 2008. WISE 2220−3628 is a brown dwarf of spectral type Y, and hence one of the coolest star-like objects known. It has been calculated as being around 26 light-years distant from Earth.

In July 2019, astronomers reported finding a star, S5-HVS1, traveling 1755 km/s, faster that any other star detected so far. The star is in the Grus constellation in the southern sky, and about 29,000 light-years from Earth, and may have been propelled out of the Milky Way galaxy after interacting with Sagittarius A*, the supermassive black hole at the center of the galaxy.

Deep-sky objects
Nicknamed the spare-tyre nebula, IC 5148 is a planetary nebula located around 1 degree west of Lambda Gruis. Around 3000 light-years distant, it is expanding at 50 kilometres a second, one of the fastest rates of expansion of all planetary nebulae.

Northeast of Theta Gruis are four interacting galaxies known as the Grus Quartet. These galaxies are NGC 7552, NGC 7590, NGC 7599, and NGC 7582. The latter three galaxies occupy an area of sky only 10 arcminutes across and are sometimes referred to as the "Grus Triplet," although all four are part of a larger loose group of galaxies called the IC 1459 Grus Group. NGC 7552 and 7582 are exhibiting high starburst activity; this is thought to have arisen because of the tidal forces from interacting. Located on the border of Grus with Piscis Austrinus, IC 1459 is a peculiar E3 giant elliptical galaxy. It has a fast counterrotating stellar core, and shells and ripples in its outer region. The galaxy has an apparent magnitude of 11.9 and is around 80 million light-years distant.

NGC 7424 is a barred spiral galaxy with an apparent magnitude of 10.4. located around 4 degrees west of the Grus Triplet. Approximately 37.5 million light-years distant, it is about 100,000 light-years in diameter, has well defined spiral arms and is thought to resemble the Milky Way. Two ultraluminous X-ray sources and one supernova have been observed in NGC 7424. SN 2001ig was discovered in 2001 and classified as a Type IIb supernova, one that initially showed a weak hydrogen line in its spectrum, but this emission later became undetectable and was replaced by lines of oxygen, magnesium and calcium, as well as other features that resembled the spectrum of a Type Ib supernova. A massive star of spectral type F, A or B is thought to be the surviving binary companion to SN 2001ig, which was believed to have been a Wolf–Rayet star.

Located near Alnair is NGC 7213, a face-on type 1 Seyfert galaxy located approximately 71.7 million light-years from Earth. It has an apparent magnitude of 12.1. Appearing undisturbed in visible light, it shows signs of having undergone a collision or merger when viewed at longer wavelengths, with disturbed patterns of ionized hydrogen including a filament of gas around 64,000 light-years long. It is part of a group of ten galaxies.

NGC 7410 is a spiral galaxy discovered by British astronomer John Herschel during observations at the Cape of Good Hope in October 1834. The galaxy has a visual magnitude of 11.7 and is approximately 122 million light-years distant from Earth.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Grus (constellation)


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Gia (disambiguation)

Gia is a 1998 film about Gia Marie Carangi.

GIA or Gia may also refer to:

People

 * Gia (name), a given name (including a list of people with the name)

Places

 * Gia, Leh, a village in India
 * Gan International Airport, Maldives
 * Glasgow International Airport, Scotland, UK

Groups, companies, organizations

 * GIA Publications, an American music publisher
 * Gemological Institute of America
 * Georgetown International Academy, in Guyana
 * Georgia Interscholastic Association, formed 1948, merged to Georgia High School Association in 1970

Airlines

 * Garuda Indonesian Airways, former name of Garuda Indonesia, the national airline of Indonesia
 * Ghana International Airlines
 * Gambia International Airlines

Government and political organizations

 * Armed Islamic Group of Algeria, (French: Groupe Islamique Armé)
 * Gallup International Association, a polling organization
 * General Intelligence Agency of Mongolia
 * Gia people, an Aboriginal Australian people of the state of Queensland.
 * Government Information Awareness, an American open government project

Entertainment

 * Gia (album), a 2001 album by Greek singer Despina Vandi
 * "Gia" (song), a 2001 single by Despina Vandi, taken from the album

Other uses

 * Gia (protein), a protein in Drosophila
 * Glacial isostatic adjustment
 * Gross internal area

title: Gia (disambiguation)


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Talk:Galaxy groups and clusters

Expansion
A list of members for each group and cluster is a good start, but I think it would be more useful to give distances and locations, plus maybe diameters. Anyone have access to that sort of information? My books are all back in Calgary. --Josh Grosse

All this information came from the internet. Article is a work in progress feel free to add information. Very difficult to find complete information for some of these groups. Mathew Carrier

Entropy
I think there is a better place for the entropy calculation somewhere else. It is not done correctly anyway. Oth (talk) 18:12, 3 March 2008 (UTC)

How does one calculate the number of galaxy groups or clusters? or super-clusters of galaxies? —Preceding unsigned comment added by Quaker phil (talk • contribs) 22:55, 13 October 2009 (UTC)

Proposal to merge Galaxy cluster into this page
There's really no need to have multiple pages on groups and clusters, as they differ only in size, and there's no sharp physical change. (Historically, clusters could be detected without redshift information, while groups couldn't, but almost all data today uses redshift information for cluster detection anyway.) It makes more sense to me to have a single article covering groups and clusters of all mass ranges. --Infophile (Talk) (Contribs) 19:01, 4 January 2012 (UTC)

Rhetorically speaking... by differing in size do you mean just by mass and not volume, or by both? The point is there are other differences; superheated gas exists in clusters but not in groups, to name one. Any merging of both articles will have to outline their similarities as well as their differences instead of simply copying and pasting both articles together (to whoever decides to do this, if it gets decided on). Here's an excellent starting point: [| The Difference Between Clusters and Groups: A Journey from Cluster Cores to Their Outskirts and Beyond]. I'll hopefully be able to contribute, if I find the time. Tom.Reding (talk) 05:39, 14 February 2012 (UTC)

Either these articles should be merged into one, or there should be two separate articles - Galaxy cluster and galaxy group. It's confusing to have one article overlapping another. If a group is substantially different from a cluster, it should have its own article. --George100 (talk) 04:24, 4 June 2012 (UTC)

