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Io (moon)

Io (moon)

Io (, eye'-oe, Greek Ιώ, Latin Īō) is the innermost of the four Galilean moons of Jupiter. It is named after the Greek mythological figure Io, one of the many lovers of Zeus (who is also known as Jupiter in the Roman mythology). Although the name "Io" was suggested by Simon Marius soon after its discovery in 1610, this name and the names of the other Galilean satellites fell into disfavor for a considerable time, and were not revived in common use until the mid-20th century. In much of the earlier astronomical literature, Io is simply referred to by its Roman numeral designation as "Jupiter I", or simply as "the first satellite of Jupiter".

Volcanism

Roman numeral Io is most noteworthy for its volcanic nature; it is the most volcanically active body in the Solar System. Similarly to volcanoes on Earth, Ionian volcanoes emit sulfur and sulfur dioxide. Originally it was thought that many lava flows consisted of sulfurous substances. However, nowadays it is thought that many of them are molten silicate rock like on the Earth. The energy for this activity probably derives from tidal interactions among Io, Jupiter, and two other moons of Jupiter, Europa and Ganymede. The three moons are locked into Laplace-resonant orbits such that Io orbits twice for each orbit of Europa, which in turn orbits twice for each orbit of Ganymede; furthermore, Io always keeps the same face towards Jupiter. The gravitational interaction of Europa, Ganymede and Jupiter cause Io to "stretch" and "bend" by as much as 100 meters, a process which generates heat through internal friction. Some of Io's volcanic plumes have been measured rising over 300 km above the surface before falling back, with material ejected from the surface at approximately one kilometre per second. The volcanic eruptions change rapidly; in just four months between the arrivals of Voyager 1 and Voyager 2 some eruptions stopped and others began. The deposits surrounding the vents also changed visibly during this time. Another source of energy is that Io cuts across Jupiter's magnetic field lines, generating an electric current. Though not a large source of energy compared to the tidal heating, this current may carry more than 1,000 gigawatts with a potential of 400 kilovolts. It also strips ionized atoms from Io at the rate of a thousand kilograms per second. Due to the rapid rotation of Jupiter's magnetic field, these particles are swept along the orbit in front of Io where they form a torus of intense radiation around Jupiter that glows brightly in the ultraviolet. Particles escaping from this torus are partially responsible for Jupiter's unusually large magnetosphere, their outward pressure inflating it from within. Recent data from the Galileo orbiter indicate that Io might have its own magnetic field. The location of Io with respect to the Earth and Jupiter has a strong influence on the Jovian radio emissions as seen from the earth: When Io is visible, radio signals from Jupiter increase considerably. In February 2001, the largest recorded volcanic eruptions in the solar system occurred on Io [http://www2.keck.hawaii.edu/news/archive/eruption/].

Physical characteristics

solar system Unlike most moons in the outer solar system, Io may be somewhat similar in bulk composition to the terrestrial planets, primarily composed of molten silicate rock. Recent data from the Galileo orbiter indicates that Io has a core of iron (perhaps mixed with iron sulfide), the core's radius being at least 900 km. When Voyager 1 first returned images of Io in 1979, scientists expected to see numerous craters, the density of which across Io's surface would give clues to the moon's age. However, they were surprised to discover that Io's surface is almost completely lacking in craters, due to the tremendous amount of volcanic activity constantly reshaping the landscape. Since the surface features visible today were formed relatively recently, the Ionian surface is described as "young", as is the terrestrial surface. In contrast, celestial bodies with heavily cratered features, such as Earth's Moon, are considered to have "old" surfaces, since they have remained in their current state for billions of years. Moon Moon In addition to volcanoes, Io's surface includes nonvolcanic mountains, numerous lakes of molten sulfur, calderas up to several kilometres deep, and extensive flows hundreds of kilometres long of low-viscosity fluid (possibly some form of molten sulfur or silicate). Sulfur and its compounds take on a wide range of colors and are responsible for Io's variegated appearance. Analysis of the Voyager images led scientists to believe that the lava flows on Io's surface were composed mostly of various compounds of molten sulfur. However, subsequent ground-based infrared studies indicate that they are too hot for liquid sulfur; some of the hottest spots on Io may reach temperatures as high as 2000 K, 1300 K higher than the boiling point of sulfur, though the average is much lower, at around 130 K. One current theory is that Io's lavas are molten silicate rock. Recent Hubble Space Telescope observations indicate that the material may be rich in sodium. There may be a variety of different materials in different locations. Io has a thin atmosphere composed of sulfur dioxide and perhaps other gases. Unlike the other Galilean satellites, Io has little or no water. This is probably because Jupiter was hot enough early in the evolution of the solar system to drive off the volatile elements in the vicinity of Io, but not hot enough to do so farther out.

