Planet

A planet, as defined by the International Astronomical Union (IAU), is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.[a][1][2]

The term planet is ancient, with ties to history, science, myth, and religion. The planets were originally seen by many early cultures as divine, or as emissaries of the gods. Even today, many people believe in astrology, which holds that the movement of the planets affects people's lives, although such a causation is rejected by the scientific community. As scientific knowledge advanced, human perception of the planets changed, incorporating a number of disparate objects. Even now there is no uncontested definition of what a planet is. In 2006, the IAU officially adopted a resolution defining planets within the Solar System. This definition has been both praised and criticized, and remains disputed by some scientists.

The planets were thought by Ptolemy to orbit the Earth in deferent and epicycle motions. Though the idea that the planets orbited the Sun had been suggested many times, it was not until the 17th century that this view was supported by evidence from the first telescopic astronomical observations, performed by Galileo Galilei. By careful analysis of the observation data, Johannes Kepler found the planets' orbits to be not circular, but elliptical. As observational tools improved, astronomers saw that, like Earth, the planets rotated around tilted axes, and some share such features as ice-caps and seasons. Since the dawn of the Space Age, close observation by probes has found that Earth and the other planets share characteristics such as volcanism, hurricanes, tectonics, and even hydrology. Since 1992, through the discovery of hundreds of extrasolar planets (planets around other stars), scientists are beginning to understand that planets throughout the Milky Way Galaxy share characteristics in common with our own.

Planets are generally divided into two main types: large, low-density gas giants, and smaller, rocky terrestrials. Under IAU definitions, there are eight planets in the Solar System. In order from the Sun, they are the four terrestrials, Mercury, Venus, Earth, and Mars, then the four gas giants, Jupiter, Saturn, Uranus, and Neptune. Many of these planets are orbited by one or more moons, which can be larger than small planets. As of January 13th 2009, there are 335 known extrasolar planets, ranging from the size of gas giants to that of terrestrial planets.[3] This brings the total number of identified planets to at least 343. The Solar System also contains at least five dwarf planets: Ceres, Pluto (formerly considered to be the Solar System's ninth planet), Makemake, Haumea and Eris. No extrasolar dwarf planets have yet been detected.

Medicine

Medicine is the art and science of healing. It encompasses a range of health care practices evolved to maintain and restore health by the prevention and treatment of illness. Early records on medicine have been discovered from early Ayurvedic medicine in the Indian subcontinent, ancient Egyptian medicine, traditional Chinese medicine, the Americas, and ancient Greek medicine. Early Grecian doctors Hippocrates, who is also called the Father of Medicine,[4][5] and Galen laid a foundation for later developments in a rational approach to medicine. After the fall of Rome and the onset of the Dark Ages.

Islamic physicians made major medical breakthroughs, supported by the translation of Hippocrates' and Galen's works into Arabic. Notable Islamic medical pioneers include polymath Avicenna, who is also called the Father of Modern Medicine,[6][7] Abulcasis, the father of surgery, Avenzoar, the father of experimental surgery, Ibn al-Nafis, the father of circulatory physiology, and Averroes.[8] Rhazes, who is called the father of pediatrics, first disproved the Grecian theory of humorism, which nevertheless remained influential in Western medieval medicine. While major developments in medicine were occurring in the Islamic world during the medieval period, the Western world remained dependent upon the Greco-Roman theory of humorism, which led to questionable treatments such as bloodletting. 

Islamic medicine and medieval medicine collided during the crusades, with Islamic doctors receiving mixed impressions.[9] As the medieval ages ended, important early figures in medicine emerged in Europe, including Gabriele Falloppio and William Harvey. The major shift in medical thinking was the gradual rejection, especially during the Black Death in the 14th and 15th centuries, of what may be called the 'traditional authority' approach to science and medicine. This was the notion that because some prominent person in the past said something must be so, then that was the way it was, and anything one observed to the contrary was an anomaly (which was paralleled by a similar shift in European society in general - see Copernicus's rejection of Ptolemy's theories on astronomy). Physicians like 

Modern scientific biomedical research (where results are testable and reproducible) began to replace early Western traditions based on herbalism, the Greek "four humours" and other such pre-modern notions. The modern era really began with Robert Koch's discoveries around 1880 of the transmission of disease by bacteria, and then the discovery of antibiotics around 1900. The post-18th century modernity period brought more groundbreaking researchers from Europe. From Germany and Austrian doctors such as Rudolf Virchow, Wilhelm Conrad Röntgen, Karl Landsteiner, and Otto Loewi) made contributions. In the United Kingdom Alexander Fleming, Joseph Lister, Francis Crick, and Florence Nightingale are considered.

Baseball

Baseball is a bat-and-ball sport played between two teams of nine players each. The goal of baseball is to score runs by hitting a thrown ball with a bat and touching a series of four markers called bases arranged at the corners of a ninety-foot square, or diamond. Players on one team (the batting team) take turns hitting while the other team (the fielding team) tries to stop them from scoring runs by getting hitters out in any of several ways. A player on the batting team can stop at any of the bases and hope to score on a teammate's hit. The teams switch between batting and fielding whenever the fielding team gets three outs. One turn at bat for each team constitutes an inning; nine innings make up a professional game. The team with the most runs at the end of the game wins.

