title: Tree

paragraphs: A tree is a tall plant with a trunk and branches made of wood. Trees can live for many years. The oldest tree ever discovered is approximately 5,000 years old and the oldest tree from the UK is about 1,000. The four main parts of a tree are the roots, the trunk, the branches, and the leaves.

paragraphs: The roots of a tree are usually under the ground. However, this is not always true. The roots of the mangrove tree are often under water. A single tree has many roots. The roots carry nutrients and water from the ground through the trunk and branches to the leaves of the tree. They can also breathe in air. Sometimes, roots are specialized into aerial roots, which can also provide support, as is the case with the banyan tree.

paragraphs: The trunk is the main body of the tree. The trunk is covered with bark which protects it from damage. Branches grow from the trunk. They spread out so that the leaves can get more sunlight.

paragraphs: The leaves of a tree are green most of the time, but they can come in many colors, shapes and sizes. The leaves take in sunlight and use water and food from the roots to make the tree grow, and to reproduce.

paragraphs: Trees and shrubs take in water and carbon dioxide and give out oxygen with sunlight to form sugars. This is the opposite of what animals do in respiration. Plants also do some respiration using oxygen the way animals do. They need oxygen as well as carbon dioxide to live. Trees are renewable resources because, if cut down, other trees can grow in their place.

paragraphs: The parts of a tree are the roots, trunk(s), branches, twigs and leaves. Tree stems are mainly made of support and transport tissues (xylem and phloem). Wood consists of "xylem" cells, and bark is made of "phloem" and other tissues external to the vascular cambium.

paragraphs: As a tree grows, it may produce growth rings as new wood is laid down around the old wood. In areas with seasonal climate, wood produced at different times of the year may alternate light and dark rings. In temperate climates, and tropical climates with a single wet-dry season alternation, the growth rings are annual, each pair of light and dark rings being one year of growth. In areas with two wet and dry seasons each year, there may be two pairs of light and dark rings each year; and in some (mainly semi-desert regions with irregular rainfall), there may be a new growth ring with each rainfall.

paragraphs: In tropical rainforest regions, with constant year-round climate, growth is continuous. Growth rings are not visible and there is no change in the wood texture. In species with annual rings, these rings can be counted to find the age of the tree. This way, wood taken from trees in the past can be dated, because the patterns of ring thickness are very distinctive. This is dendrochronology. Very few tropical trees can be accurately dated in this manner.

paragraphs: The roots of a tree are almost always underground, usually in a ball shaped region centered under the trunk, and extending no deeper than the tree is high. Roots can also be above ground, or deep underground. Some roots are short, some are meters long.

paragraphs: Roots provide support for the parts above ground, holding the tree upright, and keeping it from falling over in high wind.

paragraphs: Roots take in water, and nutrients, from the soil. Without help from fungus for better uptake of nutrients, trees would be small or would die. Most trees have a favorite species of fungus that they associate with for this purpose.

paragraphs: Above ground, the trunk gives height to the leaf-bearing branches, competing with other plant species for sunlight. In all trees the shape of the branches improves the exposure of the leaves to sunlight. Branches start at the trunk, big and thick, and get progressively smaller the farther they grow from the trunk. Branches themselves split into smaller branches, sometime very many times, until at the end they are quite small. The small ends are called twigs.

paragraphs: The leaves of a tree are held by the branches. Leaves are usually held at the ends of the branches. The, although some have leaves along the branches. The main functions of leaves are photosynthesis and gas exchange. A leaf is often flat, so it absorbs the most light, and thin, so that the sunlight can get to the green parts in the cells, which convert sunlight, carbon dioxide from the atmosphere, and water from the roots, into glucose and oxygen. Most of a tree's biomass comes from this process.

paragraphs: Most leaves have stomata, which open and close, and regulate carbon dioxide, oxygen, and water vapour exchange with the atmosphere.

paragraphs: Trees with leaves all year round are evergreens, and those that shed their leaves are deciduous. Deciduous trees and shrubs generally lose their leaves in autumn as it gets cold. Before this happens, the leaves change colour. The leaves will grow back in spring.

paragraphs: The word "tree" in English means a long lived plant having obvious main stem, and growing to a considerable height and size. Thus not all trees have all the organs or parts as mentioned above. For example, most (tree-like) palms are not branched, and tree ferns do not produce bark. There are also more exceptions.

paragraphs: Based on their general shape and size, all of these are nonetheless generally regarded as trees. Trees can vary a lot. A plant that is similar to a tree, but generally smaller, and may have multiple trunks, or have branches that arise near the ground, is called a "shrub", or a "bush". Since these are common English words there is no precise differentiation between shrubs and trees. Given their small size, bonsai plants would not technically be "trees", but are indeed "trees". Do not confuse the use of tree for a species of plant, with the size or shape of individual specimens. A spruce seedling does not fit the definition of a tree, but all spruces are trees.

paragraphs: A tree is a plant form that can be found in many different orders and families of plants. Trees show many growth forms, leaf type and shape, bark traits and organs.

paragraphs: The tree form has changed separately in classes of plants that are not related, in response to similar problems (for the tree). With about 100,000 types of trees, the number of tree types in the whole world might be one fourth of all living plant types. Most tree species grow in tropical parts of the world and many of these areas have not been surveyed yet by botanists (they study plants), making species difference and ranges not well understood.

paragraphs: The earliest trees were tree ferns, horsetails and lycophytes, which grew in forests in the Carboniferous period; tree ferns still survive, but the only surviving horsetails and lycophytes are not of tree form. Later, in the Triassic Period, conifers, ginkgos, cycads and other gymnosperms appeared, and subsequently flowering plants in the Cretaceous period. Most species of trees today are flowering plants (Angiosperms) and conifers.

paragraphs: A small group of trees growing together is called a grove or copse, and a landscape covered by a dense growth of trees is called a forest. Several biotopes are defined largely by the trees that inhabit them; examples are rainforest and taiga (see ecozones). A landscape of trees scattered or spaced across grassland (usually grazed or burned over periodically) is called a savanna. A forest of great age is called old growth forest or ancient woodland (in the UK). A very young tree is called a sapling.

paragraphs: Scientists in the UK and Malaysia say they have discovered the world's tallest tropical tree measuring more than 100m (328ft) high.

paragraphs: A coast redwood: , in Redwood National Park, California had been measured as tallest, but may no longer be standing.

paragraphs: The tallest trees in Australia are all eucalypts, of which there are more than 700 species. The so-called 'mountain ash'. with a slim, straight trunk, grows to over 300 feet.

paragraphs: The stoutest living single-trunk species in diameter is the African baobab: , Glencoe baobab (measured near the ground), Limpopo Province, South Africa. This tree split up in November 2009 and now the stoutest baobab could be Sunland Baobab (South Africa) with diameter 10.64 m and circumference of 33.4 m.

paragraphs: Some trees develop multiple trunks (whether from an individual tree or multiple trees) which grow together. The sacred fig is a notable example of this, forming additional 'trunks' by growing adventitious roots down from the branches, which then thicken up when the root reaches the ground to form new trunks; a single sacred fig tree can have hundreds of such trunks.

paragraphs: The life-span of trees is determined by growth rings. These can be seen if the tree is cut down or in cores taken from the edge to the center of the tree. Correct determination is only possible for trees which make growth rings, generally those which occur in seasonal climates. Trees in uniform non-seasonal tropical climates are always growing and do not have distinct growth rings. It is also only possible for trees which are solid to the center of the tree; many very old trees become hollow as the dead heartwood decays away. For some of these species, age estimates have been made on the basis of extrapolating current growth rates, but the results are usually little better than guesses or speculation. White proposed a method of estimating the age of large and veteran trees in the United Kingdom by correlation between a tree's stem diameter, growth character and age.

paragraphs: Other species suspected of reaching exceptional age include European Yew "Taxus baccata" (probably over 2,000 years) and western redcedar "Thuja plicata". The oldest known European yew is the Llangernyw yew in the Churchyard of Llangernyw village in North Wales which is estimated to be between 4,000 and 5,000 years old.

paragraphs: The oldest reported age for an angiosperm tree is 2293 years for the Sri Maha Bodhi sacred fig ("Ficus religiosa") planted in 288 BC at Anuradhapura, Sri Lanka; this is said to be the oldest human-planted tree with a known planting date.

paragraphs: The earliest fossilised trees date to 386 million years ago in the Devonian period. They have been found at an abandoned quarry in Cairo, New York. The forest was so vast it originally stretched beyond Pennsylvania.

paragraphs: This discovery two or three million years older than the previous oldest forest at Gilboa, also in New York State.

paragraphs: Studies have shown that trees contribute as much as 27% of the appraised land value in certain markets.

paragraphs: These most likely use diameter measured at breast height (dbh), 4.5 feet (140 cm) above ground—not the larger base diameter. A general model for any year and diameter is:

paragraphs: Tree climbing is an activity where one moves around in the crown of trees.

paragraphs: Use of a rope, helmet, and harness are the minimum requirements to ensure the safety of the climber. Other equipment can also be used depending on the experience and skill of the tree climber. Some tree climbers take special hammocks called "Treeboats" and Portaledges with them into the tree canopies where they can enjoy a picnic or nap, or spend the night.

paragraphs: Tree climbing is an "on rope" activity that puts together many different tricks and gear originally derived from rock climbing and caving. These techniques are used to climb trees for many purposes, including tree care (arborists), animal rescue, recreation, sport, research, and activism.

paragraphs: The three big sources of tree damage are biotic (from living sources), abiotic (from non-living sources) and deforestation (cutting trees down). Biotic sources would include insects which might bore into the tree, deer which might rub bark off the trunk, or fungi, which might attach themselves to the tree.

