title: Metaphor

paragraphs: Metaphor is a term for a figure of speech. It does not use a word in its basic literal sense. Instead, it uses a word in a kind of comparison. We run, and we also say rivers run. We may run into trouble, especially if we run up a bill at the bar.

paragraphs: So a metaphor uses words to make a picture in our mind. It takes a word from its original context, and uses it in another.

paragraphs: Metaphors are an essential part of language: it is not possible to speak or write without them. A simple example is the word "run". This has a basic meaning of "moving quickly" or "go with quick steps on alternate feet, never having both feet on the ground at the same time". The "Concise Oxford Dictionary" then gives

paragraphs: 34 other uses as a verb; 21 uses as a noun; about 50 uses in short phrases. All of these are metaphors, although we do not usually notice this.

paragraphs: We use metaphors to make "indirect" comparisons, but without using 'like' or 'as' – because that would be a simile. A simile is a "direct" comparison: "Jane is like a child".

paragraphs: A metaphor very often uses the verb 'to be': "love "is" war", for example, not "love "is like" war" (that is a simile).

paragraphs: Poetry includes much metaphor, usually more than prose.

paragraphs: Spam is an example that any email user knows about – this word was originally a metaphor, from 'Spam', a type of canned meat. Servers putting unwanted email into somebody's inbox was similar to waiters putting unwanted Spam into food. This was originally suggested by a Monty Python scene. When we use a metaphor very often and we forget the old meaning, or forget that the two meanings are connected, this is a 'dead metaphor'.

paragraphs: Originally "metaphor" was a Greek word for 'transfer'. It came from "meta" ('beyond') and "pherein" ('carry'). So the word "metaphor" in English was a metaphor, too. Today in Greek, "metaphor" is a trolley (a thing that is pushed for carrying shopping or bags).

paragraphs: A simple metaphor has a single link between the subject and the metaphoric vehicle. The vehicle thus has a single meaning which is transferred directly to the subject.

paragraphs: In the simple metaphor, the effort to understand what the author or speaker intends is relatively low, and hence it may easily be used with a wider and less sophisticated audience.

paragraphs: A complex metaphor happens where a simple metaphor is based on a secondary metaphoric element. For example, using a metaphor of 'light' for 'understanding' may be complexified by saying 'throwing light' rather than 'shining light'. 'Throwing' is an extra metaphor for how light arrives.

paragraphs: A compound metaphor is one where there are multiple parts in the metaphor that are used to snag the listener. These parts may be enhancement words such as adverbs, adjectives, etc.

paragraphs: Each part in the compound metaphor may be used to signify an additional item of meaning.

paragraphs: Compound metaphors are like a multiple punch, hitting the listener repeatedly with metaphoric elements. Where the complex metaphor uses stacked layers to enhance the metaphor, the compound metaphor uses sequential words. The compound metaphor is also known as a loose metaphor.

paragraphs: A live metaphor is one which a reader notices. A dead metaphor is one no-one notices because it has become so common in the language.

paragraphs: Two people walk off a tennis court. Someone asks the loser: "What happened?".


title: Metabolism

paragraphs: Reactions catalyzed by enzymes allow organisms to grow, reproduce, maintain their structures, and respond to their environments. The word ‘metabolism’ can also refer to digestion and the transport of substances into and between different cells.

paragraphs: Metabolism is usually divided into two categories. Catabolism breaks down organic matter and harvests energy by way of cellular respiration. Anabolism uses energy to construct molecules such as proteins and nucleic acids.

paragraphs: The chemical reactions of metabolism are organized into metabolic pathways, or cycles, like the Krebs cycle. One chemical is transformed through a series of steps into another chemical by a series of enzymes.

paragraphs: 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, the metabolic rate, influences how much food an organism will need, and how it is able to get that food.

paragraphs: A striking feature of metabolism is the similarity of the basic metabolic pathways and components between even vastly different species. For example, the set of carboxylic acids that are best known as the intermediates in the citric acid cycle are present in all known organisms, being found in species as diverse as the unicellular bacterium "Escherichia coli" and huge multicellular organisms like elephants. These striking similarities in metabolic pathways are likely due to their early appearance in the evolution of life, and kept because of their efficiency.


title: Microscope

paragraphs: A microscope is a scientific instrument. It makes small objects look larger. This lets people see the small things. People who use microscopes frequently in their jobs include doctors and scientists. Students in science classes such as biology also use microscopes to study small things.

paragraphs: The earliest microscopes had only one lens and are called "simple microscopes". "Compound microscopes" have at least two lenses. In a compound microscope, the lens closer to the eye is called the "eyepiece". The lens at the other end is called the "objective". The lenses multiply up, so a 10x eyepiece and a 40x objective together give 400x magnification.

paragraphs: Microscopes make things seem larger than they are, to about 1000 times larger. This is much stronger than a magnifying glass which works as a simple microscope.

paragraphs: There are many types of microscopes. The most common kind of microscope is the compound light microscope. In a compound light microscope, the object is illuminated: light is thrown on it. The user looks at the image formed by the object. Light passes through two lenses and makes the image bigger.

paragraphs: The second most common kind are a few kinds of electron microscopes. Transmission electron microscopes (TEMs) fire cathode rays into the object being looked at. This carries information about how the object looks into a magnetic "lens". The image is then magnified onto a television screen. Scanning electron microscopes also fire electrons at the object, but in a single beam. These lose their power when they strike the object, and the loss of power results in something else being generated—usually an X-ray. This is sensed and magnified onto a screen. Scanning tunneling microscopes were invented in 1984.

paragraphs: A fluorescence microscope is a special kind of light microscope. In 2014, the Nobel Prize in Chemistry was awarded to Eric Betzig, William Moerner, and Stefan Hell for "the development of super-resolved fluorescence microscopy". The citation says it brings "optical microscopy into the nanodimension".


title: Mass

paragraphs: The mass of an object is a measure of the amount of matter in a body. A mountain has typically more mass than a rock, for instance. Mass should not be confused with the related but quite different concept of weight. A large mass like the Earth will attract a small mass like a human being with enough force to keep the human being from floating away. "Mass attraction" is another word for gravity, a force that exists between all matter.

paragraphs: The unit of mass in the International System of Units is the kilogram, which is represented by the symbol 'kg'. Fractions and multiples of this basic unit include the gram (one thousandth of a kg, symbol 'g') and the tonne (one thousand kg), amongst many others.

paragraphs: In some fields or applications, it is convenient to use different units to simplify the discussions or writings. For instance,

paragraphs: Traditional units are still in encountered in some countries: imperial units such as the 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), not to be confused with the metric tonne (1,000 kg).

paragraphs: Mass is an intrinsic property of the object: it does not depend on its volume, or position in space, for instance. For a long time (at least since the works of Antoine Lavoisier in the second half of the eighteen century), it has been known that the sum of the masses of objects that interact or of the chemicals that react remain conserved throughout these processes. This remains an excellent approximation for everyday life and even most laboratory work.

paragraphs: However, Einstein has shown through his special theory of relativity that the mass "m" of an object moving at speed "v" with respect to an observer must be higher than the mass of the same object observed at rest "m" with respect to the observer. The applicable formula is

paragraphs: where "c" stands for the speed of light. This change in mass is only important when the speed of the object with respect to the observer becomes a large fraction of "c".


title: Mercury (planet)

paragraphs: 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. Mercury is bright when it is visible from Earth, ranging from −2.0 to 5.5 in apparent magnitude. It cannot be easily seen as it is usually too close to the Sun. Because Mercury is normally lost in the glare of the Sun, Mercury can only be seen in the morning or evening twilight or during a solar eclipse.

paragraphs: Less is known about Mercury than about other planets of our Solar System. Telescopes on the Earth show only a small, bright crescent, and putting a satellite in orbit around it is difficult. The first of two spacecraft to visit the planet was Mariner 10, which mapped only about 45% of the planet’s surface from 1974 to 1975. The second is the MESSENGER spacecraft, which finished mapping the planet in March 2013.

paragraphs: Mercury looks like Earth's Moon. It has many craters and areas of smooth plains, no moons around it and no atmosphere as we know it. However, Mercury does have an extremely thin atmosphere, known as an exosphere. Unlike Earth's Moon, Mercury has a large iron core, which gives off a magnetic field about 1% as strong as that of the Earth. It is a very dense planet due to the large size of its core. Surface temperatures can be anywhere from about 90 to (−183 °C to 427 °C, −297 °F to 801 °F), with the subsolar point being the hottest and the bottoms of craters near the poles being the coldest.

paragraphs: 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: one able to be seen only at sunrise, which they called Apollo; the other that was only able to be seen at sunset, which they called Hermes. The English name for the planet is from the Romans, who named it after the Roman god Mercury, which they thought to be the same as the Greek god Hermes. The symbol for Mercury is based on Hermes' staff.

paragraphs: Even though Mercury is the closest planet to the Sun, it is not the warmest. This is because it has no greenhouse effect, so any heat that the Sun gives to it quickly escapes into space. The hottest planet is Venus.

