Symbol

A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. 　Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different concepts and experiences. 　All communication (and data processing) is achieved through the use of symbols. 　Symbols take the form of words, sounds, gestures, ideas, or visual images and are used to convey other ideas and beliefs. 　For example, a red octagon is a common symbol for "STOP"; on maps, blue lines often represent rivers; and a red rose often symbolizes love and compassion. 　Numerals are symbols for numbers; letters of an alphabet may be symbols for certain phonemes; and personal names are symbols representing individuals. 　The variable 'x', in a mathematical equation, may symbolize the position of a particle in space.　[citation needed] The academic study of symbols is semiotics. 　In cartography, an organized collection of symbols forms a legend for a map.

Nu (mythology)

Nu ("Watery One") or Nun ("The Inert One") (Ancient Egyptian: nnw Nānaw; Coptic: Ⲛⲟⲩⲛ Noun), is the personification of the primordial watery abyss which existed at the time of creation and from which the creator sun god Ra arose, in ancient Egyptian religion. 　Nu is one of the eight deities of the Ogdoad representing ancient Egyptian primordial Chaos from which the primordial mound arose. 　Nun can be seen as the first of all the gods and the creator of reality and personification of the cosmos. 　Nun is also considered the god that will destroy existence and return everything to the Nun from whence it came. 　No cult was addressed to Nun. 　The consort of Nun was the goddess Nunut or Naunet (Ancient Egyptian: nnwt). 　The names of Nu and Naunet are written with the determiners for sky and water.

Revenue

In accounting, revenue is the total amount of income generated by the sale of goods and services related to the primary operations of the business. 　Commercial revenue may also be referred to as sales or as turnover. 　Some companies receive revenue from interest, royalties, or other fees. 　"Revenue" may refer to income in general, or it may refer to the amount, in a monetary unit, earned during a period of time, as in "Last year, Company X had revenue of $42 million". 　Profits or net income generally imply total revenue minus total expenses in a given period. 　In accounting, in the balance statement, revenue is a subsection of the Equity section and revenue increases equity, it is often referred to as the "top line" due to its position on the income statement at the very top. 　This is to be contrasted with the "bottom line" which denotes net income (gross revenues minus total expenses). 　In general usage, revenue is the total amount of income by the sale of goods or services related to the company's operations. 　Sales revenue is income received from selling goods or services over a period of time. 　Tax revenue is income that a government receives from taxpayers. 　Fundraising revenue is income received by a charity from donors etc. to further its social purposes. 　In more formal usage, revenue is a calculation or estimation of periodic income based on a particular standard accounting practice or the rules established by a government or government agency. 　Two common accounting methods, cash basis accounting and accrual basis accounting, do not use the same process for measuring revenue. 　Corporations that offer shares for sale to the public are usually required by law to report revenue based on generally accepted accounting principles or on International Financial Reporting Standards. 　In a double-entry bookkeeping system, revenue accounts are general ledger accounts that are summarized periodically under the heading "Revenue" or "Revenues" on an income statement. 　Revenue account-names describe the type of revenue, such as "repair service revenue", "rent revenue earned" or "sales".

Rifle

A rifle is a long-barreled firearm designed for accurate shooting, with a barrel that has a helical pattern of grooves (rifling) cut into the bore wall. 　In keeping with their focus on accuracy, rifles are typically designed to be held with both hands and braced firmly against the shooter's shoulder via a buttstock for stability during shooting. 　Rifles are used extensively in warfare, law enforcement, hunting, shooting sports, and crime. 　The term was originally rifled gun, with the verb rifle referring to the early modern machining process of creating groovings with cutting tools. 　By the 20th century, the weapon had become so common that the modern noun rifle is now often used for any long-shaped handheld ranged weapon designed for well-aimed discharge activated by a trigger (e.g., personnel halting and stimulation response rifle, which is actually a laser dazzler). 　Like all typical firearms, a rifle's projectile (bullet) is propelled by the contained deflagration of a combustible propellant compound (originally black powder, later cordite, and now nitrocellulose), although other propulsive means are used, such as compressed air in air rifles, which are popular for vermin control, small game hunting, competitive target shooting and casual sport shooting (plinking). 　The distinct feature that separates a rifle from the earlier smoothbore long guns (e.g., arquebuses, muskets) is the rifling within its barrel. 　The raised areas of a barrel's rifling are called lands; they make contact with and exert torque on the projectile as it moves down the bore, imparting a spin. 　When the projectile leaves the barrel, this spin persists and lends gyroscopic stability to the projectile due to conservation of angular momentum, increasing accuracy and hence effective range. 　Early long rifles were muzzle-loaders firing spherical balls; the introduction of breech-loading allowed the use of elongated and aerodynamically efficient bullets, which did not yaw or tumble significantly in flight due to the spin.　[citation needed]

