title: Black hole

text: As of spring 2019, there was an image of a black hole, or rather, the things orbiting the black hole. The image required many photos from different locations. One of the team members (Katie Bouman) made a compilation of all the images into one singular image.


title: Black hole

text: In 2020, Roger Penrose, Reinhard Genzel and Andrea Ghez were awarded the Nobel Prize in Physics for their work on the theory of black holes.


title: Black hole

text: The gravitational collapse of huge (high-mass) stars cause "stellar mass" black holes. Star formation in the early universe may have created very big stars. When they collapsed they made black holes of up to 10 solar masses. These black holes may be the seeds of the supermassive black holes found in the centers of most galaxies.


title: Black hole

text: Most of the energy released in gravitational collapse is given off very quickly. A distant observer sees the material falling in slowly and then stop just above the event horizon because of gravitational time dilation. The light given off just before the event horizon is delayed an infinite amount of time. So the observer never sees the formation of the event horizon. Instead, the collapsing material seems to become dimmer and increasingly red-shifted, eventually fading away.


title: Black hole

text: Black holes have also been found in the middle of almost every galaxy in the known universe. These are called supermassive black holes (SBH), and are the biggest black holes of all. They formed when the Universe was very young, and also helped to form all the galaxies.


title: Black hole

text: Quasars are believed to be powered by gravity collecting material into supermassive black holes in the centers of distant galaxies. Light cannot escape the SBHs at the center of quasars, so the escaping energy is made outside the event horizon by gravitational stresses and immense friction on the incoming material.


title: Black hole

text: Huge central masses (10 to 10 solar masses) have been measured in quasars. Several dozen nearby large galaxies, with no sign of a quasar nucleus, have a similar central black hole in their nuclei. Therefore, it is thought that all large galaxies have one, but only a small fraction are active (with enough accretion to power radiation) and so are seen as quasars.


title: Black hole

text: At the middle of a black hole, there is a gravitational center called a singularity. It is impossible to see into it because the gravity prevents any light escaping. Around the tiny singularity, there is a large area where light which would normally pass by gets sucked in as well. The edge of this area is called the event horizon. The area inside the event horizon is the black hole. The gravity of the black hole gets weaker at a distance. The event horizon is the place farthest away from the middle of the black hole where the gravity is still strong enough to trap light.


title: Black hole

text: Outside the event horizon, light and matter will still be pulled toward the black hole. If a black hole is surrounded by matter, the matter will form an "accretion disk" (accretion means "gathering") around the black hole. An accretion disk looks something like the rings of Saturn. As it gets sucked in, the matter gets very hot and shoots x-ray radiation into space. Think of this as the water spinning around the hole before it falls in.


title: Black hole

text: Most black holes are too far away for us to see the accretion disk and jet. The only way to know a black hole is there is by seeing how stars, gas and light behave around it. With a black hole nearby, even objects as big as a star move in a different way, usually faster than they would if the black hole was not there.


title: Black hole

text: Since we cannot see black holes, they must be detected by other means. When a black hole passes between us and a source of light, the light bends around the black hole creating a mirror image. That effect is called gravitational lensing.


title: Black hole

text: Hawking radiation is black body radiation which is emitted by black hole, due to quantum effects near the event horizon. It is named after the physicist Stephen Hawking, who provided a theoretical argument for its existence in 1974.


title: Black hole

text: Hawking radiation reduces the mass and the energy of the black hole and is therefore also known as "black hole evaporation". This happens because of the virtual particle-antiparticle pairs. Due to quantum fluctuations, this is when one of the particles falls in and the other gets away with the energy/mass. Because of this, black holes that lose more mass than they gain through other means are expected to shrink and ultimately vanish. Micro black holes (MBHs) are predicted to be larger net emitters of radiation than larger black holes and should shrink and dissipate faster.


title: Black hole

text: The no hair theorem states that a stable black hole has only three independent physical properties: mass, charge, and angular momentum. If this is true, then any two black holes that have the same values for these three properties will look the same. As of 2020, it is unclear if the no hair theorem is true for real black holes.


title: Black hole

text: The properties are special, because all three can be measured from outside the black hole. For example, a charged black hole repels other like charges just like any other charged object. Similarly, the total mass inside a sphere containing a black hole can be found by using the gravitational analog of Gauss's law, far away from the black hole. The angular momentum or spin can also be measured from far away.


title: Climate change

text: Climate change is the climate of Earth changing. The Earth's climate has been much hotter and colder than it is today. Climate change this century and last century is sometimes called global warming, because the average temperature on the surface has risen. The climate is now changing much faster than it has in the recent past. This is because people are putting heat-trapping greenhouse gases in Earth's atmosphere. When people talk about climate change they are usually talking about the problem of human-caused global warming, which is happening now (see global warming for more details). But the climate of the Earth has changed over not just thousands of years, but tens or hundreds of millions of years.


title: Climate change

text: Sometimes, before there were people, the Earth's climate was much hotter than it is today. For example about 60 million years ago there were a lot of volcanoes, which burnt a lot of underground "organic matter" (squashed and fossilized dead plants and animals like coal, gas and oil) so a lot of carbon dioxide and methane went up in the air like nowadays. This made the Earth hot enough for giant tortoises and alligators to live in the Arctic.


title: Climate change

text: At times in the past, the temperature was much cooler, with the last glaciation ending about ten thousand years ago. Ice Ages are long times when the Earth got colder, and more ice froze at the North and South Poles. Sometimes even the whole Earth was covered in ice, and was much colder than today. There is no one reason why there are Ice Ages. Changes in the Earth's orbit around the Sun, and the Sun getting brighter or dimmer are events which do happen. Also how much the Earth is tilted compared to the Sun might make a difference. Another source of change is the activities of living things (see Great Oxygenation Event and Huronian glaciation).


title: Climate change

text: At times in the past, the temperature was much cooler, with the last glaciation ending about ten thousand years ago.


title: Climate change

text: Ice Ages are long times (much much longer than glaciations) when the Earth got colder, and more ice froze at the North and South Poles. Sometimes even the whole Earth was covered in ice, and was much colder than today. There is no one reason why there are Ice Ages. Changes in the Earth's orbit around the Sun, and the Sun getting brighter or dimmer are events which do happen. Also how much the Earth is tilted compared to the Sun might make a difference. Another source of change is the activities of living things (see Great Oxygenation Event and Huronian glaciation).


title: Climate change

text: Joseph Fourier in 1824, Claude Poulliet in 1827 and 1838, Eunace Foote (18191888) in 1856, Irish physicist John Tyndall (1820–1893) in 1863 onwards, Svante Arrhenius in 1896, and Guy Stewart Callendar (1898–1964) discovered the importance of carbon dioxide (CO) in climate change. Foote's work was not appreciated, and not widely known. Tyndall proved there were other greenhouse gases as well. Nils Gustaf Ekholm in 1901 invented the term.


title: Climate change

text: The Sun gets a little bit hotter and colder every 11 years. This is called the 11-year sunspot cycle. The change is so small that scientists can barely measure how it affects the temperature of the Earth. If the Sun was causing the Earth to warm up, it would warm both the surface and high up in the air. But the air in the upper stratosphere is actually getting colder. Therefore the changes in the Sun are not causing the global warming which is happening now.


title: Microsoft Windows

text: Microsoft Windows is an operating system for computers made by the United States-based company Microsoft. Windows is used by almost 90% of desktop and laptop computers.


title: Microsoft Windows

text: The first version of Windows, Windows 1.0, came out on November 20, 1985. The newest version, Windows 11, came out October 5, 2021. Most personal computers made after 2015 come with Windows 10. However, some older or cheaper personal computers may come with Windows 8.1 or Windows 7.


title: Microsoft Windows

text: Windows makes it easier to run programs (applications) than MS-DOS did. DOS required typed commands to make the computer do something. DOS required correct syntax of each command. Making mistakes caused the computer to usually give an error message and do nothing.


title: Microsoft Windows

text: Users control their Windows computer by its graphical user interface (or GUI for short). It only needs a keyboard "or" a mouse to work. In later versions, a touch screen works as well. However, using both a keyboard and a mouse makes many tasks easier. By clicking a few buttons on the screen, Windows helps keep your files safe, and easier to change and move. Versions of Windows after 2005 make it even easier for some users with disabilities because these versions have touch screens. For use of a touch screen, some mobile devices come with Windows. Tablet computers and smartphones such as Microsoft Surface and Microsoft Lumia use Windows.