paragraphs: Abiotic sources include lightning, vehicles impacts, and construction activities. Construction activities can involve a number of damage sources, including grade changes that prevent aeration to roots, spills involving toxic chemicals such as cement or petroleum products, or severing of branches or roots. People can damage trees also.

paragraphs: Both damage sources can result in trees becoming dangerous, and the term "hazard trees" is commonly used by arborists, and industry groups such as power line operators. Hazard trees are trees which due to disease or other factors are more susceptible to falling during windstorms, or having parts of the tree fall.

paragraphs: The process of finding the danger a tree presents is based on a process called the quantified tree risk assessment.

paragraphs: Trees are similar to people. Both can take a lot of some types of damage and survive, but even small amounts of certain types of trauma can result in death. Arborists are very aware that established trees will not tolerate any appreciable disturbance of the root system. Even though that is true, most people and construction professionals do not realize how easily a tree can be killed.

paragraphs: One reason for confusion about tree damage from construction involves the dormancy of trees during winter. Another factor is that trees may not show symptoms of damage until 24 months or longer after damage has occurred. For that reason, persons who do not know about caring for trees may not link the actual cause with the later damaged effect.

paragraphs: Various organizations have long recognized the importance of construction activities that impact tree health. The impacts are important because they can result in monetary losses due to tree damage and resultant remediation or replacement costs, as well as violation of government ordinances or community or subdivision restrictions.

paragraphs: As a result, protocols (standard ways) for tree management prior to, during and after construction activities are well established, tested and refined (changed). These basic steps are involved:

paragraphs: The tree has always been a cultural symbol. Common icons are the World tree, for instance Yggdrasil, and the tree of life. The tree is often used to represent nature or the environment itself. A common mistake (wrong thing) is that trees get most of their mass from the ground. In fact, 99% of a tree's mass comes from the air.

paragraphs: A Wish Tree (or wishing tree) is a single tree, usually distinguished by species, position or appearance, which is used as an object of wishes and offerings. Such trees are identified as possessing a special religious or spiritual value. By tradition, believers make votive offerings in order to gain from that nature spirit, saint or goddess fulfillment of a wish.

paragraphs: Tree worship refers to the tendency of many societies in all of history to worship or otherwise mythologize trees. Trees have played a very important role in many of the world's mythologies and religions, and have been given deep and sacred meanings throughout the ages. Human beings, seeing the growth and death of trees, the elasticity of their branches, the sensitiveness and the annual (every year) decay and revival of their foliage, see them as powerful symbols of growth, decay and resurrection. The most ancient cross-cultural symbolic representation of the universe's construction is the 'world tree'.

paragraphs: The tree, with its branches reaching up into the sky, and roots deep into the earth, can be seen to dwell in three worlds - a link between heaven, the earth, and the underworld, uniting above and below. It is also both a feminine symbol, bearing sustenance; and a masculine, phallic symbol - another union.

paragraphs: For this reason, many mythologies around the world have the concept of the World tree, a great tree that acts as an "Axis mundi", holding up the cosmos, and providing a link between the heavens, earth and underworld. In European mythology the best known example is the tree Yggdrasil from Norse mythology.

paragraphs: The world tree is also an important part of Mesoamerican mythologies, where it represents the four cardinal directions (north, south, east, and west). The concept of the world tree is also closely linked to the motif of the Tree of life.

paragraphs: In literature, a mythology was notably developed by J.R.R. Tolkien, his Two Trees of Valinor playing a central role in his 1964 "Tree and Leaf". William Butler Yeats describes a "holy tree" in his poem "The Two Trees" (1893).

paragraphs: There are many types of trees. Here is a list of some of them:


title: Tragedy

paragraphs: In theatre, a tragedy as defined by Aristotle is a play that ends badly for the hero or heroine or others. A tragedy is usually about a person who has many good qualities, but also has one poor quality (called a "tragic flaw") that causes trouble for him, and maybe his family or friends.

paragraphs: Often in a tragedy, there is one possible event that the hero fears and tries to prevent, but no matter what he does, it makes this thing more and more sure to happen. Tragedies originated in Ancient Greek theatre, where they were performed at religious festivals. The three most famous Greek tragedy writers were Aeschylus, Sophocles and Euripides. Later famous writers include Shakespeare and Jean Racine.

paragraphs: Sometimes the word tragedy is also used to mean something with a bad outcome in real life.


title: Taxonomy

paragraphs: Taxonomy is a branch of science. It is about the laws and principles of classifying things. From one type of taxonomy, many classifications might be produced.

paragraphs: The best-known kind of taxonomy is used for the classification of lifeforms (living and extinct). Each organism has a scientific name. This name is part of the biological classification of that species. The name is the same all over the world, so scientists from different places can understand each other. In addition, a species has a position in the tree of life. Thus the crow is "Corvus corone", a member of the Corvidae family, and they are passerine birds. That is well agreed, but the classification of some groups is not agreed at present, and often several classifications are being discussed.

paragraphs: Living things are classified into three domains: bacteria, archaea and eukaryotes. The highest rank in a domain is the kingdom. Each kingdom has many smaller groups in it, called phyla. Each phylum has more smaller groups in it, called classes. This pattern looks like branches on a tree with smaller branches growing from them. Each species is put into a group because of what it does, how and what it eats, special body parts, and so on. At the end of the pattern, the groups (genera) are very small. Then each species in the genus is given its own name.

paragraphs: When someone writes about a living thing and its formal scientific name, they write the genus and species name. This is known as binomial nomenclature, because it uses two names for each organism. The first is the genus name, and the second is the species in that genus. The scientific name of the domestic cat is "Felis catus". Sometimes it is enough to write "F. catus".

paragraphs: These are the major groups (ranks) used in taxonomy:

paragraphs: Kingdom --> Phylum --> Class --> Order --> Family --> Genus --> Species

paragraphs: Some mnemonics (sayings to help a person remember something):

paragraphs: When people started naming species, Latin was a language widely used in Europe. All species names are still written in Latin. This has some advantages. Since Latin is no longer spoken, it is unchanging, and is owned by no-one. It gets over the problem of every language having its own names for animals and plants.

paragraphs: Scientists used to write the official description of each new species in Latin. On 1 January 2012, the International Botanical Congress changed to allow English (as well as Latin) for describing new plant species. The International Code of Zoological Nomenclature recommends choosing a language that is widely used, and that is used in the places where the species lives.

paragraphs: An important modern approach to taxonomy is cladism. This approach is based on the branching (tree-like) course of evolution. Like traditional Linnaean classification, it uses traits to decide on the branches of the classification. It insists on groups being monophyletic. This has the effect that birds are not a class but a sub-group of dinosaurs. It also means the ranking system described above would be abolished.

paragraphs: So cladism has different principles of taxonomy, and produces a different kind of taxonomy. Decisions, where possible, are supported by DNA sequence analysis. Present-day biological classification is a mixture of the old Linnaean and the modern cladistic principles of taxonomy. In parts, it is changing rapidly. The classifications presented in Wikipedia at present are often a compromise between the two systems. The details are regularly discussed.

paragraphs: Today, there are many changes in the classification of living things. This turmoil in taxonomy has led to many alternative classifications. It is caused partly from the move from Linnaean to cladistic principles, and partly by the use of DNA sequence data in taxonomy. An example is: the way derived groups like birds should not be classified at the same level as the group they evolved from. Yet birds have traditionally been a class under the Linnaean system.

paragraphs: The turmoil sometimes results in differences between related pages. Pages may rely on different references and different authors' opinions as to the present best arrangement.

paragraphs: The following source is good on the differences between cladistic and taxonomic classification systems:


title: The Sun

paragraphs: The Sun is the star at the center of the Solar System.


title: Temple

paragraphs: A temple is a building where people go to practice their religion. In a temple people may perform religious rituals, ceremonies, and pray. Thus, a temple is a general term for a house of worship. Christians usually call their religious buildings churches.

paragraphs: Some examples of temples from different religions:


title: Theft

paragraphs: Theft is when one person or group takes from another persons or state any object, money, or information without permission. A person who has been convicted of theft may be called a thief. However, the practice of engaging in theft is also called stealing. There are many different types of theft, such as pickpocketing and shoplifting. Burglary and robbery are separate crimes which involve theft.

paragraphs: Stealing is basic and is illegal almost everywhere. Thieves steal things sometimes because they want to have something for themselves, or because they want to sell something for money. Sometimes thieves will make plans to rob a store, bank, house, or person, and sometimes they will just see a chance to steal something and take it. Some thieves have kleptomania.

paragraphs: When thieves steal things for money, they usually pick cars, electronics, laptops, or other things they can sell easily. Sometimes thieves use pawn shops to sell things easily to someone who will not ask questions.


title: United Kingdom

paragraphs: The United Kingdom of Great Britain and Northern Ireland, simply called the United Kingdom (UK), Great Britain or just Britain, is a sovereign country. It is a constitutional monarchy that is made up of four separate countries: England, Wales, Scotland and Northern Ireland. It is a member of the United Nations, the Commonwealth, NATO and the G8. It has the fifth or sixth largest economy in the world.

paragraphs: Around 66 million people live in the UK (2018). They can be divided into four big nationalities based on the countries where they live (or where they were born or their ancestry).

paragraphs: The UK has many cities. England is home to London, the biggest city in the UK and also its capital city. There are also many other big cities in England including Birmingham, Manchester, Liverpool, Leeds, Bristol and Newcastle upon Tyne. Scotland has the big cities of Edinburgh and Glasgow. Cardiff and Swansea are in Wales and Belfast is in Northern Ireland.