Galaxy subgroup, Galaxy subcluster
Galaxy subgroup and Galaxy subcluster redirect here, but aren't explained in the article. -- Beland (talk) 05:11, 13 October 2012 (UTC)

Caption for image of MACS J0152.5-2852 incorrect
the image for the article, a picture of MACS J0152.5-2852, a galaxy cluster - the caption states that almost every "pixel" in the image is a galaxy, while the details provided alongside the photograph clearly state that it's every "object" in the image that's a galaxy, which makes a lot more sense, as most pixels seen are in fact dead space or not in field of view.

meow <3 -jade 2600:6C47:A0F0:8390:B9D8:C97C:BD5A:512F (talk) 18:56, 8 July 2023 (UTC)

title: Talk:Galaxy groups and clusters


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Galba

Galba (, ; born Servius Sulpicius Galba; 24 December 3 BC – 15 January AD 69) was Roman emperor, ruling from AD 68 to 69. He was the first emperor in the Year of the Four Emperors and assumed the throne following Emperor Nero's suicide.

Born into a wealthy family, Galba held at various times the positions of praetor, consul, and governor to the provinces of Gallia Aquitania, Germania Superior, and Africa during the first half of the first century AD. He retired from his positions during the latter part of Claudius' reign (with the advent of Agrippina the Younger), but Nero later granted him the governorship of Hispania. Taking advantage of the defeat of Vindex's rebellion and Nero's suicide, he became emperor with the support of the Praetorian Guard.

Galba's physical weakness and general apathy led to his rule being dominated by favorites. Unable to gain popularity with the people or maintain the support of the Praetorian Guard, Galba was murdered on the orders of Otho, who became emperor in his place.

Origins and family life
Galba was not related to any of the emperors of the Julio-Claudian dynasty, but he was a member of a distinguished noble family. The origin of the cognomen Galba is uncertain. Suetonius offers a number of possible explanations; the first member of the gens Sulpicia to bear the name might have gotten the name from the term galba, which the Romans used to describe the Gauls, or after an insect called galbae. One of Galba's ancestors had been consul in 200 BC, and another of his ancestors was consul in 144 BC; the later emperor's father and brother, both named Gaius, would hold the office in 5 BC and AD 22 respectively. Galba's grandfather was a historian and his son was a barrister whose first marriage was to Mummia Achaica, granddaughter of Quintus Lutatius Catulus and great-granddaughter of Lucius Mummius Achaicus; Galba prided himself on his descent from his great-grandfather Catulus. According to Suetonius, he fabricated a genealogy of paternal descent from the god Jupiter and maternal descent from the legendary Pasiphaë, wife of Minos. Reportedly, Galba was distantly related to Livia to whom he had much respect and in turn by whom he was advanced in his career; in her will she left him fifty million sesterces; Emperor Tiberius however cheated Galba by reducing the amount to five hundred thousand sesterces and never even paid Galba the reduced amount.

Servius Sulpicius Galba was born near Terracina on 24 December 3 BC. His elder brother Gaius fled from Rome and committed suicide because the emperor Tiberius would not allow him to control a Roman province. Livia Ocellina became the second wife of Galba's father, whom she may have married because of his wealth; he was short and hunchbacked. Ocellina adopted Galba, and he took the name "Lucius Livius Ocella Sulpicius Galba", although he probably kept his original name in unofficial context, as evidenced by the fact that he reverted back to it upon his accession as emperor. Galba preferred males over females in terms of sexual attraction; according to Suetonius, he "preferred full-grown, strong men". Nevertheless, he married a woman named Aemilia Lepida and had two sons. Aemilia and their sons died during the early years of the reign of Claudius (r. 41–54). Galba would remain a widower for the rest of his life.

Public service
Galba became praetor in about 30, then governor of Aquitania for about a year, then consul in 33. In 39 the emperor Caligula learned of a plot against himself in which Gnaeus Cornelius Lentulus Gaetulicus, the general of the legions of Germania Superior, was an important figure; Caligula installed Galba in the post held by Gaetulicus. According to one report Galba ran alongside Caligula's chariot for twenty miles. As commander of the legions of Germania Superior, Galba gained a reputation as a disciplinarian. Suetonius writes that Galba was advised to take the throne following the assassination of Caligula in 41, but loyally served Caligula's uncle and successor Claudius (r. 41–54); this story may simply be fictional. Galba was appointed as governor of Africa in 44 or 45. He retired at an uncertain time during the reign of Claudius, possibly in 49. He was recalled in 59 or 60 by the emperor Nero (r. 54–68) to govern Hispania.

A rebellion against Nero was orchestrated by Gaius Julius Vindex in Gaul on the anniversary of the death of Nero's mother, Agrippina the Younger, in 68. Shortly afterwards Galba, in rebellion against Nero, rejected the title "General of Caesar" in favor of "General of The Senate and People of Rome". He was supported by the imperial official Tigellinus. At midnight on 8 June, another imperial official, Nymphidius Sabinus, falsely announced to the Praetorian Guard that Nero had fled to Egypt, and the Senate proclaimed Galba emperor. Nero then committed assisted suicide with help from his secretary.

Rule
Upon becoming emperor, Galba was faced by the rebellion of Nymphidius Sabinus, who had his own aspirations for the imperial throne. However, Sabinus was killed by the Praetorians before he could take the throne. While Galba was arriving to Rome with the Lusitanian governor Marcus Salvius Otho, his army was attacked by a legion that had been organized by Nero; a number of Galba's troops were killed in the fighting. Galba, who suffered from chronic gout by the time he came to the throne, was advised by a corrupt group which included the general Titus Vinius, commander of one of the legions in Hispania; the praetorian prefect Cornelius Laco, and Icelus, a freedman of Galba. Galba seized the property of Roman citizens, disbanded the Germanian legions, and did not pay the Praetorians and the soldiers who fought against Vindex. These actions caused him to become unpopular.