Io in fiction

- Io plays an important role in both the book and the film of Arthur C. Clarke's 2010: Odyssey Two (1984). A spacecraft is found tumbling end over end in orbit around Io, coated with sulfur from the erupting volcanoes beneath it.
- Peter Hyams, the director of 2010, had previously made a film called Outland (1981), set in a mining colony on Io, although the moon itself had little importance to the plot.
- In the animated television series Exosquad (1993–1995), Io is the location of an Exofleet base and the scene of several critical battles between Terran and Neosapien forces
- In the science fiction TV series Babylon 5 (1993–), Io is home to an Earth Alliance colony, second in size only to the colony on Mars.
- Michael Swanwick's Hugo award-winning short story "The Very Pulse of the Machine" (1998) is set on Io, and features elements of the volcanic, sulfurous landscape, as well as the powerful electrical flux between Io and Jupiter.
- In the BBC docudrama Space Odyssey: Voyage To The Planets (2005), about a possible manned mission to various points of the Solar System, one astronaut lands on Io to collect samples of its rocks. However, due to radiation risks and the astronaut becoming exhausted, the EVA on Io is aborted early and the samples are abandoned.
- In the computer game ZeroZone, Io is one of the settings.
- Io is the setting of the computer game POD.

External links

- [http://www.nineplanets.org/io.html Bill Arnett's Io webpage]
- [http://www.martiana.org/mars/jupiter/jupifrm.htm The Calendars of Jupiter]
- [http://www.cosis.net/abstracts/EAE03/07912/EAE03-J-07912.pdf The Conundrum Posed by Io's Minimum Surface Temperatures]
- [http://www.windows.ucar.edu/tour/link=/jupiter/moons/io_composition_overview.html&edu=high Io's Composition]
... | Thebe | Io | Europa | ... Category:Jupiter's moons als:Io (Mond) ja:イオ (衛星)

Natural satellite

The common noun moon (not capitalized) is used to mean any natural satellite of the other planets. There are at least 140 moons within Earth's solar system, and presumably many others orbiting the planets of other stars. The large gas giants have extensive systems of moons, including half a dozen comparable in size to Earth's moon. Mercury and Venus have no moons at all, Earth has one large moon ("The Moon"), Mars has two tiny moons, and Pluto has three, including a large companion called Charon (Pluto and Charon are sometimes considered a double planet).

Origin

Most moons are assumed to have been formed out of the same collapsing region of protoplanetary disk that gave rise to its primary. However, there are many exceptions and variations to this standard model of moon formation that are known or theorized. Several moons are thought to be captured asteroids; others may be fragments of larger moons shattered by impacts, or (in the case of Earth's Moon) a portion of the planet itself blasted into orbit by a large impact. As most moons are known only through a few observations via probes or telescopes, most theories about their origins are still uncertain.

Orbital characteristics

Most moons in the solar system are tidally locked to their primaries, meaning that one side of the moon is always turned toward the planet. Exceptions are Saturn's moon Hyperion, which rotates chaotically due to a variety of external influences, and the outermost moons of the gas giants, which are too far away to become 'locked' (an example is Saturn's moon Phoebe). It is not possible for a moon to have moons of its own: the tidal effects of their primaries would make such a system unstable. However, several moons have small companions in the Lagrangian points of their orbits (e.g., Saturn's moons Tethys and Dione). The recent discovery of 243 Ida's moon Dactyl confirms that some asteroids also have moons. Some, like 90 Antiope, are double asteroids with two equal-sized components. The asteroid 87 Sylvia has two moons. See asteroid moon for further information.

Moons of the Solar system

The largest moons in the solar system (those bigger than about 3000 km across) are Earth's Moon, Jupiter's Galilean moons Io, Europa, Ganymede, and Callisto, Saturn's moon Titan, and Neptune's captured moon Triton. For smaller moons see the articles on the appropriate planet. The following is a comparative table classifying the moons of the solar system by diameter. The column on the right includes some notable planets, asteroids and Kuiper belt objects for comparison.

Diameter(km)	Earth	Mars	Jupiter	Saturn	Uranus	Neptune	Pluto	Other objects
5000-6000			Ganymede	Titan
4000-5000			Callisto					Mercury
3000-4000	Luna		Io Europa
2000-3000						Triton		Pluto
1000-2000				Rhea Iapetus Dione Tethys	Titania Oberon Umbriel Ariel		Charon	90377 Sedna 90482 Orcus 50000 Quaoar 20000 Varuna 28978 Ixion
100-1000			Himalia Amalthea	Enceladus Mimas Hyperion Phoebe Janus Epimetheus Prometheus	Miranda Sycorax Puck Portia	Proteus Nereid Larissa Galatea Despina	S/2005 P 1² S/2005 P 2²	1 Ceres 2 Pallas 4 Vesta 10 Hygiea 511 Davida 704 Interamnia 3 Juno (and many others)
50-100			Thebe Elara Pasiphaë	Pandora	Caliban Juliet Belinda Cressida Rosalind Desdemona Bianca	Thalassa Naiad S/2002 N 4		(Too many to list)
10-50		Phobos Deimos	Carme Metis Sinope Lysithea Ananke Leda Adrastea	Siarnaq Atlas Helene Albiorix Telesto Pan Paaliaq Calypso Ymir Kiviuq Tarvos Ijiraq	Ophelia Cordelia Setebos Prospero Stephano Perdita S/2001 U 2 S/2001 U 3 Margaret Trinculo Mab Cupid	S/2002 N 1 S/2002 N 2 S/2002 N 3 Psamathe		(Too many to list)
less than 10	Cruithne¹		At least 47, see Jupiter's natural satellites for a listing.	Erriapo Narvi Skathi Mundilfari Suttungr Thrymr Pallene Polydeuces Methone S/2004 S 3 Daphnis				(Too many to list)