Evolving from older bat-and-ball games, an early form of baseball was being played in England by the mid-eighteenth century. This game, as well as the related game of rounders, were brought by British and Irish immigrants to North America, where the modern version of baseball developed. By the late nineteenth century, baseball was widely recognized as the national sport of the United States. Baseball on the professional, amateur, and youth levels is now popular in North America, Central America, parts of South America and the Caribbean, and parts of East Asia and Southeast Asia.

In North America, professional Major League Baseball teams are divided into the National League (NL) and American League (AL). Each league has three divisions: East, West, and Central. Every year, the champion of Major League Baseball is determined by playoffs culminating in the World Series. Four teams make the playoffs from each league: the three regular season division winners, plus one wild card team. The wild card is the team with the best record among the non–division winners in the league. In the National League, the pitcher is required to bat, per the traditional rules. In the American League, there is a tenth player, a designated hitter, who bats for the pitcher. Each major league team has a "farm system" of minor league teams at various levels. 

The distinct evolution of baseball from among the various bat-and-ball games is difficult to trace with precision. A French manuscript from 1344 contains an illustration of clerics playing a game, possibly la soule, with certain similarities to baseball; two other old French games, théque and la balle empoisonée, also appear to be related.[1] Consensus used to hold that today's baseball is a North American development from the older game rounders, popular in Great Britain and Ireland. However a 2005 book.

Basketball

Basketball is a team sport in which two teams of five active players each try to score points against one another by propelling a ball through a 10 feet (3 m) high hoop (the goal) under organized rules. Basketball is one of the most popular and widely viewed sports in the world.[1] Points are scored by shooting the ball through the basket above; the team with more points at the end of the game wins. The ball can be advanced on the court by bouncing it (dribbling) or passing it between teammates. Disruptive physical contact (foul) is not permitted and there are restrictions on how the ball can be handled (violations).

Through time, basketball has developed to involve common techniques of shooting, passing and dribbling, as well as players' positions, and offensive and defensive structures. Typically, the tallest members of a team will play center or one of two forward positions, while shorter players or those who possess the best ball handling skills and speed, play the guard positions. While competitive basketball is carefully regulated, numerous variations of basketball have developed for casual play. In some countries, basketball is also a popular spectator sport.While competitive basketball is primarily an indoor sport, played on a basketball court, less regulated variations have become exceedingly popular as an outdoor sport among both inner city and rural groups.

In early December 1891, Dr. James Naismith,[2] a Canadian physical education professor from McGill University of Montréal and instructor at YMCA Training School[3] (today, Springfield College) in Springfield, Massachusetts, USA, sought a vigorous indoor game to keep his students occupied and at proper levels of fitness during the long New England winters. After rejecting other ideas as either too rough or poorly suited to walled-in gymnasiums, he wrote the basic rules and nailed a peach basket onto a 10-foot (3.05 m) elevated track. In contrast with modern basketball nets, this peach basket retained its bottom, and balls had to be retrieved manually after each "basket" or point scored; this proved inefficient, however, so a hole was drilled into the bottom of the basket, allowing the balls to be poked out with a long dowel each time. The peach baskets were used until 1906 when they were finally replaced by metal hoops with backboards. A further change was soon made, so the ball merely passed through, paving the way for the game we know today.

 A soccer ball was used to shoot goals. Whenever a person got the ball in the basket, his team would gain a point. Whichever team got the most points won the game.[4] The baskets were originally nailed to the mezzanine balcony of the playing court, but this proved impractical when spectators on the balcony began to interfere with shots. The backboard was introduced to prevent this interference; it had the additional effect of allowing rebound shots.[5]  

Chess

Chess is a recreational and competitive game played between two players. Sometimes called Western chess or international chess to distinguish it from its predecessors and other chess variants, the current form of the game emerged in Southern Europe during the second half of the 15th century after evolving from similar, much older games of Indian and Persian origin. Today, chess is one of the world's most popular games, played by millions of people worldwide at home, in clubs, online, by correspondence, and in tournaments.

The game is played on a square chequered chessboard with 64 squares arranged in an eight-by-eight grid. At the start, each player (one controlling the white pieces, the other controlling the black pieces) controls sixteen pieces: one king, one queen, two rooks, two knights, two bishops, and eight pawns. The object of the game is to checkmate the opponent's king, whereby the king is under immediate attack (in "check") and there is no way to remove it from attack on the next move.

The tradition of organized competitive chess started in the 16th century and has developed extensively. Chess today is a recognized sport of the International Olympic Committee. The first official World Chess Champion, Wilhelm Steinitz, claimed his title in 1886; Viswanathan Anand is the current World Champion. Theoreticians have developed extensive chess strategies and tactics since the game's inception. Aspects of art are found in chess composition. One of the goals of early computer scientists was to create a chess-playing machine. Today's chess is deeply influenced by the abilities of current chess programs and the ability to play against others online. In 1997, Deep Blue became the first computer to beat the reigning World Champion in a match when it defeated Garry Kasparov.