Moral

A moral (from Latin morālis) is a message that is conveyed or a lesson to be learned from a story or event. 　The moral may be left to the hearer, reader, or viewer to determine for themselves, or may be explicitly encapsulated in a maxim. 　A moral is a lesson in a story or in real life.

Iowa

Iowa (/ˈaɪəwə/ (listen)) is a state in the Midwestern region of the United States, bordered by the Mississippi River to the east and the Missouri River and Big Sioux River to the west. 　It is bordered by six states: Wisconsin to the northeast, Illinois to the east and southeast, Missouri to the south, Nebraska to the west, South Dakota to the northwest, and Minnesota to the north. 　During the 18th and early 19th centuries, Iowa was a part of French Louisiana and Spanish Louisiana; its state flag is patterned after the flag of France. 　After the Louisiana Purchase, people laid the foundation for an agriculture-based economy in the heart of the Corn Belt. 　In the latter half of the 20th century, Iowa's agricultural economy transitioned to a diversified economy of advanced manufacturing, processing, financial services, information technology, biotechnology, and green energy production. 　Iowa is the 26th most extensive in total area and the 31st most populous of the 50 U.S. states, with a population of 3,190,369, according to the 2020 census. 　The state's capital, most populous city, and largest metropolitan area fully located within the state is Des Moines. 　A portion of the larger Omaha, Nebraska, metropolitan area extends into three counties of southwest Iowa. 　Iowa has been listed as one of the safest U.S. states to live in.

Plastic

Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. 　Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. 　This adaptability, plus a wide range of other properties, such as being lightweight, durable, flexible, and inexpensive to produce, has led to its widespread use. 　Plastics typically are made through human industrial systems. 　Most modern plastics are derived from fossil fuel-based chemicals like natural gas or petroleum; however, recent industrial methods use variants made from renewable materials, such as corn or cotton derivatives. 　9.2 billion tonnes of plastic are estimated to have been made between 1950 and 2017. 　More than half this plastic has been produced since 2004. 　In 2020, 400 million tonnes of plastic were produced. 　If global trends on plastic demand continue, it is estimated that by 2050 annual global plastic production will reach over 1,100 million tonnes. 　The success and dominance of plastics starting in the early 20th century has caused widespread environmental problems, due to their slow decomposition rate in natural ecosystems. 　Most plastic produced has not been reused, either being captured in landfills or persisting in the environment as plastic pollution. 　Plastic pollution can be found in all the world's major water bodies, for example, creating garbage patches in all of the world's oceans and contaminating terrestrial ecosystems. 　Of all the plastic discarded so far, some 14% has been incinerated and less than 10% has been recycled. 　In developed economies, about a third of plastic is used in packaging and roughly the same in buildings in applications such as piping, plumbing or vinyl siding. 　Other uses include automobiles (up to 20% plastic), furniture, and toys. 　In the developing world, the applications of plastic may differ; 42% of India's consumption is used in packaging. 　In the medical field, polymer implants and other medical devices are derived at least partially from plastic. 　Worldwide, about 50 kg of plastic is produced annually per person, with production doubling every ten years. 　The world's first fully synthetic plastic was Bakelite, invented in New York in 1907, by Leo Baekeland, who coined the term "plastics". 　Dozens of different types of plastics are produced today, such as polyethylene, which is widely used in product packaging, and polyvinyl chloride (PVC), used in construction and pipes because of its strength and durability. 　Many chemists have contributed to the materials science of plastics, including Nobel laureate Hermann Staudinger, who has been called "the father of polymer chemistry" and Herman Mark, known as "the father of polymer physics".