paragraphs: Mercury is one of four inner planets in the Solar System, and has a rocky body like the Earth. It is the smallest planet in the Solar System, with a radius of . Mercury is even smaller than some of the largest moons in the solar system, such as Ganymede and Titan. However, it has a greater mass than the largest moons in the solar system. Mercury is made of about 70% metallic and 30% silicate material. Mercury's density is the second highest in the Solar System at 5.427 g/cm³, only a little bit less than Earth’s.

paragraphs: Mercury's surface looks similar to the surface of the Moon. It has plains that look like mares and has lots of craters. Mercury have been hit by a lot of comets and asteroids 4.6 billion years ago. Mercury have also been hit during a period called the Late Heavy Bombardment. Mercury has lots of craters because it does not have any atmosphere to slow objects down. Images gotten by "MESSENGER" have shown that Mercury may have shield volcanoes.

paragraphs: The surface temperature of Mercury ranges from 100 to 700 K (−173 to 427 °C; −280 to 800 °F) at the most extreme places. Even though the temperature at the surface of Mercury in the day is very high, observations suggest that there is frozen water on Mercury.

paragraphs: Mercury is too small and hot for its gravity to keep any thick atmosphere for long a long time. It does have a thin exosphere that contains hydrogen, helium, oxygen, sodium, calcium, potassium. This exosphere is lost 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.

paragraphs: Mercury has the most eccentric orbit of all the planets; its eccentricity is 0.21. Its distance from the Sun ranges from 46,000,000 to 70,000,000 km (29,000,000 to 43,000,000 mi). It takes 87.969 Earth days to go around the Sun. Mercury's axial tilt is 0.027 degrees which is best measurement of the axial tilt.

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

paragraphs: The first spacecraft to visit Mercury was NASA's Mariner 10. It stayed in Mercury's orbit from 1974–1975. Mariner 10 provided the first close-up pictures of Mercury's surface. It showed many types of geological features, such as the craters. Unfortunately, the same face of the planet was day at each time Mariner 10 flew close to Mercury. This made close observation of both sides of the planet impossible. In the end, less than 45% of the planet's surface was mapped.

paragraphs: The Mariner 10 came close to Mercury three times. At the first time, instruments found a magnetic field, which surprised planetary geologists because Mercury's rotation was too slow to generate a magnetic field. The second time was mainly used to take pictures of Mercury's surface. At the third time, more information about the magnetic field were obtained. It showed that the planet's magnetic field is much like Earth's.

paragraphs: On March 24, 1975, just eight days after its final close approach, Mariner 10 ran out of fuel. Because its orbit could no longer be controlled, mission controllers instructed the probe to shut down. Mariner 10 is thought to still be orbiting the Sun.

paragraphs: The second satellite to reach 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. Most of the hemisphere not mapped by "Mariner 10" was mapped during these fly-bys. The satellite entered an elliptical orbit around the planet on March 18, 2011. The first image of Mercury orbiting the Sun was gotten on March 29, 2011.

paragraphs: MESSENGER was made to study Mercury's high density, the history of Mercury's geology, its magnetic field, the structure of its core, whether it has ice at its poles, and where its thin atmosphere comes from. "MESSENGER" crashed into Mercury's surface on April 30, 2015.

paragraphs: The European Space Agency and the Japanese Space Agency developed and launched a joint mission 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.


title: Mars

paragraphs: Mars is the fourth planet from the Sun in the Solar System and the second smallest planet. Mars is a cold terrestrial planet with polar ice caps of frozen 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.

paragraphs: Space probes such as the Viking program landers are the main tools for the exploration of Mars.

paragraphs: Mars is a terrestrial planet and made of rock. 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.

paragraphs: The average thickness of the planet's crust is about 50 km (31 mi), with a maximum thickness of 125 km (78 mi).

paragraphs: Mars has two small moons, called Phobos and Deimos.

paragraphs: The origin of Mars' moons is unknown and controversial. One theory is that the moons are captured asteroids. However, the moons' near circular orbits and low inclination relative to the Martian equator are not in agreement with the capture hypothesis.

paragraphs: Estimates of the mass ejected by a large Borealis-size impact vary. Simulations suggest that a body about 0.02 of Mars mass (~0.002 Earth mass) in size can produce a sizable debris disk in Martian orbit. Much of the material would stay close to Mars. There are several other large impact basins on Mars that could also have ejected enough debris to form the moons.

paragraphs: Mars does not have a global magnetic field. Despite this, observations show that parts of the planet's crust have been magnetized. This suggests that polarity reversals have occurred in the past. This paleomagnetism is similar to the magnetic striping found on Earth's ocean floors. One theory is that these bands suggest plate tectonic activity on Mars four billion years ago, before the planetary dynamo stopped working and the planet's magnetic field faded.

paragraphs: A Martian day is called a "sol", and is a little longer than an Earth day. Mars rotates in 24 hours and 37 minutes. It rotates on a tilted axis, just like the Earth does, so it has four different seasons. Of all the planets in the Solar System, the seasons of Mars are the most Earth-like, due to their similar axial tilt. The lengths of the Martian seasons are almost twice those of Earth's, as Mars's greater distance from the Sun leads to the Martian year being almost two Earth years long.

paragraphs: Martian surface temperatures vary from lows of about (at the winter polar caps) to highs of up to (in equatorial summer). The wide range in temperatures is due mostly to the thin atmosphere which cannot store much solar heat. The planet is also 1.52 times as far from the Sun as Earth, resulting in just 43% of the amount of sunlight.

paragraphs: A 2015 report says Martian dark streaks on the surface were affected by water.

paragraphs: Liquid water cannot exist on the surface of Mars due to its low atmospheric pressure (there's not enough air to hold it in), except at the lowest elevations for short periods. The two polar ice caps appear to be made largely of frozen water. The amount of ice in the south polar ice cap, if melted, would be enough to cover the entire planet's surface 11 meters deep. A permafrost mantle stretches from the pole to latitudes of about 60°.

paragraphs: Geological evidence gathered by unmanned missions suggest that Mars once had much liquid water on its surface. In 2005, radar data revealed the presence of large quantities of water ice at the poles, and at mid-latitudes. The Mars rover "Spirit" sampled chemical compounds containing water molecules in March 2007. The "Phoenix" lander found water ice in shallow Martian soil in July 2008.

paragraphs: Landforms seen on Mars strongly suggest that liquid water at some time existed on the planet's surface. Huge areas of ground have been scraped and eroded.

paragraphs: Mars has two permanent polar ice caps. During a pole's winter, it lies in continuous darkness, chilling the surface and causing the deposition of 25–30% of the atmosphere into slabs of CO ice (dry ice). When the poles are again exposed to sunlight, the frozen CO sublimes (turns to vapor), creating enormous winds that sweep off the poles as fast as 400 km/h. Each season this moves large amounts of dust and water vapor, giving rise to Earth-like frost and large cirrus clouds and dust storms. Clouds of water-ice were photographed by the "Opportunity" rover in 2004.

paragraphs: The polar caps at both poles consist primarily of water ice.

paragraphs: 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 does change 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.

paragraphs: After the formation of the planets, 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 yet discovered. This theory 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.

paragraphs: 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.

paragraphs: Mars is home to the highest known mountain in the Solar System, Olympus Mons. Olympus Mons is about 17 miles (or 27 kilometres) 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.

paragraphs: Our records of watching and recording Mars start with ancient Egyptian astronomers in the 2nd millennium BC.

paragraphs: 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. Indian and Islamic astronomers estimated the size of Mars and its distance from Earth. Similar work was done by Chinese astronomers.

paragraphs: In the 16th century, Nicholas Copernicus proposed a model for the Solar System in which the planets follow circular orbits about the Sun. This 'heliocentric' model was the beginning of modern astronomy. It was revised by Johannes Kepler, who gave an elliptical orbit for Mars which better fit the data from our observations.

paragraphs: The first observations of Mars by telescope was by Galileo Galilei in 1610. Within a century, astronomers discovered distinct albedo features (changes in brightness) on the planet, including the dark patch and polar ice caps. They were able to find the planet's day (rotation period) and axial tilt.

paragraphs: Better telescopes developed early in the 19th century allowed permanent Martian albedo features to be mapped in detail. The first crude map of Mars was published in 1840, followed by better maps from 1877 onward. Astronomers mistakenly thought they had detected the spectroscopic mark of water in the Martian atmosphere, and the idea of life on Mars became popular among the public.

paragraphs: Yellow clouds on Mars have been observed since the 1870s, which were windblown sand or dust. During the 1920s, the range of Martian surface temperature was measured; it ranged from 85 to 7 C. The planetary atmosphere was found to be arid with only traces of oxygen and water. In 1947, Gerard Kuiper showed that the thin Martian atmosphere contained extensive carbon dioxide; roughly double the quantity found in Earth's atmosphere. The first standard naming of Mars surface features was set in 1960 by the International Astronomical Union.