title: Microsoft Windows

text: Windows has several kinds of applications/programs available. Popular applications include games, word processors (to write words) or additional programs like Adobe Flash Player (to watch some videos and play many games on internet sites). Adding new applications to Windows is called "installing". Applications can be bought/purchased on a CD or DVD. Applications can also be downloaded from the Internet.  Some internet applications can be downloaded for free, and others can be bought using the internet.


title: Microsoft Windows

text: Many users complain that Windows creates problems for them. Some users complain that Windows made their computers slower when they changed from DOS. Many people also complain about problems that make their computer less safe to use, even though Microsoft tries to fix these problems. Many computer viruses are created to infect computers running Windows since it is such a popular operating system. Windows was the most popular operating system until recently (today mobile operating systems such as Android are more popular).


title: Ghoti

text: Ghoti is an artificial word used to illustrate irregularities in English spelling. It is a respelling of the word "fish": i.e., it is supposed to be pronounced /ˈfɪʃ/. It is made of these phonemes:


title: Ghoti

text: In fact, "ghoti" is likely to be spontaneously pronounced [goʊtaɪ] or [gəʊtaɪ] (like "go" + "tie"), or [goʊti] ("go" + "tea"), but certainly not like "fish" since : "gh" is never pronounced [f] (cf. "ghost") at the beginning of a word neither "ti" is pronounced [ʃ] at the end of a word.


title: Jack Tweed

text: Tweed started his career as Jade Goody's partner. He became widely known in 2007 after being on "Celebrity Big Brother UK". He caused controversy when he called housemate Shilpa Shetty a "cunt" and "Paki" and said that she should remove objects from the toilet with her teeth. After "Celebrity Big Brother", Goody miscarried his child in 2007. He married her on 22 February 2009 and she died of cervical cancer a month later. He appeared in 2010 ITV2 programme "The Only Way Is Essex". In 2010, he had a relationship with Chanelle Hayes.


title: Jack Tweed

text: Tweed has had several legal issues. These include an 18-month prison sentence in September 2008 for assault occasioning actual bodily harm for attacking a 16-year-old boy with a golf club in December 2006. In March 2009, he was found guilty of common assault for attacking a taxi driver in May 2008. He was tried for the rape of a 19-year-old woman in April 2010, but found not guilty. In January 2011 he punched a man, for which he was convicted of common assault in August 2011.


title: Miami

text: Miami is a city located on the southeastern part of the U.S. state of Florida. It is a known tourist stop and it is well known for its Cuban, Puerto Rican and Haitian culture. Miami has one of the largest Hispanic communities in the United States, with over 70% of the population being of Hispanic and Latino American descent. Miami is also the county seat (and largest city) of Miami-Dade County.


title: Miami

text: The Tequesta tribe lived in what is now Miami before Spain claimed it. In 1566, Pedro Menéndez de Avilés, Florida's first governor, claimed the area from the Tequesta for Spain. Spain ruled Florida until Spain gave it to the United States in 1821. Florida became a state in 1845. On July 28, 1896, Miami officially became a city. It was named after the Mayaimi tribe.


title: Miami

text: Miami experienced rapid growth during the Florida land boom of the 1920s. However, this land boom was affected by the 1926 Miami hurricane. Many Cubans migrated to Miami after Fidel Castro rose to power in Cuba following the 1959 Cuban Revolution, and the population rapidly increased. The majority of these Cuban immigrants now live in Little Havana.


title: Miami

text: During the 1980s, Miami was a primary location for drug trafficking from South America, mainly Colombia. This brought in millions of dollars into the city's economy, and it allowed the construction of luxury hotels, skyscrapers, nightclubs and car dealerships.


title: Miami

text: Miami has a tropical monsoon climate. Summers have average temperatures of during the day and at night, with average monthly rainfall around . Winters have average temperatures of during the day and at night, with average monthly rainfall around .


title: Miami

text: Miami-Dade County Public Schools is the school district for public schools in Miami. There are also some private schools there. There are many colleges and universities in and around Miami. A few of these include: Florida International University, University of Miami, Miami Dade College, and Florida Atlantic University.


title: Miami

text: There are several professional sports teams that play in and around Miami, including the Miami Marlins of Major League Baseball, the Miami Heat of the National Basketball Association, the Florida Panthers of the National Hockey League, the Miami Dolphins of the National Football League, and Inter Miami CF of Major League Soccer.


title: Miami

text: Also, three universities in and around Miami are members of NCAA Division I, the top division of college sports in the U.S.:


title: Miami

text: The population of Miami, Florida as of 2011 is 1.3 Million, with 41.4% suffering from poverty. According to the DNA North American Studies Institute, the racial-makeup of Miami is:


title: Giant panda

text: Although it belongs to the order Carnivora, the panda's diet is 99% bamboo. Pandas in the wild occasionally eat other grasses, wild tubers, or even meat in the form of birds, rodents or carrion. In captivity, they may get honey, eggs, fish, yams, shrub leaves, oranges, or bananas along with specially prepared food.


title: Giant panda

text: The giant panda lives in a few mountain ranges in central China, mainly in Sichuan province, but also in the Shaanxi and Gansu provinces.


title: Giant panda

text: As a result of farming, deforestation and other development, the panda has been driven out of the lowland areas where it once lived.


title: Giant panda

text: Giant pandas are bears. They have black and white fur all around them. The black fur is on their ears, around their eyes, on their legs, and on their shoulders.


title: Giant panda

text: Giant pandas are about the size of an American black bear. They are about tall at the shoulder when they are standing on all four legs. They are about long. Males weigh up to in the wild. Females usually weigh less than .


title: Giant panda

text: Wild giant pandas have lived in the mountains of central China. They live in forests of tall trees. They eat the bamboo that grows under the trees. The weather is rainy and misty in the mountain forests. There are thick clouds almost all the time.


title: Giant panda

text: Bamboo is the main diet of pandas. Ninety-nine percent of the food they eat is bamboo. They eat as much as of bamboo every day. They spend 10 to 16 hours every day looking for food and eating it.


title: Giant panda

text: Bamboo is a grass. Sometimes giant pandas eat other grasses. They also eat little rodents or musk deer babies (fawns). In zoos, giant pandas eat bamboo, sugar cane, vegetables, and fruit.


title: Giant panda

text: Giant pandas get a lot of water from the bamboo they eat. They need more water though. They drink from the freshwater streams and rivers in the mountain. Melting snow high in the mountains runs into these streams and rivers.


title: Giant panda

text: There are two kinds of giant pandas. They both live in China. The best known is the black and white panda. Its scientific name is "Ailuropoda melanoleuca melanoleuca".


title: Giant panda

text: The other giant panda has dark brown and light brown fur. Its skull is smaller than the other giant panda. It has larger molars. This panda lives only in the Qinling Mountains. Its scientific name is "Ailuropoda melanoleuca qinlingensis".


title: Giant panda

text: Giant pandas are ready to have babies (cubs) when they are between the ages of four and eight years. They may be able to have babies until about age 20. Female pandas are ready to have a baby only once a year. This is in the springtime. There are only two or three days during which a baby panda can form in the mother's belly. Calls and scents bring the males and female pandas to each other.


title: Giant panda

text: Female pandas may give birth to two young. Usually only one lives. Giant panda cubs may stay with their mothers for up to three years. Then they leave her for a life of their own.


title: Giant panda

text: Today, the giant panda is a symbol for China. It is protected by the Chinese government. Killing a giant panda is a crime. The giant panda may become extinct. It will die out if the forests of bamboo continue to disappear.


title: Giant panda

text: People outside of eastern Asia did not know about the giant panda until 1869. The first "Westerner" to see a live panda was a German zoologist in 1916. In 1936, Ruth Harkness became the first Westerner to bring a live giant panda out of China. It was a cub (baby panda) named Su-Lin. The cub was taken to live at the Brookfield Zoo in Chicago.


title: Giant panda

text: In the 1970s, China began showing giant pandas in zoos in the United States and Japan as a type of diplomacy. This happened until 1984, when China changed how this was done. Starting in 1984, China would allow zoos to keep the giant pandas for 10 years, but the zoo would have to pay China up to $1,000,000 each year. Also, the zoo would have to agree that any cubs born would belong to China.


title: Giant panda

text: The giant panda is an endangered species. It may become extinct. In 2013, it was estimated that there were less than 2,500 mature giant pandas living in the wild. Illegal hunting is no longer a problem. Hunting for pandas is a crime. The penalties are harsh if you hunt pandas.


title: Giant panda

text: The greatest threat to survival is the loss of living areas. People are ruining the areas where pandas live. They are cutting down trees. They are building farms. Groups of pandas are forced to live in small areas. They are isolated. They cannot mix other panda groups.