paragraphs: Between the 17th and mid 20th-centuries, Britain was a world power. It became a colonial empire that controlled large areas of Africa, Asia, North America and Oceania. At its height in 1922, more than 458 million people lived in the British Empire, one-fifth of the Earth's population. Its area was 13,012,000 square miles: almost a quarter of the Earth's land area. The empire was sometimes called 'the empire on which the sun never sets', which describes a large empire where the sun is always shining on at least one of its territories. Almost all countries left and became independent from the empire in the 20th century, although Britain keeps links with most countries of its former empire.

paragraphs: Archaeological remains show that the first group of modern people to live in the British Isles were hunter-gatherers after the last ice age ended. The date is not known: perhaps as early as 8000 but certainly by 5000. They built mesolithic wood and stone monuments. Stonehenge was built between 3000 and 1600. Celtic tribes arrived from mainland Europe. Britain was a changing collection of tribal areas, with no overall leader. Julius Caesar tried to invade (take over) the island in 55 but was not able to do so. The Romans successfully invaded in 43.

paragraphs: Written history began in Britain when writing was brought to Britain by the Romans. Rome ruled in Britain from 44AD to 410AD, but they only ruled England and Wales. The Romans never ruled Scotland north of the Clyde-Forth valley, or Ireland; their northern boundary varied from time to time, and was marked for a while at Hadrian's Wall.

paragraphs: After the Romans, two waves of immigrants came to Britain. The first were German tribes: the Angles, Saxons and Jutes. English, the language, is a development from Anglo-Saxon Old English, and is a Germanic language. The second were the Vikings.

paragraphs: After a long period when England was split into various kingdoms, it was made into one country by Æthelstan (Athelstan) in 945. England and Wales were unified by Edward I (Longshanks) by force in the 13th century.

paragraphs: Union with Scotland took much longer; there were hundreds of years of conflicts between both parts of Britain. This union between England and Scotland in 1707 formed the United Kingdom of Great Britain, which merged Scotland and England into one country.

paragraphs: In 1603, when Queen Elizabeth I of England died, her closest relative was King James VI of Scotland. He became king of England as well as king of Scotland. In 1707, the Scottish and English Parliaments agreed the Treaty of Union, which joined the two countries into one country called "The Kingdom of Great Britain" under Queen Anne.

paragraphs: By 1800, both Scotland and England had already independently had much influence over Ireland since 1200. In that year laws were passed in Great Britain and Ireland to merge the two states. The new country was called the "United Kingdom of Great Britain and Ireland". In 1922 much of Ireland became independent as the Irish Free State (now called Ireland) from the United Kingdom. However, six northern counties (called Northern Ireland) continue to be part of the United Kingdom. The country was renamed "The United Kingdom of Great Britain and Northern Ireland".

paragraphs: The British people are represented by members of Parliament, not ruled by monarchs. After the English Civil War, Oliver Cromwell became Lord Protector, and the monarchy was disbanded. Although the monarchy was restored after his death, the Crown slowly became the secondary power, and Parliament the first. Members of Parliament (called MPs) were elected, but until the early twentieth century, only men who owned property could vote. In the nineteenth century, more people were given suffrage (the right to vote), but even so, by 1900, women could not vote, and only 40% of men were rich enough to vote. But in 1928, all men and women got the vote: this is called universal suffrage.

paragraphs: Parliament is in Westminster in London, but it has power over the whole of the UK. Wales, Scotland and Northern Ireland now each have their own parliaments but they have more limited powers. Scotland has the Scottish Parliament at Holyrood. Wales has the National Assembly for Wales in Cardiff and the Northern Ireland has the Northern Ireland Assembly at Stormont. England does not have a separate parliament. There are also parliaments in the Isle of Man and in Jersey and Guernsey (the Channel Islands, which are all independent island states for which the UK has some responsibility in international law.

paragraphs: Almost all members of Parliament belong to political parties. The biggest parties are the Conservative Party, Labour Party, the Scottish National Party and the Liberal Democrats. Members of the same party agree to act and vote more or less together. A party with more than half the seats (a majority) forms the government; the leader of the party becomes the Prime Minister, who then appoints other ministers. Because the government has a majority in Parliament, it can normally control what laws are passed.

paragraphs: Major languages spoken in the United Kingdom other than English include Polish (500,000 approximate number of speakers in the United Kingdom), Eastern Panjabi or Punjabi (471,000), Bengali (400,000), Urdu (400,000), Cantonese (300,000), Greek (200,000), Southwestern Caribbean Creole English (170,000).

paragraphs: The UK is made up of four different countries: Wales, England and Scotland and Northern Ireland. The capital city of Wales is Cardiff. The capital city of England is London. The capital city of Scotland is Edinburgh and the capital city of Northern Ireland is Belfast. Other large cities in the UK are Birmingham, Bristol, Manchester, Liverpool, Newcastle upon Tyne, Leeds, Sheffield, Glasgow, Southampton, Leicester, Coventry, Bradford and Nottingham.

paragraphs: The UK is north-west off the coast of mainland Europe. Around the UK are the North Sea, the English Channel and the Atlantic Ocean. The UK also rules, usually indirectly, a number of smaller places (mostly islands) round the world, which are known as "overseas territories". They are remnants of the British Empire.

paragraphs: The weather of the United Kingdom is changeable and unpredictable. Summers are moderately warm, winters are cool to cold. Rain falls throughout the year, and more on the west than the east because of its northerly latitude and the warm water from the Atlantic Ocean's Gulf Stream. The usually moderate prevailing winds from the Atlantic may be interrupted by Arctic air from the north-east or hot air from the Sahara.

paragraphs: The UK is a parliamentary democracy based on a constitutional and hereditary monarchy. The people of the United Kingdom vote for a members of Parliament to speak for them and to make laws for them. Queen Elizabeth II is the queen of the UK and is the head of state. Even though she is the head of state, she does not actually govern the country. The government, led by the Prime Minister, governs the country and decides policy. Today, the Prime Minister is Boris Johnson, who is the leader of the Conservative party and was not directly elected by the people of the country.

paragraphs: Parliament is where laws are made. It has three parts: the House of Commons, the House of Lords, and the Queen. The House of Commons is the most powerful part. It is where Members of Parliament sit. The Prime Minister sits here as well, because they are a Member of Parliament. The people who sit in the House of Lords are called peers: they are not chosen by the people. Most peers are now appointed by the government. There are some who are hereditary peers (their fathers were peers); and a few others, such as certain bishops in the established Church of England, and the Judiciary (Law Lords).

paragraphs: Scotland has its own devolved Parliament with power to make laws on things like education, health and Scottish law. Northern Ireland and Wales have their own devolved Assemblies which have some powers but less than the Scottish parliament. The UK Parliament remains sovereign and it could end the devolved administrations at any time.

paragraphs: The UK has a military of around 223,000 people, not including reserve forces. The UK has one of the most advanced militaries in the world, alongside such countries such as the USA and France, and operates a large army (British Army), a sizable navy (Royal Navy) and air force (Royal Air Force). From the 18th century to the early 20th century, the UK was one of the most powerful nations in the world, with a huge navy (due to the fact it was surrounded by sea, so a large navy was the most practical option). This status has faded in recent times, but the UK remains a member of various military groups such as the UN Security Council and NATO. It is also still seen as a great military power.

paragraphs: The UK is a developed country with the sixth largest economy in the world. It was a superpower during the 18th, 19th and early 20th century and was considered since the early 1800s to be the most powerful and influential nation in the world, in politics, economics (For it was the wealthiest country at the time.) and in military strength. Britain continued to be the biggest manufacturing economy in the world until 1908 and the largest economy until the 1920s. The economic cost of two world wars and the decline of the British Empire in the 1950s and 1960s reduced its leading role in global affairs. The UK has strong economic, cultural, military and political influence and is a nuclear power. It was a member state of the European Union until the UK left on February 1st, 2020. The UK holds a permanent seat on the United Nations Security Council, and is a member of the G8, NATO, World Trade Organization and the Commonwealth of Nations.

paragraphs: London, the capital, is famous as being the largest centre of finance in the world, along with New York City in the United States.

paragraphs: William Shakespeare was an English playwright. He wrote plays in the late 16th century. Some of his plays were "Romeo and Juliet" and "Macbeth". In the 19th century, Jane Austen and Charles Dickens were novelists. Twentieth century writers include the science fiction novelist H.G. Wells and J.R.R. Tolkien. The children's fantasy "Harry Potter" series was written by J.K. Rowling. Aldous Huxley was also from the United Kingdom.

paragraphs: English language literature is written by authors from many countries. Eight people from the United Kingdom have won the Nobel Prize in Literature. Seamus Heaney is a writer who was born in Northern Ireland.

paragraphs: Arthur Conan Doyle from Scotland wrote the Sherlock Holmes detective novels. He was from Edinburgh. The poet Dylan Thomas brought Welsh culture to international attention.

paragraphs: England, Northern Ireland, Scotland, and Wales have separate, but similar, systems of education. They all have rules that education is required from ages five to eighteen, except for in Scotland where school departure is allowed from the age of sixteen. Many children attend state schools and other children attend private schools.

paragraphs: Britain's universities are the University of Cambridge and University of Oxford, and London universities (University College London, the London School of Economics, King's College London and Imperial College London) which collectively form the Golden Triangle of UK universities.

paragraphs: A broader group of twenty universities form the Russell Group, which account for two thirds of research grants and contract funding out of the total of 100 universities.

paragraphs: Road traffic in the United Kingdom drives on the left hand side of the road (unlike the Americas and some of Europe), and the driver steers from the right hand side of the vehicle. The road network on the island of Great Britain is extensive, with most local and rural roads having evolved from Roman and Medieval times. Major routes developed in the mid 20th Century were made to the needs of the motor car. The high speed motorway (freeway) network was mostly constructed in the 1960s and 1970s and links together major towns and cities.