paragraphs: Since the 1960s, multiple robotic spacecraft and rovers have been sent to explore Mars from orbit and the surface. The planet has remained under observation by ground and space-based instruments across a broad range of the electromagnetic spectrum (visible light, infrared and others). The discovery of meteorites on Earth that came from Mars has allowed laboratory examination of the chemical conditions on the planet.

paragraphs: During the 1877 opposition, Italian astronomer Giovanni Schiaparelli 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.

paragraphs: Other astronomers thought they could see the canals too, especially the American astronomer Percival Lowell who drew maps of an artificial network of canals on Mars.

paragraphs: Although these results were widely accepted, they were contested. Greek astronomer Eugène M. Antoniadi and English naturalist Alfred Russel Wallace were against the idea; Wallace was extremely outspoken. As bigger and better telescopes were used, fewer long, straight "canali" were observed. During an observation in 1909 by Flammarion with a telescope, irregular patterns were observed, but no "canali" were seen.

paragraphs: 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 the kind of life, if any, would be some simple bacteria-type organism.

paragraphs: NASA maintains a catalog of 34 Mars meteorites, that is, meteorites which originally came from Mars. These assets are highly valuable since they are the only physical samples available of Mars.

paragraphs: Studies at NASA's Johnson Space Centre 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.

paragraphs: Over the past few decades, scientists have agreed that when using meteorites from other planets found on Earth (or rocks brought back to Earth), various things are needed to be sure of life. Those things include:

paragraphs: 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. Re-examinations of the biomorphs found in the three Martian meteorites are underway.

paragraphs: Liquid water is necessary for life and metabolism, so if water was present on Mars, the chances of life evolving is improved. The Viking orbiters found evidence of possible river valleys in many areas, erosion and, in the southern hemisphere, branched streams. Since then, rovers and orbiters have also looked closely and eventually proved water was on the surface at one time, and is still found as ice in the polar ice caps and underground.

paragraphs: So far, scientists have not found life on Mars, either living or extinct. Several space probes have gone to Mars to study it. Some have orbited (gone around) the planet, and some have landed on it. There are pictures of the surface of Mars that were sent back to Earth by the probes. Some people are interested in sending astronauts to visit Mars. They could do a better search, but getting astronauts there would be difficult and expensive. The astronauts would be in space for many years, and it could be very dangerous because of radiation from the sun. So far we have only sent unmanned probes.

paragraphs: The most recent probe to the planet is the Mars Science Laboratory. It landed on Aeolis Palus in Gale Crater on Mars on 6 August 2012. It brought with it a mobile explorer called 'Curiosity'. It is the most advanced space probe ever. Curiosity has dug up Martian soil and studied it in its laboratory. It has found sulfur, chlorine, and water molecules.

paragraphs: Some famous stories were written about this idea. 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.


title: Mac OS

paragraphs: "For the Apple computer family, see macOS"

paragraphs: The Macintosh Operating System (Mac OS) is a program that allows a Macintosh computer to operate and be used. Mac OS was first made by Apple Inc. in 1984. In those days Mac OS was called Macintosh System Software – which was shortened to System or SSW (System Software). The term "Mac OS" first appeared in the splash screen for System 7.5.1, but was not adopted as the new name until the release of Mac OS 7.6.

paragraphs: The latest version of Mac OS is Mac OS 10.15 Catalina.


title: Apple Macintosh

paragraphs: 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.

paragraphs: The Apple–Intel transition was when Apple changed the CPU of Macintosh computers from PowerPC processors to Intel x86 processors. It was announced at the 2005 World Wide Developers Conference. Steve Jobs announced it.

paragraphs: 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. Today, Macs are sold with Intel quad-core i7 chips.

paragraphs: The Mac does not have the Windows operating system installed on it. It has its own range of operating systems, known as macOS. The newest operating system is known as “Catalina". Macs can run both Windows and macOS at the same time with help of a program called “Boot Camp”, which comes on every Mac.

paragraphs: In general, Macintosh computers cost more than other computers of the same speed.


title: Metre

paragraphs: A metre (US spelling, "meter") is the basic unit of length in the SI measurement system. The symbol for the metre is m. The first meaning (in the French Revolution) was one ten-millionth of the distance between the Earth's equator and the North Pole along the Paris meridian. The metre is now defined as the distance light travels in a vacuum in 1/299,792,458 of a second.

paragraphs: In the imperial system of measurement, one yard is 0.9144 metres (after international agreement in 1959), so a metre is very close to 39.37 inches: about 3.281 feet, or 1.0936 yards.

paragraphs: "*Note: units in bold are the most commonly used."


title: Magnifying glass

paragraphs: A magnifying glass is a lens through which can be used to make things appear bigger, so you can see them better. It is used in many applications and manual operations, e.g., for examining postage stamps in philately.

paragraphs: The magnifying glass consists of a piece of convex-shaped glass or plastic. It has to be held at the right distance between the eye and the object for the object to be in focus. The magnifying glass usually comes with a handle. A telescope is a more advanced kind of magnifying glass and consists of at least two glass lenses.

paragraphs: A pair of binoculars is like a telescope for each eye. "Spectacles" or eyeglasses also use lenses to correct a person's vision.


title: Molecule

paragraphs: A molecule is the smallest amount of a chemical substance that can exist. If a molecule were split into smaller pieces, it would be a different substance.

paragraphs: Molecules are made up of atoms that are stuck together in a particular shape or form. Not all combinations of atoms are equally possible; atoms make certain shapes in preference to others. Also, they have different valency. For example, oxygen atoms always have two bonds with other atoms, carbon atoms always have four bonds with other atoms, and nitrogen atoms always have three bonds with other atoms.

paragraphs: In the kinetic theory of gases, the term "molecule" is often used for any gaseous particle regardless of its composition. According to this definition, noble gas atoms are considered molecules as they are in fact monoatomic molecules.

paragraphs: In gases like air, the molecules are just flying around. In liquids like water, the molecules are stuck together but they can still move. In solids like sugar, the molecules can only vibrate. In the fourth state of matter known as plasma, the atoms are ionized and cannot form molecules.

paragraphs: With a molecular formula, you can write down the numbers of all atoms in a molecule. For example, the molecular formula of glucose is CHO. That means that one molecule of glucose is made up of six carbon atoms, twelve hydrogen atoms and six oxygen atoms.

paragraphs: For a molecule to exist, atoms have to stick together. This happens when two atoms share electrons. Instead of circling just one atom, the electron now circles around two. This is called a covalent bond. Sometimes, more than one electron is shared. The more electrons are shared, the stronger the bond gets and the stronger the atoms stick together.

paragraphs: 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.


title: Moral reasoning

paragraphs: Moral reasoning is a topic studied in psychology and in moral philosophy. It studies how people think about moral issues, problems, and questions. Psychologists who have studied it include Lawrence Kohlberg and Elliot Turiel. Kohlberg said that moral understanding develops in three main stages as a person gets older, but Turiel said that there are three domains of moral understanding that develop at the same time as a person gets older.

paragraphs: Moral philosophy, or ethics, is a major branch of philosophy. It is the study of value or quality. It covers the analysis and use of concepts such as right, wrong, good, evil, and responsibility.


title: Mosque

paragraphs: A mosque is a place where Peoples worship. The word "mosque" comes from the Arabic word "masjid". A larger, 'collective', mosque is called a "masjid jāmi". Larger mosques offer more services to their community.

paragraphs: For many Muslim people, a mosque is more than a place of worship. Muslims worship, study and discuss Islam, and do many other things in a mosque and its compounds. In the United Kingdom, many mosques are used as community centres. They are also used to teach about Islam. Religious festivals and gatherings are held in mosques. Weddings are one example. Mosques have rules to control what people do inside. One of these is that it is disrespectful to disturb another person who is worshipping.

paragraphs: Many mosques are known for their Islamic architecture. The earliest mosques, opened in 7th century were open-air spaces. They are the "Quba Mosque" and "Masjid al-Nabawi". Later Mosques were buildings that were specially designed. Nowadays, mosques are in every continent, except Antarctica.

paragraphs: Many mosques are famous works of architecture. They are often built in a style that has stayed the same for many centuries. Many mosques have prayer halls, domes, and minarets. They may also have a courtyard. Mosques are often built with patterned walls.

paragraphs: Mosques were first built on the Arabian Peninsula. The Muslims who built them used old architectural styles. They also combined these styles in new ways. A major influence was the palaces built during the Parthian and Sassanid dynasties of Persia. The "Sarvestan palace" from the Sassanid era is a good example of this. It has an arched entrance and a central dome. These features already existed in Persia before Islam.

paragraphs: After the Arab invasion of Persia, the new style, with its Sassanid influence, was used for the new Islamic world. Many forms of mosques have developed in different regions of the Islamic world. Important mosque types include the early Abbasid mosques, T-type mosques, and the central-dome mosques of Anatolia. In the 20th century, many countries that grew rich from oil paid for the building of many new mosques. The rulers of these countries often hired leading architects to design these mosques. They included non-Muslims.

paragraphs: Many early mosques have a square or rectangular plan. They also have a prayer hall and an enclosed courtyard. This is known as "Arab-plan". The first mosques of this type were built during the Umayyad Dynasty.