title: Giant panda

text: Giant pandas eat bamboo. Sometimes the bamboo dies off. At one time, pandas could move to an area where bamboo was still growing. Moving has become more and more difficult. People are living and working in panda areas. Pandas cannot move about as freely as they once did.


title: Giant panda

text: China set up the first giant panda nature reserve in 1963. Other nature reserves were also set up. There were 40 giant panda reserves in 2006.


title: Pitbull (rapper)

text: Armando Christian Pérez (born January 15, 1981), better known by his stage name Pitbull, is an American rapper, singer and businessman. He was born in Miami, Florida, to parents who are Cuban.


title: Pitbull (rapper)

text: In 2004, he released his first album "M.I.A.M.I." under TVT Records. Pitbull later released his second album, "El Mariel", in 2006. His third album, "The Boatlift", followed in 2007.


title: Pitbull (rapper)

text: His fourth album, "Rebelution" (2009), included the hit single "I Know You Want Me (Calle Ocho)". It was his first internationally popular song. "I Know You Want Me" peaked at number two on the "Billboard" Hot 100.


title: The Pentagon

text: The Pentagon is the headquarters of the United States Department of Defense. It is in Arlington, Virginia (near Washington, D.C.). It has limestone walls. It is in the shape of a pentagon, and has seven floors.


title: The Pentagon

text: The Pentagon is the largest office building in the world, but any place in the building can be reached within 7 minutes.


title: The Pentagon

text: Construction began on September 11, 1941. Exactly sixty years later, on September 11, 2001, it was hit with an airplane by terrorists. The crash killed a total of 189 victims (125 in The Pentagon, 64 in plane).


title: The Pentagon

text: It has a total floor area of 6,500,000 sq ft (604,000 m). Offices are 3,700,000 sq ft (344,000 m). Approximately 25,000 military and civilian employees work in The Pentagon. It has five sides, five floors above ground, two basement levels, and five ring corridors per floor with a total of of corridors. The Pentagon includes a five-acre (20,000 m) central plaza, which is shaped like a pentagon.


title: The Pentagon

text: The concentric rings are named (from the center out) as "A" through "E" (with in addition "F" and "G" in the basement). "E" Ring offices are the only ones with outside views and are generally occupied by senior officials. Office numbers go clockwise around each of the rings, and have two parts: a nearest-corridor number (1 to 10) followed by a bay number (00 to 99), so office numbers range from 100 to 1099. These corridors radiate out from the central courtyard, with corridor 1 beginning with the Concourse's south end. Each numbered radial corridor intersects with the corresponding numbered group of offices (for example, corridor 5 divides the 500 series office block). There are a number of historical displays in the building, particularly in the "A" and "E" rings.


title: The Pentagon

text: Floors in The Pentagon are lettered "B" for Basement and "M" for Mezzanine, both of which are below ground level. The concourse is located on the second floor at the metro entrance. Above ground floors are numbered 1 to 5. Room numbers are given as the floor, concentric ring, and office number (which is in turn the nearest corridor number followed by the bay number). So, office 2B315 is on the second floor, B ring, and nearest to corridor 3 (between corridors 2 and 3). One way to get to this office would be to go to the second floor, get to the A (innermost) ring, go to and take corridor 3, and then turn left on ring B to get to bay 15.


title: The Pentagon

text: Just south of The Pentagon are Pentagon City and Crystal City, extensive shopping and high-density residential districts in Arlington. Arlington National Cemetery is to the north. The Washington Metro Pentagon station is also located at the Pentagon, on the Blue and Yellow Lines. The Pentagon is surrounded by the Capital Beltway Every day, thousands of commuters traveling between Arlington, Virginia and Washington, DC drive on the roads of the Pentagon Reservation.


title: The Pentagon

text: The Pentagon Athletic Center (PAC) is a fitness center for military and civilian staff. It opened in a separate building on the north side of The Pentagon in 2004. Each year, the Pentagon grounds hold the Marine Corps Marathon and the Army Ten-Miler running events.


title: The Pentagon

text: The public may take a 60 minute long tour of the building. Tourists can also visit the Pentagon Memorial that is on the building's west side.The Pentagon receives around 106,000 visitors per year.


title: The Pentagon

text: On September 11, 2001, American Airlines Flight 77 flew into the western side of the Pentagon. September 11 was also the date the Pentagon began to be constructed. There were much fewer deaths because that side was being renovated. 189 people died. There is now a memorial remembering the people who died that day called the Pentagon Memorial. Each person that died is represented by a bench, for a total of 189 benches. It was opened on September 11, 2008, exactly 7 years after the attacks.


title: Harry Potter

text: Harry Potter is a series of seven fantasy novels and eight movies by J. K. Rowling, a British author. It is named for its protagonist and hero, Harry Potter. Seven books in the series have sold over 500 million copies across the world in over 70 languages including Latin, Welsh and Ancient Greek, and is the best-selling book series of all time. They were adapted into movies by the Warner Bros. The first one was released in 2001. The second, third, fourth, and fifth were released respectively in 2002, 2004, 2005 and 2007. The sixth movie, "Harry Potter and the Half Blood Prince", was released in 2009. The final movie was divided into two parts. The first part, "Harry Potter and the Deathly Hallows: Part 1", was released in 2010. "Harry Potter and the Deathly Hallows: Part 2" was released in 2011. Later, several spin-off movies were released in 2016, 2018, and 2022 respectively, and as well as some TV specials for HBO Max in 2022.


title: Harry Potter

text: Harry Potter was born in Surrey, England, United Kingdom. His parents, Lily and James Potter, were killed by an evil wizard named Lord Voldemort, while Voldemort was trying to kill Harry. Yet Harry escaped with no harm except a scar in the shape of lightning bolt, and Voldemort ends up mostly dead. Harry is raised by his non-magical Aunt Petunia, Uncle Vernon, and cousin (Dudley), and is mistreated by them. He believes the false words of the Dursleys that Harry's parents were killed by a car crash. As a child, he did not know that he was a wizard. He eventually discovers that there are many magical people, living secretly and hiding from non-wizards (known as "Muggles"). When Harry turned eleven on July 31, he received a letter inviting him to go to a school called Hogwarts for young witches and wizards. Each book tells the story of one year of his life at the school and tells how he struggles. On Hogwarts Express, the train they use to get to Hogwarts, he meets Ron Weasley and Hermione Granger, who become his best friends. Voldemort tries several times to return to life and kill Harry. In the fourth book, Voldemort comes to life with help from his follower, Peter Pettigrew. The series ends with an epic battle between Harry and Lord Voldemort and a final epilogue that shows Harry and his friends safe and happy with their partners and children.


title: Harry Potter

text: The seven books were all adapted into different forms of media, including toys, movies, spin-off movies, TV specials, video games, and a stage play as well.


title: Harry Potter

text: "Harry Potter and the Cursed Child" is a play based on a new story by J.K Rowling, Jack Thorne, and John Tiffany. It is billed as being the "eighth story, nineteen years later." It stars Jamie Parker as Harry, Noma Dumezweni as Hermione, and Paul Thornley as Ron.


title: Harry Potter

text: The book has many non-human magical characters. Some of them are from mythology and others Rowling wrote herself. Some of these magical creatures have their own culture and some are like animals. According to the real-world book, "Fantastic Beasts and Where to Find Them", the Ministry of Magic makes three groups of creatures: Being, Beast and Spirit. Beings are creatures like humans and house elves, who are smart enough to manage their own business and Beasts are not.


title: President of the United States

text: The president of the United States (POTUS) is the head of state and head of government of the United States of America and the commander in chief of the United States Armed Forces. The president is the head of the executive branch of the federal government of the United States and is the chairman of the US cabinet.


title: President of the United States

text: Grover Cleveland served two non-consecutive terms in office, and is counted as the nation's 22nd and 24th president. There are currently five living former presidents. The most recent death of a former president was the death of George H. W. Bush on November 30, 2018. He was also the most recently serving president to die.


title: President of the United States

text: On November 7, 2020, Joe Biden was elected to be the 46th president of the United States. He was formally inaugurated on January 20, 2021.


title: President of the United States

text: The president is indirectly elected by the people through the Electoral College to a four-year term, and is one of only two nationally elected federal officers, the other being the vice president of the United States. A president must receive more than 270 electoral college votes in order to win an election. Ronald Reagan received 525 votes which is the most electoral votes of any president.


title: President of the United States

text: A president can only serve two terms as president, which is eight years. Franklin D. Roosevelt served four terms as president. He died shortly after beginning his fourth term. After his death, Congress passed an amendment that limits the number of terms a president can have.


title: President of the United States

text: William Henry Harrison served the shortest term, one month, because he died in office from pneumonia.