paragraphs: The system of rail transport was invented in England and Wales, so the United Kingdom has the oldest railway network in the world. It was built mostly during the Victorian era. At the heart of the network are five long distance main lines which radiate from London to the major cities and secondary population centres with dense commuter networks within the regions. The newest part of the network connects London to the Channel Tunnel from St Pancras station and is built to the same standard as the French TGV system. The British Rail network is part privatised, with privately owned train operating companies providing service along particular lines or regions, whilst the tracks, signals and stations are owned by a Government controlled company called Network Rail. In Northern Ireland the NI Railways is the national railway. The system of underground railways in London, known as the Tube, has been copied by many other cities.

paragraphs: Most domestic air travel in the United Kingdom is between London and the major cities in Scotland and the North of England and Belfast. London-Heathrow is the nation’s largest airport and is one of the most important international hubs in the world. Other major airports with principal international service include London-Gatwick, Birmingham, Manchester and Glasgow.

paragraphs: An extensive system of ferry networks operate between the Scottish islands, and major ferry routes operate between England and France (via the English Channel), Scotland-Northern Ireland (via the Irish Sea) and England/Wales-Republic of Ireland (from Liverpool/Holyhead).


title: Universe

paragraphs: The Universe is all of time and space and its contents. It is made of many millions of millions of stars and planets and enormous clouds of gas separated by a gigantic space.

paragraphs: Astronomers can use telescopes to look at very distant galaxies. This is how they see what the Universe looked like a long time ago. This is because the light from distant parts of the Universe takes a very long time to reach us. From these observations, it seems the physical laws and constants of the Universe have not changed.

paragraphs: Physicists are currently unsure if anything existed before the Big Bang. They are also unsure whether the size of the Universe is infinite.

paragraphs: People have long had ideas to explain the Universe. Most early models had the Earth at the centre of the Universe. Some ancient Greeks thought that the Universe has infinite space and has existed forever. They thought it had a set of celestial spheres which corresponded to the fixed stars, the Sun and various planets. The spheres circled about a round but unmoving Earth.

paragraphs: Over hundreds of years, better observations led to Copernicus's Sun-centred model. This was very controversial at the time, and was fought by religious authorities, most famously by the Christian church (see Giordano Bruno and Galileo).

paragraphs: The invention of the telescope in the Netherlands, 1608, was a very important moment in astronomy. By the middle of the 1800s, telescopes were good enough for other galaxies to be seen. The modern optical (uses visible light) telescope is still more advanced. Meanwhile, Isaac Newton improved the ideas of gravity and dynamics (equations) and showed how the Solar System worked.

paragraphs: In the 1900s, even better telescopes led astronomers to realize that the Solar System is in a galaxy made of billions of stars, which we call the Milky Way. They also realized that other galaxies exist outside it, as far as we can see. This started a new kind of astronomy called cosmology, in which astronomers study what these galaxies are made of and how they are spread out through so they can learn more about the history of the Universe and how it works. By measuring the redshift of galaxies, cosmologists soon discovered that the Universe is expanding (see: Hubble).

paragraphs: The most used scientific model of the Universe is known as the Big Bang theory, which says the Universe expanded from a single point that held all the matter and energy of the Universe. There are many kinds of scientific evidence that support the Big Bang idea. Astronomers think that the Big Bang happened about 13.73 billion years ago, making the Universe 13.73 billion years old. Since then, the universe has expanded to be at least 93 billion light years, or 8.80 metres, in diameter. It is still expanding right now, and the expansion is getting faster.

paragraphs: However, astronomers are still not sure what is causing the universe to expand. Because of this, astronomers call the mysterious energy causing the expansion dark energy. By studying the expansion of the Universe, astronomers have also realized most of the matter in the Universe may be in a form which cannot be observed by any scientific equipment we have. This matter has been named dark matter. Just to be clear, dark matter and energy have not been observed directly (that is why they are called 'dark'). However, many astronomers think they must exist, because many astronomical observations would be hard to explain if they didn't.

paragraphs: Some parts of the universe are expanding even faster than the speed of light. This means the light will never be able to reach us here on Earth, so we will never be able to see these parts of the universe. We call the part of the universe we can see the observable universe.

paragraphs: The word "Universe" comes from the Old French word "Univers", which comes from the Latin word "universum". The Latin word was used by Cicero and later Latin authors in many of the same senses as the modern English word is used.

paragraphs: A different interpretation (way to interpret) of "unvorsum" is "everything rotated as one" or "everything rotated by one". This refers to an early Greek model of the Universe. In that model, all matter was in rotating spheres centered on the Earth; according to Aristotle, the rotation of the outermost sphere was responsible for the motion and change of everything within. It was natural for the Greeks to assume that the Earth was stationary and that the heavens rotated about the Earth, because careful astronomical and physical measurements (such as the Foucault pendulum) are required to prove otherwise.

paragraphs: The most common term for "Universe" among the ancient Greek philosophers from Pythagoras onwards was "το παν" (The All), defined as all matter ("το ολον") and all space ("το κενον").

paragraphs: The broadest word meaning of the Universe is found in "De divisione naturae" by the medieval philosopher Johannes Scotus Eriugena, who defined it as simply everything: everything that exists and everything that does not exist.

paragraphs: Time is not considered in Eriugena's definition; thus, his definition includes everything that exists, has existed and will exist, as well as everything that does not exist, has never existed and will never exist. This all-embracing definition was not adopted by most later philosophers, but something similar is in quantum physics.

paragraphs: Usually the Universe is thought to be everything that exists, has existed, and will exist. This definition says that the Universe is made of two elements: space and time, together known as space-time or the vacuum; and matter and different forms of energy and momentum occupying space-time. The two kinds of elements behave according to physical laws, in which we describe how the elements interact.

paragraphs: A similar definition of the term "universe" is everything that exists at a single moment of time, such as the present or the beginning of time, as in the sentence "The Universe was of size 0".

paragraphs: In Aristotle's book "The Physics", Aristotle divided το "παν" (everything) into three roughly analogous elements: "matter" (the stuff of which the Universe is made), "form" (the arrangement of that matter in space) and "change" (how matter is created, destroyed or altered in its properties, and similarly, how form is altered). Physical laws were the rules governing the properties of matter, form and their changes. Later philosophers such as Lucretius, Averroes, Avicenna and Baruch Spinoza altered or refined these divisions. For example, Averroes and Spinoza have "active" principles governing the Universe which act on "passive" elements.

paragraphs: It is possible to form space-times, each existing but not able to touch, move, or change (interact with each other. An easy way to think of this is a group of separate soap bubbles, in which people living on one soap bubble cannot interact with those on other soap bubbles. According to one common terminology, each "soap bubble" of space-time is denoted as a universe, whereas our particular space-time is denoted as "the Universe", just as we call our moon "the Moon". The entire collection of these separate space-times is denoted as the multiverse. In principle, the other unconnected universes may have different dimensionalities and topologies of space-time, different forms of matter and energy, and different physical laws and physical constants, although such possibilities are speculations.

paragraphs: According to a still-more-restrictive definition, the Universe is everything within our connected space-time that could have a chance to interact with us and vice versa.

paragraphs: According to the general idea of relativity, some regions of space may never interact with ours even in the lifetime of the Universe, due to the finite speed of light and the ongoing expansion of space. For example, radio messages sent from Earth may never reach some regions of space, even if the Universe would exist forever; space may expand faster than light can traverse it.

paragraphs: It is worth emphasizing that those distant regions of space are taken to exist and be part of reality as much as we are; yet we can never interact with them, even in principle. The spatial region within which we can affect and be affected is denoted as the "observable universe".

paragraphs: Strictly speaking, the observable Universe depends on the location of the observer. By travelling, an observer can come into contact with a greater region of space-time than an observer who remains still, so that the observable Universe for the former is larger than for the latter. Nevertheless, even the most rapid traveler may not be able to interact with all of space. Typically, the 'observable Universe' means the Universe seen from our vantage point in the Milky Way Galaxy.

paragraphs: The Universe is huge and possibly infinite in volume. The matter which can be seen is spread over a space at least 93 billion light years across. For comparison, the diameter of a typical galaxy is only 30,000 light-years, and the typical distance between two neighboring galaxies is only 3 million light-years. As an example, our Milky Way Galaxy is roughly 100,000 light years in diameter, and our nearest sister galaxy, the Andromeda Galaxy, is located roughly 2.5 million light years away. The observable Universe contains more than 2 trillion (10) galaxies and, overall, as many as an estimated stars (more stars than all the grains of sand on planet Earth).

paragraphs: Typical galaxies range from dwarf galaxies with as few as ten million (10) stars up to giants with one trillion (10) stars, all orbiting the galaxy's center of mass. Thus, a very rough estimate from these numbers would suggest there are around one sextillion (10) stars in the observable Universe; though a 2003 study by Australian National University astronomers resulted in a figure of 70 sextillion (7 x 10).

paragraphs: The matter that can be seen is spread throughout the Universe when averaged over distances longer than 300 million light-years. However, on smaller length-scales, matter is observed to form 'clumps', many atoms are condensed into stars, most stars into galaxies, most galaxies into galaxy groups and clusters and, lastly, the largest-scale structures such as the Great Wall of galaxies.

paragraphs: The present overall density of the Universe is very low, roughly 9.9 × 10 grams per cubic centimetre. This mass-energy appears to consist of 73% dark energy, 23% cold dark matter and 4% ordinary matter. The density of atoms is about a single hydrogen atom for every four cubic meters of volume. The properties of dark energy and dark matter are not known. Dark matter slows the expansion of the Universe. Dark energy makes its expansion faster.

paragraphs: The Universe is old, and changing. The best good guess of the Universe's age is 13.798±0.037 billion years old, based on what was seen of the cosmic microwave background radiation. Independent estimates (based on measurements such as radioactive dating) agree, although they are less precise, ranging from 11–20 billion years.