Suetonius wrote the following descriptions of Galba's character and physical description:

"Even before he reached middle life, he persisted in keeping up an old and forgotten custom of his country, which survived only in his own household, of having his freedmen and slaves appear before him twice a day in a body, greeting him in the morning and bidding him farewell at evening, one by one.""His double reputation for cruelty and avarice had gone before him; men said that he had punished the cities of the Spanish and Gallic provinces which had hesitated about taking sides with him by heavier taxes and some even by the razing of their walls, putting to death the governors and imperial deputies along with their wives and children. Further, that he had melted down a golden crown of fifteen pounds weight, which the people of Tarraco had taken from their ancient temple of Jupiter and presented to him, with orders that the three ounces which were found lacking be exacted from them. This reputation was confirmed and even augmented immediately on his arrival in the city. For having compelled some marines whom Nero had made regular soldiers to return to their former position as rowers, upon their refusing and obstinately demanding an eagle and standards, he not only dispersed them by a cavalry charge, but even decimated them. He also disbanded a cohort of Germans, whom the previous Caesars had made their body-guard and had found absolutely faithful in many emergencies, and sent them back to their native country without any rewards, alleging that they were more favourably inclined towards Gnaeus Dolabella, near whose gardens they had their camp. The following tales too were told in mockery of him, whether truly or falsely: that when an unusually elegant dinner was set before him, he groaned aloud; that when his duly appointed steward presented his expense account, he handed him a dish of beans in return for his industry and carefulness; and that when the flute player Canus greatly pleased him, he presented him with five denarii, which he took from his own purse with his own hand." "Accordingly, his coming was not so welcome as it might have been, and this was apparent at the first performance in the theatre; for when the actors of an Atellan farce began the familiar lines "Here comes Onesimus from his farm" all the spectators at once finished the song in chorus and repeated it several times with appropriate gestures, beginning with that verse.

Thus his popularity and prestige were greater when he won, than while he ruled the empire, though he gave many proofs of being an excellent prince; but he was by no means so much loved for those qualities as he was hated for his acts of the opposite character."

- Suetonius

Particularly bad was his becoming under the influence of Vinius, Laco and Icelus:

"...To these brigands, each with his different vice, he so entrusted and handed himself over as their tool, that his conduct was far from consistent; for now he was more exacting and niggardly, and now more extravagant and reckless than became a prince chosen by the people and of his time of life.

He condemned to death distinguished men of both orders on trivial suspicions without a trial. He rarely granted Roman citizenship, and the privileges of threefold paternity to hardly one or two, and even to those only for a fixed and limited time. When the jurors petitioned that a sixth division be added to their number, he not only refused, but even deprived them of the privilege granted by Claudius, of not being summoned for court duty in winter and at the beginning of the year."

- Suetonius

In regard to his appointment of Vitellius to Germania Inferior:

"Galba surprised everyone by sending him to Lower Germany. Some think that it was due to Titus Vinius, who had great influence at the time, and whose friendship Vitellius had long since won through their common support of the Blues. But since Galba openly declared that no men were less to be feared than those who thought of nothing but eating, and that Vitellius's bottomless gullet might be filled from the resources of the province, it is clear to anyone that he was chosen rather through contempt than favour."

- Suetonius

Further on his physical appearance and end of reign:

"He was of average height, very bald, with blue eyes and a hooked nose. His hands and feet were so distorted by gout that he could not endure a shoe for long, unroll a book, or even hold one. The flesh on his right side too had grown out and hung down to such an extent, that it could with difficulty be held in place by a bandage. It is said that he was a heavy eater and in winter time was in the habit of taking food even before daylight, while at dinner he helped himself so lavishly that he would have the leavings which remained in a heap before him passed along and distributed among the attendants who waited on him..... He met his end in the seventy-third year of his age and the seventh month of his reign. The senate, as soon as it was allowed to do so, voted him a statue standing upon a column adorned with the beaks of ships, in the part of the Forum where he was slain; but Vespasian annulled this decree, believing that Galba had sent assassins from Spain to Judaea, to take his life."

- Suetonius

Tacitus comments on the character of Galba: "He seemed too great to be a subject so long as he was subject, and all would have agreed that he was equal to the imperial office if he had never held it."

Suetonius went on to say that Galba was visited by the Roman Goddess Fortuna in his dreams twice; on the latter occasion she "withdrew her support". This happened right before his later downfall.

Mutiny on the frontier and assassination
On 1 January 69, the day Galba and Vinius took the office of consul, the fourth and twenty-second legions of Germania Superior refused to swear loyalty to Galba. They toppled his statues, demanding that a new emperor be chosen. On the following day, the soldiers of Germania Inferior also refused to swear their loyalty and proclaimed the governor of the province, Aulus Vitellius, as emperor. Galba tried to ensure his authority as emperor was recognised by adopting the nobleman Lucius Calpurnius Piso Licinianus as his successor. Nevertheless, Galba was killed by the Praetorians on 15 January. Otho was angry that he had been passed over for adoption, and organised a conspiracy with a small number of Praetorian Guards to murder the aged emperor and elevate himself. The soldiery in the capital, composed not just of Praetorians but of Galba's legion from Hispania and several detachments of men from the Roman fleet, Illyria, Britannia, and Germania, were angered at not having received a donative. They also resented Galba's purges of their officers and fellow soldiers (this was especially true of the men from the fleet). Many in the Praetorian Guard were shaken by the recent murder of their Prefect Nymphidius Sabinus – some of the waverers were convinced to come over to Otho's side out of fear Galba might yet take revenge on them for their connection to Sabinus.

According to Suetonius, Galba put on a linen corset although remarking it was little protection against so many swords; when a soldier claimed to have killed Otho, Galba snapped "On what authority?". He was lured out to the scene of his assassination in the Forum by a false report of the conspirators. Galba either tried to buy his life with a promise of the withheld bounty or asked that he be beheaded. The only help for him was a centurion in the Praetorian Guard named Sempronius Densus, who was killed trying to defend Galba with a pugio; one hundred and twenty persons later petitioned Otho that they had killed Galba; they would be executed by Vitellius. A company of Germanic soldiers to whom he had once done a kindness rushed to help him; however they took a wrong turn and arrived too late. He was killed near the Lacus Curtius. Vinius tried to run away, calling out that Otho had not ordered him killed, but was run through with a spear. Laco was banished to an island where he was later murdered by soldiers of Otho. Icelus was publicly executed. Piso was also killed; his head along with Galba's and Vinius' were placed on poles and Otho was then acclaimed as emperor. Galba's head was brought by a soldier to Otho's camp where camp boys mocked it on a lance – Galba had angered them previously by remarking his vigor was still unimpeded. Vinius' head was sold to his daughter for 2500 drachmas; Piso's head was given to his wife. Galba's head was bought for 100 gold pieces by a freeman who threw it at Sessorium where his master Patrobius Neronianus had been killed by Galba. The body of Galba was taken up by Priscus Helvidius with the permission of Otho; at night Galba's steward Argivus took both the head and body to a tomb in Galba's private gardens on the Aurelian Way.

