adityasasidhar/Wikipedia_Cleaned huggingface dataset:
In rural areas books may be taken in a bookmobile, or mobile library to remote places.
COVID-19 pandemic has further changed how libraries operate in year 2020 and many of them around the world were faced with really hard choices as to which services to offer and which services to shut down for a limited time.
Provinces and autonomous regions are broken into prefectures and sub-provincial cities.
The following items are fruits according to the scientific definition, but are sometimes considered to be vegetables:
London is the capital of the United Kingdom (UK), and its largest city. It is also the city with the highest population in the UK. The population is just under 9 million. The city is the largest in western Europe by population and area.
On the Thames, London has been a central city since it was founded by the Romans two millennia ago as Londinium. The Romans bridged the river Thames and built a road network to connect Londinium with the rest of the country.
London's original city centre, the City of London is England's smallest city. In 2011 it had 7,375 inhabitants on an area of . The term "London" is used for the urban region which developed around this city centre. This area forms the region of London, the Greater London administrative unit led by the Mayor of London and the London Assembly.
London is one of the world's most important political, economic and cultural centres. London was the capital of the British Empire and so for almost three centuries the centre of power for large parts of the world.
The city has about 9.1 million inhabitants (2018). If one counts the entire metropolitan area of London (London Metropolitan Area), it has about 15 million people. The climate is moderate.
The Romans built the city of "Londinium" along the River Thames in AD 43. The name "Londinium" (and later 'London') came from the Celtic language of the Ancient Britons. In AD 61, the city was attacked and destroyed. Then the Romans rebuilt the city, and London became an important trading hub.
After the decline of the Roman Empire, few people remained in London. The Anglo-Saxon people of sub-Roman Britain were mainly agricultural. Once the Romans had gone, trade with Continental Europe got less. In the 9th century, more people started living in London again. It became the largest city in England. However, it did not become the capital city of England again until the 12th century. For a long time after the Romans, England was not unified, and so had no capital.
Trade grew and the East India Company was founded as a monopoly trader. Trade expanded to the New World. London became the main North Sea port, and migrants went from England and abroad. The population rose from about 50,000 in 1530 to about 225,000 in 1605.
The 17th century saw Londoners suffer from the plague and the fire of London. The century starts with the famous Gunpowder Plot.
In the 17th century the Stuart kings ruled: James I and Charles I. Charles Stuart was defeated by Cromwell, so the century was remarkable in that respect. Cromwell marks the beginning of the modern system whereby Parliament is more important than the monarch. The war between Cromwell and Charles was bitterly fought. London was the key city, and Oxford was also important.
The century also had two great disasters: the Great Plague and the Great Fire of London. The control of London by Cromwell and Parliament was one of the decisive factors in the civil war. Cromwell's victory was followed by his death in 1658, and the country for a time moved back to royal rule under Charles II.
The plague virus, carried by fleas on rats, came to Britain from Europe.
The Great Fire of London broke out at the beginning of September 1666. Unfortunately there were warehouses full of timber, pitch, tallow, wine and tar. These caught fire and, in the end, all the riverfront buildings were destroyed. The fire eventually destroyed about 60% of the city, (mainly the City of London, rather than the large city we have today). Old St Paul's Cathedral was destroyed. Some fires burnt more widely, up to present-day Southwark and even Highgate (which are not in the city, but are in London).
Another famous old part of Greater London is Westminster, which was a different city from the City of London. In Westminster is Westminster Abbey (a cathedral), the Palace of Westminster (the Houses of Parliament, and 10 Downing Street (where the Prime Minister lives).
After the railways were built, London grew much larger. Greater London has 33 boroughs (neighbourhoods) and a mayor. The old City of London is only a square mile in size but has its own Lord Mayor.
In stages, London has several times increased in size by statute in Parliament. The main motive for this has been taxation, and the increase in houses in what was once countryside. Since taxation was paid to the counties surrounding London, there was a motive for absorbing the countryside into London. This happened in several stages.
Outside London, local taxes are paid to the County Councils; inside London they are paid to the Greater London Council. One county has been lost entirely (Middlesex) and all the others have lost land and revenue. The London Boroughs and the GLA (Greater London Authority) both raise taxes, and the representatives are elected. There is a London Plan which sets out the priorities. The number of local authorities which raise local taxes and spend it is 33: 32 London boroughs and the City of London.
One aspect of its geology had big consequences. North of the Thames London is on chalk, which is easy (with modern equipment) to tunnel through. South of the Thames London is on clay, which was, and still is, much more difficult to dig out. So most of the subterranean engineering is north of the Thames. The road system south of the Thames is also inadequate by modern standards. This difference is reflected in the prices for property, the road transport, the Underground railway and the definition of "London" as a taxable area. The growth of London has been more vigorous North of the Thames, and has included the complete absorption of Middlesex, once a separate county.
London's largest industry is finance. This includes banks, stock exchanges, investment companies and insurance companies The Bank of England is in the City of London and is the second oldest bank in the world.