paragraphs: The Universe has not been the same at all times in its history. This getting bigger accounts for how Earth-bound people can see the light from a galaxy 30 billion light-years away, even if that light has traveled for only 13 billion years; the very space between them has expanded. This expansion is consistent with the observation that the light from distant galaxies has been redshifted; the photons emitted have been stretched to longer wavelengths and lower frequency during their journey. The rate of this spatial expansion is accelerating, based on studies of Type Ia supernovae and other data.

paragraphs: The relative amounts of different chemical elements — especially the lightest atoms such as hydrogen, deuterium and helium — seem to be identical in all of the Universe and throughout all of the history of it that we know of. The Universe seems to have much more matter than antimatter. The Universe appears to have no net electric charge. Gravity is the dominant interaction at cosmological distances. The Universe also seems to have no net momentum or angular momentum. The absence of net charge and momentum is expected if the Universe is finite.

paragraphs: The Universe appears to have a smooth space-time continuum made of three spatial dimensions and one temporal (time) dimension. On the average, space is very nearly flat (close to zero curvature), meaning that Euclidean geometry is experimentally true with high accuracy throughout most of the Universe. However, the Universe may have more dimensions, and its spacetime may have a multiply connected global topology.

paragraphs: The Universe has the same physical laws and physical constants throughout. According to the prevailing Standard Model of physics, all matter is composed of three generations of leptons and quarks, both of which are fermions. These elementary particles interact via at most three fundamental interactions: the electroweak interaction which includes electromagnetism and the weak nuclear force; the strong nuclear force described by quantum chromodynamics; and gravity, which is best described at present by general relativity.

paragraphs: Special relativity holds in all the Universe in local space and time. Otherwise, general relativity holds. There is no explanation for the particular values that physical constants appear to have throughout our Universe, such as Planck's constant "h" or the gravitational constant "G". Several conservation laws have been identified, such as the conservation of charge, conservation of momentum, conservation of angular momentum and conservation of energy.

paragraphs: Accurate predictions of the Universe's past and future require an accurate theory of gravitation. The best theory available is Albert Einstein's general theory of relativity, which has passed all experimental tests so far. However, since rigorous experiments have not been carried out on "cosmological" length scales, general relativity could conceivably be inaccurate. Nevertheless, its predictions appear to be consistent with observations, so there is no reason to adopt another theory.

paragraphs: General relativity provides of a set of ten nonlinear partial differential equations for the spacetime metric (Einstein's field equations) that must be solved from the distribution of mass-energy and momentum throughout the Universe. Since these are unknown in exact detail, cosmological models have been based on the cosmological principle, which states that the Universe is homogeneous and isotropic. In effect, this principle asserts that the gravitational effects of the various galaxies making up the Universe are equivalent to those of a fine dust distributed uniformly throughout the Universe with the same average density. The assumption of a uniform dust makes it easy to solve Einstein's field equations and predict the past and future of the Universe on cosmological time scales.

paragraphs: Einstein's field equations include a cosmological constant (Lamda: "Λ"), that is related to an energy density of empty space. Depending on its sign, the cosmological constant can either slow (negative "Λ") or accelerate (positive "Λ") the expansion of the Universe. Although many scientists, including Einstein, had speculated that "Λ" was zero, recent astronomical observations of type Ia supernovae have detected a large amount of dark energy that is accelerating the Universe's expansion. Preliminary studies suggest that this dark energy is related to a positive "Λ", although alternative theories cannot be ruled out as yet.

paragraphs: The prevailing Big Bang model accounts for many of the experimental observations described above, such as the correlation of distance and redshift of galaxies, the universal ratio of hydrogen:helium atoms, and the ubiquitous, isotropic microwave radiation background. As noted above, the redshift arises from the metric expansion of space; as the space itself expands, the wavelength of a photon traveling through space likewise increases, decreasing its energy. The longer a photon has been traveling, the more expansion it has undergone; hence, older photons from more distant galaxies are the most red-shifted. Determining the correlation between distance and redshift is an important problem in experimental physical cosmology.

paragraphs: Other experimental observations can be explained by combining the overall expansion of space with nuclear physics and atomic physics. As the Universe expands, the energy density of the electromagnetic radiation decreases more quickly than does that of matter, since the energy of a photon decreases with its wavelength. Thus, although the energy density of the Universe is now dominated by matter, it was once dominated by radiation; poetically speaking, all was light. As the Universe expanded, its energy density decreased and it became cooler; as it did so, the elementary particles of matter could associate stably into ever larger combinations. Thus, in the early part of the matter-dominated era, stable protons and neutrons formed, which then associated into atomic nuclei. At this stage, the matter in the Universe was mainly a hot, dense plasma of negative electrons, neutral neutrinos and positive nuclei. Nuclear reactions among the nuclei led to the present abundances of the lighter nuclei, particularly hydrogen, deuterium, and helium. Eventually, the electrons and nuclei combined to form stable atoms, which are transparent to most wavelengths of radiation; at this point, the radiation decoupled from the matter, forming the ubiquitous, isotropic background of microwave radiation observed today.

paragraphs: Other observations are not clearly answered by known physics. According to the prevailing theory, a slight imbalance of matter over antimatter was present in the Universe's creation, or developed very shortly thereafter. Although the matter and antimatter mostly annihilated one another, producing photons, a small residue of matter survived, giving the present matter-dominated Universe.

paragraphs: Several lines of evidence also suggest that a rapid cosmic inflation of the Universe occurred very early in its history (roughly 10 seconds after its creation). Recent observations also suggest that the cosmological constant ("Λ") is not zero, and that the net mass-energy content of the Universe is dominated by a dark energy and dark matter that have not been characterized scientifically. They differ in their gravitational effects. Dark matter gravitates as ordinary matter does, and thus slows the expansion of the Universe; by contrast, dark energy serves to accelerate the Universe's expansion.

paragraphs: Some people think that there is more than one universe. They think that there is a set of universes called the multiverse. By definition, there is no way for anything in one universe to affect something in another.

paragraphs: The multiverse is not yet a scientific idea because there is no way to test it. An idea that cannot be tested or is not based on logic is not science. So it is not known if the multiverse is a scientific idea.

paragraphs: The future of the Universe is a mystery. However, there has a couple of theories based on the possible shapes of the Universe:


title: Unit of measurement

paragraphs: Units of measurement provide "standards" so that the numbers from our measurements refer to the same thing. Measurement is a process that uses numbers to describe a physical quantity. We can measure how big things are, how warm they are, how heavy they are, and lots of other features as well.

paragraphs: For example, the metre is a standard unit to measure length. Before 1982, it was defined as the distance between two markers on a special rod. Now scientists define the metre by using the speed of light. Saying something has a length of two metres means that it is exactly twice as long as that rod used to define the metre.

paragraphs: In past centuries many different units were used in different countries. Today, most units of measure fall into one of three systems:

paragraphs: The older two, the British imperial system and the closely related US customary system use the foot as a measure of length, the pound as a measure for weight, and the second as a measure for time. They use other units as well. The number of smaller units that make the bigger units in these two systems varies: For example, there are 12 inches in a foot and 16 ounces in a pound.

paragraphs: The newest and most used of the three systems is the metric system or SI system which use 10, 100 or 1000 of a smaller unit to make a bigger one. For instance, there are 100 centimetres in one metre or 1000 grams in one kilogram. This system uses the metre for length and kilogram for mass.

paragraphs: The common, non-metric measurement of time does not follow this pattern. The second is the basis for time measurement, and it is based on the sexagesimal system: 60 seconds make one minute, and 60 minutes make one hour.

paragraphs: The property of the thing being measured is given as a number of units of measure. The number only has sense when the unit of measurement is also given.

paragraphs: For example, The Eiffel Tower in Paris, France is tall. That is, the distance from the top to the bottom of the Eiffel Tower is 300 metres. The property of the Eiffel Tower being measured is a distance. The number measured is 300. 300 of what? The unit of measurement is the metre.

paragraphs: Standards are special objects that are used to make measurements. A metre stick is an example of a standard. When you measure something with a metre stick, you can compare that measurement to anything else that is also measured with a metre stick. This makes measurement easier and comparisons between measurements easier.

paragraphs: Science, medicine and engineering use smaller units of measurement to measure small things with less error. It is easy to measure large things using larger units of measurement. Astronomical measurements like the width of a galaxy use light years and parsecs.

paragraphs: Small measurements like the mass of an atom use special units of measurement.

paragraphs: There are many different standards and units used all over the world. Some became less used during the 19th and 20th centuries.

paragraphs: The metric system is a system of measurement used in most of the world. It is also called the International System of Units, or SI.

paragraphs: Units of measure in the metric system include:

paragraphs: Imperial units were defined in the United Kingdom in 1824. These units were based on similar units that were in use before 1824. Imperial units were used in countries that were part of the British Empire. While many of these countries, including the United Kingdom, have officially adopted SI, the older system of units are still used.

paragraphs: US customary units are the official units used in the US. These are similar to the British imperial units and also based on the units used in the United Kingdom from before American Independence. Some of the units are different to the British ones. For example, there are 20 imperial fluid ounces in an imperial pint, but 16 US fluid ounces in a US pint. Additionally, the US fluid ounce is slightly bigger than the imperial fluid ounce. The result is that US pints and gallons are smaller than imperial pints and gallons. In the United States, the metric system has been legal for trade since 1866 but other measurements such as the gallon, inch, and the pound are still widely used.

paragraphs: Imperial and US units of measurement include:

paragraphs: The ounces for weight and volume are different. Even when measuring water, the number of ounces of weight is not the same as the number of fluid ounces.