paragraphs: The flat roof of the prayer hall was supported by columns. Many rows of columns were needed to support such roofs; this is called "hypostyle architecture". One of the most famous hypostyle mosques is the Mezquita de Córdoba in Spain. It is supported by over 850 columns.

paragraphs: In the warm Mediterranean and Middle Eastern climates, the courtyard served to hold the large number of worshippers during Friday prayers. Often, hypostyle mosques have outer arcades. They allow the visitors to enjoy the shade. Arab-plan mosques were built mostly during the Umayyad and Abbasid dynasties. The Arab plan was very simple, which did not allow for much further development. This caused that style of mosque to fall out of favour.

paragraphs: The Ottomans began building "central dome mosques" in the fifteenth century. These mosques have a large dome centered over the prayer hall. There may also be smaller domes, which are off-center over the prayer hall or the rest of the mosque. This style was heavily influenced by the Byzantine religious architecture with its use of central domes.

paragraphs: "Iwan mosques" are famous for their domed rooms and "iwans". Iwans are spaces with an arched roof. They have an opening at one end. One or more iwans face a central courtyard that serves as the prayer hall. The style borrows from pre-Islamic Iranian architecture. Most mosques with this style are in Iran.

paragraphs: Most mosques have minarets. Minarets are tall towers. Usually they are at one of the corners of the mosque. The top of the minaret is the highest point in the mosque, and usually the highest point in the area around the mosque. The tallest minaret in the world is in the Hassan II Mosque in Casablanca, Morocco.

paragraphs: The first mosques had no minarets. The most conservative Islamic groups, like "Wahhabis", still avoid building minarets. They see them as simply a fancy decoration and unnecessary. The first minaret was built in 665 in Basra during the reign of the Umayyad caliph Muawiyah I. Muawiyah encouraged the building of minarets, as they were supposed to be the same as bell towers on Christian churches. Because of this, mosque architects used the shape of the bell tower for their minarets. Both the minaret and the bell tower serve the same purpose — to call the faithful to prayer.

paragraphs: Before the five required daily prayers, a "muezzin" calls the worshippers to prayer from the minaret. In many countries like Singapore where Muslims are not the majority, mosques are stopped from loudly playing the call to prayer. The main problem is the use of electronic amplification of the call, which is now widely used by mosques.

paragraphs: The domes were often placed directly above the main prayer hall. They represent the universe that Allah created. At first, these domes were small. They only took up a small part of the roof near the "mihrab". Later, they took the whole roof above the prayer hall.

paragraphs: Domes normally have the shape of a hemisphere. The Mughals in India popularized onion-shaped domes in South Asia and Persia. Some mosques have several domes, as well as the main large dome. The other domes are often smaller.

paragraphs: Domes would help the "imam" be heard, as the sound waves would bounce in and then out of the dome making the voice louder.

paragraphs: All mosques have a prayer hall, which is also called "musalla". Normally, there is no furniture in it except for prayer mats or rugs. These are necessary, as Islamic prayer is usually done kneeling.

paragraphs: Some mosques have Arabic calligraphy and "Qur'anic" verses on the walls to help worshipers focus on the beauty of Islam and its holiest book, the "Qur'an", as well as for decoration.

paragraphs: The "qiblah wall" is usually at the other side of the entrance to the prayer hall. This wall is specially decorated. In a properly sited mosque, it will be set perpendicular to a line leading to Mecca. People pray in rows parallel to the "qiblah" wall. They arrange themselves so they face Mecca. In the "qiblah" wall, usually at its center, is the "mihrab", a niche or depression showing the direction of Mecca. The "mihrab" serves as the place where the imam leads the five daily prayers.

paragraphs: All people must wash themselves before they pray. Mosques often have fountains or other facilities for washing in their entrances or courtyards, so that people can perform the washing ritual before prayer.

paragraphs: At very small mosques, worshippers may use restrooms for their ritual washing, or wu'du. In traditional mosques, there is often a building specially for washing. This is often in the center of the courtyard. In the prayer halls, people must not wear shoes for much the same reason.

paragraphs: Modern mosques should appeal to the community they serve. For this reason, other facilities may also be available at the mosque, like health clinics, libraries, and sports halls.

paragraphs: There may be decorative tiles, plaster or coloured mosaics on the walls. There are no pictures or statues.

paragraphs: Adult Muslims are expected to pray five times a day. Most mosques have formal prayers for each of these times. If performing the prayer is difficult, for example for ill people, then exceptions are made.

paragraphs: Mosques also hold a special prayer service, called "jumuah". This is done once a week. It is a form of Sabbath and replaces the Friday prayers at the mosque. Daily prayers can be done anywhere. However, Muslims are expected to do their Friday prayer at the mosque.

paragraphs: When a Muslim dies, a funeral prayer is normally held. It is held outdoors in a courtyard or square close to the mosque. The prayers have all the worshippers present, including the imam, taking part. During eclipses, mosques will host special prayers called eclipse prayers.

paragraphs: There are two large holidays ("Eids") in the Islamic calendar. During these days, there are special prayers at mosques in the morning. Larger mosques will normally hold them for their own communities as well as the people from smaller local mosques. Mosques, especially those in countries where Muslims are the majority, will also host "Eid" prayers outside in courtyards or town squares.

paragraphs: There are many events in "Ramadan", Islam's holiest month. During "Ramadan", Muslims must fast during the day. Mosques organise "iftar" dinners after sunset. These are done after the fourth required prayer of the day. Part of the food is given by members of the community, which creates nightly potluck dinners. The community contribution to these dinners is required. For this reason, mosques with smaller communities may not be able to hold the "iftar" dinners daily.

paragraphs: Some mosques will also hold meals in the morning before dawn. Mosques will often invite poorer members of the community to these meals. Islam sees giving charity during Ramadan as good acts.

paragraphs: Larger mosques sometimes offer special, optional prayers. They are done after the last required prayer of the day. During each night of prayers, one member of the community who has memorized the entire Qur’an will recite a part of the book. It can last for up to two hours. Sometimes, several such people (not necessarily of the local community) take turns to do this. During the last ten days of Ramadan, larger mosques will host all-night programs to observe "Laylat al-Qadr". It is the night Muslims believe that the Islamic prophet Muhammad first received Qur'anic revelations. On that night, between sunset and sunrise, mosques employ speakers to teach the worshipers about Islam. Mosques or the community usually provide meals at times through the night.

paragraphs: During the late twentieth century, more and more mosques have been used for political purposes. Modern-day mosques in the Western world want to educate good citizens. The details differ greatly from mosque to mosque and from country to country.

paragraphs: Countries with small Muslim populations use mosques as a way to support civic participation. They are more likely to do this than Muslim-majority countries of the Greater Middle East. American mosques host voter registration and civic participation drives. In the United States, Muslims are often immigrants, or the children of immigrants. Mosques want to interest these people for politics. They also want to keep them informed about issues that concern the Muslim community. People who attend the services at the mosque regularly are more likely to take part in protests, to sign petitions, and to involve themselves in political matters.

paragraphs: A link between political views and mosque attendance can still be seen in other parts of the world. After the al-Askari Mosque bombing in February 2006, imams and other Islamic leaders used mosques and Friday prayers to call for calm and peace during the widespread violence.

paragraphs: Beginning in the late twentieth century and continuing into the early twenty-first century, a small number of mosques have also become a base for extremist imams to support terrorism and extreme Islamic ideals. Finsbury Park Mosque in London is a mosque that has been used in this manner.

paragraphs: Like other places of worship, mosques can be at the center of social conflicts.

paragraphs: Babri Mosque was the centre of such a conflict up until the early 1990s when it was demolished. Before a solution could be found, the mosque was destroyed by about 200,000 Hindus. It took place on 6 December 1992. The mosque was built by Babur to mark the birthplace of Ram. It was believed to be on a site of an earlier Hindu temple. The conflict over the mosque was directly linked to rioting in Bombay (present-day Mumbai) as well as bombings in 1993 that killed 257 people.

paragraphs: In February 2006, a bombing seriously damaged Iraq's al-Askari Mosque. This increased the existing tensions. The conflict between two Muslim groups in Iraq had already led to other bombings. However mosque bombings are not limited to Iraq. In June 2005, a suicide bomber killed at least 19 people at an Afghan mosque. In April 2006, there were two explosions at India's Jama Masjid.

paragraphs: After the September 11 attacks, several American mosques were targets of attacks. These ranged from simple vandalism to arson.

paragraphs: The Jewish Defense League was suspected of plotting to bomb the King Fahd Mosque in Culver City, California. There were similar attacks in the United Kingdom after the 7 July 2005 London bombings. Outside the Western world, in June 2001, the Hassan Bek Mosque was the target of attacks. The attacks involved hundreds of Israelis angry at Arabs for a previous attack.

paragraphs: Saudi involvement in building mosques around the world only goes back to the 1960s.

paragraphs: 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.

paragraphs: In a mosque, people should keep focused on worshiping "Allah". For this reason, there are a number of rules about the correct behaviour in a mosque. Some of these rules are the same all over the world, such as no shoes should be worn in the prayer hall. Other rules are different from mosque to mosque.