¹) Cruithne is not a real moon; it is mainly placed here for comparison's sake.
²) Diameters of the new Plutonian satellites are still very poorly known, but they are estimated to lie between 64 and 200 km.
In addition to the moons of the various planets there are also over 30 known asteroid moons, asteroids that orbit other asteroids.

External links

Jupiter's moons

- [http://www.ifa.hawaii.edu/~sheppard/satellites/jupsatdata.html Data on Jupiter's satellites]
- [http://www.ifa.hawaii.edu/faculty/jewitt/jmoons/jmoons.html Jupiter's new moons (discovered in 2000)]
- [http://www.ifa.hawaii.edu/~sheppard/satellites/jup.html Jupiter's new moons (discovered in 2002)]
- [http://www.ifa.hawaii.edu/~sheppard/satellites/jup2003.html Jupiter's new moons (discovered in 2003)]

Saturn's moons

- [http://www.news.cornell.edu/releases/Oct00/Saturn.moons.deb.html Saturn's new moons (discovered in 2000)]
- [http://www.ifa.hawaii.edu/~sheppard/satellites/sat2003.html Saturn's new moon (discovered in 2003)]

Neptune's moons

- [http://sse.jpl.nasa.gov/whatsnew/pr/030113A.html Neptune's new moons (discovered in 2003)]

All moons

- [http://www.planetary.org/learn/solarsystem/moons.html Moons of the Solar System (The Planetary Society)]
- [http://www.ifa.hawaii.edu/~sheppard/satellites Scott Sheppard's page]
- [http://ssd.jpl.nasa.gov JPL's Solar System Dynamics page]
- [http://www.space.com/scienceastronomy/planet_photo_040910.html Moon of an Object? First Photo of Satellite Beyond the Solar System]
- [http://planetarynames.wr.usgs.gov/append7.html USGS list of named moons] ----
- als:Satellit (Astronomie) ko:위성 ms:Satelit semulajadi ja:衛星 th:ดาวบริวาร

Io (mythology)

This article is about the mythological figure. For the moon of Jupiter, see Io (moon). Io (moon) In Greek mythology, Io (IPA or ) was the daughter of Inachus, a river god (it should be noted that the early genealogy of the House of Argos is very confusing; depending on the source, Io had different parents). In most accounts, she is a priestess of Hera. One day, Zeus noticed the maiden, and he lusted after her. Some say she rejected his advances until he caused her own father to drive her out into the fields. Here, Zeus covered her with clouds to hide her from the eyes of his jealous wife, Hera, who nonetheless came to investigate. In a vain attempt to hide his crimes, Zeus turned himself into a white cloud and transformed Io into a beautiful white heifer. Hera was not fooled. She demanded the heifer as a present. Hera placed Io in the charge of Argus (the many-eyed monster) to keep her separated from Zeus. Zeus commanded Hermes to kill Argus, which he did by lulling all 100 eyes to sleep. Hera then forced Io to wander the earth without rest, plagued by a gadfly (Οίστρος > oestrus > estrus [see etymology]) to sting her into madness. Io eventually crossed the path between Propontis and Black Sea, which thus took the name Bosporus (meaning ox passage), where she met Prometheus. Prometheus had been chained on Mt. Caucasus by Zeus for teaching Man how to make fire and tricking him into accepting the worse part of a sacrifice while the mortals kept the best part (meat); every day, a giant eagle fed on Prometheus's liver. Despite his agony, he tried to comfort Io. He told her that she would be restored to human form and become the ancestress of the greatest of all heroes, Heracles. Io escaped across the Ionian Sea to Egypt, where she was restored to human form by Zeus. There, she gave birth Zeus's son, Epaphus. She later married Egyptian king Telegonus. Their grandson, Danaos, eventually returned to Greece with his fifty daughters (the Danaids), as recalled in Aeschylus' play The Suppliants. The term Io fly is derived from the gadfly Hera sent to torment Io into fleeing to Egypt after Argus was slain. Io is the subject of one of Antonio Correggio's most famous paintings. Category: Greek mythology Category:Shapeshifting als:Io (Mythologie) ko:이오 (신화) ja:イオ