Ancient sources

 * Cassius Dio, Roman History, fragments of Book 63 (English translation by Earnest Cary on LacusCurtius).
 * Plutarch, Life of Galba (English translation by A.H. Clough on Wikisource).
 * Suetonius, The Twelve Caesars, Galba (English translation by John Carew Rolfe on Wikisource).

title: Galba


text:
Giga-

Giga- ( or ) is a unit prefix in the metric system denoting a factor of a short-scale billion or long-scale milliard (109 or 1,000,000,000). It has the symbol G.

Giga- is derived from the Greek word γίγας (gígas), meaning "giant". The Oxford English Dictionary reports the earliest written use of giga in this sense to be in the Reports of the IUPAC 14th Conférence Internationale de Chimie in 1947: "The following prefixes to abbreviations for the names of units should be used: G giga 109×." However, it was already used in 1932 by the German organization Verband deutscher Elektrotechniker.

When referring to information units in computing, such as gigabyte, giga may sometimes mean 1 073  741  824 (230); this causes ambiguity. Standards organizations discourage this and use giga- to refer to 109 in this context too. Gigabit is only rarely used with the binary interpretation of the prefix. The binary prefix gibi has been adopted for 230, while reserving giga exclusively for the metric definition.

Pronunciation
In English, the prefix giga can be pronounced (a hard g as in giggle), or  (a soft g as in gigantic, which shares giga Ancient Greek root). A prominent example of this latter pronunciation is found in the pronunciation of gigawatts in the 1985 film Back to the Future.

According to the American writer Kevin Self, a German committee member of the International Electrotechnical Commission proposed giga as a prefix for 109 in the 1920s, drawing on a verse (evidently "Anto-logie") by the German humorous poet Christian Morgenstern that appeared in the third (1908) edition of his Galgenlieder (Gallows Songs). This suggests that a hard German was originally intended as the pronunciation. Self was unable to ascertain when the (soft g) pronunciation came into occasional use, but claimed that as of 1995 it had returned to  (hard g).

In 1998, a poll by the phonetician John C. Wells found that 84% of Britons preferred the pronunciation of gigabyte starting with (as in gig), 9% with  (as in jig), 6% with  (guy), and 1% with  (as in giant).

Common usage

 * gigahertz—clock rate of a CPU, for instance, 3 GHz = 3 000  000  000  Hz
 * gigabit—bandwidth of a network link, for instance, 1 Gbit/s = 1 000  000  000  bit/s.
 * gigabyte—for instance, for hard disk capacity, 120 GB = 120 000  000  000  bytes;
 * gigayear or gigaannum—one billion (109) years, sometimes abbreviated Gyr, but the preferred usage is Ga or, for years ago, GA.

Binary prefix
The notation $1 GB$ represents 1,000,000,000 bytes or, in deprecated usage, 1,073,741,824 (230) bytes. Per IEC 60027-2 A.2 and ISO/IEC 80000 standards, the correct notation of 230 is gibi (symbol Gi). One gibibyte ($1 GiB$) is 1,073,741,824 bytes or $1.074 GB$. Despite international standards, the use of $1 GB$ = 230 B is widespread. A laptop advertised as having $8 GB$ has 8,589,934,592 bytes of memory: $8.59 B$, or $8 GiB$.

title: Giga-


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George Stephenson

George Stephenson (9 June 1781 – 12 August 1848) was an English civil engineer and mechanical engineer during the Industrial Revolution. Renowned as the "Father of Railways", Stephenson was considered by the Victorians as a great example of diligent application and thirst for improvement. His chosen rail gauge, sometimes called "Stephenson gauge", was the basis for the 4 ft standard gauge used by most of the world's railways.

Pioneered by Stephenson, rail transport was one of the most important technological inventions of the 19th century and a key component of the Industrial Revolution. Built by George and his son Robert's company Robert Stephenson and Company, the Locomotion No. 1 was the first steam locomotive to carry passengers on a public rail line, the Stockton and Darlington Railway in 1825. George also built the first public inter-city railway line in the world to use locomotives, the Liverpool and Manchester Railway, which opened in 1830.

Childhood
George Stephenson was born on 9 June 1781 in Wylam, Northumberland, which is 9 miles (15 km) west of Newcastle upon Tyne. He was the second child of Robert and Mabel Stephenson, neither of whom could read or write. Robert was the fireman for Wylam Colliery pumping engine, earning a very low wage, so there was no money for schooling. At 17, Stephenson became an engineman at Water Row Pit in Newburn nearby. George realised the value of education and paid to study at night school to learn reading, writing and arithmetic – he was illiterate until the age of 18.

In 1801 he began work at Black Callerton Colliery south of Ponteland as a 'brakesman', controlling the winding gear at the pit. In 1802 he married Frances Henderson and moved to Willington Quay, east of Newcastle. There he worked as a brakesman while they lived in one room of a cottage. George made shoes and mended clocks to supplement his income.

Their first child Robert was born in 1803, and in 1804 they moved to Dial Cottage at West Moor, near Killingworth where George worked as a brakesman at Killingworth Pit. Their second child, a daughter, was born in July 1805. She was named Frances after her mother. The child died after just three weeks and was buried in St Bartholomew's Church, Long Benton north of Newcastle.

In 1806 George's wife Frances died of consumption (tuberculosis). She was buried in the same churchyard as their daughter on 16 May 1806, though the location of the grave is lost.

George decided to find work in Scotland and left Robert with a local woman while he went to work in Montrose. After a few months he returned, probably because his father was blinded in a mining accident. He moved back into a cottage at West Moor and his unmarried sister Eleanor moved in to look after Robert. In 1811 the pumping engine at High Pit, Killingworth was not working properly and Stephenson offered to improve it. He did so with such success that he was promoted to enginewright for the collieries at Killingworth, responsible for maintaining and repairing all the colliery engines. He became an expert in steam-driven machinery.