Chess is played on a square board of eight rows (called ranks and denoted with numbers 1 to 8) and eight columns (called files and denoted with letters a to h) of squares. The colors of the sixty-four squares alternate and are referred to as "light squares" and "dark squares". The chessboard is placed with a light square at the right hand end of the rank nearest to each player, and the pieces are set out as shown in the diagram, with each queen on its own color.

Cricket

Cricket is a bat-and-ball team sport that originated in England, possibly as early as 1300, and is now played in more than 100 countries.[citation needed] There are several forms of cricket, at its highest level is Test cricket, in which the current world leading team is Australia,[1] followed by One Day International cricket, whose last World Cup was also won by Australia; the tournament was televised in over 200 countries to a viewing audience estimated at more than two billion viewers.[2][3]

A cricket match is contested by two teams, usually of eleven players each[4] and is played on a grass field in the centre of which is a flat strip of ground 22 yards (20 m) long called a pitch. A wicket, usually made of wood, is placed at each end of the pitch and used as a target. The bowler, a player from the fielding team, bowls a hard leather, fist-sized, 5.5 ounces (160 g) cricket ball from the vicinity of one wicket towards the other, which is guarded by the batsman, a player from the opposing team. The ball usually bounces once before reaching the batsman. In defence of his wicket, the batsman plays the ball with a wooden cricket bat. Meanwhile, the other members of the bowler's team stand in various positions around the field as fielders, players who retrieve the ball in an effort to stop the batsman scoring runs, and if possible to get him or her out. The batsman — if he or she does not get out — may run between the wickets, exchanging ends with a second batsman (the "non-striker"), who has been stationed at the other end of the pitch. Each completed exchange of ends scores one run. 

There are several variations as to how long a game of cricket can last. In professional cricket this can be anything from a match limited to 20 overs per side to a game played over 5 days. Depending on the length of the game being played, there are different rules that govern how a game is won, lost, drawn or tied. Cricket is essentially an outdoor sport, certainly at major level, and some games are played under floodlights. For example, it is played during the summer in the United Kingdom, Australia, New Zealand and South Africa, while in the West Indies, India, Pakistan, Sri Lanka and Bangladesh it is played mostly during the winter after the monsoon season.

Governance rests primarily with the International Cricket Council (ICC), based in Dubai, which organises the sport worldwide via the domestic controlling bodies of the member countries. The ICC administers both men's and women's cricket, both versions being played at international level. Although men cannot play women's cricket, the rules do not disqualify women from playing in a men's team.The rules are in the form of a code known as The Laws of Cricket [5] and these are maintained by the Marylebone Cricket Club (MCC), based in London, in consultation with the ICC and the domestic boards of control.

Plastic

Plastic is the general common term for a wide range of synthetic or semisynthetic organic solid materials suitable for the manufacture of industrial products. Plastics are typically polymers of high molecular weight, and may contain other substances to improve performance and/or reduce costs. The word derives from the Greek πλαστικός (plastikos), "fit for molding", from πλαστός (plastos) "molded" [1] [2]. It refers to their malleability, or plasticity during manufacture, that allows them to be cast, pressed, or extruded into an enormous variety of shapes—such as films, fibers, plates, tubes, bottles, boxes, and much more.

The common word "plastic" should not be confused with the technical adjective "plastic", which is applied to any material which undergoes a permanent change of shape (a "plastic deformation") when strained beyond a certain point. Aluminum, for instance, is "plastic" in this sense, but not "a plastic" in the common sense; while some plastics, in their finished forms, will break before deforming — and therefore are not "plastic" in the technical sense. Plastics can be classified by their chemical structure, namely the molecular units that make up the polymer's backbone and side chains. Some important groups in these classifications are the acrylics, polyesters, silicones, polyurethanes, and halogenated plastics. Plastics can also be classified by the chemical process used in their synthesis, e.g. as condensation, polyaddition, cross-linking, etc.[3]

Other classifications are based on qualities that are relevant for manufacturing or product design. Examples of such classes are the thermoplastic and thermoset, elastomer, structural, biodegradable, electrically conductive, etc. containers that is made of plastic can also be used as water containers. Due to their relatively low cost, ease of manufacture, versatility, and imperviousness to water, plastics are used in an enormous and expanding range of products, from paper clips to spaceships. They have already displaced many traditional materials—such as wood, stone, horn and bone, leather, paper, metal, glass and ceramic—in most of their former uses.

The use of plastics is constrained chiefly by their organic chemistry, which seriously limits their hardness, density, and their ability to resist heat, organic solvents, oxidation, and ionizing radiation. In particular, most plastics will melt or decompose when heated to a few hundred celsius. While plastics can be made electrically conductive to some extent, they are still no match for metals like copper or aluminum. Plastics are still too expensive to replace wood, concrete and ceramic in bulky items like ordinary buildings, bridges, dams, pavement, railroad ties, etc.