Jupiter (god)

In Roman mythology, Jupiter held the same role as Zeus in the Greek pantheon. He was called Jupiter Optimus Maximus (Jupiter Highest, Greatest) as the patron deity of the Roman state, in charge of laws and social order. Jupiter is, properly speaking, a derivation of Jove and pater (Latin for father) This article focuses on Jupiter in early Rome and in cultic practice. For information on mythological accounts of Jupiter, which are heavily influenced by Greek mythology, see Zeus. The name of the god was also adopted as the name of the planet Jupiter, and was the original namesake of the weekday that would come to be known in English as Thursday (the etymological root is more apparent in French jeudi, from Jovis Dies). Ironically, linguistic studies identify him as deriving from the same god as the Germanic Tiwaz, whose name was given to Tuesday. Another etymological reference is Dyaus Pita of the Vedic religion.

Other titles of Roman Jupiter:

#Jupiter Caelestis ("heavenly") #Jupiter Fulgurator ("of the lightning") #Jupiter Latarius ("God of Latium") #Jupiter Lucetius ("of the light") #Jupiter Pluvius ("sender of rain") See also Pluvius #Jupiter Stator (from stare meaning "standing") #Jupiter Terminus or Jupiter Terminalus (defends boundaries). See also Terminus #Jupiter Tonans ("thunderer") #Jupiter Victor (led Roman armies to victory) #Jupiter Summanus (sender of nocturnal thunder) #Jupiter Feretrius ("who carries away [the spoils of war]") #Juptier Optimus Maximus (best and greatest)

Jupiter and Roman sovereignty

The several aspects of sovereignty implied by some of Jupiter's titles are made explicit in the legendary history of early Rome (as transmitted, for example, in Plutarch's Roman Lives and the first few books of Livy). Thus the warlike Romulus invokes Jupiter Stator to halt and terrify Rome's enemies, while the peaceful legislator Numa Pompilius has a close relationship with Dius Fidius, who presides over oaths. Jupiter also stands at the head of the Archaic Triad of Jupiter, Mars and Quirinus. This grouping has been seen as a religious representation of early Roman society, wherein:
- Jupiter stands in for the ritual and augural authority of the Flamen Dialis (high priest of Jupiter) and the chief priestly colleges.
- Mars, with his warrior and agricultural functions, stands in for the power of the king and young nobles to bring prosperity and victory through sympathetic magic with rituals like the October Horse and the Lupercalia.
- Quirinus, from co-viri "men together", stands in for the combined strength of the Roman populus. Later, during the Imperial period, the emperors Claudius and Domitian adopted traits of Jupiter in their portraiture, to emphasize their sovereignty over the whole world.

Capitoline Jupiter

The largest temple in Rome was that of Jupiter Optimus Maximus on the Capitoline Hill. Here he was worshipped alongside Juno and Minerva, forming the Capitoline Triad. Temples to Jupiter Optimus Maximus or the Capitoline Triad as a whole were commonly built by the Romans at the center of new cities in their colonies.

In language

It was once believed that the Roman god Jupiter (Zeus in Greece) was in charge of cosmic Justice, and in ancient Rome, people swore to Jove in their courts of law, which lead to the common expression "By Jove," that many people use today.

References

- Article "Jupiter" in The Oxford Classical Dictionary. ISBN 0198606419.
- Georges Dumézil, Archaic Roman Religion. ISBN 0801854814.
- Georges Dumézil, Mitra-Varuna. ISBN 0942299132. Category:Sky and weather gods Category:Thunder gods Category:Roman gods ko:유피테르 ja:ユピテル

Simon Marius

:For the 18th-century composer, see Simon Mayr. Simon Mayr Simon Marius (in Latin; German Simon Mayr) (January 10, 1573 – December 26, 1624) was a German astronomer. He was born in Gunzenhausen, but most of his lifetime he spent in the city of Ansbach. In 1614 Marius published his work Mundus Iovialis describing the planet Jupiter and its moons. Here he claimed to have discovered the planet's four major moons some days before Galileo. This led to a dispute with Galileo, who showed that Marius provided only one observation as early as Galileo's, and it matched Galileo's diagram for the same date, as published in 1610. It is considered possible that Marius discovered the moons independently, but at least some days later than Galileo; if so, he is the only person known to have observed the moons in the period before Galileo published his obeservations. Regardless of priority, the mythological names by which these satellites are known today (Io, Europa, Ganymede and Callisto) are those given them by Marius. Simon Marius also claimed to be the discoverer of the Andromeda Galaxy, which had in fact already been known to Arab astronomers of the Middle Ages.