paragraphs: It is generally seen as good to have someone who leads the prayers, though this is not strictly necessary. The person who usually leads the prayers is called "imam". He must be a free and honest man. He should also be an authority when it comes to answering questions on religion. In mosques that were built or that are kept up by the government, the imam is selected by the ruler. In private mosques, the community selects the imam, through majority voting.

paragraphs: Only men may lead prayers for men. Women are allowed to lead prayers for congregations where there are only women.

paragraphs: In addition to washing, there are other rules that also apply to those who enter the mosque, even if they do not wish to pray there. It is forbidden to wear shoes in the carpeted area of the prayer hall. Some mosques also do not allow wearing shoes in other parts, even though these may not be devoted to praying.

paragraphs: Islam requires that its believers wear clothes that show modesty. As a result, both men and women must follow this rule when they attend a mosque (though mosques may not always enforce the rules). Men are supposed to come to the mosque wearing loose and clean clothes that do not show the shape of the body. Similarly, women who come to the mosque are expected to wear loose clothing, shirts, pants that cover to the wrists and ankles and cover their heads such as with a hijab. Many Muslims, regardless of their ethnic background, wear Middle eastern clothing associated with Arabic Islam to special occasions and prayers at mosques.

paragraphs: Mosques are places of worship. For this reason, those inside the mosque should be respectful to those who are praying. Loud talking or discussion of topics that could be disrespectful, is forbidden in areas where people are praying. It is also considered as rude to walk in front of Muslims in prayer or otherwise disturb them.

paragraphs: Islamic law requires men and women to be separated in the prayer hall. Ideally, women should pray behind men. The second caliph Umar at one time stopped women from attending mosques, especially at night, because he feared they may be teased by males, so he made them to pray at home. Sometimes a special part of the mosque was railed off for women; for example, the governor of Mecca in 870 had ropes tied between the columns to make a separate place for women.

paragraphs: Many mosques today will put the women behind a barrier or partition or in another room. Mosques in South and Southeast Asia put men and women in separate rooms, as the divisions were built into them centuries ago. In nearly two-thirds of American mosques, women pray behind partitions or in separate areas, not in the main prayer hall; some mosques do not admit women at all. Although there are sections only for women and children, the Grand Mosque in Mecca is desegregated.

paragraphs: A few scholars of Islamic law believe that non-Muslims may be allowed into mosques, as long as they do not sleep or eat there. Followers of the "Maliki" school of Islamic jurisprudence disagree. They say that non-Muslims may not be allowed into mosques at all.

paragraphs: Different countries have different opinions on the question. Nearly all the mosques in the Arabian Peninsula as well as Morocco do not allow non-Muslims. The Hassan II Mosque in Casablanca is one of only two mosques in Morocco currently open to non-Muslims.

paragraphs: In modern-day Saudi Arabia, the Grand Mosque and all of Mecca are open only to Muslims. Likewise, the Masjid al-Nabawi and the city of Medina that surrounds it are also off-limits to those who do not practice Islam. For mosques in other areas, it has most commonly been taken that non-Muslims may only enter mosques if granted permission to do so by Muslims and if they have a proper reason.

paragraphs: In modern Turkey non-Muslim tourists are allowed to enter any mosque, but must obey the rules of decorum. Visiting a mosque is allowed only between prayers; visitors must wear long trousers and take off their shoes; women must cover their heads; no photos; no loud talk is allowed. No references to other religions are allowed (no crosses on necklaces, no cross gestures etc.).

paragraphs: However, there are also many other places in the west as well as the Islamic world where non-Muslims are welcome to enter mosques. Most mosques in the United States, for example, report receiving non-Muslim visitors every month. Many Mosques throughout the United States welcome non-Muslims as a sign of openness to the rest of the community and to encourage conversions to Islam.

paragraphs: Dogs are usually banned from entering mosques, but on 24 September 2008, the Muslim Law Council UK made special ruling, called a "fatwa", which granted a blind Muslim permission to take his guide dog into the mosque.

paragraphs: 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(pbuh) 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.

paragraphs: A madrassa is a little different from a mosque. A madrassa focuses on teaching Islam, usually to children and young people.

paragraphs: When Spain was under Muslim control, some of the most beautiful buildings were mosques. After 1491, Spain was under Christian control. However, the Christians did not tear down the mosques. They simply put a crucifix in them to make them into churches. These mosques influenced the Renaissance architecture (way of building) in Europe.


title: Mammal

paragraphs: Mammals are a group of vertebrate animals which form the class Mammalia. They have fur or hair and a very precise kind of temperature regulation.

paragraphs: With the exception of the monotremes, all mammals bear live young. Unlike other vertebrates, they are the only animals that produce milk for the young through their mammary glands. Parental care of the young is universal among mammals, and it is essential because live birth limits the number of offspring.

paragraphs: Most marsupial and eutherian mammals have a reproductive cycle known as the oestrous cycle (U.S: estrous cycle). Females are sexually active only during the oestrous stage, when they are 'on heat' for a few days each month. If an ovum is not fertilized, the endometrium (uterus lining) is resorbed. Oestrus cycles may occur once or twice a year, or many times a year. Each group of mammals has its own frequency.

paragraphs: 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.

paragraphs: One diagnostic feature is the lower jaw which, unlike earlier forms, is composed of 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. Mammals have three little bones in their inner ear, the ear ossicles. The ear ossicles are bones which were, long ago, part of the lower jaw in early proto-mammals.

paragraphs: There are quite a number of other features, particularly in the skull and limbs, so that it is usually possible identify and describe a mammal from its skeleton alone.

paragraphs: Another diagnostic feature is the neocortex of the brain, which no other vertebrate has. This is involved in the kind of flexible behavior and learning typical of mammals. Reptiles and birds have much of their behavior controlled by "inherited behavior chains", which roughly translates as "instincts". Almost all animals can do some learning, but mammals do far more than other vertebrates. Their behavior is much more flexible than lizards, for example, and that is made possible by their neocortex.

paragraphs: Other things in the life of mammals seem to be connected with this flexibility and learning. Play is a kind of early learning period in which, according to one theory, mammals develop skills which they will need in life. All mammalian young play, and this is very obvious in the more intelligent mammals (primates, cats).

paragraphs: The emotions of mammals are very noticeable, and rather similar to ours. It is possible, and quite common, for humans to have a friendly relationship with another mammal. It is quite impossible for a human to have any kind of relationship with a snake or a gecko (for example). This is because the reptile simply does not have the same basic emotions as a human.

paragraphs: There are about 50 characters which are typical of mammals, and 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:

paragraphs: In the language of cladistics, these 50 unique characters are apomorphies which prove that mammals are a clade descended from a common ancestor.

paragraphs: Almost all mammal species give birth to live young. There are only two mammals that lay eggs, called monotremes, the duck-billed platypus "Ornithorhynchus", and the spiny anteater "Echidna", with four species. All are confined to Australia and New Guinea, and are the sole survivors of an earlier group of mammals. However, like other mammals, they feed milk to their young, and protect and look after them.

paragraphs: Other mammals are divided into the marsupials and the Eutheria, the placental mammals. Marsupials are mammals with pouches to carry young in, like the kangaroo.

paragraphs: In terms of 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.

paragraphs: Despite this, many zoologists do regard mammals as a successful group of animals. One reason is that they are successful in all habitats on Earth. In the air, in the water, in forests, in the colder regions of the world, and above all on grasslands, where they are outstandingly successful.

paragraphs: In the air, the bats (Chiroptera) are the mammalian order with the most species. They 'own' the nighttime, since birds are largely diurnal (daytime) animals. Bats are hugely successful, mostly as nighttime predators of insects.

paragraphs: Seagoing mammals, the Cetacea and the pinnipeds, are very successful and significant predators. This includes the whales, seals, walrus, dolphins and others.

paragraphs: The terrestrial mammals are fewer in number of species than lizards, but they are huge in individual numbers, and far more important in the life of the terrestrial biomes. Their ability to move from place to place and adapt has made them a most effective group. Many mammals live in cold places. These mammals have thick hair or blubber to keep them warm. Others may live in rainforests. On land the rodents (rats, mice) are hugely successful, more common in numbers than any other mammals. Large mammals on land have been hunted to extinction in some parts of the world, but the ones which remain are now better protected.

paragraphs: 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 savannahs as grassland replaced forests. Mankind is the result of this shift into the savannahs.

paragraphs: The evolutionary relationships among land vertebrates is as follows:

paragraphs: This sort of classification is not traditional, but it does reflect our knowledge of palaeontology and evolution.

paragraphs: A somewhat standardized classification system has been adopted by most current mammalogy classroom textbooks. It is based on living animals. The following taxonomy of extant and recently extinct mammals is from Vaughan et al. 2000.

paragraphs: Mammals can be divided in a number of orders:

paragraphs: 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.

paragraphs: Kemp explains the problem with that approach: "If the definition of a mammal is based rigorously upon possession of all the characters of living mammals, then some fossil forms that are extremely mammalian in anatomy... are excluded".