Legend

Look up legend in Wiktionary, the free dictionary. 　A legend is a genre of folklore that consists of a narrative featuring human actions, believed or perceived, both by teller and listeners, to have taken place in human history. 　Narratives in this genre may demonstrate human values, and possess certain qualities that give the tale verisimilitude. 　Legend, for its active and passive participants may include miracles. 　Legends may be transformed over time to keep them fresh and vital. 　Many legends operate within the realm of uncertainty, never being entirely believed by the participants, but also never being resolutely doubted. 　Legends are sometimes distinguished from myths in that they concern human beings as the main characters rather than gods, and sometimes in that they have some sort of historical basis whereas myths generally do not. 　The Brothers Grimm defined legend as "folktale historically grounded". 　A by-product of the "concern with human beings" is the long list of legendary creatures, leaving no "resolute doubt" that legends are "historically grounded." 　A modern folklorist's professional definition of legend was proposed by Timothy R. Tangherlini in 1990: Legend, typically, is a short (mono-) episodic, traditional, highly ecotypified historicized narrative performed in a conversational mode, reflecting on a psychological level a symbolic representation of folk belief and collective experiences and serving as a reaffirmation of commonly held values of the group to whose tradition it belongs.

Seattle

Seattle (/siˈætəl/ (listen) see-AT-əl) is a seaport city on the West Coast of the United States. 　It is the seat of King County, Washington. 　With a 2020 population of 737,015, it is the largest city in both the state of Washington and the Pacific Northwest region of North America. 　The Seattle metropolitan area's population is 4.02 million, making it the 15th-largest in the United States. 　Its growth rate of 21.1% between 2010 and 2020 makes it one of the nation's fastest-growing large cities. 　Seattle is situated on an isthmus between Puget Sound (an inlet of the Pacific Ocean) and Lake Washington. 　It is the northernmost major city in the United States, located about 100 miles (160 km) south of the Canadian border. 　A major gateway for trade with East Asia, Seattle is the fourth-largest port in North America in terms of container handling as of 2021[update]. 　The Seattle area was inhabited by Native Americans for at least 4,000 years before the first permanent European settlers. 　Arthur A. Denny and his group of travelers, subsequently known as the Denny Party, arrived from Illinois via Portland, Oregon, on the schooner Exact at Alki Point on November 13, 1851. 　The settlement was moved to the eastern shore of Elliott Bay and named "Seattle" in 1852, in honor of Chief Si'ahl of the local Duwamish and Suquamish tribes. 　Today, Seattle has high populations of Native, Scandinavian, European American, Asian American and African American people, as well as a thriving LGBT community that ranks sixth in the United States by population. 　Logging was Seattle's first major industry, but by the late 19th century, the city had become a commercial and shipbuilding center as a gateway to Alaska during the Klondike Gold Rush. 　Growth after World War II was partially due to the local Boeing company, which established Seattle as a center for aircraft manufacturing. 　The Seattle area developed into a technology center from the 1980s onwards with companies like Microsoft becoming established in the region; Microsoft founder Bill Gates is a Seattleite by birth. 　Internet retailer Amazon was founded in Seattle in 1994, and major airline Alaska Airlines is based in SeaTac, Washington, serving Seattle's international airport, Seattle–Tacoma International Airport. 　The stream of new software, biotechnology, and Internet companies led to an economic revival, which increased the city's population by almost 50,000 between 1990 and 2000. 　Seattle also has a significant musical history. 　Between 1918 and 1951, nearly two dozen jazz nightclubs existed along Jackson Street, from the current Chinatown/International District to the Central District. 　The jazz scene nurtured the early careers of Ray Charles, Quincy Jones, Ernestine Anderson, and others. 　Seattle is also the birthplace of rock musician Jimi Hendrix, as well as the origin of the bands Nirvana, Pearl Jam, Soundgarden, Heart, Alice in Chains, Foo Fighters, and the alternative rock movement grunge.

Electricity

Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. 　Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwell's equations. 　Various common phenomena are related to electricity, including lightning, static electricity, electric heating, electric discharges and many others. 　The presence of an electric charge, which can be either positive or negative, produces an electric field. 　The movement of electric charges is an electric current and produces a magnetic field. 　When a charge is placed in a location with a non-zero electric field, a force will act on it. 　The magnitude of this force is given by Coulomb's law. 　If the charge moves, the electric field would be doing work on the electric charge. 　Thus we can speak of electric potential at a certain point in space, which is equal to the work done by an external agent in carrying a unit of positive charge from an arbitrarily chosen reference point to that point without any acceleration and is typically measured in volts. 　Electricity is at the heart of many modern technologies, being used for: Electric power where electric current is used to energise equipment; Electronics which deals with electrical circuits that involve active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies. 　Electrical phenomena have been studied since antiquity, though progress in theoretical understanding remained slow until the seventeenth and eighteenth centuries. 　The theory of electromagnetism was developed in the 19th century, and by the end of that century electricity was being put to industrial and residential use by electrical engineers. 　The rapid expansion in electrical technology at this time transformed industry and society, becoming a driving force for the Second Industrial Revolution. 　Electricity's extraordinary versatility means it can be put to an almost limitless set of applications which include transport, heating, lighting, communications, and computation. 　Electrical power is now the backbone of modern industrial society.