External links

- [http://galileo.rice.edu/sci/marius.html The Galileo Project] — biography of Simon Marius. Marius, Simon Marius, Simon Marius, Simon als:Simon Marius

20th century

The 20th century lasted from 1901 to 2000 in the Gregorian calendar. Common usage sometimes regards it as lasting from 1900 to 1999, but this is incorrect since counting of calendar years begins with the year 1. The 20th century is also sometimes known as the nineteen hundreds (1900s). Decades are almost always considered as starting with the "0" year and named accordingly ("1960s", etc.). However, a number of arguments have been used to justify the common usage. One was advanced, erroneously, by Stephen Jay Gould. He claimed that the first decade had only nine years, thus contradicting the definition of decade equaled 10 years. Another argument is that the astronomical year numbering system for years does have a year zero, the year normally known as 1 BC. In 2000 the International Organization for Standardization clarified ISO 8601 to use the astronomical year numbering system, which could be interpreted as retrospectively endorsing all the people who had celebrated the new century a few months earlier. The term is also used to describe various periods that overlap with the calendar definition, most notably the Short twentieth century, which claims that the 20th Century spanned from 1914 to 1989, rendering the pre-WWI 1900s into the 19th Century and putting the 1990s at the beginning of the 21st Century. Indeed, the part of the 20th Century before World War I is quite identical to the late 1800s culturally and technologically and the 1990s decade pointed in many ways (such as the rise of the Internet) to the 21st Century and is seen by some as not being truly a part of the 20th Century.

Overview

The twentieth century saw a remarkable shift in the way that vast numbers of people lived, as a result of technological, medical, social, ideological, and political innovations. Terms like ideology, world war, genocide, and nuclear war entered common usage and became an influence on the lives of everyday people. War reached an unprecedented scale and level of sophistication; in the Second World War (1939-1945) alone, approximately 57 million people died, mainly due to massive improvements in weaponry. The trends of mechanization of goods and services and networks of global communication, which were begun in the 19th century, continued at an ever-increasing pace in the 20th. In spite of the terror and chaos, the 20th century saw many attempts at world peace. As the 35th President of the United States John F. Kennedy said: :What kind of peace do we seek? I am talking about a genuine peace, the kind of peace that makes life on earth worth living. Not merely peace in our time, but peace in all time. Our problems are man-made, therefore they can be solved by man. For in the final analysis, our most basic common link is that we all inhabit this small planet, we all breathe the same air, we all cherish our children's future, and we are all mortal. Virtually every aspect of life in virtually every human society changed in some fundamental way or another during the twentieth century and for the first time, any individual could influence the course of history no matter their background. Arguably, the 20th century re-shaped the face of the planet in more ways than any previous century.
- Death rates
- Infant mortality
- Infectious disease
- Life expectancy
- Maternal death rates
- Battles Scientific discoveries such as relativity and quantum physics radically changed the worldview of scientists, causing them to realize that the universe was much more complex than they had previously believed, and dashing the hopes at the end of the preceding century that the last few details of knowledge were about to be filled in. For a more coherent overview of the historical events of the century, see The 20th century in review. The 20th century has sometimes been called, both within and outside the United States, the American Century, though this is a controversial term.

Important developments, events and achievements

Science and technology

- The assembly line and mass production of motor vehicles and other goods allowed manufacturers to produce more and cheaper products. This allowed the automobile to become the most important means of transportation.
- The invention of heavier-than-air flying machines and the jet engine allowed for the world to become "smaller". Space flight increased knowledge of the rest of the universe and allowed for global real-time communications via geosynchronous satellites.
- Mass media technologies such as film, radio, and television allow the communication of political messages and entertainment with unprecedented impact
- Mass availability of the telephone and later, the computer, especially through the Internet, provides people with new opportunities for near-instantaneous communication
- Applied electronics, notably in its miniaturized form as integrated circuits, made possible the above mentioned rise of mass media, telecommunications, ubiquitous computing, and all kinds of "intelligent" appliances; as well as many advances in natural sciences such as physics, by the use of exponentially growing calculation power (see supercomputer).
- The development of Nitrogen fertilizer, pesticides and herbicides resulted in significantly higher agricultural yield.
- Advances in fundamental physics through the theory of relativity and quantum mechanics led to the development of nuclear weapons (known informally as "the Bomb" and dropped on the industrial town of Hiroshima and the historic one of Nagasaki), the nuclear reactor, and the laser. Fusion power was studied extensively but remained an experimental technology at the end of the century.
- Inventions such as the washing machine and air conditioning led to an increase in both the quantity and quality of leisure time for the middle class in Western societies.
- Most influential inventions in the 20th century: antibiotics, oral contraceptives, new plastics, transistors, Internet
- More...