paragraphs: The unit of time is the second. The minute (60 seconds) and hour (60 minutes or 3600 seconds) are larger units. A day is defined as 24 hours, but the Earth’s rotation has slowed. The difference is corrected at the end of some years with what is called a leap second. A week (7 days) and month are also standard units.

paragraphs: A unit of measurement that applies to money is called a unit of account. This is normally a currency issued by a country. For instance, the United States use dollars. Each dollar is 100 cents. The United Kingdom uses pounds. Each pound is 100 pennies or pence. The European Union uses the Euro. There are 100 cents in the Euro.

paragraphs: The units for electricity, magnetism and radiation were mostly invented in the 19th century when scientists learned how to measure them. Most were originally given imperial systems, but it is usual to use metric systems for them today.


title: United States customary units

paragraphs: U.S customary units is the system of units of measurement used to measure things in the United States. The system of Imperial units is similar and in some parts identical.

paragraphs: Length or distance units include the inch, foot, yard and mile.

paragraphs: Land units include square miles (2589998.47032 square meter) and acres (4046.8726 square meter).

paragraphs: Common volume units are the teaspoon, tablespoon (3 teaspoons), fluid ounce (two tablespoons), cup (8 ounces), pint (2 cups, or 16 fluid ounces), quart (2 pints, or 32 fluid ounces), US gallon (16 cups, 128 fluid ounces, or 3.8 liters).

paragraphs: Temperature is measured in degrees Fahrenheit (°F). Here is a formula to convert from °C to °F: formula_1

paragraphs: Units of weight and mass include the pound (453.6 grams), which contains 16 ounces. This should not be confused with the British pound which is a type of money. The different uses of the word "pound" can cause confusion. Different sizes of ounce are also in use.

paragraphs: Some people have been trying to replace these units with the metric system since the 1820s. Much infrastructure in the United States and British Empire was built in past centuries using the old measures. During the 20th century some sectors such as science, medicine and the military of the United States converted to metric but Americans still use the old units for daily purposes. On the other hand, world trade is conducted using the metric system and except for the US, the world uses the metric system for almost all purposes.


title: Uranus

paragraphs: Uranus is the seventh planet from the Sun in the Solar System. It is a gas giant. It is the third largest planet in the solar system.

paragraphs: The planet is made of ice, gases and liquid metal. Its atmosphere contains hydrogen (H), helium (He) and methane. The temperature on Uranus is near the top of its atmosphere, but its small solid core (about 55% the mass of Earth) is probably about .

paragraphs: The planet is tilted on its axis so much that it is sideways. It has five big moons, many small ones, and a small system of 13 planetary rings.

paragraphs: The distance between Uranus and the Sun is about 2.8 billion km. Uranus completes its orbit around the Sun in 84 earth years. It completes a spin around itself in 17 hours and 14 minutes. This means there are about 43,000 Uranian days in one Uranian year.

paragraphs: Uranus was discovered in 1781. This planet can be seen with the naked eye under perfect conditions. John Flamsteed saw it decades earlier but mistook it for a star (34 Tauri).

paragraphs: Uranus is named after the Greek god Uranus, who was a god of sky.

paragraphs: Uranus has 27 known moons. They are named for characters from the works of Shakespeare and Alexander Pope. The five biggest moons are Miranda, Ariel, Umbriel, Titania and Oberon. Many moons have yet to be discovered.

paragraphs: In 1986, NASA's "Voyager 2" visited Uranus. This is the only space probe that tried to investigate the planet from a short distance.

paragraphs: Uranus is covered in blue clouds. The top clouds, made of methane, are difficult to see. Lower clouds are thought to be frozen water. There are also violent storms. Wind speeds can reach . Scientists are studying the clouds to try to understand the storms on the planet.

paragraphs: The planet Uranus has a system made of 13 rings which is far fewer than the rings of Saturn but more than those around Jupiter and Neptune. The rings of Uranus were discovered in 1977. More than 200 years ago, William Herschel also reported observing rings, but modern astronomers do not believe that he saw them, because they are very dark and faint. Two additional rings were discovered in 1986 in images taken by Voyager 2, and two outer rings were found in 2003–2005 by the Hubble Space Telescope. The rings are probably mainly composed of frozen water.

paragraphs: The rings of Uranus are thought to be relatively young, not more than 600 million years old. The Uranian ring system probably began from the collisional fragmentation of moons that once existed around the planet. After colliding, the moons probably broke up into many particles, which survived as narrow, optically dense rings only in zones of maximum stability.

paragraphs: The ring system of Uranus has thirteen distinct rings. In order of increasing distance from the planet they are: 1986U2R/ζ, 6, 5, 4, α, β, η, γ, δ, λ, ε, ν, μ rings. They can be divided into three groups: nine narrow main rings (6, 5, 4, α, β, η, γ, δ, ε), two dusty rings (1986U2R/ζ, λ) and two outer rings (μ, ν). The rings of Uranus consist mainly of macroscopic particles and little dust, although dust is known to be present in 1986U2R/ζ, η, δ, λ, ν and μ rings.

paragraphs: In addition to these well-known rings, there may be numerous optically thin dust bands and faint rings between them. These faint rings and dust bands may exist only temporarily. Some of them became visible during a series of ring plane-crossing events in 2007. A number of dust bands between the rings were observed in forward-scattering geometry by "Voyager 2". All rings of Uranus show azimuthal brightness variations.

paragraphs: The rings are made of an extremely dark material. The rings are slightly red in the ultraviolet and visible parts of the spectrum and grey in near-infrared. They show no identifiable spectral features. The chemical composition of the ring particles is not known. However, they cannot be made of pure water ice like the rings of Saturn because they are too dark, darker than the inner moons of Uranus. This shows that they are probably a mixture of the ice and a dark material. The nature of this material is not clear, but it may be organic compounds considerably darkened by the charged particle irradiation from the Uranian magnetosphere. The rings' particles may consist of a heavily processed material which was initially similar to that of the inner moons.

paragraphs: As a whole, the ring system of Uranus is unlike either the faint dusty rings of Jupiter or the broad and complex rings of Saturn, some of which are composed of very bright material—water ice. However, there are similarities with some parts of the latter ring system; the Saturnian F ring and the ε ring are both narrow, relatively dark and are shepherded by a pair of moons. The newly discovered outer rings of Uranus are similar to the outer G and E rings of Saturn. Narrow ringlets existing in the broad Saturnian rings also resemble the narrow rings of Uranus. In addition, dust bands observed between the main rings of Uranus may be similar to the rings of Jupiter. In contrast, the Neptunian ring system is quite similar to that of Uranus, although it is less complex, darker and contains more dust. The Neptunian rings are also positioned further from the planet.

paragraphs: Uranus revolves around the Sun once every 84 Earth years. Its average distance from the Sun is roughly 3 billion km (about 20 AU). The intensity of sunlight on Uranus is about 1/400 that on Earth. Its orbital elements were first calculated in 1783 by Pierre-Simon Laplace. With time, discrepancies began to appear between the predicted and observed orbits, and in 1841, John Couch Adams first proposed that the differences might be due to the gravitational tug of an unseen planet. In 1845, Urbain Le Verrier began his own independent research into Uranus's orbit. On September 23, 1846, Johann Gottfried Galle found a new planet, later called Neptune, at nearly the position predicted by Le Verrier.

paragraphs: The rotational period of the interior of Uranus is 17 hours, 14 minutes, clockwise (retrograde). As on all giant planets, its upper atmosphere experiences very strong winds in the direction of rotation. At some latitudes, such as about two-thirds of the way from the equator to the south pole, visible features of the atmosphere move much faster, making a full rotation in as little as 14 hours.


title: University

paragraphs: A university is a higher learning institution. The word "university" comes from the Latin "universitas magistrorum et scholarium", roughly meaning "community of teachers and scholars". Students can go to university to get an academic degree. Unlike the schooling they have done before, the courses at university are specialised. A person studying biology at university has many courses about biology and fewer courses in other fields such as languages or history. To get a higher degree, people must do some research.

paragraphs: Not all subjects are offered at universities. Mainly, universities offer courses which are about knowledge. They usually do not offer courses in practical trades. In some cases such as law, where there are both knowledge and practical issues, the university does mainly the theoretical side of the subject. Practical qualifications are dome elsewhere.

paragraphs: The universities were born in Europe during the Middle Ages. The first institution of this type was the University of Bologna, which later became a model for other centres of education.

paragraphs: At first, the universities had formed themselves according to the model of the professional groups and like almost everything in the Middle Ages, they remained tied to the Catholic Church. At the beginning, they had worked to teach the so-called "seven liberal arts" (the "trivium" and the "quadrivium"):

paragraphs: That earliest division caused the present divisions between literary and scientific fields. From one point of view, the world's oldest university is Qarawiyyin university. However, teaching religion is not the definition used by most people. A university should in theory teach every subject.

paragraphs: The university is generally regarded as a formal institution that has its origin in the Medieval Christian tradition. European higher education took place for hundreds of years in cathedral schools or monastic schools ("scholae monasticae"). There, monks and nuns taught classes: evidence of these dates back to the 6th century.

paragraphs: The Universities of Paris and Oxford were founded by members of the church. Later universities were founded by kings.

paragraphs: In the early medieval period, most new universities were founded from pre-existing schools, usually when these schools became mainly sites of higher education. Pope Gregory VII promoted the concept of modern university as his 1079 Papal Decree. He ordered the establishment of cathedral schools, which eventually turned into the first European universities.

paragraphs: A university can include several campuses or different places where classes are taught by professors. In each campus there are several faculties and university schools (mainly for teaching), and also laboratories, departments and institutes of research. Many campuses also have housing for students in buildings called dormitories and structures like libraries, study rooms and gymnasiums for students that live there. Each school offers many courses that students take to earn a degree. The person with the highest right to control and to command in a university is the rector, who governs the university with the help of the party of vice-rectors and of other organs such as the social council and the governing body.