The Victorians built many train systems in the mid-19th century (1850s). Their main stations are in London, and the lines go to every part of Great Britain. There were originally five major companies but the five companies became a national rail network in modern times. Their terminals at King's Cross, St. Pancras, Paddington, Waterloo and Charing Cross are still used as terminals.
There are five airports, though only one is actually in London (London City Airport). The most used airport is Heathrow Airport, although it is actually outside the city. There is the London end of the LondonBirmingham canal, which was important to the industrial 19th century. Really heavy goods can be best transported on water by canal or sea.
The London Underground is a system of electric trains which are in London. It is the oldest underground railway in the world. It started running in 1863 as the "Metropolitan Railway". Later, the system was copied in other cities, for example Paris, New York, Moscow and Madrid. Even though it is called the London Underground, about half of it is above the ground. The "Tube" is the name used for the London Underground, because the tunnels for some the central lines are semi-round tubes running through the ground. The Underground has 274 stations and over 250 miles (402 km) of track. Over one billion passengers used the Underground each year.
There is a black taxi system regulated by the Metropolitan Police, and various other private enterprise hire car companies. Efforts are being made to make roads safer for cyclists.
London's biggest tunnel has just been completed to take sewage from the capital to the East where it is processed.
Summers are generally warm, sometimes hot. Winters are generally cool. Spring and autumn are mild.
Temperature extremes in London range from at Heathrow Airport on 19 July 2022 down to at Northolt on 1 January 1962.
The metric system was first introduced in France in 1791. That system did not have its own unit of capacity or volume because volume can be measured in cubic metres. In 1793 work to make the metric system compulsory in France was started by the Temporary Commission of Republican Weights and Measures. Due to public demand, the commission said that the cubic metre was too big for everyday use. They said that a new unit based on the old cadil should be used instead. One cadil was to be 0.001 cubic metres. This was equivalent to a cube with sides 10 cm. The "cadil" was also known as the "pinte" or the "litron". The "pinte" had been an old French unit of measure of capacity. In 1795 the definition was revised. The "cadil" was given the name "litre".
In Europe, milk is sold in one litre cartons. One litre bottle is also a popular package for soft drinks. Most alcoholic drinks are sold as 1/3 litre (0.33 l), litre (0.5 l) or 3/4 litre (0.75 l) bottles.
Lime is a green fruit, and the tree fruit itself. They are citrus fruits similar to lemons. Citrus fruits like limes are rich in vitamin C. Sailors from Britain were given lemon or lime juice to stop them falling ill with scurvy. This is how they got the nickname "Limey". There are several citrus trees whose fruits are called limes. They include the key lime "Citrus aurantiifolia", the Persian lime, the kaffir lime, and the desert lime "Citrus glauca".
It is the study of:
Applied math is useful for solving problems in the real world. People working in business, science, engineering, and construction use mathematics.
Mathematics solves problems by using logic. One of the main tools of logic used by mathematicians is deduction. Deduction is a special way of thinking to discover and prove new truths using old truths. To a mathematician, the reason something is true (called a proof) is just as important as the fact that it is true, and this reason is often found using deduction. Using deduction is what makes mathematical thinking different from other kinds of scientific thinking, which might rely on experiments or on interviews.
Logic and reasoning are used by mathematicians to create general rules, which are an important part of mathematics. These rules leave out information that is not important so that a single rule can cover many situations. By finding general rules, mathematics solves many problems at the same time as these rules can be used on other problems. These rules can be called theorems (if they have been proven) or conjectures (if it is not known if they are true yet). Most mathematicians use non-logical and creative reasoning in order to find a logical proof.
These theorems and conjectures have interested mathematicians and amateurs alike:
These theorems and hypotheses have greatly changed mathematics:
These are a few conjectures that have been called "revolutionary":
There is no Nobel Prize in mathematics. Mathematicians can receive the Abel Prize and the Fields Medal for important works.
There are many tools used to do math or find answers to math problems.
March (Mar.) is the third month of the year in the Gregorian calendar, coming between February and April. It has 31 days. March is named after Mars, the Roman god of war.
In ancient Rome, March was called Martius. It was named after the war god (Mars) and the Romans thought that it was a lucky time to begin a war. Before Julius Caesar's calendar reform, March was the first month of the year in the Roman calendar, as the winter was considered to be a monthless period. It is one of seven months to have 31 days.
March begins on the same day of the week as February in common years and November every year, as each other's first days are exactly 4 weeks (28 days) and 35 weeks (245 days) apart respectively. March ends on the same day of the week as June every year, as each other's last days are exactly 13 weeks (91 days) apart.
May is the fifth month of the year in the Julian and Gregorian calendars, coming between April and June. It has 31 days. The month of May might have been named for the Roman goddess Maia, or more likely the Roman goddess of fertility Bona Dea, whose festival was held in May.