title: President of the United States

text: A president officially becomes president after being inaugurated on January 20th. The president must be given the oath of office by the Chief Justice of the United States. It is traditionally held at the United States Capitol.


title: President of the United States

text: If the president dies or retires between elections, or is otherwise removed from office, the acting president will become president, who is usually the vice president.


title: President of the United States

text: Abraham Lincoln, James A. Garfield, William McKinley, and John F. Kennedy were assassinated while in office. William Henry Harrison, Zachary Taylor,Warren G. Harding and Franklin Roosevelt died from illness while president. John Tyler was the first vice president of the United States to become president. Calvin Coolidge became president, when Warren G. Harding, the 29th president, died in office.


title: President of the United States

text: Gerald Ford, Richard Nixon's vice president, became president after Nixon resigned. Nixon is the only president to have resigned.


title: President of the United States

text: A president travels by either traveling on Air Force One, Marine One, or by the Presidential state car. At all times, the president is protected by Secret Service agents. Sometimes, the president may travel to Camp David for either relaxation or to do some work in peace.


title: President of the United States

text: By a majority of historical sources by historians or by the American people; Abraham Lincoln, George Washington, Franklin D. Roosevelt , Dwight D. Eisenhower , Woodrow Wilson, Ronald Reagan, John F. Kennedy, Calvin Coolidge, Bill Clinton and Thomas Jefferson are ranked high on polls.


title: President of the United States

text: On the other hand; James Buchanan, Warren G. Harding, Herbert Hoover, Richard Nixon, George W. Bush and Franklin Pierce are thought to be the worst.


title: President of the United States

text: Since Herbert Hoover, each president has created a institutional place known as a presidential library for preserving and making available his papers, records, and other documents and materials. There are currently thirteen presidential libraries in the NARA system.


title: President of the United States

text: There are also presidential libraries maintained by state governments and private foundations, such as the Abraham Lincoln Presidential Library and Museum, which is run by the State of Illinois.


title: President of the United States

text: Several presidential libraries contain the graves of the president such as Richard Nixon at his library in Yorba Linda, California and Ronald Reagan at his library in Simi Valley, California.


title: Temperate climate

text: In geography, temperate latitudes of the Earth lie between the subtropics and the polar circles. Average yearly temperatures in these regions are not extreme, not burning hot nor freezing cold. Temperate means moderate.


title: Temperate climate

text: Unlike in the tropics, temperatures can change greatly here, between summer and winter. So, most places with a temperate climate have four seasons: summer, autumn, winter and spring. Other areas with a temperate climate can have very unpredictable weather. One day it may be sunny, the next may be rainy, and after that it may be cloudy. This is normal in summer as well as in winter. These are the main types of temperate climate:


title: Society

text: Society is the term to describe human beings together (collective, the sum of their social networks and social interactions). The term comes from the Latin idea of "societas", or the connection between friends or allies (friend or ally being "socius"). It can also mean a specific group of people who interact, as well as a wider society of which they are members. People form societies in order to gain greater benefits as a group than would be possible separately. Many animals beside humans also do this, such as wolves or eusocial insects. Sociology is the name for the study of society.


title: Society

text: A society is often considered in terms of citizenship, rights, and ethics. The strength and unity of any society's members' willingness to help each other is to be measured can be called social capital.


title: Society

text: A social contract sets out the rules and roles for this kind of cooperation. One kind of social contract is a constitution – which outlines to some extent what society in a given state is intended to look like.


title: Michelangelo

text: Michelangelo di Lodovico Buonarroti Simoni (6 March 1475 – 18 February 1564), known as Michelangelo, was an Italian Renaissance painter, sculptor, architect, poet, and engineer. Along with Leonardo da Vinci, he is often called a "Renaissance Man" which means that he had great talent in many areas.


title: Michelangelo

text: Michelangelo lived an extremely busy life, creating a great number of artworks. Some of Michelangelo's works are among the most famous that have ever been made. They include two very famous marble statues, "the Pieta" in Saint Peter's Basilica and "David" which once stood in a plazza in Florence but is now in the Accademia Gallery. His most famous paintings are huge frescos, the Sistine Chapel Ceiling and the "Last Judgement". His most famous work of architecture is the east end and dome of Saint Peter's Basilica.


title: Michelangelo

text: A lot is known about Michelangelo's life because he left many letters, poems and journals. Because he was so famous, he became the very first artist to have his biography (story of his life) published while he was still living. His biographer, Giorgio Vasari, said that he was the greatest artist of the Renaissance. He was sometimes called "Il Divino" ("the divine one").


title: Michelangelo

text: Other artists said that he had "terribilità", (his works were so grand and full of strong emotion that they were scary). Many other artists who saw his work tried to have the same emotional quality. From this idea of "terribilità" came a style of art called Mannerism.


title: Michelangelo

text: Michelangelo was born on 6 March 1475 in Caprese near Arezzo, Tuscany. His father was Lodovico di Leonardo di Buonarroti di Simoni, and his mother was Francesca di Neri del Miniato di Siena. The Buonarrottis were a banking family from Florence. They claimed they were descended from the noble Countess Matilda of Canossa. Michelangelo's father had lost most of the bank’s money, so he worked for the local government in the town of Chiusi. When Michelangelo was a baby, the family moved back to Florence. As he was sickly, Michelangelo was sent to live on a small farm with a stonecutter and his wife and family. The stonecutter worked at a marble quarry owned by Michelangelo's father. Many years later Michelangelo said that the two things that had helped him to be a good artist were being born in the gentle countryside of Arezzo and being raised in a house where, along with his nurse's milk, he was given the training to use a chisel and hammer. His mother died when he was only six.


title: Michelangelo

text: Michelangelo’s father then brought him back to Florence and sent him to study with a tutor, Francesco da Urbino. Michelangelo was not interested in his school lessons. He explored the great churches of the city and drew copies of the frescos that he saw there. When he was thirteen, he was apprenticed to the painter Domenico Ghirlandaio. Ghirlandaio had a large busy studio. He had rich patrons who worked for the Medici. He painted frescos in their family chapels. Michelangelo was able to learn the art of fresco painting very well, from Ghirlandaio. In a large workshop such as Ghirlandaio’s, artists would have been working in all sorts of different media, including sculpture, metalwork and painting altarpieces. Michelangelo would have learned about all these things. When Michelangelo was only fourteen, his father persuaded Ghirlandaio to pay his apprentice as an artist, which was highly unusual at the time.


title: Michelangelo

text: The richest, most powerful family in Florence were the Medici. They had an academy where some of the most famous philosophers, poets, and artists met to share their ideas. The Medici family were important patrons of the arts. In 1489, Lorenzo de' Medici, the head of the family, asked Ghirlandaio to send his two best pupils to the academy. Michelangelo was one of the students chosen and he attended the academy from 1490 to 1492. He heard the teaching and discussion of Marsilio Ficino, Pico della Mirandola and Angelo Poliziano. The philosophy that they taught was called Humanism. It was based on the philosophy of the ancient Greek Plato. Michelangelo’s ideas and his art were influenced by these teachings.


title: Michelangelo

text: Michelangelo and another young sculptor called Pietro Torrigiano studied sculpture under Bertoldo di Giovanni. Michelangelo had an argument with Torrigiano, who punched him on the nose so that it was badly broken and spoilt his appearance for the rest of his life. Michelangelo sculpted some reliefs (flat panels with raised figures on them). One was ‘’the Battle of the Centaurs’’ which was made for Lorenzo de Medici.


title: Michelangelo

text: In 1492, Michelangelo’s patron, Lorenzo de' Medici died. This brought about a big change in Michelangelo’s life. He went back to live at his father’s house. Michelangelo asked the prior at the Church of Santo Spirito to allow him to study the anatomy of the bodies of people who had died at the church’s hospital. In 1493, as a “thank-you” gift to the prior, Michelangelo carved a large wooden Crucifix which still hangs in the church. In January 1494, there were very heavy snowfalls. Lorenzo de’ Medici’s son, Piero de Medici commissioned Michelangelo to make a snow statue. So Michelangelo began to work for the Medici again.


title: Michelangelo

text: In 1494, a new leader rose up in Florence. He was a Dominican friar called Savonarola. His strong preaching caused people to burn their books, throw away their jewellery and chase the rich families out of the city. The Medici had to go. For Michelangelo, it was a good time to travel. He stayed for a while in Venice, then moved to Bologna. In Bologna he soon got work sculpting three figures for the big marble Shrine of Saint Dominic. When things calmed down in Florence, Michelangelo returned and worked for another member of the Medici family, Lorenzo di Pierfrancesco de' Medici.