paragraphs: There is a group of famous universities called the Ivy League. They are:


title: Value

paragraphs: Value is how much something is worth. Often the best way to find the value of something is to use the price that it can be sold for. However Oscar Wilde wrote that 'people know the price of everything but the value of nothing'- in other words true value does not depend on money alone.

paragraphs: In math, a value is a number which is concrete, something everyone can agree upon. However people may disagree on the value of water, depending if you live in a desert or next to a river. Disagreements on the value of things can create fights between nations, political parties, religions, etc.


title: Volapük

paragraphs: Volapük is a constructed language created in 1880 by Johann Martin Schleyer. Schleyer was a Catholic priest from Germany. He felt that God had told him in a dream to make an international language. Volapük conventions took place in 1884, 1887, and 1889. The aim was to help people from different cultures speak to each other.

paragraphs: Volapük became less popular after 1887 when Esperanto was published. Part of the reason was that Esperanto is easier to learn with a simpler grammar. There are believed to only be 20-30 Volapük speakers in the world today.

paragraphs: The vocabulary of Volapük is mostly English, with some words from German and French.

paragraphs: "Vol" and "pük" come from the English words "world" and "speech". The grammar is based on Indo-European languages.

paragraphs: An example of Volapük is the translation of the "Lord's prayer":


title: Vocabulary

paragraphs: The vocabulary a person uses is all the words that person knows and uses. In general, a person who is five knows about 4,000 to 5,000 words. Adults who go to college may know 20,000 words. A hearing vocabulary and reading vocabulary are bigger than a speaking vocabulary or writing vocabulary, as people understand some words that they do not use.

paragraphs: The number of words in a language is more than the words listed in one dictionary. One dictionary may have a list of 500,000 (half a million) words. Another dictionary may have some other words that the other dictionary does not have. When you add all the words in those dictionaries, there are about 750,000 words in English. There may be more words than that.

paragraphs: You may think to yourself, ""If there are 750,000 words, how can we talk with only 3000 words?"" Because, we do not need to know all the words. You can say most things with around 3,000 words.

paragraphs: The most used words are short words. That is true in all languages. The 50 most common words in English have fewer than seven letters. Half of these words have fewer than four letters.

paragraphs: The vocabulary of a language is always changing. New words are made or words change their meaning. Words about computers, like "download" are new to the English language. The new word "bling" came from hip hop. Words like "cool" have developed new meanings.


title: Vegetable oil

paragraphs: Vegetable oils are triglyceride oils made from plants. They are used in food and for cooking. In past centuries they were much used as fuel in oil lamps. Some kinds of plant oils that people use are palm oil, maize, olive, peanut, rapeseed, soy, and sunflower.

paragraphs: Margarine is an artificial butter made from vegetable oil.


title: Verb

paragraphs: A verb is a kind of word (part of speech) that tells about an action or a state. It is the main part of a sentence: every sentence has a verb. In English, verbs are the only kind of word that changes to show past or present tense.

paragraphs: Every language in the world has verbs, but they are not always used in the same ways. They also can have different properties in different languages. For example, in some other languages e.g., Chinese & Indonesian) verbs do not change for past and present tense. This means the definition above only works well for English verbs.

paragraphs: There are sixteen verbs used in . They are: "be, , , , go, see, , , , , , , , , , ."

paragraphs: The word "verb" originally comes from "*were-", a Proto-Indo-European word meaning "a word". It comes to English through the Latin "verbum" and the Old French "verbe".

paragraphs: In simple sentences, the verb may be one word: "The cat "sat" on the mat". However, the verb may be a phrase: "The cat "will sit" on the mat".

paragraphs: Verbal phrases can be extremely difficult to analyse: "I'm afraid I will need to be going soon". There seem to be three verbal phrases here, which mean something like "Sorry, I must go soon".

paragraphs: In English and many other languages, verbs change their form. This is called inflection. Most English verbs have six inflected forms (see the table), but "be" has eight different forms.

paragraphs: You should notice that some of the verb forms look the same. You can say they have the same shape. For example, the plain present and the plain form of "walk" have the same shape. The same is true for the past and the past participle. But these different forms can have different shapes in other verbs. For example, the plain present of "be" is usually "are" but the plain form is "be". Also, the past of "eat" is "ate", but the past participle is "eaten". When you look for a verb in the dictionary, it is usually the plain form that you look for.

paragraphs: An English sentence must have at least one primary-form verb. Each main clause can only have one primary-form verb.

paragraphs: English has two main kinds of verbs: normal verbs (called lexical verbs) and auxiliary verbs. The difference between them is mainly in where they can go in a sentence. Some verbs are in both groups, but there are very few auxiliary verbs in English. There are also two kinds of auxiliary verbs: modal verbs and non-modal verbs. The table below shows most of the English auxiliaries and a small number of other verbs.

paragraphs: The following verbs are "modal auxiliaries".

paragraphs: Auxiliary verbs also inflect for negation. Usually this is done by adding "not" or "n't".

paragraphs: Sometimes the verb "do" is used with other verbs. It does not really change the meaning, but it can be used to make a strong statement.

paragraphs: It is also used in the negative when no other auxiliary verbs are used.

paragraphs: Sometimes it comes before the subject. This is called inversion and it usually means the sentence is a question.

paragraphs: Many other languages do not use the verb "do" as an auxiliary verb. They use the simple present for "do", and the simple past or perfect for "did".

paragraphs: There are three main systems related to the verb: tense, aspect, and mood.

paragraphs: Tense is mainly used to say when the verb happens: in the past, present, or future. In order to explain and understand tense, it is useful to imagine time as a line on which past tense, present tense and future tense are positioned.

paragraphs: Some languages have all three tenses, some have only two, and some have no tenses at all. English and Japanese for example have only two tenses: past and present. Chinese and Indonesian verbs do not show tense. Instead they use other words in the sentence to show when the verb happens.

paragraphs: Aspect usually shows us things like whether the action is finished or not, or if something happens regularly. English has two aspects: progressive and perfect. In English, aspect is usually shown by using participle verb forms. Aspect can combine with present or past tense.

paragraphs: English uses the gerund-participle, usually together with the auxiliary "be" (and its forms am, is, are, was, and were) to show the progressive aspect.

paragraphs: Many other languages, such as French, do not use progressive tenses.

paragraphs: The past perfect can be used to express an unrealized hope, wish, etc.

paragraphs: After If, wish and would rather, the past perfect can be used to talk about past events that never happened.

paragraphs: Finally, English mood is now usually shown by using modal verbs. In the past, English had a full mood system but that has almost completely disappeared. The subjunctive mood now uses the plain form. There is also a form of "be" that is used in conditionals to show that something is not true (e.g., If I were a bird, I would fly to California.)

paragraphs: Certain parts of a sentence naturally come before verbs or after them, but these are not always the same for all verbs. The main sentence parts are: subject, object, complement, and modifier.

paragraphs: Almost all English sentences have subjects, but sentences that are orders (called imperatives) usually do not have any subjects. A subject usually comes before a verb, but it can also come after auxiliary verbs. In the following examples, the subject is underlined and the primary verb is in bold.

paragraphs: Many verbs can be followed by an object. These verbs are called transitive verbs. In fact, some verbs must have an object (e.g., "take"), but some verbs never take an object (e.g., "sleep"). Verbs that do not take an object are called intransitive verbs. Some verbs can even have two objects. They are called ditransitive verbs. In the following examples, the object is underlined and the primary verb is in bold.

paragraphs: Some verbs can or must be followed by a complement. These verbs are called linking verbs or copula. In the following examples, the complement is underlined and the verb is in bold.

paragraphs: Verbs can be modified by various modifiers, mainly adverbs. Note that verbs generally do not need modifiers; it's usually a choice. In the following examples, the adverb is underlined and the verb is in bold.

paragraphs: Verbs also commonly take a variety of other modifiers including prepositions.

paragraphs: Sometimes a verb and another word can have the same shape. In these cases you can usually see the difference by looking at various properties of the words.

paragraphs: Sometimes a verb and an adjective can have the same shape. Usually this happens with participles. For example, the present participle "interesting" and the adjective "interesting" look the same. Verbs are different from adjectives, though, because they cannot be modified by "very", "more", or "most". For example, you can say "That is very interesting," so you know interesting is an adjective here. But you cannot say "My teacher is very interesting me in math" because in this sentence "interesting" is a verb. On the other hand, if you cannot change the 'be' verb to 'seem' or 'become', it is probably a verb.

paragraphs: The gerund-particle sometimes looks like a noun. This is especially true when it is used as a subject, as in the following example:

paragraphs: The main differences between these verbs and nouns are: modifiers, number, and object/complement

paragraphs: Verbs cannot generally be modified by adjectives and nouns cannot generally be modified by adverbs. So, in "Running regularly is good for you", "running" is a verb because it is modified by "regularly", an adverb.

paragraphs: Verbs cannot change for number, so if you can make the word plural, it is a noun, not a verb. For example, "this drawing is nice" can change to "these drawings are nice", so "drawing" is a noun. But "drawing trees is fun" cannot change to "drawings trees is fun", so it is a verb here.

paragraphs: Many verbs can take objects or complements, but nouns cannot. So, in "parking the car is hard", "parking" is a verb because it takes the object "the car". But, if you say, "there's no parking", parking may be a noun because it does not have an object.

paragraphs: Some verbs have become prepositions. Again, usually these share a shape with participles. Here are some examples:

paragraphs: The main difference between verbs and prepositions is that verbs have a subject. Even if the subject is not written, you can understand what it is. Prepositions do not have a subject.