Grave

A grave is a location where a dead body (typically that of a human, although sometimes that of an animal) is buried or interred after a funeral. 　Graves are usually located in special areas set aside for the purpose of burial, such as graveyards or cemeteries. 　Certain details of a grave, such as the state of the body found within it and any objects found with the body, may provide information for archaeologists about how the body may have lived before its death, including the time period in which it lived and the culture that it had been a part of. 　In some religions, it is believed that the body must be burned or cremated for the soul to survive; in others, the complete decomposition of the body is considered to be important for the rest of the soul (see bereavement).

Organ (biology)

In biology, an organ is a collection of tissues joined in a structural unit to serve a common function. 　In the hierarchy of life, an organ lies between tissue and an organ system. 　Tissues are formed from same type cells to act together in a function. 　Tissues of different types combine to form an organ which has a specific function. 　The intestinal wall for example is formed by epithelial tissue and smooth muscle tissue. 　Two or more organs working together in the execution of a specific body function form an organ system, also called a biological system or body system. 　An organ's tissues can be broadly categorized as parenchyma, the functional tissue, and stroma, the structural tissue with supportive, connective, or ancillary functions. 　For example, the gland's tissue that makes the hormones is the parenchyma, whereas the stroma includes the nerves that innervate the parenchyma, the blood vessels that oxygenate and nourish it and carry away its metabolic wastes, and the connective tissues that provide a suitable place for it to be situated and anchored. 　The main tissues that make up an organ tend to have common embryologic origins, such as arising from the same germ layer. 　Organs exist in most multicellular organisms. 　In single-celled organisms such as bacteria, the functional analogue of an organ is known as an organelle. 　In plants, there are three main organs. 　In the study of anatomy, viscera (singular viscus) refers to the internal organs of the abdominal, thoracic, and pelvic cavities. 　The abdominal organs may be classified as solid organs, or hollow organs. 　The solid organs are the liver, pancreas, spleen, kidneys, and adrenal glands. 　The hollow organs of the abdomen are the stomach, intestines, gallbladder, bladder, and rectum. 　In the thoracic cavity the heart is a hollow, muscular organ. 　The number of organs in any organism depends on the definition used. 　By one widely adopted definition, 79 organs have been identified in the human body.

Leather

Leather is a strong, flexible and durable material obtained from the tanning, or chemical treatment, of animal skins and hides to prevent decay. 　The most common leathers come from cattle, sheep, goats, equine animals, buffalo, pigs and hogs, and aquatic animals such as seals and alligators. 　Leather can be used to make a variety of items, including clothing, footwear, handbags, furniture, tools and sports equipment, and lasts for decades. 　Leather making has been practiced for more than 7,000 years and the leading producers of leather today are China and India. 　Critics of tanneries claim that they engage in unsustainable practices that pose health hazards to the people and the environment near them.

Root

In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. 　They are most often below the surface of the soil, but roots can also be aerial or aerating, that is, growing up above the ground or especially above water.

Rotation

Rotation, or spin, is the circular movement of an object around a central axis. 　A two-dimensional rotating object has only one possible central axis and can rotate in either a clockwise or counterclockwise direction. 　A three-dimensional object has an infinite number of possible central axes and rotational directions. 　If the rotation axis passes internally through the body's own center of mass, then the body is said to be autorotating or spinning, and the surface intersection of the axis can be called a pole. 　A rotation around a completely external axis, e.g. the planet Earth around the Sun, is called revolving or orbiting, typically when it is produced by gravity, and the ends of the rotation axis can be called the orbital poles.