The Safety Lamp
In 1815, aware of the explosions often caused in mines by naked flames, Stephenson began to experiment with a safety lamp that would burn in a gaseous atmosphere without causing an explosion. At the same time, the eminent scientist and Cornishman Humphry Davy was also looking at the problem. Despite his lack of scientific knowledge, Stephenson, by trial and error, devised a lamp in which the air entered via tiny holes, through which the flames of the lamp could not pass.

A month before Davy presented his design to the Royal Society, Stephenson demonstrated his own lamp to two witnesses by taking it down Killingworth Colliery and holding it in front of a fissure from which firedamp was issuing. The two designs differed; Davy's lamp was surrounded by a screen of gauze, whereas Stephenson's prototype lamp had a perforated plate containing a glass cylinder. For his invention Davy was awarded £2000, whilst Stephenson was accused of stealing the idea from Davy, because he was not seen as an adequate scientist who could have produced the lamp by any approved scientific method.

Stephenson, having come from the North-East, spoke with a broad Northumberland accent and not the 'Language of Parliament,' which made him seem lowly. Realizing this, he made a point of educating his son Robert in a private school, where he was taught to speak in Standard English with a Received Pronunciation accent. It was due to this, in their future dealings with Parliament, that it became clear that the authorities preferred Robert to his father.

A local committee of enquiry gathered in support of Stephenson, exonerated him, proved he had been working separately to create the 'Geordie Lamp', and awarded him £1,000, but Davy and his supporters refused to accept their findings, and would not see how an uneducated man such as Stephenson could come up with the solution he had. In 1833 a House of Commons committee found that Stephenson had equal claim to having invented the safety lamp. Davy went to his grave believing that Stephenson had stolen his idea. The Stephenson lamp was used almost exclusively in North East England, whereas the Davy lamp was used everywhere else. The experience gave Stephenson a lifelong distrust of London-based, theoretical, scientific experts.

In his book George and Robert Stephenson, the author L.T.C. Rolt relates that opinion varied about the two lamps' efficiency: that the Davy Lamp gave more light, but the Geordie Lamp was thought to be safer in a more gaseous atmosphere. He made reference to an incident at Oaks Colliery in Barnsley where both lamps were in use. Following a sudden strong influx of gas the tops of all the Davy Lamps became red hot (which had in the past caused an explosion, and in so doing risked another), whilst all the Geordie Lamps simply went out.

There is a theory that it was Stephenson who indirectly gave the name of "Geordies" to the people of the North East of England. By this theory, the name of the Geordie Lamp attached to the North East pit men themselves. By 1866 any native of Newcastle upon Tyne could be called a Geordie.

Locomotives
Cornishman Richard Trevithick is credited with the first realistic design for a steam locomotive, the "Puffing Devil", in 1801. Later, he visited Tyneside and built an engine there for a mine-owner. Several local men were inspired by this, and designed their own engines.

Stephenson designed his first locomotive in 1814, a travelling engine designed for hauling coal on the Killingworth wagonway named Blücher after the Prussian general Gebhard Leberecht von Blücher (It was suggested the name sprang from Blücher's rapid march of his army in support of Wellington at Waterloo). Blücher was modelled on Matthew Murray's locomotive Willington, which George studied at Kenton and Coxlodge colliery on Tyneside, and was constructed in the colliery workshop behind Stephenson's home, Dial Cottage, on Great Lime Road. The locomotive could haul 30 tons of coal up a hill at 4 mi/h, and was the first successful flanged-wheel adhesion locomotive: its traction depended on contact between its flanged wheels and the rail.

Altogether, Stephenson is said to have produced 16 locomotives at Killingworth, although it has not proved possible to produce a convincing list of all 16. Of those identified, most were built for use at Killingworth or for the Hetton colliery railway. A six-wheeled locomotive was built for the Kilmarnock and Troon Railway in 1817 but was withdrawn from service because of damage to the cast-iron rails. Another locomotive was supplied to Scott's Pit railroad at Llansamlet, near Swansea, in 1819 but it too was withdrawn, apparently because it was under-boilered and again caused damage to the track.

The new engines were too heavy to run on wooden rails or plate-way, and iron edge rails were in their infancy, with cast iron exhibiting excessive brittleness. Together with William Losh, Stephenson improved the design of cast-iron edge rails to reduce breakage; rails were briefly made by Losh, Wilson and Bell at their Walker ironworks.

According to Rolt, Stephenson managed to solve the problem caused by the weight of the engine on the primitive rails. He experimented with a steam spring (to 'cushion' the weight using steam pressure acting on pistons to support the locomotive frame), but soon followed the practice of 'distributing' weight by using a number of wheels or bogies. For the Stockton and Darlington Railway Stephenson used wrought-iron malleable rails that he had found satisfactory, notwithstanding the financial loss he suffered by not using his own patented design.

Hetton Railway
Stephenson was hired to build the eight-mile (13-km) Hetton colliery railway in 1820. He used a combination of gravity on downward inclines and locomotives for level and upward stretches. This, the first railway using no animal power, opened in 1822. This line used a gauge of which Stephenson had used before at the Killingworth wagonway.

Other locomotives include:
 * 1817–1824 The Duke for the Kilmarnock and Troon Railway

Stockton and Darlington Railway
In 1821, a parliamentary bill was passed to allow the building of the Stockton and Darlington Railway (S&DR). The 25 mi railway connected collieries near Bishop Auckland to the River Tees at Stockton, passing through Darlington on the way. The original plan was to use horses to draw coal carts on metal rails, but after company director Edward Pease met Stephenson, he agreed to change the plans. Stephenson surveyed the line in 1821, and assisted by his 18-year-old son Robert, construction began the same year.

A manufacturer was needed to provide the locomotives for the line. Pease and Stephenson had jointly established a company in Newcastle to manufacture locomotives. It was set up as Robert Stephenson and Company, and George's son Robert was the managing director. A fourth partner was Michael Longridge of Bedlington Ironworks. On an early trade card, Robert Stephenson & Co was described as "Engineers, Millwrights & Machinists, Brass & Iron Founders". In September 1825, the works at Forth Street, Newcastle, completed the first locomotive for the railway: originally named Active, it was renamed Locomotion and was followed by Hope, Diligence and Black Diamond. The Stockton and Darlington Railway opened on 27 September 1825. Driven by Stephenson, Locomotion hauled an 80-ton load of coal and flour 9 mi in two hours, reaching a speed of 24 mph on one stretch. The first purpose-built passenger car, Experiment, was attached and carried dignitaries on the opening journey. It was the first time passenger traffic had been run on a steam locomotive railway.