title: Michelangelo

text: Michelangelo made a marble statue of Cupid asleep. Lorenzo di Pierfrancesco told Michelangelo that it looked just like a real Ancient Roman statue and said that if he made it dirty and knocked a few chips off, someone would pay a lot of money for it. Lorenzo sold it to a Cardinal who discovered that it was a fraud. He thought that Michelangelo’s work was so good that he told the pope about it. The pope then invited Michelangelo to go to Rome and work for him.


title: Michelangelo

text: Michelangelo arrived in Rome 25 June 1496 at the age of 21. He lived near the Church of Santa Maria di Loreto on the Gianicolo hill.


title: Michelangelo

text: In 1496 he got an important “commission” (he was given a paid job) from Cardinal Raffaele Riario. The Cardinal wanted Michelangelo to make a marble statue, larger than life-size, of Bacchus, the Ancient Roman God of wine. Michelangelo worked hard at the statue. He carved Bacchus as a young man who was quite drunk and looked as if he was staggering as he raised his cup to make a toast. The cardinal did not like the drunken Bacchus and would not pay for it. A banker called Jacopo Galli bought it for his garden.


title: Michelangelo

text: Michelangelo’s next important commission was from the French Ambassador who asked him to make a statue of the Virgin Mary mourning over the dead body of her son Jesus. This type of artwork, either a painting or a statue, is called by the Italian name “Pieta” (say: “Pe-ay-ta”). Michelangelo’s Pieta is the most famous Pieta that has ever been made. It is now in Saint Peter's Basilica and is visited by thousands of people every day. Giorgio Vasari wrote: "It is a miracle that a shapeless block of stone could have been carved away to make something so perfect that even nature could hardly have made it better, using real human flesh."


title: Michelangelo

text: In 1499 Michelangelo returned to Florence. The priest Savonarola had made so many people angry that he had been put to death in 1498. Life in Florence started to return to normal. Many years earlier the Guild of Woolworkers had commissioned some artists to make statues of the heroes of the city. A sculptor called Agostino di Duccio had started carving a huge statue of David, the hero of the Bible story of David and Goliath. For 40 years the Guild of Woolworkers owned the huge block of marble, with the statue hardly begun. In 1501 they commissioned the young Michelangelo to carve it. It took him three years to complete.


title: Michelangelo

text: Once again Michelangelo made a statue that became world-famous. The statue shows a young man, naked in the way that statues of ancient gods were made, just pausing for a moment and looking with fierce eyes at the huge soldier Goliath that he is about to kill. The statue is 5.17 meter (17 ft) tall. It was placed in the piazza (public square) outside the Palazzo Vecchio where the town council met. After many years, the statue was put into an art gallery, the Accademia. A copy now stands in the piazza. People still go great distances to see the statue that he made.


title: Michelangelo

text: In 1505 Michelangelo was invited to Rome by the newly elected Pope Julius II. Pope Julius was an old man. He wanted Michelangelo to design a grand tomb. It was to stand inside a church and have many carved figures which were to include several slaves to hold up part of the tomb and Old Testament prophets to sit in niches (openings in the walls). Michelangelo started work. He made a magnificent statue of Moses which is now in the Church of San Pietro in Vincoli (St. Peter in Chains) in Rome. Many people go to look at this statue. The slaves were only partly carved. Four of them are now in the Accademia in Florence. The rest of the great plan was unfinished.


title: Michelangelo

text: The main reason that Pope Julius' tomb was not finished was that the Pope had an idea for another artwork. The Sistine Chapel near St. Peter's Basilica had its walls painted by some famous artists from Florence. The Pope decided that Michelangelo should paint the ceiling. Michelangelo did not want to. He said that he was not a painter. But the Pope bullied Michelangelo until he agreed to do it. He told the Pope that he would do it "for God" and that he would only do it if the Pope let him paint it "in his own way".


title: Michelangelo

text: The chapel was long and wide. Its curved ceiling was held up by twelve fan-shaped pieces of wall called "pendentives". Pope Julius told Michelangelo to paint one of the twelve apostles of Jesus on each pendentive. Michelangelo started to do this. Then he got a different idea and scraped off the work that he had done. Instead of apostles, he painted twelve prophets. Seven of them were men from the Old Testament but the other five were women and did not come from the Bible. They were five prophets from the Classical world. Like the prophets in the Bible, they had all told people about the birth of Jesus.


title: Michelangelo

text: On the middle of the ceiling, instead of painting a starry sky, Michelangelo painted scenes from the Bible telling the story of Creation and the downfall of humanity. The most famous scene is the picture of God creating Adam. The ceiling was so famous that many artists tried to copy the way that Michelangelo had arranged and painted the figures.


title: Michelangelo

text: In 1513 Pope Julius II died. The next pope was Pope Leo X, a member of the Medici family. He gave Michelangelo several jobs in Florence, including designing the Medici Chapel to hold the tombs of his family members. Although not all the tombs were built, Michelangelo finished seven large statues including a "Madonna and Child". His pupils later completed the chapel.


title: Michelangelo

text: In 1527, the people of Florence became angry at the Medici for acting like princes. That was not the right way for a family to act, in a city that was a republic. The people threw the Medici out, but the Medici came back with an army and took over the city. Michelangelo was so upset at the behaviour of the Medici that he left his beloved city and never went back.


title: Michelangelo

text: Pope Clement VII called Michelangelo back to the Sistine Chapel to paint the wall behind the altar with a huge scene of "The Last Judgement". He worked on it from 1534 to 1541. At the centre it shows Jesus, surrounded by saints, sitting in judgement over the people of the Earth. To the left, people are rising from their graves and many are welcomed into Heaven. To the right, other people are being sent to Hell where they are dragged down by demons. It is a huge painting with many figures in it.


title: Michelangelo

text: Like Adam and Eve on the ceiling, all the figures were shown naked. Some of the cardinals in the church said that it was wicked to paint saints, including the Virgin Mary, with no clothes on. They called Michelangelo "the painter of rude bits". There was a long argument about this because some people said that God had created everyone naked, so clothes would not be needed in Heaven. After Michelangelo's death another artist, Daniele da Volterra was called in to paint drapes on the figures. For the rest of his life, he was known as "the painter of pants".


title: Michelangelo

text: In 1546, when Michelangelo was in his seventies, he was given one of his most important jobs. The old St. Peter's Basilica had been partly demolished and a new one designed by Bramante. But many architects had worked on it and it was still just at the beginning stages. Michelangelo was made the architect. He immediately improved the plan, had important parts made much stronger, and designed a huge dome, taller than any other domes in the world. He died before it was completed, but he left drawings and models so that the next architect, Giacomo della Porta, could finish what he had started. The dome of St. Peter's Basilica still stands as one of the greatest monuments of Christianity, and as a symbol of the city of Rome.


title: Michelangelo

text: When Michelangelo died, his body was taken back to Florence and buried in the Basilica of Santa Croce (Church of the Holy Cross). On his tomb sit three mourning figures who symbolize Architecture, Painting and Sculpture.


title: Maximum and minimum

text: In mathematics, the maximum and minimum of a set A is the largest and smallest element of A. They are written as formula_1 and formula_2, respectively. Similarly, the maximum and minimum of a function are the largest and smallest value that the function takes at a given point. Together, they are known as the extrema (the plural of extremum).


title: Maximum and minimum

text: Minimum means the least you can do of something. For example, if the minimum amount of dollars you must pay for something is seven, then you cannot pay six dollars or less (you must pay at least seven). You can do more than the minimum, but no less. Maximum means the most you can have of something. For example, if the maximum amount of oranges you can juggle is five, you cannot juggle more than five oranges. You can do the maximum or less.


title: Maximum and minimum

text: For a differentiable function formula_3, if formula_4 is an extreme value for the set of all values formula_5, and if formula_6 is in the interior of the domain of formula_3, then formula_6 is a critical point, by Fermat's theorem.


title: Belarus

text: Belarus (officially called Republic of Belarus) is a country in Eastern Europe. About nine million people live there. Its capital is Minsk. It was part of the Soviet Union until 1991. The president of Belarus has been Alexander Lukashenko since 1994. It is bordered by Russia, Ukraine, Poland, Lithuania and Latvia. Over forty percent of its is forested.


title: Belarus

text: The State is a member of the UN, the CIS, Collective Security Treaty Organization, the Eurasian Economic Community, the Union State of Russia and Belarus (from 2 April 1997), as well as a member of other international organizations.