May comes between April and June and is the fifth month of the year in the Gregorian calendar. It is one of the seven months to have 31 days. In the older Roman calendar, May was the third month of the year. It is a spring month in the Northern Hemisphere and an autumn month in the Southern Hemisphere. In each hemisphere, it is the seasonal equivalent of November in the other. May is likely to have been named after the Roman goddess Maia, though there is a theory that May might have its name from the Latin "Maiores", meaning "Seniors". The same theory suggests that June would then be named from "Iuniores", meaning "Juniors".
No other month of any year either begins or ends on the same day of the week as May; this month is the only one that has both of these properties.
Music is a form of art that uses sound organised in time. Music is also a form of entertainment that puts sounds together in a way that people like, find interesting or dance to. Most music includes people singing with their voices or playing musical instruments, such as the piano, guitar, drums or bass.
These and other attempts, do not capture all aspects of music, or leave out examples which definitely are music. Music is a special shared relationship between a person, the persons behavior, and a sounding object. Musical experience and the music, together, are called phenomena, and the activity of describing phenomena is called phenomenology.
The oldest flute ever discovered may be the Divje Babe flute, found in the Slovenian cave Divje Babe I in 1995. It is not certain that it is really a flute. The item in question is a piece of the femur of a young cave bear, and is about 43,000 years old. However, whether it is a musical instrument or just a bone that got chewed on is an ongoing debate.
In 2008, archaeologists discovered a bone flute in the Hohle Fels cave near Ulm, Germany. The five-holed flute has a V-shaped mouthpiece and is made from a vulture wing bone. The discovery is the oldest confirmed find of any musical instrument in history. Other flutes were also found in the cave. This flute was found next to the Venus of Hohle Fels and a short distance from the oldest known human carving. When they announced their discovery in 2009, the scientists suggested that the find showed that there was a well-established musical tradition when humans colonized Europe.
The oldest known wooden pipes were discovered near Greystones, Ireland, in 2004. A wood-lined pit contained a group of six flutes made from yew wood, between 30 and 50 cm long, tapered at one end, but without any finger holes. They may once have been strapped together.
In 1986 several bone flutes were found in Jiahu in Henan Province, China. They date to about 6,000 BC. They have between 5 and 8 holes each and were made from the hollow bones of a bird, the Red-crowned Crane. At the time of the discovery, one was still playable. The bone flute plays both the five- or seven-note scale of Xia Zhi and six-note scale of Qing Shang of the ancient Chinese musical system.
It is not known what the earliest human music was like. Some architecture and paintings are thousands of years old, but old music could not survive until people learned to write it down. The only way we can guess about early music is by looking at very old paintings that show people playing musical instruments, or by finding instruments in archaeological digs (digging underground to find old things). The earliest piece of music that was ever written down and that has not been lost was discovered on a tablet written in Hurrian, a language spoken in and around northern Mesopotamia (where Iraq is today), from about 1500 BC.
Another surviving piece of early written music was a round called "Sumer Is Icumen In". It was written down by a monk around the year 1250. Much of the music in the Middle Ages (roughly 450-1420) was folk music played by working people who wanted to sing or dance. When people played instruments, they were usually playing for dancers. However, most of the music that was written down was for the Catholic church. This music was written for monks to sing in church. It is called Chant (or Gregorian chant).
People can enjoy music by listening to it. They can go to concerts to hear musicians perform. Classical music is usually performed in concert halls, but sometimes huge festivals are organized in which it is performed outside, in a field or stadium, like pop festivals. People can listen to music on CD's, Computers, iPods, television, the radio, cassette/record-players and even mobile phones.
Anyone can make up their own pieces of music. It is not difficult to compose simple songs or melodies (tunes). It's easier for people who can play an instrument themselves. All it takes is experimenting with the sounds that an instrument makes. Someone can make up a piece that tells a story, or just find a nice tune and think about ways it can be changed each time it is repeated. The instrument might be someone's own voice.
Montreal is built on an island sitting in the Saint Lawrence River. More than three million people live in the Montreal region. At the centre of Montreal is a mountain called Mount Royal. The suburb of Westmount is a very rich suburb on the island of Montreal.
Most of the people who live in Montreal speak French.
Some video game companies like Ubisoft also have studios in Montreal.
Ice hockey was invented in Montreal. A lot of Montrealers are interested in the sport, and the city is home to its own ice hockey team called the Montreal Canadiens who play in the National Hockey League (NHL).
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more than one kind of Macadamia tree. Only two kinds are grown for food.
Maui is a volcanic doublet: an island formed from two volcanic mountains that are joined. The older volcano, Mauna Kahalawai, is much older and has been very worn down. In common talk it is called the West Maui Mountain. The larger volcano, Haleakala, rises above 10,000 feet (3,050 m). The last eruption of Haleakala happened over 200 years ago, and this lava flow can be seen between Ahihi Bay and La Perouse Bay on the southeast shore.
The only big town is named Kaunakakai, which is also the main or chief port on the island. The airport is in Central Molokai. Also on the island is Kalaupapa, which is a place for people who have a disease called leprosy.