Jacob

Jacob (/ˈdʒeɪkəb/; Hebrew: יַעֲקֹב‎, Modern: Yaʿaqōv (help·info), Tiberian: Yaʿăqōḇ; Arabic: يَعْقُوب, romanized: Yaʿqūb; Greek: Ἰακώβ, romanized: Iakṓb), later given the name Israel, is regarded as a patriarch of the Israelites and is an important figure in Abrahamic religions, such as Judaism, Christianity, and Islam. 　Jacob first appears in the Book of Genesis, where he is described as the son of Isaac and Rebecca, and the grandson of Abraham, Sarah, and Bethuel. 　According to the biblical account, he was the second-born of Isaac's children, the elder being Jacob's fraternal twin brother, Esau. 　Jacob is said to have bought Esau's birthright and, with his mother's help, deceived his aging father to bless him instead of Esau. 　Later in the narrative, following a severe drought in his homeland of Canaan, Jacob and his descendants, with the help of his son Joseph (who had become a confidant of the pharaoh), moved to Egypt where Jacob died at the age of 147. 　He is supposed to have been buried in the Cave of Machpelah. 　Jacob had twelve sons through four women, his wives, Leah and Rachel, and his concubines, Bilhah and Zilpah, who were, in order of their birth, Reuben, Simeon, Levi, Judah, Dan, Naphtali, Gad, Asher, Issachar, Zebulun, Joseph, and Benjamin, all of whom became the heads of their own family groups, later known as the Twelve Tribes of Israel. 　He also had a daughter named Dinah. 　According to Genesis, Jacob displayed favoritism among his wives and children, preferring Rachel and her sons, Joseph and Benjamin, causing tension within the family—culminating in Joseph's older brothers selling him into slavery. 　Scholars have taken a mixed view as to Jacob's historicity, with archaeology so far producing no evidence for his existence.

Bathroom

A bathroom or washroom is a room, typically in a home or other residential building, that contains either a bathtub or a shower (or both). 　The inclusion of a wash basin is common. 　In some parts of the world e.g. India, a toilet is typically included in the bathroom; in others, the toilet is typically given a dedicated room separate from the one allocated for personal hygiene activities. 　In North American English the word 'bathroom' is sometimes used to refer to any room in a residence that contains a toilet, regardless of the inclusion of a bath or shower. 　Historically, bathing was often a collective activity, which took place in public baths. 　In some countries the shared social aspect of cleansing the body is still important, as for example with sento in Japan and the "Turkish bath" (also known by other names) throughout the Islamic world.

Portrait

A portrait is a painting, photograph, sculpture, or other artistic representation of a person, in which the face and its expressions are predominant. 　The intent is to display the likeness, personality, and even the mood of the person. 　For this reason, in photography a portrait is generally not a snapshot, but a composed image of a person in a still position. 　A portrait often shows a person looking directly at the painter or photographer, in order to most successfully engage the subject with the viewer.

Shopping

Shopping is an activity in which a customer browses the available goods or services presented by one or more retailers with the potential intent to purchase a suitable selection of them. 　A typology of shopper types has been developed by scholars which identifies one group of shoppers as recreational shoppers, that is, those who enjoy shopping and view it as a leisure activity. 　Online shopping has become a major disruptor in the retail industry as consumers can now search for product information and place product orders across different regions. 　Online retailers deliver their products directly to the consumers' home, offices, or wherever they want. 　The B2C (business to consumer) process has made it easy for consumers to select any product online from a retailer's website and to have it delivered relatively quickly. 　Using online shopping methods, consumers do not need to consume energy by physically visiting physical stores. 　This way they save time and the cost of traveling. 　A retailer or a shop is a business that presents a selection of goods and offers to trade or sell them to customers for money or other goods. 　Shoppers' shopping experiences may vary. 　They are based on a variety of factors including how the customer is treated, convenience, the type of goods being purchased, and mood.

Snapped

Snapped is an American true crime television series produced by Jupiter Entertainment. 　The series depicts high profile or bizarre cases of women accused of murder. 　Each episode outlines the motivation for murder, whether it be revenge against a cheating husband or lover, a large insurance payoff, or the ending to years of abuse, with each murder's circumstances as unique as the women profiled. 　Snapped premiered on August 6, 2004 on Oxygen. 　It has since become the network's longest-running original series, with its 28 defined seasons and sixteen years in production (and two spin-offs) outlasting the seventeen seasons and thirteen years of the Bad Girls Club. 　The show also played a large role in the decision by parent company NBCUniversal to relaunch Oxygen as a crime network in 2017. 　As of November 22, 2020[update], 500 original episodes of Snapped have aired.