title: Belarus

text: Until the 20th century, the lands of modern-day Belarus belonged to several countries. These included the Principality of Polotsk, the Grand Duchy of Lithuania, the Polish–Lithuanian Commonwealth, and the Russian Empire. After the Russian Revolution, Belarus became part of the Soviet Union. It was renamed the Byelorussian Soviet Socialist Republic (BSSR). The borders of Belarus took their modern shape in 1939. Some lands occupied by Poland in 1921 were added into it after the 1939. The nation and its territory were devastated in World War II. Belarus lost about a third of its population and more than half of its economic resources. In 1945 the Belorussian SSR became a founding member of the United Nations, along with the Soviet Union and the Ukrainian SSR.


title: Belarus

text: The parliament of the republic declared the sovereignty of Belarus on 1990. During the dissolution of the Soviet Union, Belarus became independent on 1991.


title: Belarus

text: Over 70% of Belarus's population of 9.49 million live in the urban areas. More than 80% of the population are ethnic Belarusians. Most of the rest are Russians, Poles and Ukrainians. The country has two official languages: Belarusian and Russian. The main religion in the country is Russian Orthodox Christianity. The second most popular, Roman Catholicism, has a much smaller following.


title: Belarus

text: Both Homo erectus and Neanderthal remains have been found in the region. From 5,000 to 2,000 BCE, Bandkeramik cultures lived here. Cimmerians were in the area by 1,000 BCE. By 500 BCE, Slavs moved in. The Huns and Avars came through around 400–600 CE. They were unable to move the Slavs.


title: Belarus

text: The region that is now Belarus was first settled by Slavic tribes in the 6th century. They came into contact with the Varangians, who were bands of Scandinavian warriors and traders. They formed Kievan Rus' in 862. Polotsk and Turov become the capitals of the first principalities of today Byelorussia.


title: Belarus

text: When Kievan Rus' ruler Yaroslav I the Wise died, the state split. Later some were added into the Grand Duchy of Lithuania. Lithuania made a union with Poland. The union ended in 1795. The land of Belarus went to the Russian Empire. The land stayed with Russia until going to the German Empire during World War I.


title: Belarus

text: Belarus said they were free from Germany on 1918. They formed the Belarusian People's Republic. Then the Polish–Soviet War started. A part of Belarus under Soviet rule became the Belorussian Soviet Socialist Republic in 1919. Then it added to the Lithuanian–Belorussian Soviet Socialist Republic. The Belorussian SSR became a founding member of the Union of Soviet Socialist Republics in 1922. The western part of modern Belarus stayed part of Poland as a result of the Treaty of Riga.


title: Belarus

text: In BSSR Byelorussian language was officially recognized together with Russian, Polish and Yiddish. A motto “Workers of all countries, unite” was written on all of this 4 languages on the republican emblem. Schools with teaching on the national languages began operating.


title: Belarus

text: In 1939, Nazi Germany invaded Poland. This was the beginning of World War II. After Polish powers left the county, the Soviet troops entered into lands with Ukrainian and Byelorussian majority, that were controlled by Poland before it. Parts of West Byelorussia were added to the Belorussian Soviet Socialist Republic. They are now West Belarus.


title: Belarus

text: Nazi Germany invaded the Soviet Union in 1941. BSSR was the hardest-hit Soviet republic in World War II. During that time, Germany destroyed 209 out of 290 cities in the republic, 85% of the republic's industry, and more than one million buildings. Casualties were between two and three million. The population of Belarus did not come back to its pre-war level until 1971.


title: Belarus

text: In 1986, the Belorussian SSR had nuclear fallout from the explosion at the Chernobyl power plant in neighboring Ukrainian SSR.


title: Belarus

text: Belarus said it was free on 1990. With the support of the Communist Party, the country's name was changed to the Republic of Belarus on 1991.


title: Belarus

text: Belarus is landlocked and mostly flat. It has a lot of marshy land. Many streams and 11,000 lakes are found in Belarus. Three major rivers run through the country: the Neman, the Pripyat, and the Dnieper.


title: Belarus

text: The highest point is Dzyarzhynskaya Hara at . Belarus has a hemiboreal humid continental climate ("Dfb" in the Koeppen climate classification).


title: Belarus

text: Natural resources include peat deposits, small amounts of oil and natural gas, granite, dolomite (limestone), marl, chalk, sand, gravel, and clay. About 70% of the radiation from neighboring Ukraine's 1986 Chernobyl nuclear disaster entered Belarusian territory. The farmland continues to be affected by radiation fallout.


title: Belarus

text: Lukashenko has described himself as having an "authoritarian ruling style". Western countries have described Belarus under Lukashenko as a dictatorship. The Council of Europe has stopped Belarus from membership since 1997 for undemocratic voting.


title: Belarus

text: The Armed Forces of Belarus have three branches: the Army, the Air Force, and the Ministry of Defense joint staff. Lieutenant General Yuri Zhadobin heads the Ministry of Defense. Alexander Lukashenko (as president) is Commander-in-Chief.


title: Belarus

text: Belarus is divided into six regions. They are named after the cities that are their administrative centers.


title: Belarus

text: Most of the Belarusian economy is state-controlled. It has been described as "Soviet-style." The country relies on Russia for some imports, including petroleum. As of 1994, Belarus's main exports included heavy machinery (especially tractors), agricultural products, and energy products.


title: Belarus

text: According to 2019 census, the population is 9,413,446. Ethnic Belarusians are 84.9% of Belarus' total population. The next largest ethnic groups are: Russians (7.5%), Poles (3.1%), and Ukrainians (1.7%). Minsk, the nation's capital and largest city, is home to 2,018,281 residents as of 2019. Gomel, with 481,000 people, is the second-largest city and is the capital of the Homiel Voblast. Other large cities are Mogilev (365,100), Vitebsk (342,400), Hrodna (314,800) and Brest (298,300). For other places in Belarus see List of settlements in Belarus.


title: Belarus

text: Belarusian literature began with 11th- to 13th-century religious scripture. By the 16th century, Polotsk resident Francysk Skaryna translated the Bible into Belarusian. The modern era of Belarusian literature began in the late 19th century. One important writer was Yanka Kupala. Several poets and authors went into exile after the Nazi occupation of Belarus. They would not return until the 1960s. The last major revival of Belarusian literature was in the 1960s with novels published by Vasil Bykaŭ and Uladzimir Karatkievich.


title: Belarus

text: In the 19th century, Polish composer Stanisław Moniuszko made operas and chamber music pieces while living in Minsk. At the end of the 19th century, major Belarusian cities formed their own opera and ballet companies.


title: Belarus

text: The National Academic Theatre of Ballet, in Minsk, was awarded the Benois de la Dance Prize in 1996 as the top ballet company in the world. Rock music has become more popular in recent years, though the Belarusian government has tried to limit the amount of foreign music aired on the radio. Since 2004, Belarus has been sending artists to the Eurovision Song Contest.


title: Belarus

text: The traditional Belarusian dress is from the Kievan Rus' period. Due to the cool climate, clothes were made to keep body heat and were usually made from flax or wool.


title: Belarus

text: Belarusian cuisine is mainly vegetables, meat (especially pork), and breads. Foods are usually either slowly cooked or stewed. A typical Belarusian eats a light breakfast and two hearty meals, with dinner being the largest meal of the day. Wheat and rye breads are eaten in Belarus. Rye is more plentiful because conditions are too harsh for growing wheat. To show hospitality, a host will give an offering of bread and salt when greeting a guest or visitor. Popular drinks in Belarus include Russian wheat vodka and "kvass", Kvass is a drink made from fermented malted brown bread or rye flour. "Kvass" may also be added with sliced vegetables to create a cold soup called "okroshka".


title: Belarus

text: Belarus has four World Heritage Sites: the Mir Castle Complex, the Nesvizh Castle, the Belovezhskaya Pushcha (shared with Poland), and the Struve Geodetic Arc (shared with nine other countries).


title: Harrison Schmitt

text: Dr. Harrison Hagan "Jack" Schmitt (born July 3, 1935) is an American geologist, retired NASA astronaut, university professor, former U.S. senator from New Mexico. He is the most recent living person to have walked on the Moon. As of 2018, he is also the last living crew member of Apollo 17.


title: Harrison Schmitt

text: Schmitt resigned from NASA in August 1975 in order to run for election to the United States Senate as a member from New Mexico. He ran as a Republican. He won his election in 1976, and he was a senator for six years, but he lost his re-election campaign in 1982.


title: Red

text: Red is the color that is on the edge of the rainbow. It is one of the three primary colors, along with blue and yellow. Red light has a wavelength between 630 and 740 nanometers.


title: Clothing

text: Clothing are items used to cover the human body. Humans are the only animals that wear clothing. During the many thousands of years between loosing body hair and learning to make clothes, humans were naked. Some native people in warm, humid climates continue to be naked in everyday life.