Money, also sometimes called currency, can be defined as anything that people use to buy goods and services. Money is what many people receive for selling their own things or services.
Multiplication is the inverse of division, and has many uses, one of them being checking your division work.
Multiplication is an arithmetic operation for finding the "product" of two numbers in mathematics. It is often represented by symbols such as formula_1 and formula_2. Multiplication is the third operation in math, after addition which is the first, and subtraction which is the second. It can also be defined on number mathematical objects as well.
The definition of multiplication as repeated addition provides a way to arrive at a set-theoretic interpretation of multiplication of cardinal numbers. A more accurate representation is to think of it as scaling quantities. This animation illustrates 3 being multiplied by 2, giving 6 as a result. Notice that the blue dot in the blue segment of length 3 is placed at position 1, and the blue segment is scaled so that this dot is placed at the end of the red segment (of length 2). For multiplication by any X, the blue dot will always start at 1 and end at X. This works even if X is smaller than 1, or negative.
The company also makes and promotes a video game console, Xbox. It lets people play video games on their televisions. The games were first stored on CDs, but many recent games are downloaded from the Internet. There have been three generations of Xbox. The first generation came out in 2001 and was just called Xbox, while the second, the Xbox 360, was released in 2005. The third model is the Xbox One in May 2013. In 2020, Microsoft introduced Xbox Series X and Xbox Series S. Beginning with the Xbox 360, Microsoft introduced Xbox Live, which lets people play games online against other people anywhere in the world. The Xbox has become very popular and more than 150 million units have been sold worldwide. Because of this, Microsoft is considered one of the three big companies that make video game consoles, along with Nintendo and Sony.
The Islamic world or Muslim world consists of all people who believe in Islam. It is not an exact location, but rather a community. When they do things together as Muslims, they are the "umma", which means "community" referring to all of the believers. The faith emphasizes unity and defense of fellow Muslims, so it is common for these nations to cooperate. Recent conflicts in the Muslim world have sometimes spread because of this desire to cooperate (see below). It is also likely that some have been made shorter and less damaging because of it. Some might even have never started.
The word "multiverse" was created in 1895 by psychologist William James as a philosophical concept.
The cosmological multiverse tries to explain why the universe we can see sometimes called <nowiki>"our universe"</nowiki> is one that life can exist in. Even small changes to the way physics works would make life impossible. In a multiverse a large number of universes are randomly created and some happen to favour life emerging there. Many inhospitable universes would also have been created, but there would be no life there to observe their existence.
The quantum multiverse is another version in which our universe splits into alternative futures with every quantum event. This is called Many-worlds interpretation of quantum mechanics.
MediaWiki is the name of the software that runs all of the Wikimedia projects and . MediaWiki was released in 2003. It is a free server-based software which is licensed under the GNU General Public License (GPL). This means it is free content, or open source.
MediaWiki is designed to be run on a large web server farm for a website that gets millions of hits per day. MediaWiki is a very powerful, scalable software and a feature-rich wiki implementation. It uses PHP to process and display data stored in its MySQL database. Pages use MediaWiki's Wikitext format, so that users without knowledge of XHTML or CSS can edit them easily.
Because MediaWiki is flexible, many websites that want people to contribute information use MediaWiki rather than other types of wiki software. Those operated by Fandom are among them.
As MediaWiki is a complex software, there would always be bugs in the software, especially for new extensions. Therefore, Wikimedia has created a Bugzilla website for people who see a bug to tell the developers of MediaWiki.
Users can change MediaWiki's appearance. They may use one of the several "skins". At different times different skins have been default. For example, Wikipedia once used Monobook before adopting the new Vector skin in version 1.16.
A first language (also mother language, mother tongue, native language, arterial language, or L1) often means the language that a person learns first. It helps one understand words and concepts in the style of that language.
Sometimes, but not often, "first language" means the language that a person speaks best (the second language is then spoken less well than the first language, etc.). In that sense, a person could have more than one first or second language.
The first languages of the national majority usually are to be recognized as national languages of the nation.
The earliest facial hair above the lip, as a style, is credited to the Iron Age Celts. Diodorus Siculus, a Greek historian,wrote this about the Celtic people:
A mile is a unit of length. There are many different kinds of mile but "mile" on its own usually means the statute mile.
Margarine is an artificial butter. It can be made from vegetable oil, or animal fat. It may also contain skimmed milk, salt and emulsifiers. Margarine is used in many baked products. It contains less fat than butter, so is often chosen instead of it. There are also "low fat" margarines, which contain even less fat. However, many types of margarine are made with hydrogenated oils. Products with hydrogenated oil have trans fats, which are unhealthy and can cause heart disease. Other fats, like olive oil, and butter, are a better choice for cooking.
The Milky Way is our home galaxy. It contains around 400 billion stars, including our Sun.