Wars and politics

- Democratic nations began to extend voting privileges to all adults.
- Rising nationalism and increasing national awareness were among the causes of World War I, the first of two wars to involve all the major world powers including Germany, France, Italy, Japan, the United States and the British Commonwealth. World War I led to the creation of many new countries, especially in Eastern Europe. Ironically, it was said by many to be the 'War to end all Wars'.
- The economic and political aftermath of World War I led to the rise of Fascism and Nazism in Europe, and shortly to World War II. This war also involved Asia and the Pacific, in the form of Japanese aggression against China and the United States. While the First World War mainly cost lives among soldiers, civilians suffered greatly in the Second -- from the bombing of cities on both sides, and in the unprecedented German genocide of the Jews and others, known as the Holocaust.
- During World War I, in Russia the Bolshevik putsch led to the Russian Revolution of 1917. After the Soviet Union's involvement in World War II, Communism became a major force in global politics, spreading all over the world: notably, to Eastern Europe, China, Indochina and Cuba. This led to the Cold War and proxy wars with the western world, including wars in Korea (1950-53) and Vietnam (1957 - 75).
- The "fall of Communism" in the late 1980s freed Eastern and Central Europe from Soviet supremacy. It also led to the dissolution of the Soviet Union and Yugoslavia into successor states, many rife with ethnic nationalism, and left the United States as the world's superpower.
- Through the League of Nations and, after World War II, the United Nations, international cooperation increased. Other efforts included the formation of the European Union, leading to a common currency in much of Western Europe, the euro around the turn of the millennium.
- The end of colonialism led to the independence of many African and Asian countries. During the Cold War, many of these aligned with the USA, the USSR, or China for defense.
- The creation of Israel, a Jewish state in a mostly Arab region of the world, fueled many conflicts in the region, which were also influenced by the vast oil fields in many of the Arab countries.
- The term Southeast Asia coined.

Culture and entertainment

- Movies, music and the media had a major influence on fashion and trends in all aspects of life. As many movies and music originate from the United States, American culture spread rapidly over the world.
- After gaining political rights in the United States and much of Europe in the first part of the century, and with the advent of new birth control techniques women became more independent throughout the century.
- Rock and Roll and Jazz styles of music are developed in the United States, and quickly become the dominant forms of popular music in America, and later, the world. The Beatles, a 1960s British Rock and Roll band, becomes one of the most successful acts of all time, and is credited, in their experimental later albums, with permanently changing what was thought possible in popular music.
- Modern art developed new styles such as expressionism, cubism, and surrealism.
- The automobile provided vastly increased transportation capabilities for the average member of Western societies in the early to mid-century, spreading even further later on. City design throughout most of the West became focused on transport via car. The car became a leading symbol of modern society, with styles of car suited to and symbolic of particular lifestyles.
- Sports became an important part of society, becoming an activity not only for the privileged. Watching sports, later also on television, became a popular activity.

Disease and medicine

- Although the availability and quality of medicine continued to improve, epidemic diseases continued to spread, aided by modern transportation. An influenza pandemic, the Spanish Flu, killed 25 million between 1918 and 1919, while AIDS is yet uncured and treatments remain too expensive for wide use in developing countries.
- Advances in medicine, such as the invention of antibiotics, decreased the number of people dying from diseases. Contraceptive drugs and organ transplantation were developed. The discovery of DNA molecules and the advent of molecular biology allowed for cloning and genetic engineering.

Natural resources and the environment

- The widespread use of petroleum in industry -- both as a chemical precursor to plastics and as a fuel for the automobile and airplane -- led to the vital geopolitical importance of petroleum resources. The Middle East, home to many of the world's oil deposits, became a center of geopolitical and military tension throughout the latter half of the century. (For example, oil was a factor in Japan's decision to go to war against the United States in 1941, and the oil cartel, OPEC, used an oil embargo of sorts in the wake of the Yom Kippur War in the 1970s).
- A vast increase in fossil fuel consumption leads to depletion of natural resources, while air pollution has led to the develoment of an ozone hole and, many believe, global warming and both local and global climate change. The problem is increased by world-wide deforestation, also causing a loss of biodiversity. The problem of a depletion of natural resources is decreased by advances in drilling technology which led to a net increase in the amount of fossil fuel that is readily obtainable at the end of the century, as compared with the amount considered obtainable at the beginning of the century.

Significant people

Roman numeral

The system of Roman numerals is a numeral system originating in ancient Rome, and was adapted from Etruscan numerals. The system used in antiquity was slightly modified in the Middle Ages to produce the system we use today. It is based on certain letters which are given values as numerals: :I or i for one, :V or v for five, :X or x for ten, :L or l for fifty, :C or c for one hundred (centum), :D or d for five hundred, :M or m for one thousand (mille). For larger numbers (five thousand and above), a bar is placed above a base numeral to indicate multiplication by 1000. : for five thousand : for ten thousand : for fifty thousand : for one hundred thousand : for five hundred thousand : for one million Roman numerals are commonly used today in numbered lists (in outline format), clockfaces, pages preceding the main body of a book, chord triads in music analysis, the numbering of movie sequels, and the numbering of some sport events, like the Super Bowls or Olympic Games. For arithmetics involving Roman numerals, see Roman arithmetic and Roman abacus.