title: Clothing

text: Clothing is worn where the human body needs protection; from the sun and dust in hot, dry countries lacking shade and from the cold and wet in temperate climates. Clothing such as thick wool coats and boots keeps the human body warm in very cold temperatures (such as in the arctic).


title: Clothing

text: Clothing is also worn for decoration, as a fashion. People from different cultures wear different clothing, and have different beliefs and customs about what type of clothing should be worn. For many people, clothing is a status symbol. It helps people project an image. Often, clothing is a form of self-expression. Adults in different social or work situations present different views of themselves by the clothes they wear. Young people have an entirely different form of dress to express their personalities. Often people will simply follow popular fashion styles so that they will fit in. Clothing is far more than just a means to protect our bodies.


title: Clothing

text: Clothing is usually made of fabric sewn together, but may also be animal skins. Each body part has a typical item of clothing. The torso can be covered by shirts, arms by sleeves, legs by pants or skirts, hands by gloves, feet by footwear, and head by headgear or masks. In cold climates, people also wear heavy, thick coats such as trenchcoats.


title: Clothing

text: There is no easy way to be sure when clothing was first developed, because it was prehistoric and clothing is perishable. One of the earliest that has been found is a cloak made of the fur of squirrels, from a cave in Italy, dated to 23.000 years ago.


title: Clothing

text: Some estimates come from studying the biology of lice. The body louse lives in clothing, and diverged from head lice about 107,000 years ago. This suggests that clothing existed at that time. Other louse-based estimates put the introduction of clothing at around 44,000–74,000 years ago. In September 2021, scientists reported evidence of clothes being made 120,000 years ago based on findings in deposits in Morocco, a country in the northwestern part of Africa.


title: Clothing

text: Some archeologists think Neanderthals became extinct because they never invented the sewing needle, and were then unable to make fitted clothing or footwear to survive the extreme cold of the last ice age.


title: Clothing

text: People often decorate their bodies with makeup or perfume, and they also cut or change the hair on their heads and faces. They might also go in for body modification: tattoos, scarifications, and body piercings. But makeup and tattoos are not kinds of clothing.


title: Clothing

text: Things that are carried and not worn, like wallets, purses, canes, and umbrellas, are called accessories, but they are not kinds of clothing, either. Jewelry and eyeglasses are also accessories that are put on the body. Nail polish is also put on the fingertips and can be interpreted as makeup.


title: Constituency

text: A constituent is a voting member of a community or organization and has the power to appoint or elect. A constituency is all of the constituents of a representative. Constituents also have the power to remove their representative from the position to which they have appointed him or her. All of the constituents who are registered to vote are called the "electorate".


title: Constituency

text: In the United Kingdom, a parliamentary constituency is a district that elects a member of parliament. It is sometimes called a "Parliamentary seat" or a "Division". Constituencies for local government elections are called either "Wards" or "electoral divisions".


title: Constituency

text: Northern Ireland has 18 constituencies, each of which elect six MLAs to the Northern Ireland Assembly under the Single Transferable Vote system.


title: Constituency

text: The Scottish Parliament has 73 single-member constituencies, with the remaining 56 seats being selected by the Additional Member System (AMS). Until the passage of the Scottish Parliament (Constituencies) Act 2004, the constituencies of the Scottish Parliament were identical to those of the House of Commons.


title: Constituency

text: The National Assembly for Wales has 40 constituencies which are identical to the Welsh constituencies of the House of Commons. Its remaining 20 seats are selected by AMS.


title: Constituency

text: The United States House of Representatives has 435 constituencies called "Congressional districts" each electing one member.


title: Constituency

text: The term "constituency" is usual in many countries, especially in members of the Commonwealth of Nations.


title: Tulsidas

text: Tulsidas (1541-1623) was an Indian writer. He wrote many books which are manifestations of Sanatan dharma and Indian ideology. His most famous book is the "Ramcharitmanas". This book was written in a language called Awadhi, a dialect of Hindi. The book tells the story of Lord Rama and his war and victory over Ravan, the king of Lanka. Rama fought for his wife Sita and brought her back from Lanka to Ayodhya.


title: Tulsidas

text: Tulsidas was born in Rajapur, in what is now Uttar Pradesh, in Samvat 1589 or 1532 A.D. He was a Sarayuparina Brahmin by birth and is regarded as an incarnation of Valmiki, the author of the "Ramayana". His father's name was Atmaram Dubey and his mother's name Hulsi. Tulsidas conceived of god in the form of Rama. Tulsidas's composition 'Ramcharitmanas.' written in Awadhi is important both as an expression of his devotion and as a literary work. His devotion to the literary world is very important. He founded the Sankatmochan Temple dedicated to Lord Hanuman in Varanasi.


title: Duck

text: Ducks are birds in the family Anatidae. Ducks are closely related to swans and geese, which are in the same family.


title: Duck

text: Ducks are not a monophyletic group. They are a 'form taxon'. Swans and geese are in the same family but are not called ducks. The main difference is that ducks have shorter necks, and are smaller.


title: Duck

text: Other swimming and diving birds, like grebes and loons, are not ducks. A baby duck is called a "duckling", and a male duck is called a "drake". Most ducks are aquatic birds. They can be found in both saltwater and fresh water.


title: Duck

text: The subfamily Anatinae ("dabbling ducks") feed on the surface of water or on land, or as deep as they can reach by up-ending without completely submerging.


title: Duck

text: Ducks lay eggs once a year and are omnivorous, eating aquatic plants and tiny animals. Along the edge of the beak there is a comb-like structure called a "pecten". This strains the water squirting from the side of the beak and traps any food. The pecten is also used to preen feathers. Diving ducks dive deep to get their food.


title: Duck

text: Many ducks are migratory. This means that they spend the summer months in a different place than the winter months. Ducks show a cosmopolitan distribution, they can be found all over the world, except for Antarctica. Some duck species live on the South Georgia and Auckland Islands, which are subantarctic. Many species have established themselves on remote islands, such as Kerguelen or Hawaii.


title: Duck

text: Ducks are sometimes kept as pets. They are often kept by groups of people on public ponds for their beauty and calming nature. People commonly feed ducks in ponds stale bread, thinking that the ducks will like to have something to eat. However bread is not healthy for ducks and can kill them. In nature, ducks eat grasses, aquatic plants, fish, insects, small amphibians, worms, and small molluscs.


title: Duck

text: Some ducks are bred and kept by humans. They are not wild ducks. They are kept to provide food (meat and eggs), or to use their feathers for pillows and other items in the house. Especially in Asia, many people like to eat duck.


title: Desert

text: A desert is an arid (dry) biome. They get less than of rainfall a year. A source defines it as "any region that can have a moisture deficit over the course of a year. In other words, they can have less rainfall in a year than they give up through evaporation".


title: Desert

text: Including the semi-arid regions, deserts may cover about 33% of the land on Earth. That includes much of Antarctica, where large areas get no snow at all. The largest hot desert is the Sahara desert, in northern Africa, covering nine million square kilometres.


title: Desert

text: Deserts land surfaces are varied. Examples are stones, sand dunes and snow. They may have some animals and plants. Deserts sometimes expand (desertification), and sometimes contract.


title: Desert

text: Deserts are mostly in the western part of the Americas, Western Asia, Central and western Australia, Namibia and North Africa. Some, such as the Sahara, are very hot during the day and have cold nights, but there are also cold deserts such as the Atacama in South America which are frozen day and night.


title: Desert

text: Cold deserts can be found close to the poles. That is why they are also called polar deserts. Other regions of the world have cold deserts too, for instance high altitude areas like the Himalayas. These are called montane deserts. Antarctica is the world's largest cold desert. The second largest one is the Arctic desert, but that is warming up a bit now.


title: Desert

text: Hot deserts are mostly in the subtropics. They can be covered by sand, rock, salt lakes, stony hills and even mountains. Most non-polar deserts are hot in the day and chilly at night. The temperature in the daytime can reach or higher in the summer, and dip to or lower at night time in the winter. The largest hot desert in the world is the Sahara in North Africa. It is almost as large as Europe or the United States.


title: Desert

text: It may be the oldest desert on Earth. It has been a desert for at least three million years. It is the oldest continuously arid region on Earth.


title: Desert

text: It does rain in the desert, but not often. One place in the Atacama Desert had no rain for 401 years. In other deserts it may rain every year or once every few years. Rains in a desert may bring a great amount of water to the ground in a short time. Some rain passes straight into the dry soil, but the rest may form a temporary river. Wadis, stream channels that are normally dry, can quickly fill after heavy rain, causing a flash flood.