Blues

Blues is a music genre and musical form which originated in the Deep South of the United States around the 1860s. 　Blues incorporated spirituals, work songs, field hollers, shouts, chants, and rhymed simple narrative ballads from the African-American culture. 　The blues form is ubiquitous in jazz, rhythm and blues, and rock and roll, and is characterized by the call-and-response pattern, the blues scale, and specific chord progressions, of which the twelve-bar blues is the most common. 　Blue notes (or "worried notes"), usually thirds, fifths or sevenths flattened in pitch, are also an essential part of the sound. 　Blues shuffles or walking bass reinforce the trance-like rhythm and form a repetitive effect known as the groove. 　Blues as a genre is also characterized by its lyrics, bass lines, and instrumentation. 　Early traditional blues verses consisted of a single line repeated four times. 　It was only in the first decades of the 20th century that the most common current structure became standard: the AAB pattern, consisting of a line sung over the four first bars, its repetition over the next four, and then a longer concluding line over the last bars. 　Early blues frequently took the form of a loose narrative, often relating the racial discrimination and other challenges experienced by African-Americans. 　Many elements, such as the call-and-response format and the use of blue notes, can be traced back to the music of Africa. 　The origins of the blues are also closely related to the religious music of the Afro-American community, the spirituals. 　The first appearance of the blues is often dated to after the ending of slavery and, later, the development of juke joints. 　It is associated with the newly acquired freedom of the former slaves. 　Chroniclers began to report about blues music at the dawn of the 20th century. 　The first publication of blues sheet music was in 1908. 　Blues has since evolved from unaccompanied vocal music and oral traditions of slaves into a wide variety of styles and subgenres. 　Blues subgenres include country blues, such as Delta blues and Piedmont blues, as well as urban blues styles such as Chicago blues and West Coast blues. 　World War II marked the transition from acoustic to electric blues and the progressive opening of blues music to a wider audience, especially white listeners. 　In the 1960s and 1970s, a hybrid form called blues rock developed, which blended blues styles with rock music.

Atmosphere

An atmosphere (from Ancient Greek ἀτμός (atmós) 'vapour, steam', and σφαῖρα (sphaîra) 'sphere') is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. 　A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. 　A stellar atmosphere is the outer region of a star, which includes the layers above the opaque photosphere; stars of low temperature might have outer atmospheres containing compound molecules. 　The atmosphere of Earth is composed of nitrogen (78%), oxygen (21%), argon (0.9%), carbon dioxide (0.04%) and trace gases. 　Most organisms use oxygen for respiration; lightning and bacteria perform nitrogen fixation to produce ammonia that is used to make nucleotides and amino acids; plants, algae, and cyanobacteria use carbon dioxide for photosynthesis. 　The layered composition of the atmosphere minimises the harmful effects of sunlight, ultraviolet radiation, the solar wind, and cosmic rays to protect organisms from genetic damage. 　The current composition of the atmosphere of the Earth is the product of billions of years of biochemical modification of the paleoatmosphere by living organisms. 　Evolution of the Atmosphere

Orbit

In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a planet, moon, asteroid, or Lagrange point. 　Normally, orbit refers to a regularly repeating trajectory, although it may also refer to a non-repeating trajectory. 　To a close approximation, planets and satellites follow elliptic orbits, with the center of mass being orbited at a focal point of the ellipse, as described by Kepler's laws of planetary motion. 　For most situations, orbital motion is adequately approximated by Newtonian mechanics, which explains gravity as a force obeying an inverse-square law. 　However, Albert Einstein's general theory of relativity, which accounts for gravity as due to curvature of spacetime, with orbits following geodesics, provides a more accurate calculation and understanding of the exact mechanics of orbital motion.

Intersection

In mathematics, the intersection of two or more objects is another object consisting of everything that is contained in all of the objects simultaneously. 　For example, in Euclidean geometry, when two lines in a plane are not parallel, their intersection is the point at which they meet. 　More generally, in set theory, the intersection of sets is defined to be the set of elements which belong to all of them. 　Unlike the Euclidean definition, this does not presume that the objects under consideration lie in a common space. 　Intersection is one of the basic concepts of geometry. 　An intersection can have various geometric shapes, but a point is the most common in a plane geometry. 　Incidence geometry defines an intersection (usually, of flats) as an object of lower dimension that is incident to each of original objects. 　In this approach an intersection can be sometimes undefined, such as for parallel lines. 　In both cases the concept of intersection relies on logical conjunction. 　Algebraic geometry defines intersections in its own way with intersection theory.