Origins

Although the Roman numerals are now written with letters of the Roman alphabet, they were originally separate symbols. The Etruscans, for example, used I Λ X ⋔ 8 ⊕ for I V X L C M. They appear to derive from notches on tally sticks, such as those used by Italian and Dalmatian shepherds into the 19^th century. Thus, the I descends from a notch scored across the stick. Every fifth notch was double cut (⋀, ⋁, ⋋, ⋌, etc.), and every tenth was cross cut (X), much like European tally marks today. This produced a positional system: Eight on a counting stick was eight tallies, IIIIΛIII, but this could be written ΛIII (or VIII), as the Λ implies the four prior notches. Likewise, number four on the stick was the I-notch that could be felt just before the cut of the V, so it could be written as either IIII or IV. Thus the system was neither additive nor subtractive in its conception, but ordinal. When the tallies were later transfered to writing, the marks were easily identified with the existing Roman letters I, V, X. (A folk etymology has it that the V represented a hand, and that the X was made by placing two Vs on top of each other, one inverted.) The tenth V or X along the stick received an extra stroke. Thus 50 was written variously as N, И, K, Ψ, ⋔, etc., but perhaps most often as a chicken-track shape like a superimposed V and I. This had flattened to ⊥ (an inverted T) by the time of Augustus, and soon thereafter became identified with the graphically similar letter L. Likewise, 100 was variously Ж, ⋉, ⋈, H, or as any of the symbols for 50 above plus an extra stroke. The form Ж (that is, a superimposed X and I) came to predominate, was written variously as >I< or ƆIC, was then shortened to Ɔ or C, with C finally winning out because, as a letter, it stood for centum (Latin for 'hundred'). The hundredth V or X was marked with a box or circle. Thus 500 was like a Ɔ superposed on a ⋌ or ⊢ (that is, like a Þ with a cross bar), becoming a struck-through D or a Ð by the time of Augustus, under the graphic influence of the letter D. It was later identified as the letter D. Meanwhile, 1000 was a circled X: Ⓧ, ⊗, ⊕, and by Augustinian times was partially identified with the Greek letter Φ. It then evolved along several independent routes. Some variants, such as Ψ and CD (more accurately a reversed D adjacent to a regular D), were historical dead ends (although folk etymology later identified D for 500 as half of Φ for 1000 because of the CD variant), while two variants of ↀ survive to this day. One, CIƆ, lead to the convention of using parentheses to indicate multiplication by 1000 (later extended to double parentheses as in ↁ, ↂ, etc.); in the other, ↀ became ∞ and ⋈, eventually changing to M under the influence of the word mille ('thousand').

Zero

In general, the number zero did not have its own Roman numeral, but the concept of zero as a number was well known by all medieval computists (responsible for calculating the date of Easter). They included zero (via the Latin word nulla meaning nothing) as one of nineteen epacts, or the age of the moon on March 22. The first three epacts were nullae, xi, and xxii (written in minuscule or lower case). The first known computist to use zero was Dionysius Exiguus in 525, but the concept of zero was no doubt well known earlier. Only one instance of a Roman numeral for zero is known. About 725, Bede or one of his colleagues used the letter N, the initial of nullae, in a table of epacts, all written in Roman numerals. A notation for the value zero is quite distinct from the role of the digit zero in a positional notation system. The lack of a zero digit prevented Roman numerals from developing into a positional notation, and led to their gradual replacement by Arabic numerals in the early second millennium.

IIII or IV?

The notation of Roman numerals has varied through the centuries. Originally, it was common to use IIII to represent "four", because IV represented the god Jove (and later YHWH). The subtractive notation (which uses IV instead of IIII) has become universally used only in modern times. For example, Forme of Cury, a manuscript from 1390, uses IX for "nine", but IIII for "four". Another document in the same manuscript, from 1381, uses IV and IX. A third document in the same manuscript uses both IIII and IV, and IX. Constructions such as IIX for "eight" have also been discovered. In many cases, there seems to have been a certain reluctance in the use of the less intuitive subtractive notation. Its use increased the complexity of performing Roman arithmetic, without conveying the benefits of a full positional notation system.