title: Desert

text: People sometimes bring water from wet places to hot deserts so plants can grow. This is called irrigation.


title: Desert

text: A sandstorm or dust storm arises when wind blows loose sand and dust from a dry surface. Clouds of sand or dust are often so dense that they obscure the sun. A sandstorm can move whole sand dunes. Sandstorms are common in large, dusty deserts.


title: Desert

text: There are not many animals in the desert, but some animals are able to survive. They have different ways to survive the intense conditions of the desert. Examples of animals that live in hot deserts are lizards, small rodents, snakes, and camels. Plants and animals in hot deserts must live with very little water.


title: Desert

text: Xerophytic plants which live in the desert have special adaptations. They may survive by growing roots that are very near the surface to absorb the rain that may fall before it evaporates. Plants such as the cactus have thick, fleshy stems that help them store water.


title: Desert

text: Small animals such as lizards and small rodents often escape the hot rays by digging underground burrows where they live. They only come out at night to search for food. Like the plants, desert animals must live on as little water as possible. Most of the water used by these animals comes from seeds and stems that absorb and hold water. Camels survive in hot deserts by storing water in body fat in their humps. Like other desert animals, the camel loses little water in its wastes (urine and feces).


title: Earth's crust

text: The Earth's crust is the Earth's hard outer layer. It is less than 1% of Earth's volume. The crust is made up of different types of rocks: igneous, metamorphic, and sedimentary rocks.


title: Earth's crust

text: Below the crust is the mantle. The crust and the upper mantle make up the lithosphere. The lithosphere is broken up into tectonic plates that can move.


title: Earth's crust

text: The crust is of two different types. One is the continental crust (under the land) and the other is the oceanic crust (under the ocean).


title: Earth's crust

text: The temperature of the crust increases with depth because of geothermal energy. Where the crust meets the mantle the temperatures can be between 200 °C (392 °F) to 400 °C (752 °F). The crust is the coldest layer because it is exposed to the atmosphere.


title: Earth's crust

text: Igneous rocks make up over 90% of Earth's crust by volume. This is not noticeable because they are mostly covered by sedimentary and metamorphic rocks.


title: Earth's crust

text: A single family of silicates, the feldspars, account for about half of the material in the crust (60% by weight), and quartz is a sizeable proportion of the rest. Other common minerals are mica and hornblende.


title: Earth's crust

text: Only 8% of Earth's crust is non-silicate minerals, and this includes carbonates, sulfides, chlorides and oxides.


title: Earth's crust

text: Earth's mantle and crust formed about 100 million years after the formation of the planet, about 4.6 billion years ago. At first the crust was very thin, and was probably changed often as the tectonic plates shifted around a lot more than they do now. The crust would have been destroyed many times by asteroids hitting Earth, which was much more common in the Late Heavy Bombardment.


title: Earth's crust

text: The oldest oceanic basalt crust today is only about 200 million years. Most of the continental crust is much older. The oldest continental crustal rocks on Earth are cratons between 3.7 and 4.28 billion years old. These have been found in the Narryer Gneiss Terrane in Western Australia, in the Acasta Gneiss in the Northwest Territories on the Canadian Shield, and on the Fennoscandian Shield. A few zircons at least 4.3 billion years old have been found in the Narryer Gneiss Terrane in Western Australia.


title: Earth's crust

text: The average age of Earth's continental crust is about 2.0 billion years. Most crustal rocks formed before 2.5 billion years ago are in cratons. Such old continental crust and the mantle below it are less dense than other places in the Earth. These are not easily destroyed when the plates shift. The making of new continental crust is linked to times of major orogeny or mountain building. This happens at the same time as the formation of the supercontinents such as Rodinia, Pangaea and Gondwana. The crust forms in part by the coming together of island arcs including granite and metamorphic fold belts. They are kept together partly by the subduction of the mantle below the crust, which makes a mantle on which the crust can float.


title: Capital city

text: A capital city, or capital town or capital, is a city or town, specified by law or constitution, by the government of a country, or part of a country, such as a state, province, or county. It usually serves as the location of the government's central meeting place and offices. Most of the country's leaders, embassy and officials work in the capital city. This doesn't have to be the case though: Monaco, Nauru, Switzerland and Vatican City are examples of countries that do not have a capital city. Israel said Jerusalem was its capital: Most countries don't recognise this, and most embassies are in Tel Aviv. In Japan, the city of Tokyo, which was the capital, was disbanded in 1943. Today, the 23 city districts (called wards) have the role of capital city. Each district is a city of its own, though. "Capital city" can also mean a city most famous for something, in this case, Capital of the World is a nickname.


title: Capital city

text: Capitals are usually among the largest cities in their regions and often are the biggest. For example, Montevideo is Uruguay's capital and its biggest city. The capital may also be the most important center of commerce, as in London or Bangkok.


title: Capital city

text: However, a capital is not always the largest city in a country. For example, the capital of India is New Delhi, which is smaller than Mumbai.


title: Capital city

text: In countries with subdivisions like the United States, the capitals of the federated states are often not the biggest cities. For example, New York City is the biggest city in the United States and in New York State, but is not the capital of either. The capital the country is Washington, DC, and the capital of the state is Albany.


title: Capital city

text: An unusual case exists in Canada since the federal capital, Ottawa, is not the largest city in its province, Ontario, which is Toronto. However, Toronto is the capital of Ontario, so Toronto is a provincial capital but not a federal one.


title: Capital city

text: Some countries have more than one capital for different purposes. For example, Bolivia has two (Sucre and La Paz) and South Africa has three (Pretoria, Cape Town, and Bloemfontein). In a city-state like Singapore, Monaco, and the Vatican City, the capital is the country.


title: Capital city

text: Not all countries have capitals. Nauru is a country that does not officially have a capital, but the district of Yaren, which is where the government is, can be called the "de facto" capital. Also, although many people consider the city of Bern in Switzerland to be the capital of the country, it is by law not the capital but the "."


title: Capital city

text: Capitals can be in cities that are already there like Athens or Rome, or a new town can be built and made the capital like Canberra and Alexandria. Countries can change capitals from time to time. Several cities have been the capital of China. The United States once had its capital in Philadelphia and later in New York City but moved to the new city of Washington, D.C. in 1800. Rio de Janeiro was the capital of Brazil until the new city of Brasilia was built between 1956 and 1960.


title: Capital city

text: Most countries have their seat of government within their capital. However, Malaysia has its capital at Kuala Lumpur, but its seat of government is at Putrajaya. In the Netherlands, the constitution calls Amsterdam the capital, but the seat of government is The Hague.


title: Party leaders of the United States House of Representatives

text: Party leaders and whips of the United States House of Representatives are elected by their respective parties in an opened-door caucus by secret ballot and are also known as floor leaders.


text: The U.S. House of Representatives does officially use the term "Minority Leader" and so does the media. The House uses the terms "Republican Leader" or "Democratic Leader" depending on which party holds a minority of seats.


text: The current party leaders are: Majority (Democratic) Leader Steny Hoyer, and Majority (Democratic) Whip Jim Clyburn, Minority (Republican) Leader Kevin McCarthy, and Minority (Republican) Whip Steve Scalise.


title: Universe

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


title: Universe

text: 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.


title: Universe

text: Physicists are currently unsure if anything existed before the Big Bang. They are also unsure whether the size of the Universe is infinite, meaning its size never ends as it has been expanding since the Big Bang.


title: Universe

text: People have long had ideas to explain the Universe. Most early models had the Earth at the centre of the Universe. This is known as geocentrism. 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.


title: Universe

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


title: Universe

text: 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.


title: Universe

text: 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).


title: Universe

text: 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.


title: Universe

text: 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.


title: Universe

text: 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.


title: Universe

text: 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.


title: Universe

text: 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.


title: Universe

text: 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").


title: Universe

text: 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.


title: Universe

text: 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.


title: Universe

text: 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.


title: Universe

text: 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".


title: Universe

text: 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.


title: Universe

text: 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.


title: Universe

text: 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.


title: Universe

text: 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.


title: Universe

text: 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".


title: Universe

text: 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.


title: Universe

text: 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).


title: Universe

text: 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).


title: Universe

text: 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.


title: Universe

text: 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.


title: Universe

text: 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 to 20 billion years.


title: Universe

text: 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.


title: Universe

text: 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.


title: Universe

text: 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.


title: Universe

text: 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.


title: Universe

text: 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.


title: Universe

text: 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.


title: Universe

text: 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.


title: Universe

text: 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.


title: Universe

text: 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.


title: Universe

text: 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.