This galaxy belongs to the Local Group of three large galaxies and over 50 smaller galaxies. The Milky Way is one of the largest galaxies in the group, second to the Andromeda Galaxy. Its closest neighbour is the Canis Major Dwarf Galaxy, which is about 25,000 light years away from the Earth. The Andromeda Galaxy is moving towards the Milky Way Galaxy and will collide with it in about 3.75 billion years. The Andromeda Galaxy moves with a speed of about 1,800 kilometres per minute.
It is estimated to contain at least 100 billion stars, and possibly up to 400 billion stars. The figure depends on the number of very low-mass, or dwarf stars, which are hard to detect, especially more than 300 light years from our sun. Therefore, present estimates of the total number are uncertain. This can be compared to the one trillion (10) stars of the neighbouring Andromeda Galaxy.
At 220 kilometers per second it takes the Solar System about 240 million years to complete one orbit of the Galaxy (a galactic year).
The Galactic halo extends outward but is limited in size by the orbits of two Milky Way satellites, the Large and the Small Magellanic Clouds, whose closest approach is at about 180,000 light years. At this distance or beyond, the orbits of most halo objects would be disrupted by the Magellanic Clouds, and the objects would likely be ejected from the vicinity of the Milky Way.
As a guide to the relative physical scale of the Milky Way, if the Solar System out to the orbit of Pluto were reduced to the size of a US quarter (about an inch or 25 mm in diameter), the Milky Way would have a diameter of 2,000 kilometers.
The movement of material around the galactic center shows that it has a compact object of very large mass. The intense radio source named Sagittarius A*, thought to mark the center of the Milky Way, is now confirmed to be a supermassive black hole. Most galaxies are believed to have a supermassive black hole at their center.
Movement, or motion, is the state of changing something's position or changing where something is. A bird that is flying is moving. So is a person who is walking. This is, because they change where they are. They "move" from one place to another. There are many forms of science and mathematics that are related to movement.
Because of the work of scientists including Galilei and Newton, we know that "position" is relative. This means that an object's position depends on where it exists in relation to other objects. For example, a ball can be away from a box, from a chair and away from a table. Here, the box, chair and the table helped to define the position of the ball. They acted as the reference points for the observation of the ball. By telling someone how far the ball was from other objects, they were told its relative position.
The motion of an object is also relative. It depends on how its position changes in relation to other objects. For example:
A person is sitting inside a train (Train A). The train has not started moving yet. When that person looks out the window, they see another train (Train B) . Both trains are facing the same direction. If Train B moves backwards, it appears to the person on Train A that they are moving toward Train B. If a reference point it added this can be changed. If the person can also see a pole next to the trains they will see that train A did not move and train B moved backwards.
From this, it is shown that what the movement is can not bo known without a frame of reference. In this example the pole is the frame of reference.
The study of motion without considering its cause is called kinematics. Kinematics deals with terms like speed, velocity, and acceleration. Dynamics is the branch of physics that focuses on the causes and effects of motion. It deals with force, inertia, work, energy and momentum.
The muscles that control the eye are driven by the optic tectum in the midbrain. All the voluntary muscles in the body are controlled by motor neurons in the spinal cord and hindbrain. Spinal motor neurons are controlled by neural circuits of the spinal cord, and by inputs from the brain. The spinal circuits do many reflex responses, and also do rhythmic movements such as walking or swimming. The descending connections from the brain give more sophisticated control.
The brain has several areas that project directly to the spinal cord. At the highest level is the primary motor cortex. This is a strip of tissue at the back of the frontal lobe. This tissue sends a massive projection directly to the spinal cord, through the pyramidal tract. This allows for precise voluntary control of the fine details of movements. There are other brain areas which affect movement. Among the most important secondary areas are the premotor cortex, basal ganglia, and cerebellum.
In addition, the brain and spinal cord controls the autonomic nervous system. this system works by secreting hormones and by modulating the "smooth" muscles of the gut. The autonomic nervous system affects heart rate, digestion, respiration rate, salivation, perspiration, urination, sexual arousal and several other processes. Most of its functions are not under direct voluntary control. Several of them, such as respiration, can be controlled directly as well.
That lends weight to the argument.<br>They stood alone, frozen statues on the plain.<br>The ball happily danced into the net.
From 17th century English poet Andrew Marvell's poem "To His Coy Mistress".
The metabolic system of an organism decides which substances it finds nutritious and which poisonous. For example, some prokaryotes use hydrogen sulfide as a nutrient, yet this gas is poisonous to animals. The speed of metabolism, called the metabolic rate, influences how much food an organism will need, and how it is able to get that food.
Traditional units are still in encountered in some countries: imperial units such as the ounce or the pound were in widespread use within the British Empire. Some of them are still popular in the United States, which also uses units like the short ton (2,000 pounds, 907 kg) and the long ton (2,240 pounds, 1010 kg), not to be confused with the metric ton (1,000 kg).