The rails used for the line were wrought-iron, produced by John Birkinshaw at the Bedlington Ironworks. Wrought-iron rails could be produced in longer lengths than cast-iron and were less liable to crack under the weight of heavy locomotives. William Losh of Walker Ironworks thought he had an agreement with Stephenson to supply cast-iron rails, and Stephenson's decision caused a permanent rift between them. The gauge Stephenson chose for the line was 4 ft which subsequently was adopted as the standard gauge for railways, not only in Britain, but throughout the world.

Liverpool and Manchester Railway
Stephenson had ascertained by experiments at Killingworth that half the power of the locomotive was consumed by a gradient as little as 1 in 260. He concluded that railways should be kept as level as possible. He used this knowledge while working on the Bolton and Leigh Railway, and the Liverpool and Manchester Railway (L&MR), executing a series of difficult cuttings, embankments and stone viaducts to level their routes. Defective surveying of the original route of the L&MR caused by hostility from some affected landowners meant Stephenson encountered difficulty during Parliamentary scrutiny of the original bill, especially under cross-examination by Edward Hall Alderson. The bill was rejected and a revised bill for a new alignment was submitted and passed in a subsequent session. The revised alignment presented the problem of crossing Chat Moss, an apparently bottomless peat bog, which Stephenson overcame by unusual means, effectively floating the line across it. The method he used was similar to that used by John Metcalf who constructed many miles of road across marshes in the Pennines, laying a foundation of heather and branches, which became bound together by the weight of the passing coaches, with a layer of stones on top.

As the L&MR approached completion in 1829, its directors arranged a competition to decide who would build its locomotives, and the Rainhill Trials were run in October 1829. Entries could weigh no more than six tons and had to travel along the track for a total distance of 60 mi. Stephenson's entry was Rocket, and its performance in winning the contest made it famous. George's son Robert had been working in South America from 1824 to 1827 and returned to run the Forth Street Works while George was in Liverpool overseeing the construction of the line. Robert was responsible for the detailed design of Rocket, although he was in constant postal communication with his father, who made many suggestions. One significant innovation, suggested by Henry Booth, treasurer of the L&MR, was the use of a fire-tube boiler, invented by French engineer Marc Seguin that gave improved heat exchange.

The opening ceremony of the L&MR, on 15 September 1830, drew luminaries from the government and industry, including the Prime Minister, the Duke of Wellington. The day started with a procession of eight trains setting out from Liverpool. The parade was led by Northumbrian driven by George Stephenson, and included Phoenix driven by his son Robert, North Star driven by his brother Robert and Rocket driven by assistant engineer Joseph Locke. The day was marred by the death of William Huskisson, the Member of Parliament for Liverpool, who was struck by Rocket. Stephenson evacuated the injured Huskisson to Eccles with a train, but he died from his injuries. Despite the tragedy, the railway was a resounding success. Stephenson became famous, and was offered the position of chief engineer for a wide variety of other railways.

Stephenson's skew arch bridge

1830 also saw the grand opening of the skew bridge in Rainhill over the Liverpool and Manchester Railway. The bridge was the first to cross any railway at an angle. It required the structure to be constructed as two flat planes (overlapping in this case by 6 ft) between which the stonework forms a parallelogram shape when viewed from above. It has the effect of flattening the arch and the solution is to lay the bricks forming the arch at an angle to the abutments (the piers on which the arches rest). The technique, which results in a spiral effect in the arch masonry, provides extra strength in the arch to compensate for the angled abutments.

The bridge is still in use at Rainhill station, and carries traffic on the A57 (Warrington Road). The bridge is a listed structure.

Life at Alton Grange

George Stephenson moved to the parish of Alton Grange (now part of Ravenstone) in Leicestershire in 1830, originally to consult on the Leicester and Swannington Railway, a line primarily proposed to take coal from the western coal fields of the county to Leicester. The promoters of the line Mr William Stenson and Mr John Ellis, had difficulties in raising the necessary capital as the majority of local wealth had been invested in canals. Realising the potential and need for the rail link Stephenson himself invested £2,500 and raised the remaining capital through his network of connections in Liverpool. His son Robert was made chief engineer with the first part of the line opening in 1832.

During this same period the Snibston estate in Leicestershire came up for auction, it lay adjoining the proposed Swannington to Leicester route and was believed to contain valuable coal reserves. Stephenson realising the financial potential of the site, given its proximity to the proposed rail link and the fact that the manufacturing town of Leicester was then being supplied coal by canal from Derbyshire, bought the estate.

Employing a previously used method of mining in the midlands called tubbing to access the deep coal seams, his success could not have been greater. Stephenson's coal mine delivered the first rail cars of coal into Leicester dramatically reducing the price of coal and saving the city some £40,000 per annum.

Stephenson remained at Alton Grange until 1838 before moving to Tapton House in Derbyshire.

Later career
The next ten years were the busiest of Stephenson's life as he was besieged with requests from railway promoters. Many of the first American railroad builders came to Newcastle to learn from Stephenson and the first dozen or so locomotives utilised there were purchased from the Stephenson shops. Stephenson's conservative views on the capabilities of locomotives meant he favoured circuitous routes and civil engineering that were more costly than his successors thought necessary. For example, rather than the West Coast Main Line taking the direct route favoured by Joseph Locke over Shap between Lancaster and Carlisle, Stephenson was in favour of a longer sea-level route via Ulverston and Whitehaven. Locke's route was built.

Stephenson tended to be more casual in estimating costs and paperwork in general. He worked with Joseph Locke on the Grand Junction Railway with half of the line allocated to each man. Stephenson's estimates and organising ability proved inferior to those of Locke and the board's dissatisfaction led to Stephenson's resignation causing a rift between them which was never healed.

Despite Stephenson's loss of some routes to competitors due to his caution, he was offered more work than he could cope with, and was unable to accept all that was offered. He worked on the North Midland line from Derby to Leeds, the York and North Midland line from Normanton to York, the Manchester and Leeds, the Birmingham and Derby, the Sheffield and Rotherham among many others.