paragraphs: "An altogether different perspective on defining Mammalia is based on traditional palaeobiological practice. An arbitrary decision is made about which characters to select as defining characters... Characters deemed appropriate are those reflecting the... fundamental mammalian biology. The essence of mammalian life is to be found in their endothermic temperature physiology, greatly enlarged brain, dentition capable of chewing food, highly agile, energetic locomotion, and so on. The organisms that achieved this grade of overall organisation are deemed to be Mammalia... Around the end of the Triassic period, about 205 mya, a number of fossils are found of very small animals that have [most] of the skeletal characters of modern mammals".

paragraphs: This difference in outlook explains the difference in the two dates given in the taxobox.


title: Number

paragraphs: A number is a concept from mathematics, used to count or measure. Depending on the field of mathematics, where numbers are used, there are different definitions:

paragraphs: Numbers are also used for other things like counting. Numbers are used when things are measured. Numbers are used to study how the world works. Mathematics is a way to use numbers to learn about the world and make things. The study of the rules of the natural world is called science. The work that uses numbers to make things is called engineering.

paragraphs: 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.

paragraphs: A symbol for a number is made up of these ten digits. The position of the digits shows how big the number is. For example, the number 23 in the decimal number system really means (2 times 10) plus 3. Similarly, 101 means 1 times a hundred (=100) plus 0 times 10 (=0) plus 1 times 1 (=1).

paragraphs: Another number system is more common for machines. The machine number system is called the "binary" number system. The binary number system is also called the base two number system. There are two different symbols (0 and 1) used in the base two number system. These two symbols are called bits.

paragraphs: A symbol for a binary number is made up of these two bit symbols. The position of the bit symbols shows how big the number is. For example, the number 10 in the binary number system really means 1 times 2 plus 0, and 101 means 1 times four (=4) plus 0 times two (=0) plus 1 times 1 (=1). The binary number 10 is the same as the decimal number 2. The binary number 101 is the same as the decimal number 5.

paragraphs: English has special names for some of the numbers in the decimal number system that are "powers of ten". All of these power of ten numbers in the decimal number system use just the symbol "1" and the symbol "0". For example, ten tens is the same as ten times ten, or one hundred. In symbols, this is "10 × 10 = 100". Also, ten hundreds is the same as ten times one hundred, or one thousand. In symbols, this is "10 × 100 = 10 × 10 × 10 = 1000". Some other powers of ten also have special names:

paragraphs: When dealing with larger numbers than this, there are two different ways of naming the numbers in English. Under the "long scale", a new name is given every time the number is a million times larger than the last named number. It is also called the "British Standard". This scale used to be common in Britain, but is not often used in English-speaking countries today. It is still used in some other European nations.

paragraphs: Another scale is the "short scale", under which a new name is given every time a number is a thousand times larger than the last named number. This scale is a lot more common in most English-speaking nations today.

paragraphs: A salamander is not a number; it is an amphibian.

paragraphs: Natural numbers are the numbers which we normally use for counting: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc. Some people say that 0 is a natural number, too. The set of all natural numbers is written as formula_1.

paragraphs: Another name for these numbers is positive numbers. These numbers are sometimes written as +1 to show that they are different from the negative numbers. But not all positive numbers are natural (for example, formula_2 is positive, but not natural).

paragraphs: If 0 is called a natural number, then the natural numbers are the same as the whole numbers. If 0 is not called a natural number, then the natural numbers are the same as the counting numbers. So if the words "natural numbers" are not used, then there will be less confusion about whether zero is included or not. But unfortunately, some say that zero is not a whole number, while others say that whole numbers can be negative. "Positive integers" and "non-negative integers" are another way to include zero or exclude zero, but only if people know those words.

paragraphs: Negative numbers are numbers less than zero.

paragraphs: One way to think of negative numbers is to use a "number line". We call one point on this line zero. Then we will label (write the name of) every position on the line by how far to the right of the zero point is. For example, the point one is one centimeter to the right, and the point two is two centimeters to the right.

paragraphs: However, the point one centimeter to the left of the zero point cannot be point one, since there is already a point called one. We therefore call this point minus one (−1, as it is one centimeter away but in the opposite direction).

paragraphs: All the normal operations of mathematics can be done with negative numbers:

paragraphs: Since finding the square root of a negative number is impossible for real numbers (as negative times negative equals positive for real numbers), the square root of -1 is given a special name: "i". This is also called the imaginary unit.

paragraphs: Integers are all the natural numbers, all their opposites, and the number zero. Decimal numbers and fractions are not integers.

paragraphs: Rational numbers are numbers which can be written as fractions. This means that they can be written as "a" divided by "b", where the numbers "a" and "b" are integers, and "b" is not zero.

paragraphs: Some rational numbers, such as 1/10, need a finite number of digits after the decimal point to write them in decimal form. The number one tenth is written in decimal form as 0.1. Numbers written with a finite decimal form are rational. Some rational numbers, such as 1/11, need an infinite number of digits after the decimal point to write them in decimal form. There is a repeating pattern to the digits following the decimal point. The number one eleventh is written in decimal form as 0.0909090909 ... .

paragraphs: A percentage could be called a rational number, because a percentage like 7% can be written as the fraction 7/100. It can also be written as the decimal 0.07. Sometimes, a ratio is considered as a rational number.

paragraphs: Irrational numbers are numbers which cannot be written as a fraction, but do not have imaginary parts (explained later).

paragraphs: Irrational numbers often occur in geometry. For example, if we have a square which has sides of 1 meter, the distance between opposite corners is the square root of two, which equals 1.414213 ... . This is an irrational number. Mathematicians have proved that the square root of every natural number is either an integer or an irrational number.

paragraphs: One well-known irrational number is pi. This is the circumference (distance around) of a circle divided by its diameter (distance across). This number is the same for every circle. The number pi is approximately 3.1415926535 ... .

paragraphs: An irrational number cannot be fully written down in decimal form. It would have an infinite number of digits after the decimal point, and unlike 0.333333 ..., these digits would not repeat forever.

paragraphs: Real numbers is a name for all the sets of numbers listed above:

paragraphs: The real numbers form the real line. This is all the numbers that do not involve imaginary numbers.

paragraphs: Imaginary numbers are formed by real numbers multiplied by the number i. This number is the square root of minus one (−1).

paragraphs: There is no number in the real numbers which when squared, makes the number −1. Therefore, mathematicians invented a number. They called this number i, or the imaginary unit.

paragraphs: Imaginary numbers operate under the same rules as real numbers:

paragraphs: Imaginary numbers were called "imaginary" because when they were first found, many mathematicians did not think they existed. The person who "discovered" imaginary numbers was Gerolamo Cardano in the 1500s. The first to use the words "imaginary number" was René Descartes. The first people to use these numbers were Leonard Euler and Carl Friedrich Gauss. Both lived in the 18th century.

paragraphs: Complex numbers are numbers which have two parts; a "real" part and an "imaginary" part. Every type of number written above is also a complex number.

paragraphs: Complex numbers are a more general form of numbers. The complex numbers can be drawn on a number plane. This is composed of a real number line, and an imaginary number line.

paragraphs: All of normal mathematics can be done with complex numbers:

paragraphs: To multiply two complex numbers is more complicated. It is easiest to describe in general terms, with two complex numbers a + bi and c + di.

paragraphs: A real or complex number is called a "transcendental number" if it can not be obtained as a result of an algebraic equation with integer coefficients.

paragraphs: Proving that a certain number is transcendental can be extremely difficult. Each transcendental number is also an irrational number. The first people to see that there were transcendental numbers were Gottfried Wilhelm Leibniz and Leonhard Euler. The first to actually prove there were transcendental numbers was Joseph Liouville. He did this in 1844.

paragraphs: Some well-known transcendental numbers include:


title: November

paragraphs: November (Nov.) is the eleventh and penultimate (second-last) month of the year in the Gregorian calendar, coming between October and December. It has 30 days. Its name is from the Latin word "novem", which meant "nine". It was the ninth month of the year before January and February were added to the Roman Calendar.

paragraphs: November always begins on the same day of the week as March, and additionally, February in common years. November always ends on the same day of the week as August.

paragraphs: November is the eleventh month of the year in the Gregorian calendar, after October and before December, which is the last month. November has 30 days. It was the ninth month in the old Roman calendar, which is where its name comes from. It kept its name when January and February were added to the beginning of the year, despite becoming the eleventh month. The ninth month is now September.

paragraphs: November begins on the same day of the week as February in common years and March every year, as each other's first days are exactly 39 weeks (273 days) and 35 weeks (245 days) apart respectively. November ends on the same day of the week as August every year, as each other's last days are exactly 13 weeks (91 days) apart.

paragraphs: In common years, November starts on the same day of the week as June of the previous year, and in leap years, September and December of the previous year. In common years, November finishes on the same day of the week as March and June of the previous year, and in leap years, September of the previous year.