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In atomic nuclei,i.e in and ,the residual mass comes from the binding kinetic and potential energy of the quarks and gluon field. An analogy to go along with is to think of the 3 as balls with the gluons as a spring connecting the quarks. This mass accounts for ~99% of the mass of these with the remaining ~1% coming from the individual quarks which comes from quantum interactions with the Higgs field.
Mercury is the smallest planet in the Solar System. It is the closest planet to the sun. It makes one trip around the Sun once every 87.969 days.
Less is known about Mercury than about other planets of our Solar System. Even with telescopes only a small, bright crescent can be seen. It is also hard to put a satellite in orbit around it. Two spacecraft have visited Mercury. The first one was Mariner 10. It only made a map of about 45% of the Mercury's surface from 1974 to 1975. The second is the MESSENGER spacecraft, which finished mapping Mercury in March 2013.
Mercury looks like Earth's Moon. It has many craters and smooth plains. It has no moons and little atmosphere as we know it. However, Mercury does have an extremely thin atmosphere, known as an exosphere. Mercury has a large iron core. Because of this Mercury has a magnetic field about 1% as strong as that of the Earth. It is a very dense planet because its core is large.
Known sightings of Mercury date back to at least the first millennium BC. Before the 4th century BC, Greek astronomers thought that Mercury was two different objects: The one that they were only able at sunrise, they called Apollo; the other one that they were only able to see at sunset, they called Hermes. The English name for the planet is from the Romans, who named it after the Roman god Mercury. The symbol for Mercury is based on Hermes' staff.
Even though Mercury is the closest planet to the Sun, it is not the hottest. This is because it has no greenhouse effect. The heat that the Sun gives it, quickly escapes into space. The hottest planet is Venus.
Mercury's surface looks like the surface of the Moon. It has plains that look like mares and has lots of craters. Mercury was hit by a lot of comets and asteroids 4.6 billion years ago. Mercury was also hit during a period called the Late Heavy Bombardment. Mercury has many craters because its atmosphere is too faint to slow objects down. Images from "MESSENGER" have shown that Mercury may have shield volcanoes.
Mercury is too small and hot for its gravity to keep any thick atmosphere for a long time. It does have a thin exosphere that is made up of hydrogen, helium, oxygen, sodium, calcium, potassium. This exosphere is blown away and replenished from lots of sources. Hydrogen and helium may come from the solar wind. Radioactive decay of elements inside the crust of Mercury is another source of helium, and also sodium and potassium.
Mercury has the most eccentric orbit of all the planets in the Solar System. It has an eccentricity of 0.21. It ranges from 46,000,000 to 70,000,000 km (29,000,000 to 43,000,000 mi) away from the Sun. Mercury takes 87.969 Earth days to go around the Sun. Mercury's axial tilt is 0.027 degrees.
The first spacecraft to visit Mercury was NASA's Mariner 10. It stayed in Mercury's orbit from 1974 to 1975. Mariner 10 took the first close-up pictures of Mercury's surface. It showed many features, such as the craters. Unfortunately, the same side of Mercury was day each time Mariner 10 flew close to Mercury. This made observing of both sides of Mercury impossible. In the end, less than 45% of the Mercury's surface was mapped.
Mariner 10 came close to Mercury three times. At the first time, it found a magnetic field, which surprised planetary geologists because Mercury's rotation was too slow to create a magnetic field. The second time was mainly used to take pictures of Mercury's surface. At the third time, it got more information about the magnetic field. It showed that the Mercury's magnetic field is like the Earth's magnetic field.
On March 24, 1975, eight days after its last close fly by, Mariner 10 ran out of fuel. Because its orbit could no longer be controlled, mission controllers shut down the probe . Mariner 10 is thought to still be orbiting the Sun.
The second satellite to visit Mercury is NASA's MESSENGER. It stands for MErcury Surface, Space ENvironment, GEochemistry, and Ranging. It was launched on August 3, 2004. It made a fly-by of Earth in August 2005. It made another fly-by of Venus in October 2006. It made its first fly-by of Mercury happened on January 14, 2008, a second on October 6, 2008, and a third on September 29, 2009. It made a map of most of Mercury that "Mariner 10" didn't map. The first image of Mercury orbiting the Sun was gotten on March 29, 2011.
MESSENGER was made to study Mercury's high density, the history of Mercury's geology, its magnetic field, the structure of its core, if it has ice at its poles, and where its thin atmosphere comes from. "MESSENGER" crashed into Mercury's surface on April 30, 2015.
The European Space Agency and the Japanese Space Agency made and launched a spacecraft called "BepiColombo." It will orbit Mercury with two probes: one to map the planet and the other to study its magnetosphere. It was launched on October 20, 2018. "BepiColombo" is expected to reach Mercury in 2025. It will release the probe that will study the magnetosphere into an elliptical orbit. It will then release the probe the will make a map of Mercury into a circular orbit.
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System.
Mars is a terrestrial planet with caps of water and carbon dioxide. It has the largest volcano in the Solar System, and some very large impact craters.