Stephenson became a reassuring name rather than a cutting-edge technical adviser. He was the first president of the Institution of Mechanical Engineers on its formation in 1847. By this time he had settled into semi-retirement, supervising his mining interests in Derbyshire – tunnelling for the North Midland Railway revealed coal seams, and Stephenson put money into their exploitation.

Personal life
George first courted Elizabeth (Betty) Hindmarsh, a farmer's daughter from Black Callerton, whom he met secretly in her orchard. Her father refused marriage because of Stephenson's lowly status as a miner. George next paid attention to Anne Henderson where he lodged with her family, but she rejected him and he transferred his attentions to her sister Frances (Fanny), who was nine years his senior. George and Fanny married at Newburn Church on 28 November 1802. They had two children Robert (1803) and Fanny (1805) but the latter died within months. George's wife died, probably of tuberculosis, the year after. While George was working in Scotland, Robert was brought up by a succession of neighbours and then by George's unmarried sister Eleanor (Nelly), who lived with them in Killingworth on George's return.

On 29 March 1820, George (now considerably wealthier) married Betty Hindmarsh at Newburn. The marriage seems to have been happy, but there were no children and Betty died on 3 August 1845.

On 11 January 1848, at St John's Church in Shrewsbury, Shropshire, George married for the third time, to Ellen Gregory, another farmer's daughter originally from Bakewell in Derbyshire, who had been his housekeeper. Seven months after his wedding, George contracted pleurisy and died, aged 67, at noon on 12 August 1848 at Tapton House in Chesterfield, Derbyshire. He was buried at Holy Trinity Church, Chesterfield, alongside his second wife.

Described by Rolt as a generous man, Stephenson financially supported the wives and families of several who had died in his employment, due to accident or misadventure, some within his family, and some not. He was also a keen gardener throughout his life; during his last years at Tapton House, he built hothouses in the estate gardens, growing exotic fruits and vegetables in a 'not too friendly' rivalry with Joseph Paxton, head gardener at nearby Chatsworth House, twice beating the master of the craft.

Descendants
George Stephenson had two children. His son Robert was born on 16 October 1803. Robert married Frances Sanderson, daughter of a City of London professional John Sanderson, on 17 June 1829. Robert died in 1859 having no children. Robert Stephenson expanded on the work of his father and became a major railway engineer himself. Abroad, Robert was involved in the Alexandria–Cairo railway that later connected with the Suez Canal. George Stephenson's daughter was born in 1805 but died within weeks of her birth. Descendants of the wider Stephenson family continue to live in Wylam (Stephenson's birthplace) today. Also relatives connected by his marriage live in Derbyshire. Some descendants later emigrated to Perth, Australia, and Minnesota, with later generations remaining to this day.

This Stephenson engineering family is not to be confused with the lighthouse-building engineering family of Robert Stevenson, which was active in the same era. Note the spelling difference.

Influence
Britain led the world in the development of railways which acted as a stimulus for the Industrial Revolution by facilitating the transport of raw materials and manufactured goods. George Stephenson, with his work on the Stockton and Darlington Railway and the Liverpool and Manchester Railway, paved the way for the railway engineers who followed, such as his son Robert, his assistant Joseph Locke who carried out much work on his own account and Isambard Kingdom Brunel. Stephenson was farsighted in realising that the individual lines being built would eventually be joined, and would need to have the same gauge. The standard gauge used throughout much of the world is due to him. In 2002, Stephenson was named in the BBC's television show and list of the 100 Greatest Britons following a UK-wide vote, placing at no. 65.

The Victorian self-help advocate Samuel Smiles had published his first biography of George Stephenson in 1857, and although attacked as biased in the favour of George at the expense his rivals as well as his son, it was popular and 250,000 copies were sold by 1904. The Band of Hope were selling biographies of George in 1859 at a penny a sheet, and at one point there was a suggestion to move George's body to Westminster Abbey. The centenary of George's birth was celebrated in 1881 at Crystal Palace by 15,000 people, and it was George who was featured on the reverse of the Series E five pound note issued by the Bank of England between 1990 and 2003. The Stephenson Railway Museum in North Shields is named after George and Robert Stephenson.

Memorials
George Stephenson's Birthplace is an 18th-century historic house museum in the village of Wylam, and is operated by the National Trust. Dial Cottage at West Moor, his home from 1804, remains but the museum that once operated here is shut.

Chesterfield Museum in Chesterfield, Derbyshire, has a gallery of Stephenson memorabilia, including straight thick glass tubes he invented for growing straight cucumbers. The museum is in the Stephenson Memorial Hall not far from both Stephenson's final home at Tapton House and Holy Trinity Church within which is his vault. In Liverpool, where he lived at 34 Upper Parliament Street, a City of Liverpool Heritage Plaque is situated next to the front door.

Stephenson College, founded in 2001 on the Durham University's Queen's Campus in Stockton-on-Tees (relocated to Durham in 2018), is named after him. Also named after him and his son is George Stephenson High School in Killingworth, Stephenson Memorial Primary School in Howdon, the Stephenson Railway Museum in North Shields, the Stephenson Locomotive Society, the Stephenson Centre, an SEBD Unit of Beaumont Hill School in Darlington, and the Stephenson Building, home of the school of engineering at Newcastle University. His last home in Tapton, Chesterfield is now part of Chesterfield College and is called Tapton House Campus.

As a tribute to his life and works, a bronze statue of Stephenson was unveiled at Chesterfield railway station (in the town where Stephenson spent the last ten years of his life) on 28 October 2005, marking the completion of improvements to the station. At the event a full-size working replica of the Rocket was on show, which then spent two days on public display at the Chesterfield Market Festival. A statue of him dressed in classical robes stands in Neville Street, Newcastle, facing the buildings that house the Literary and Philosophical Society of Newcastle upon Tyne and the North of England Institute of Mining and Mechanical Engineers, near Newcastle railway station. The statue was sculpted in 1862 by John Graham Lough and is listed Grade II.

From 1990 until 2003, Stephenson's portrait appeared on the reverse of Series E £5 notes issued by the Bank of England. Stephenson's face is shown alongside an engraving of the Rocket steam engine and the Skerne Bridge on the Stockton to Darlington Railway.