paragraphs: In years immediately before common years, November starts on the same day of the week as August of the following year, and in years immediately before leap years, May of the following year. In years immediately before common years, November finishes on the same day of the week as May of the following year, and in years immediately before leap years, February and October of the following year.

paragraphs: In the Northern Hemisphere, November is an Autumn (Fall) month, and the further north in the hemisphere, the more likely it is to get colder as December approaches. In the Southern Hemisphere it is a Spring month. In each hemisphere, it is the seasonal equivalent of May in the other.

paragraphs: Several observances around the beginning of the month are believed to be related, linked to the old Celtic celebration of Samhain on November 1. These events include Halloween (October 31), Day of the Dead in Mexico (October 31 to November 2), All Saints Day (November 1) and All Souls Day (November 2).

paragraphs: In several mainly Christian countries, it is month in which people who died in war are commonly remembered, mainly related to the end of World War I on November 11, 1918. Near the end of the month Advent, the period leading up to Christmas, begins.


title: National anthem

paragraphs: A national anthem is a country's official national song that the people of a country use to remember and respect their country.

paragraphs: Some countries, like Spain, have a national anthem which has no lyrics (words of a song)


title: Name

paragraphs: A name is a word (or a set of words) given to things and people.

paragraphs: For example, "cat" is the name of a kind of animal. "Ryan" is a name of a person, usually a male. "Julia" is a common female name.

paragraphs: The word 'name' can also be used as a verb. To name something is to give it a name.

paragraphs: In many cultures, there are rules and customs about how to give a person a name.

paragraphs: Some of the rules are defined by laws, and others are defined by traditions (doing things in the way they have been done for a long time).

paragraphs: There are rules about different aspects of the names and naming, including the following:

paragraphs: In some cultures, a person has a one-part name, such as "ShiningWater."

paragraphs: In other cultures, a person has a two-part name, such as "John Smith."

paragraphs: In some cultures, a person can have any number of name parts. In the United States, for example, some people have three: first name, middle name, and last name. Other people have only two: a first and last name.

paragraphs: In Chinese cultures, it is typical for a person to have three-part name, such as "Cheah Ching San," where "Cheah" is the surname. Written in English format a comma is introduced making it "Ching San, Cheah."

paragraphs: 2. Relations with names of parents and other relatives

paragraphs: In some cultures, people have the same "family name" (or surname) as their parents. For example, the father of John Smith may be Mike Smith. And Mike Smith's father may be James Smith. The "Smith" part is the same for all the family.

paragraphs: In other cultures, a person has the same name as his or her father, but the name is in a different place. For example, Shafiq Hanif's son may be Hanif Kamal. Hanif is in both the father's and son's name.

paragraphs: In some cultures, a name changes when people marry, divorce, go through some religious ceremony, etc. For example, in some Spanish-speaking countries, people use two last names: their mother's father's name and their father's name. If Elena Rodriguez Gomez and Jose Sanchez Soria marry, she may change her name to Elena Rodriguez de Sanchez, and their child could be named Pilar Sanchez Rodriguez, taking the names of both of her grandfathers.

paragraphs: In some cultures, personal names come from history. In most European countries, some first names are taken from the Bible. In some cultures, names are taken from a relative. In other cultures, a name shows what the parents hope their child will be like. A baby may be given a name Wisdom because parents hope the baby will be a wise girl or boy.

paragraphs: Some cultures avoid giving people a name of an animal. For example, there is no name like dog, cat, snake, owl, or fish in Japanese people's first names. But in some cultures animal names may be good.

paragraphs: 5. Lengths, pronunciations, spelling, etc.

paragraphs: In some languages and cultures, you can tell if a word is a person's name or not by just looking at the spelling or listening to its pronunciation. There are some other linguistic patterns. For example, many Chinese names are made up of three syllables.

paragraphs: 6. Use of names, titles, nicknames, etc.

paragraphs: In some cultures, people use names when they call each other. In other cultures, people use their nicknames. In some other cultures, people use their titles ("father," "professor," etc.) when they call each other.

paragraphs: 7. Spelling of names, titles, nicknames, etc.

paragraphs: Taking note of names is taken a step farther by those who elect to celebrate a name (e.g., "Celebrate Your Name Week") whether their own name, someone else's name, or names in general, complete ownership of one's name might very well include celebrating it.

paragraphs: While some people might choose to "hide" a middle name for any number of reasons (i.e., they consider the middle name they were given to be an "embarrassment"), others have taken to celebrating their middle name (e.g., "Middle Name Pride Day").

paragraphs: In the English language, names exclusively are usually pronounced in correlation with the spelling, however can be pronounced as desired, e.g. John is (jon) but can also be (ned). However, not probable, is held true in the English rules of grammar.

paragraphs: Names can be shortened e.g. Isabelle can become Izzy or Belle.

paragraphs: Here are some things that are often found in Japanese names today. In the past, people went by different rules.

paragraphs: Japanese names have two parts. One is the family name and the other is the given name.

paragraphs: "Suzuki Ichiro" is a name of a Japanese person. Suzuki is the family name, and Ichiro is the first name. In the Japanese language, the family name comes first, and the given name comes second. (It is like writing Smith John, instead of John Smith.)

paragraphs: Only some members of the royal family do not have a family name.

paragraphs: A newborn baby gets a family name from their parents. The parents have the same family name. So, a son of Ono Yoko (female) and Ono Ken (male) is Ono something.

paragraphs: The family name Ono is mostly shared by the paternal (male) part of the family. So Ono Ken's parents have the family name Ono, but Ono Yoko's parents probably do not.

paragraphs: Names of people change when they marry and divorce. It is a custom in many parts of the world that women change their family name to that of their new husband when they marry. However, in Europe and North America especially, many women no longer do this even though their mothers and grandmothers may have. Sometimes, the man will take the woman's family name.


title: Niihau

paragraphs: Niihau (or Niʻihau) is the smallest of the inhabited islands of Hawaii, in the United States. It has a land area of 70 sq. miles (184 km). It is the oldest of the eight main islands.

paragraphs: The whole island is owned by the Robinson family. They bought it from the Kingdom of Hawaii for $10,000. It was said that the buyer, Elizabeth Sinclair (later Sinclair-Robinson), liked the island better than other places such as Waikiki, Pearl Harbor, and the island of Lanai. There is a small US Navy base where a handful of Navy people work.

paragraphs: The island has a few hundred permanent inhabitants. Almost all of them are native Hawaiians. They support themselves largely with small family farms. Many work for the ranch owned by the Robinsons. The native Hawaiians lead a rural, low-tech life. They speak the Hawaiian language and keep traditions alive. This is because Ms. Sinclair promised to help preserve Hawaiian culture and tradition when she bought the island. Niihau is the only one of the Hawaiian islands where the Hawaiian language is the main language.

paragraphs: Niihau is also known as the "Forbidden Island". This is due to the fact that until recently, the island was off-limits to all but family members, US Navy personnel, government officials and expressly invited guests. Now, tourists can go on one of a limited number of supervised tours or hunting safaris.

paragraphs: On the beaches of the island are found shells which are the only shells to be classified as gems. Niihau shells and the jewelry made from them are very popular. Many, especially those with darker and richer color, are collectors items. The sale of shells and shell jewelry brings extra money for the local people.


title: Nēnē

paragraphs: The Nēnē, or Hawaiian goose ("Branta sandvicensis") is a species of goose. It is found today on only three Hawaiian islands. It gets its name from its soft call.

paragraphs: This is an unmistakable species, with its generally brown plumage (feathers) and darker head. Its strong toes have much reduced webbing (skin between the toes), an adjustment to the lava flows on which it breeds. The Nēnē goes about on land much more than other water birds. When moulting (dropping old feathers and growing new ones), the Nēnē cannot fly, as do other geese, a factor which made it vulnerable to hunting.

paragraphs: The Nēnē was once among the most threatened waterfowl species around the world. Once common, hunting and predators brought to the islands such as mongooses, pigs and cats reduced the population to only 30 birds in the 1950s. However, this species breeds well in captivity (zoos and bird parks), and has been successfully re-introduced. There are also good numbers in wild bird collections.


title: Network

paragraphs: A communication network is a group of things that are connected or linked together. They may be used for talking or other communication to transfer information, data, signal and things as in a transport network. The pattern by which things are connected is called a network topology. A television network, for example, connects television stations. Computer networks are numerous.


title: Fishing net

paragraphs: A fishing net is a woven trap usually used to catch fish. They are usually made out of rope. A net is a kind of tool.


title: Internet slang

paragraphs: Internet slang is slang words which are used on the internet. Most of these words are new, such as Wiki and blog, which were not used before the internet became popular.

paragraphs: Some old words were given new meanings, such as mail (which now means email). This makes many metaphors on the Internet, such as boot (which otherwise mean a shoe) and link (which otherwise means a joint in a metal chain). Some existing acronyms, such as "AFK" (To mean "Away from keyboard") and "IRL" (To mean "In real life") were used on bulletin board systems before the internet became popular. These are now used on the internet, such as in chat rooms and on instant messenger software.