Mars is named after the mythological Roman god of war because it appears of red color. Anything that has to do with Mars is called "Martian".
Space probes, such as the Viking program landers, are the main tools for the exploration of Mars.
Mars is a terrestrial planet and made of rocks. The ground there is red because of iron oxide (rust) in the rocks and dust. The planet's atmosphere is very thin. It is mostly carbon dioxide with some argon and nitrogen and tiny amounts of other gases including oxygen. The temperatures on Mars are colder than on Earth, because it is farther away from the Sun and has less air to keep heat in. There is water ice and frozen carbon dioxide at the north and south poles. Mars does not have any liquid water on the surface now, but signs of run-off on the surface were probably caused by water.
The average thickness of the planet's crust is about 50 km (31 mi), with a maximum thickness of 125 km (78 mi).
Its orbit is more eccentric than the Earth's (meaning less like a circle). Probably that is one reason why the Earth's climate varies so much. In other words, its orbit affects the climate of the Earth. That is just a theory at present.
Mars has a very thin atmosphere with barely any oxygen (it is mostly carbon dioxide). Because there is an atmosphere, however thin it is, the sky changes colour when the sun rises and sets. The dust in the Martian atmosphere makes Martian sunsets somewhat blue. Mars's atmosphere is too thin to protect Mars from meteors, which is part of the reason why Mars has so many craters.
After the formation of the planets, they all experienced the "Late Heavy Bombardment". About 60% of the surface of Mars shows a record of impacts from that era. Much of the remaining surface is probably lying over the immense impact basins caused by those events. There is evidence of an enormous impact basin in the northern hemisphere of Mars, spanning , or roughly four times larger than the largest impact basin previously known. This suggests that Mars was struck by a Pluto-sized body about four billion years ago. The event is thought to be the cause of the difference between the Martian hemispheres. It made the smooth Borealis Basin that covers 40% of the planet.
Some meteorites hit Mars with so much force a few pieces of Mars went flying into space even to Earth. Rocks on Earth are sometimes found which have chemicals that are exactly like the ones in Martian rocks. These rocks also look like they fell really quickly through the atmosphere, so it is reasonable to think they came from Mars.
Spacecraft "Insight" detected seismic waves made by the biggest meteorite impacts ever seen on Mars.
Mars is home to the highest known mountain in the Solar System, Olympus Mons. Olympus Mons is about 17 miles (or 27 kilometers) high. This is more than three times the height of Earth's tallest mountain, Mount Everest. It is also home to Valles Marineris, the third largest rift system (canyon) in the Solar System, 4,000 km long.
Detailed observations of the location of Mars were made by Babylonian astronomers who developed methods using math to predict the future position of the planet. The ancient Greek philosophers and astronomers developed a model of the solar system with the Earth at the center ('geocentric'), instead of the sun. They used this model to explain the planet's motions. Vedic and Islamic astronomers estimated the size of Mars and its distance from Earth. Similar work was done by Chinese astronomers.
During the 1877 opposition, Italian astronomer Giovanni Schiaparelli in Milan used a telescope to help produce the first detailed map of Mars. What caught people's attention was that the maps had features he called "canali". These were later shown to be an optical illusion (not real). These "canali" were supposedly long straight lines on the surface of Mars to which he gave names of famous rivers on Earth. His term "canali" was popularly mistranslated in English as "canals", and thought to be made by intelligent beings.
Because Mars is the one of the closest planets to Earth in the Solar System, many have wondered if there is any kind of life on Mars. Today we know that this life, if any, would be simple organisms, alike to bacteria.
Studies at NASA's Johnson Space Center show that at least three of the meteorites contain possible evidence of past life on Mars, in the form of microscopic structures resembling fossilized bacteria (so-called biomorphs). Although the scientific evidence collected is reliable, and the rocks are correctly described, what made the rocks look like they do is not clear. To date, scientists are still trying to agree if it really is evidence of simple life on Mars.
For people to agree on past life in a geologic sample, most or all of these things must be met. This has not happened yet, but investigations are still in progress. Reexaminations of the biomorphs found in the three Martian meteorites are underway.
Some famous stories were written about the idea of life on Mars. The writers used the name "Martians" for intelligent beings from Mars. In 1898, H. G. Wells wrote "The War of the Worlds", a famous novel about Martians attacking the Earth. In 1938, Orson Welles broadcast a radio version of this story in the United States, and many people thought it was really happening and were very afraid. Beginning in 1912, Edgar Rice Burroughs wrote several novels about adventures on Mars.
The Apple Macintosh or just Mac is a line of personal computers made by the American company Apple Inc. The Macintosh was one of the first computers in which the people could use a mouse for pointing on a screen which had icons. This new way of working with a computer (interface) was known as graphical user interface. It was this feature of the Macintosh that made it so popular.
Macintoshes were different than other personal computers for many years based on their central processor unit (CPU). At the start, Macs used Motorola 68000 chips instead of Intel chips. Later, Macs used PowerPC chips. In 2006, Macs started to use Intel chips. In 2020, Macs started to use Apple Silicon chips. Today, Macs are sold with Apple M1 chips.