Calendars and clocks

Clock faces that are labelled using Roman numerals conventionally show IIII for 4 o'clock and IX for 9 o'clock, using the subtractive principle in one case and not in the other. There are several suggested explanations for this, several of which may be true:
- The four-character form IIII creates a visual symmetry with the VIII on the other side, which IV would not.
- The number of symbols on the clock totals twenty I's, four V's, and four X's, so clock makers need only a single mold with five I's, a V, and an X in order to make the correct number of numerals for the clocks, cast four times for each clock: :: V IIII IX :: VI II IIX :: VII III X :: VIII I IX :IIX and one of the IX's can be rearranged or inverted to form XI and XII. The alternative uses seventeen I's, five V's, and four X's, possibly requiring the clock maker to have several different molds.
- IIII was the preferred way for the ancient Romans to write 4, since they to a large extent avoided subtraction.
- It has been suggested that since IV is the first two letters of IVPITER, the main god of the Romans, it was not appropriate to use.
- The I symbol would be the only symbol in the first 4 hours of the clock, the V symbol would only appear in the next 4 hours, and the X symbol only in the last 4 hours. This would add to the clock's radial symmetry.
- IV is difficult to read upside down and on an angle, particularly at that location on the clock.
- Louis XIV, king of France, preferred IIII over IV, ordered his clockmakers to produce clocks with IIII and not IV, and thus it has remained.

XCIX or IC?

Rules regarding Roman numerals often state that a symbol representing 10^x may not precede any symbol larger than 10^x+1. For example, C cannot be preceded by I or V, only by X (or, of course, by a symbol representing a value larger than C). Thus, one should represent the number "ninety-nine" as XCIX, not as the "shortcut" IC. However, these rules are not universally followed. This 'problem' manifested in questions as to why 1999 was not written simply IMM or MIM.

Year in Roman numerals

In seventeenth century Europe, using Roman numerals for the year of publication for books was standard; there were many other places it was used as well. Publishers attempted to make the number easier to read by those more accustomed to Arabic positional numerals. On British title pages, there were often spaces between the groups of digits: M DCC LXI is one example. This may have come from the French, who separated the groups of digits with periods, as: M.DCC.LXI. or M. DCC. LXI. Notice the period at the end of the sequence; many foreign countries did this for Roman numerals in general, but not necessarily Britain. (Periods were also common on each side of numerals in running text, as in "commonet .iij. viros illos".) These practices faded from general use before the start of the twentieth century, though the cornerstones of major buildings still occasionally use them. Roman numerals are today still used on building faces for dates: 2005 can be represented as MMV. The film industry has used them perhaps since its inception to denote the year a film was made, so that it could be redistributed later, either locally or to a foreign country, without making it immediately clear to viewers what the actual date was. This became more useful when films were broadcast on television to partially conceal the age of films. From this came the policy of the broadcasting industry, including the BBC, to use them to denote the year in which a television program was made (the Australian Broadcasting Corporation has largely stopped this practice but still occasionally lapses).

Other modern usage by English-speaking peoples

Roman numerals remained in common use until about the 14th century, when they were replaced by Arabic numerals (thought to have been introduced to Europe from al-Andalus, by way of Arab traders and arithmetic treatises, around the 11th century). The use of Roman numerals today is mostly restricted to ordinal numbers, such as volumes or chapters in a book or the numbers identifying monarchs or popes (e.g. Elizabeth II, Benedict XVI, etc.). Sometimes the numerals are written using lower-case letters (thus: i, ii, iii, iv, etc.), particularly if numbering paragraphs or sections within chapters, or for the pagination of the front matter of a book. Undergraduate degrees at British universities are generally graded using I, IIi, IIii, III for first, upper second (often pronounced "two one"), lower second (often pronounced "two two") and third class respectively. Modern English usage also employs Roman numerals in many books (especially anthologies), movies (e.g., Star Wars), sporting events (e.g., the Super Bowl), and historic events (e.g., World War I, World War II ). The common unifying theme seems to be stories or events that are episodic or annual in nature, with the use of classical numbering suggesting importance or timelessness. In chemistry, Roman numerals were used to denote the group in the periodic table of the elements. But there was not international agreement as to whether the group of metals which dissolve in water should be called Group IA or IB, for example, so although references may use them, the international norm has recently switched to Arabic numerals. In music theory a scale degrees or diatonic functions are often identified by Roman numerals (as in chord symbols) as follows:

Modern non-English speaking usage

The above uses are customary for English-speaking countries. Although many of them are also maintained in other countries, those countries have additional uses for Roman numerals which are unknown in English-speaking regions. The French, the Portuguese, and the Spanish use capital Roman numerals to denote centuries. For example, 'XVIII' refers to the eighteenth century, so as to avoid confusion between the '18^th century' and the '1800s'. (The Italians take the opposite approach, basing names of centuries on the digits of the years; quattrocento for example is the Italian name for the fifteenth century.) Some scholars in English-speaking countries have adopted the French method, among them Lyon Sprague de Camp. In Germany, Poland, and Russia, mixed Roman numerals are used to record dates. Just as an old clock recorded the hour by Roman numerals while the minutes were measured in Arabic numerals, the month is written in Roman numerals while the day is in Arabic numerals: 14-VI-1789 is June the fourteenth, 1789. This is how dates are inscribed on the walls of the Kremlin, for example. This method has the advantage that days and months are not confused in rapid note-taking, and that any range of days or months can be expressed without confusion. For instance, V-VIII is May to August, while 1-V-31-VIII is May first to August thirty-first. In

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