title: Volume

paragraphs: The volume of an object is a measure of the amount of space occupied by that object, and is not to be confused with mass. The volume of a mountain is much larger than the volume of a rock, for instance.

paragraphs: By convention, the word volume implies a three-dimensional context where:

paragraphs: For objects at or near the Earth's surface, height or depth often refers to the dimension of the object along the local vertical. All physical objects occupy a volume, even if some are so thin that they appear to be two-dimensional, like a sheet of paper.

paragraphs: The unit of volume in the International System of Units is the cubic meter, which is represented by the symbol m.

paragraphs: In some fields or applications, one often uses different units to simplify the discussions or writings. For instance:

paragraphs: Traditional units are still in encountered in some countries: Imperial units such as the gallon or the fluid ounce were in widespread use within the British Empire. Some of them are still popular in the United States, which also uses units like the bushel, the quart, the cup and the teaspoon (in cooking recipes, for example). See U.S. customary units for more examples.

paragraphs: The volume of an object is not a fundamental property of that object: it can change with environmental conditions such as pressure and temperature, especially if the object is highly compressible.

paragraphs: The volume of a mixture of fluids (liquids, gases) may or may not be equal to the sum of their volumes before they were mixed.

paragraphs: In mathematics, the volume of simple geometric objects, written formula_1, can often be calculated on the basis of their shape and dimensions:

paragraphs: The volume of a gas is typically that of its container, but it could be ill-defined, as in the case of the atmosphere, which has no clear upper limit. The volume of a liquid is often measured by pouring it into a graduated container. The volume of a small solid can be estimated by immersing it into a graduated container partially filled with a known amount of liquid, provided the solid is not soluble in the liquid.


title: Venus

paragraphs: Venus is the second planet from the sun. It has a day longer than a year. The year length of Venus is 225 Earth days. The day length of Venus is 243 Earth days. It is a "terrestrial planet" because it has a solid, rocky surface like other planets in the inner solar system. Astronomers have known Venus for thousands of years. The ancient Romans named it after their goddess Venus. Venus is the brightest thing in the night sky except for the Moon. It is sometimes called the "morning star" or the "evening star" as at some elongations it is easily seen just before the sun comes up in the morning and, at other times, just after the sun goes down in the evening. Venus comes closer to the Earth than any other planet does. A Venusian day takes about 243 Earth days.

paragraphs: Venus is sometimes called the sister planet of Earth as they are quite similar in size and gravity. In other ways the planets are very different. Venus' atmosphere (air) is mostly carbon dioxide with clouds of sulphuric acid. Sulphuric acid is a chemical that is very poisonous to humans.

paragraphs: The thick atmosphere has made it hard to see the surface, and until the twenty-first century many people thought things might live there. The pressure on Venus' surface is 92 times that of Earth. Venus has no moons. Venus spins very slowly on its axis and it spins in the opposite direction to the other planets.

paragraphs: Venus is a terrestrial planet so, like the Earth, its surface is made of rock. Venus is much hotter than Earth. All the carbon dioxide in the atmosphere acts like a blanket, trapping heat from the Sun. This effect is called the greenhouse effect and it is very strong on Venus. This makes the surface of Venus the hottest of any planet's surface in the Solar System with an estimated average temperature of . This is hot enough to melt lead or zinc.

paragraphs: Venus has no oceans because it is much too hot for water. Venus' surface is a dry desert. Because of the clouds, only radar can map the surface. It is about 80% smooth, rocky plains, made mostly of basalt. Two higher areas called continents make up the north and south of the planet. The north is called "Ishtar Terra" and the south is called "Aphrodite Terra". They are named after the Babylonian and Greek goddesses of love.

paragraphs: The surface of Venus looks like it has been shaped by volcanic activity. Venus has a lots of volcanoes. The surface of Venus is estimated to be 300–600 million years old.

paragraphs: Venus' atmosphere is mostly carbon dioxide and nitrogen gas with clouds of sulphuric acid. Because the atmosphere is so thick or dense the pressure is very high. The pressure is 92 times the pressure on Earth, enough to crush many things.

paragraphs: It is impossible to see the planet's surface from space as the thick cloud layer reflects 60% of the light that hits it. The only way scientists are able to see it is by using infrared and ultraviolet cameras and radar.

paragraphs: Scientists believe that billions of years ago, the atmosphere of Venus could have been like Earth's atmosphere. There may have been lots of water on the surface of Venus. But after 600 million to several billion years, a greenhouse effect was caused by the evaporation of the water, which made lots of greenhouse gases in its atmosphere.

paragraphs: In 1967, Venera 4 found that the magnetic field of Venus was much weaker than that of Earth. This magnetic field is induced by an interaction between the ionosphere and the solar wind. Venus' magnetosphere is not strong enough to protect the atmosphere from cosmic rays.

paragraphs: Venus can sometimes be seen passing between the Sun and Earth. Venus looks like a black dot when seen through a special telescope. These passages are called "transits". These "transits" happen in pairs eight years apart. Then it is more than a hundred years to the next pair.

paragraphs: Venus orbits the Sun at an average distance of about 108 million km (67 million mi). It completes an orbit every 224.7 days. The rotation of Venus is slow. A Venusian day is longer than a Venusian year.

paragraphs: Many man-made satellites have been sent to Venus to study it. They are:

paragraphs: Mariner 2 was launched on August 27, 1962. It was made to study the atmosphere of Venus, its magnetic field, and mass. The last radio signal from Mariner 2 was received on January 3, 1963. Mariner 2 is still orbiting around the Sun today.

paragraphs: Venera 4 was a probe made by the Soviet Union to explore Venus. The probe had a two probes. One was designed to enter the atmosphere of Venus and use a parachute to land on the surface. Another received the information from the probe on Venus to mission controllers on Earth. Venera 4 was launched on June 12, 1967. The last radio signal from Venera 4 was received on October 18, 1967.

paragraphs: Mariner 5 was a spacecraft of the Mariner program. Mariner 5 was launched on June 14, 1967. The last radio signal from Mariner 5 was on October 14, 1968. Mariner 5 was made to study the magnetic field of Venus and to measure the hard ultraviolet spectrum, of the Venusian atmosphere.

paragraphs: Venera 9 was a spacecraft made by the Soviet Union. It consisted of a probe to orbit Venus which was called an orbiter and another probe that will land on Venus which was called a lander. It was launched on June 8, 1975. The last radio signal from the orbiter was on March 22, 1976. The last radio signal was on October 22, 1975. The orbiter was the first spacecraft to orbit Venus, while the lander was the first to return pictures from the surface of another planet.

paragraphs: Venera 10 was a spacecraft made by the Soviet Union. It consisted of an orbiter and a lander. It was launched on June 14, 1975.

paragraphs: Venera 13 was a probe in the Soviet Venera program. It was made to explore Venus. It was launched on October 30, 1981. The last radio signal from the lander was on March 1, 1982. The last radio signal from the spacecraft that took the lander to Venus was on April 25, 1983.

paragraphs: Venera 14 was a probe in the Soviet Venera program. It was made to explore Venus. It was launched on November 4, 1981. The last radio signal from the lander was on March 5, 1982. The last radio signal from the spacecraft that took the lander to Venus was on April 9, 1983.

paragraphs: Venera 15 was a spacecraft sent to Venus by the Soviet Union. It was made to map the surface of Venus. It was launched on June 2, 1983. The last radio signal from Venera 15 was on January 5, 1985.

paragraphs: Venera 16 was a spacecraft sent to Venus by the Soviet Union. It was made to map the surface of Venus. It was launched on June 7, 1983. The last radio signal from Venera 16 was on June 13, 1985.


title: Vatican City

paragraphs: Vatican City (; officially Vatican City State, ) is an independent sovereign state and the smallest country in the world by size, at 0.44 km². Its territory is completely surrounded by Italy and it is only one of three countries in the world that are enclaves of another country (the others being San Marino, also in Italy, and Lesotho in southern Africa). Also, it is the only country in the world that is an enclave of a city, as all of the land around it is part of Rome, the capital of Italy.

paragraphs: The Vatican City is the headquarters of the Roman Catholic Church and its government, the Holy See. Its head of state is the Pope which is, religiously speaking, the Bishop of Rome and head of the Roman Catholic Church. The current Pope, Pope Francis, former cardinal Jorge Mario Bergoglio, was elected on 13 March 2013.

paragraphs: Established on 11 February 1929 with the Lateran Agreement ("Patti Lateranensi") signed by Benito Mussolini and Pope Pius XI, the Vatican City is also important for its culture and art. The Vatican's masterpieces are very well known in the world: St. Peter's Square, St. Peter's Basilica, the Sistine Chapel, the Vatican Museums and the Apostolic Palace, where the Pope lives. There are also hundreds of other sculptures and pictures.

paragraphs: The Pope used to rule the Papal States, which included most of Italy. Catholic popes had generally tried to stop Italy from becoming one country because they feared they would lose their control of at least one of the Papal States. In 1861 Italy was unified under the King of Savoy, but Rome and Latium remained unconquered. On September 20, 1870 Italian troops invaded. Rome became capital of the new kingdom.

paragraphs: The Pope claimed he was a prisoner of the Italian state and excommunicated all the people who helped invade the Papal state. This stopped Catholics from taking part in public life under Catholic government.

paragraphs: In 1929 Benito Mussolini, decided to sign an agreement with the Holy See, called the Lateran Treaty, which created the Vatican State. Another treaty gave the Vatican money each year to compensate for the lost territories.

paragraphs: The government structure is theocracy with the pontifical leader being the highest authority. The pope is elected by the College of Cardinals which can lead the Roman Catholic Church and the city-state itself. The Pope also holds the title of "Bishop of Rome".

paragraphs: The religion of the city is the Roman Catholic Church.