In the imperial system of measurement, one yard is 0.9144 metres (after international agreement in 1959), so a metre is very near to 39.37 inches: about 3.281 feet, or 1.0936 yards.
Bonds can also be broken apart. Since most bonds require energy to form, they also give off energy when they are broken. But before most bonds break, the molecule has to be heated. Then the atoms start to move, and when they move too much, the bond breaks. Molecules that require less energy to break than they give off when broken are called fuels. For example, a candle will just sit there and nothing happens. But when you use a match to light it, it will burn for a long time. The match brings the energy to break the first bonds, which release enough energy to break the bonds below them, until the candle has burned down. There are also ionic bonds.
In the 1980s, the Saudi Arabian government began to pay for the building of mosques in countries around the world. An estimated US$45 billion has been spent by the Saudi Arabian government for mosques and Islamic schools in foreign countries. "Ain al-Yaqeen", a Saudi newspaper, reported in 2002 that Saudi money may have helped to build as many as 1,500 mosques and 2,000 other Islamic centers. Saudi citizens have also given a lot of money to mosques in the Islamic world, especially in countries where they see Muslims as poor and oppressed. Following the fall of the Soviet Union, in 1992, mosques in Afghanistan received money from Saudi citizens. The King Fahd Mosque in Culver City, California and the Islamic Cultural Center of Italy in Rome are two of Saudi Arabia's largest investments in foreign mosques as former Saudi king Fahd bin Abdul Aziz al-Saud gave US$8 million and US$50 million to the two mosques, respectively.
It is common for a smaller mosque to serve as a hostel for Muslims on "haj" (pilgrimage to Mecca). Sometimes mosques are used for refugees, or as temporary homes for homeless people. Obligations to neighbours in Islam are very strict, and specific. In the Qur'an Mohammed said that a person who helps others in the hour of need, and who helps the oppressed; that person God will help on the Day of Travail (agony). There are other commands, such as helping the poor and being nice to people. An important part of being Muslim, or just being part of the mosque, is taking care of people who need help. A mosque is a social, as well as a religious, group.
Mammals are animals which form the class Mammalia (from Latin , 'breast'). They are a group of vertebrate animals. They have fur or hair and a very precise kind of temperature regulation.
With the exception of the monotremes, all mammals bear live young. Unlike other vertebrates, they are the only animals that produce milk for their young through their mammary glands. Parental care of the young is universal among mammals, sometimes for extended periods.
Mammals became the dominant land animals after non-bird dinosaurs were eliminated. Recent work helped to explain their success: epigenetics seems to have started in early mammals.
Humans and primates, are quite different. They have a menstrual cycle. In this case, females are sexually receptive at any time, but only fertile when an ovum is released from an ovary. In this case, the endometrium (if not needed for an fertilised egg) is discarded. The endometrium is shed, and takes with it a certain amount of blood. In this system, eggs are released from the ovaries mostly in the middle of the cycle, away from the menstrual period. This ovulation is 'concealed', meaning, it is not obvious when it occurs. This process, so it is thought, tends to keep the male and female together, which is unusual in mammals with the oestrous cycle. Keeping males and females together is related to the long learning period of primates.
One diagnostic feature of mammals is the lower jaw. Unlike earlier forms, it is a single bone, the dentary. This is one feature which can be seen in fossils, or at least those which are complete enough to have the lower jaw. Another diagnostic feature is the ear ossicles. Mammals have three little bones in their inner ear. These ear ossicles are bones which were, long ago, part of the lower jaw in early proto-mammals.
There are about 50 characters which are typical of mammals: some of the most important are discussed above. A few more examples will make it clear that mammals are very different from reptiles and birds:
By number of species, mammals (with 5488 species), are not the most successful vertebrates. Birds, with about 10,000 species have nearly twice as many, and reptiles have just as many as birds. Fish have even more species. There are 27,000 species of fish, of which nearly 26,000 are bony fish.
Last, but certainly not least, are the primates. Their natural habitat, with few exceptions, are the forests. Most live in the trees, with hands that grasp, good colour vision, and intelligence. In the Pliocene period some moved out onto the savannas as grassland replaced forests. Mankind is the result of this shift into the savannas.
Because two quite different dates are given in the taxobox, an explanation is needed. Rowe defines mammals as "the taxon originating with the most recent common ancestor of extant (living) Monotremata and Theria". That puts the emphasis heavily on living mammals, where, as Rowe points out, the database of characters is extensive.
There are different ways of giving symbols to numbers. These methods are called number systems. The most common number system that people use is the "base ten" number system. The "base ten" number system is also called the decimal number system. The base ten number system is common because people have ten fingers and ten toes. There are 10 different symbols (0, 1, 2, 3, 4, 5, 6, 7, 8, and 9) used in the base ten number system. These ten symbols are called digits.