paragraphs: People have also created some verbs and adjectives to describe things that only happen on the internet:

paragraphs: Shorthand is where a word is written in a shorter way because it is quicker and easier to type. It is also done to fit more text into a limited space.

paragraphs: Internet slang uses many acronyms because they are quicker and easier to type. They are often shorthand for common phrases and idioms, but they can show somebody's emotions and their certainty.

paragraphs: Leet speak (written as: L33T or 1337) is the most common language on MMORPGs because rude words are not stopped by filters. This language is changing all the time because new words are made and used. A lot of the words use numbers instead of letters but some were made because of typing errors which are now done on purpose. Also, some suffixes are used, such as "-age" and "-ness".

paragraphs: Some of the numbers and symbols used instead of letters are in the table below.


title: Nauru

paragraphs: Nauru, ( ) officially the Republic of Nauru, is a sovereign island nation located in the Micronesian South Pacific. Its nearest neighbour is Banaba Island in the Republic of Kiribati, due east. Nauru is the world's smallest island nation, covering just , the smallest independent republic, and the only republican state in the world without an official capital. With 10,670 residents, it is the third least-populated country after Vatican City and Tuvalu.

paragraphs: Nauru is a phosphate rock island, and its primary economic activity since 1907 has been the export of phosphate mined from the island. English and Nauruan are the official languages of Nauru. The current president of Nauru is Lionel Aingimea.

paragraphs: Nauru is a oval-shaped island in the southwestern Pacific Ocean, south of the Equator. The island is surrounded by a coral reef, which is exposed at low tide and dotted with pinnacles. The presence of the reef has prevented the establishment of a seaport, although channels in the reef allow small boats access to the island. A fertile coastal strip wide lies inland from the beach.

paragraphs: Coral cliffs surround Nauru's central plateau. The highest point of the plateau, called the Command Ridge, is above sea level. The only fertile areas on Nauru are on the narrow coastal belt, where coconut palms flourish. The land surrounding Buada Lagoon supports bananas, pineapples, vegetables, pandanus trees, and indigenous hardwoods such as the tomano tree.

paragraphs: Nauru was one of three great phosphate rock islands in the Pacific Ocean (the others were Banaba (Ocean Island) in Kiribati and Makatea in French Polynesia). The phosphate reserves on Nauru are now almost entirely depleted. Phosphate mining in the central plateau has left a barren terrain of jagged limestone pinnacles up to high. Mining has stripped and devastated about 80 per cent of Nauru's land area, and has also affected the surrounding Exclusive Economic Zone; 40 per cent of marine life is estimated to have been killed by silt and phosphate runoff.

paragraphs: There are only about 60 recorded vascular plant species native to the island, none of which are endemic. Coconut farming, mining, and introduced species have caused serious disturbance to the native vegetation. There are no native land mammals, but there are native insects, land crabs, and birds, including the endemic Nauru Reed Warbler. The Polynesian rat, cats, dogs, pigs, and chickens have been introduced to Nauru from ships.

paragraphs: There are limited natural fresh water resources on Nauru. Rooftop storage tanks collect rainwater, but the islanders are mostly dependent on three desalination plants housed at Nauru's Utilities Agency. Nauru's climate is hot and very humid year-round because of its proximity to the equator and the ocean. Nauru is hit by monsoon rains between November and February, but does not typically experience cyclones. Annual rainfall is highly variable and is influenced by the El Niño-Southern Oscillation, with several significant recorded droughts. The temperature on Nauru ranges between and during the day and between and at night.

paragraphs: As an island, Nauru is vulnerable to climate and sea level change. Nauru is the seventh most global warming threatened nation due to flooding. At least 80 per cent of the land of Nauru is well elevated, but this area will be uninhabitable until the phosphate mining rehabilitation programme is implemented.

paragraphs: Nauru is divided into fourteen administrative districts which are grouped into eight electoral constituencies.


title: Noun

paragraphs: A noun is a kind of word (see part of speech) that is usually the name of something such as a person, place, thing, animal, or idea. In English, nouns can be singular or plural.

paragraphs: Nouns often need a word called an article or (like "the" or "that"). These words usually do not go with other kinds of words like verbs or adverbs. (For example, people do not also describe nouns). In English, there are more nouns than any other kind of word.

paragraphs: Every language in the world has nouns, but they are not always used in the same ways. They also can have different properties in different languages. In some other languages, nouns do not change for singular and plural, and sometimes there is no word for "the".

paragraphs: Examples of nouns: "time, people, way, year, government, day, world, life, work, part, number, house, system, company, end, party, information".

paragraphs: The word noun comes from the Latin "nomen" meaning "name." Words like nouns were described in early days by the Sanskrit grammarian and ancient Greeks like Dionysios Thrax.

paragraphs: In English sentences, nouns can be used as a subject, object, or complement. They often come after prepositions, as the 'object of preposition'.

paragraphs: Nouns can sometimes describe other nouns (such as a soccer ball). When they do this, they are called modifiers or adjuncts.

paragraphs: There are also verb forms that can be used in the same way as nouns (such as 'I like "running".') These are called "verbals" or "verbal nouns", and include "participles" (which can also be adjectives) and "infinitives".

paragraphs: Nouns are classified into common and proper. Pronouns have commonly been considered a different part of speech from nouns, but in the past some grammars have included them as nouns as do many modern linguists.

paragraphs: Proper nouns (also called proper name) are specific names. Examples of proper nouns are: "London, John, God, October, Mozart, Saturday, Coke, Mr. Brown, Atlantic Ocean." Proper nouns are individual things with names, not general nouns.

paragraphs: Proper nouns begin with an (capital) letter in English and many other languages that use the Roman alphabet. (However, in German, all nouns begin with an upper case letter.) The word "I" is really a pronoun, although it is capitalized in English, like a proper noun.

paragraphs: Some common nouns (see below) can also be used as proper nouns. For example, someone might be named 'Tiger Smith' -- even though he is not a tiger or a smith.

paragraphs: Common nouns are general names that are unspecific. Sometimes the same word can be either a common noun or a proper noun, depending on how it is used; for example:

paragraphs: In English and many other languages, nouns have 'number'. But some nouns are only singular (such as "furniture, physics") and others are only plural (such as "clothes, police"). Also, some nouns are countable (for example, "one piece, two pieces") but others are uncountable (for example, we do not say "one furniture, two furnitures").

paragraphs: The plural form of most nouns is created simply by adding the letter(s) -(e)s.

paragraphs: Despite plural forms being written using the letter(s) -(e)s, the pronunciation of the letter(s) will pronounced as /-s/, /-z/, or /-ız/ depending on which type of phoneme, or unique sound, comes before it. These variations of the plural morpheme are called allomorphs.

paragraphs: Note that some dictionaries list "busses" as an acceptable plural for "bus". Presumably, this is because the plural "buses" looks like it ought to rhyme with the plural of "fuse," which is "fuses." "Buses" is still listed as the preferable plural form. "Busses" is the plural, of course, for "buss," a seldom used word for "kiss."

paragraphs: There are several nouns that have irregular plural forms. Plurals formed in this way are sometimes called mutated (or mutating) plurals.

paragraphs: Many of the above irregular plural forms stem from Old English, which had more complex rules for making plural forms.

paragraphs: And, finally, there are nouns that maintain their Latin or Greek form in the plural. (See media and data and alumni, below.)

paragraphs: Nouns are words for things, and since things can be possessed, nouns can also change to show possession in grammar. In English, we usually add an apostrophe and an "s" to nouns to make them "possessive", or sometimes just an apostrophe when there is already an "s" at the end, like this:

paragraphs: Most adjectives become nouns by adding the suffix -ness. Example: Take the adjective 'natural', add 'ness' to get 'naturalness', a noun. To see a list of 100 adjectives used in Basic English, click here.

paragraphs: A noun phrase is a phrase where the head word is a noun. In English, the word order of most noun phrases is that determiners, adjectives, and modifying nouns in respective order must appear before the head word, and relative clauses must appear after the head word.


title: Nature

paragraphs: The words nature and natural are used for all the things that are normally not made by humans. Things like weather, organisms, landforms, celestial bodies and much more are part of nature. Scientists study the way the parts of nature work. Things that have been made by people are said to be man-made or called artifacts.

paragraphs: There are natural sciences that study different parts of nature, for example the science of ecology is about plants and animals as a whole, while biology studies every type of living thing.

paragraphs: From one point of view, humans are a prime example of nature, and are the most widely studied natural inhabitants of the planet earth. Humans interact with each other in their natural environment on a constant basis. Every part of nature everything from the air to the dirt on the ground is interdependent. Medicine studies humans in health and sickness.

paragraphs: From another point of view, humans and nature can be said to be in conflict. Nature is often seen by humans as natural resources. People cut down trees, mine ores, and grow crops. Fires, cars, and factories make a lot of smoke and harm many places. People who like to leave nature unharmed and those who feel they need to use more of nature often fight about what they should do. In the modern world, with many more people and many big cities, these problems are becoming more serious.

paragraphs: Nature, in the broadest sense, means the physical world as a whole. This is the meaning that physics, the study of nature (etymologically), takes.