Stephenson's profile is carved in the facade of Lisbon's victorian railway station.

North-western Milan has the street Via Giorgio Stephenson in his honour.

In popular culture
Stephenson was portrayed by actor Gawn Grainger on television in the 1985 Doctor Who serial The Mark of the Rani.

Harry Turtledove's alternate history short story "The Iron Elephant" depicts a race between a newly invented steam engine and a mammoth-drawn train in 1782. A station master called George Stephenson features as a minor character alongside an American steam engineer called Richard Trevithick, likely indicating that they were analogous rather than historical characters.

Biographical works
Ruth Maxwell M.A. George Stephenson   George Harrap & Company LTD., London, 1920. Heroes of All Time series.

title: George Stephenson


text:
Grapheme

In linguistics, a grapheme is the smallest functional unit of a writing system. The word grapheme is derived and the suffix -eme by analogy with phoneme and other names of emic units. The study of graphemes is called graphemics. The concept of graphemes is abstract and similar to the notion in computing of a character. By comparison, a specific shape that represents any particular grapheme in a given typeface is called a glyph.

Conceptualization
There are two main opposing grapheme concepts.

In the so-called referential conception, graphemes are interpreted as the smallest units of writing that correspond with sounds (more accurately phonemes). In this concept, the sh in the written English word shake would be a grapheme because it represents the phoneme /ʃ/. This referential concept is linked to the dependency hypothesis that claims that writing merely depicts speech.

By contrast, the analogical concept defines graphemes analogously to phonemes, i.e. via written minimal pairs such as shake vs. snake. In this example, h and n are graphemes because they distinguish two words. This analogical concept is associated with the autonomy hypothesis which holds that writing is a system in its own right and should be studied independently from speech. Both concepts have weaknesses.

Some models adhere to both concepts simultaneously by including two individual units, which are given names such as graphemic grapheme for the grapheme according to the analogical conception (h in shake), and phonological-fit grapheme for the grapheme according to the referential concept (sh in shake).

In newer concepts, in which the grapheme is interpreted semiotically as a dyadic linguistic sign, it is defined as a minimal unit of writing that is both lexically distinctive and corresponds with a linguistic unit (phoneme, syllable, or morpheme).

Notation
Graphemes are often notated within angle brackets: e.g. $⟨a⟩$. This is analogous to the slash notation used for phonemes. Analogous to the square bracket notation used for phones, glyphs are sometimes denoted with vertical lines, e.g..

Glyphs
In the same way that the surface forms of phonemes are speech sounds or phones (and different phones representing the same phoneme are called allophones), the surface forms of graphemes are glyphs (sometimes graphs), namely concrete written representations of symbols (and different glyphs representing the same grapheme are called allographs).

Thus, a grapheme can be regarded as an abstraction of a collection of glyphs that are all functionally equivalent.

For example, in written English (or other languages using the Latin alphabet), there are two different physical representations of the lowercase Latin letter "a": " a " and " ɑ ". Since, however, the substitution of either of them for the other cannot change the meaning of a word, they are considered to be allographs of the same grapheme, which can be written $⟨a⟩$. Similarly, the grapheme corresponding to "Arabic numeral zero" has a unique semantic identity and Unicode value U+0030 but exhibits variation in the form of slashed zero. Italic and bold face forms are also allographic, as is the variation seen in serif (as in Times New Roman) versus sans-serif (as in Helvetica) forms.

There is some disagreement as to whether capital and lower case letters are allographs or distinct graphemes. Capitals are generally found in certain triggering contexts that do not change the meaning of a word: a proper name, for example, or at the beginning of a sentence, or all caps in a newspaper headline. In other contexts, capitalization can determine meaning: compare, for example Polish and polish: the former is a language, the latter is for shining shoes.

Some linguists consider digraphs like the $⟨a⟩$ in ship to be distinct graphemes, but these are generally analyzed as sequences of graphemes. Non-stylistic ligatures, however, such as $⟨sh⟩$, are distinct graphemes, as are various letters with distinctive diacritics, such as $⟨æ⟩$.

Identical glyphs may not always represent the same grapheme. For example, the three letters $⟨ç⟩$, $⟨A⟩$ and $⟨А⟩$ appear identical but each has a different meaning: in order, they are the Latin letter A, the Cyrillic letter Azǔ/Азъ and the Greek letter Alpha. Each has its own code point in Unicode:, and.

Types of grapheme
The principal types of graphemes are logograms (more accurately termed morphograms ), which represent words or morphemes (for example Chinese characters, the ampersand "&" representing the word and, Arabic numerals); syllabic characters, representing syllables (as in Japanese kana); and alphabetic letters, corresponding roughly to phonemes (see next section). For a full discussion of the different types, see.

There are additional graphemic components used in writing, such as punctuation marks, mathematical symbols, word dividers such as the space, and other typographic symbols. Ancient logographic scripts often used silent determinatives to disambiguate the meaning of a neighboring (non-silent) word.

Relationship with phonemes
As mentioned in the previous section, in languages that use alphabetic writing systems, many of the graphemes stand in principle for the phonemes (significant sounds) of the language. In practice, however, the orthographies of such languages entail at least a certain amount of deviation from the ideal of exact grapheme–phoneme correspondence. A phoneme may be represented by a multigraph (sequence of more than one grapheme), as the digraph sh represents a single sound in English (and sometimes a single grapheme may represent more than one phoneme, as with the Russian letter я or the Spanish c). Some graphemes may not represent any sound at all (like the b in English debt or the h in all Spanish words containing the said letter), and often the rules of correspondence between graphemes and phonemes become complex or irregular, particularly as a result of historical sound changes that are not necessarily reflected in spelling. "Shallow" orthographies such as those of standard Spanish and Finnish have relatively regular (though not always one-to-one) correspondence between graphemes and phonemes, while those of French and English have much less regular correspondence, and are known as deep orthographies.

Multigraphs representing a single phoneme are normally treated as combinations of separate letters, not as graphemes in their own right. However, in some languages a multigraph may be treated as a single unit for the purposes of collation; for example, in a Czech dictionary, the section for words that start with $⟨Α⟩$ comes after that for $⟨ch⟩$. For more examples, see.

title: Grapheme