1.
Asteroid belt
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The asteroid belt is the circumstellar disc in the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets, the asteroid belt is also termed the main asteroid belt or main belt to distinguish it from other asteroid populations in the Solar System such as near-Earth asteroids and trojan asteroids. About half the mass of the belt is contained in the four largest asteroids, Ceres, Vesta, Pallas, the total mass of the asteroid belt is approximately 4% that of the Moon, or 22% that of Pluto, and roughly twice that of Plutos moon Charon. Ceres, the belts only dwarf planet, is about 950 km in diameter, whereas Vesta, Pallas. The remaining bodies range down to the size of a dust particle, the asteroid material is so thinly distributed that numerous unmanned spacecraft have traversed it without incident. Nonetheless, collisions between large asteroids do occur, and these can form a family whose members have similar orbital characteristics. Individual asteroids within the belt are categorized by their spectra. The asteroid belt formed from the solar nebula as a group of planetesimals. Planetesimals are the precursors of the protoplanets. Between Mars and Jupiter, however, gravitational perturbations from Jupiter imbued the protoplanets with too much energy for them to accrete into a planet. Collisions became too violent, and instead of fusing together, the planetesimals, as a result,99. 9% of the asteroid belts original mass was lost in the first 100 million years of the Solar Systems history. Some fragments eventually found their way into the inner Solar System, Asteroid orbits continue to be appreciably perturbed whenever their period of revolution about the Sun forms an orbital resonance with Jupiter. At these orbital distances, a Kirkwood gap occurs as they are swept into other orbits. Classes of small Solar System bodies in other regions are the objects, the centaurs, the Kuiper belt objects, the scattered disc objects, the sednoids. On 22 January 2014, ESA scientists reported the detection, for the first definitive time, of water vapor on Ceres, the detection was made by using the far-infrared abilities of the Herschel Space Observatory. The finding was unexpected because comets, not asteroids, are considered to sprout jets. According to one of the scientists, The lines are becoming more and more blurred between comets and asteroids. This pattern, now known as the Titius–Bode law, predicted the semi-major axes of the six planets of the provided one allowed for a gap between the orbits of Mars and Jupiter
2.
Natural satellite
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A natural satellite or moon is, in the most common usage, an astronomical body that orbits a planet or minor planet. In the Solar System there are six planetary satellite systems containing 178 known natural satellites, four IAU-listed dwarf planets are also known to have natural satellites, Pluto, Haumea, Makemake, and Eris. As of January 2012, over 200 minor-planet moons have been discovered, the Earth–Moon system is unique in that the ratio of the mass of the Moon to the mass of Earth is much greater than that of any other natural-satellite–planet ratio in the Solar System. At 3,474 km across, Earths Moon is 0.27 times the diameter of Earth, the first known natural satellite was the Moon, but it was considered a planet until Copernicus introduction of heliocentrism in 1543. Until the discovery of the Galilean satellites in 1610, however, galileo chose to refer to his discoveries as Planetæ, but later discoverers chose other terms to distinguish them from the objects they orbited. The first to use of the satellite to describe orbiting bodies was the German astronomer Johannes Kepler in his pamphlet Narratio de Observatis a se quatuor Iouis satellitibus erronibus in 1610. He derived the term from the Latin word satelles, meaning guard, attendant, or companion, the term satellite thus became the normal one for referring to an object orbiting a planet, as it avoided the ambiguity of moon. In 1957, however, the launching of the artificial object Sputnik created a need for new terminology, to further avoid ambiguity, the convention is to capitalize the word Moon when referring to Earths natural satellite, but not when referring to other natural satellites. A few recent authors define moon as a satellite of a planet or minor planet, there is no established lower limit on what is considered a moon. Small asteroid moons, such as Dactyl, have also been called moonlets, the upper limit is also vague. Two orbiting bodies are described as a double body rather than primary. Asteroids such as 90 Antiope are considered double asteroids, but they have not forced a clear definition of what constitutes a moon, some authors consider the Pluto–Charon system to be a double planet. In contrast, irregular satellites are thought to be captured asteroids possibly further fragmented by collisions, most of the major natural satellites of the Solar System have regular orbits, while most of the small natural satellites have irregular orbits. The Moon and possibly Charon are exceptions among large bodies in that they are thought to have originated by the collision of two large proto-planetary objects. The material that would have placed in orbit around the central body is predicted to have reaccreted to form one or more orbiting natural satellites. As opposed to planetary-sized bodies, asteroid moons are thought to form by this process. Triton is another exception, although large and in a close, circular orbit, its motion is retrograde, most regular moons in the Solar System are tidally locked to their respective primaries, meaning that the same side of the natural satellite always faces its planet. The only known exception is Saturns natural satellite Hyperion, which rotates chaotically because of the influence of Titan
3.
Mass
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In physics, mass is a property of a physical body. It is the measure of a resistance to acceleration when a net force is applied. It also determines the strength of its gravitational attraction to other bodies. The basic SI unit of mass is the kilogram, Mass is not the same as weight, even though mass is often determined by measuring the objects weight using a spring scale, rather than comparing it directly with known masses. An object on the Moon would weigh less than it does on Earth because of the lower gravity and this is because weight is a force, while mass is the property that determines the strength of this force. In Newtonian physics, mass can be generalized as the amount of matter in an object, however, at very high speeds, special relativity postulates that energy is an additional source of mass. Thus, any body having mass has an equivalent amount of energy. In addition, matter is a defined term in science. There are several distinct phenomena which can be used to measure mass, active gravitational mass measures the gravitational force exerted by an object. Passive gravitational mass measures the force exerted on an object in a known gravitational field. The mass of an object determines its acceleration in the presence of an applied force, according to Newtons second law of motion, if a body of fixed mass m is subjected to a single force F, its acceleration a is given by F/m. A bodys mass also determines the degree to which it generates or is affected by a gravitational field and this is sometimes referred to as gravitational mass. The standard International System of Units unit of mass is the kilogram, the kilogram is 1000 grams, first defined in 1795 as one cubic decimeter of water at the melting point of ice. Then in 1889, the kilogram was redefined as the mass of the prototype kilogram. As of January 2013, there are proposals for redefining the kilogram yet again. In this context, the mass has units of eV/c2, the electronvolt and its multiples, such as the MeV, are commonly used in particle physics. The atomic mass unit is 1/12 of the mass of a carbon-12 atom, the atomic mass unit is convenient for expressing the masses of atoms and molecules. Outside the SI system, other units of mass include, the slug is an Imperial unit of mass, the pound is a unit of both mass and force, used mainly in the United States
4.
Asteroid
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Asteroids are minor planets, especially those of the inner Solar System. The larger ones have also been called planetoids and these terms have historically been applied to any astronomical object orbiting the Sun that did not show the disc of a planet and was not observed to have the characteristics of an active comet. As minor planets in the outer Solar System were discovered and found to have volatile-based surfaces that resemble those of comets, in this article, the term asteroid refers to the minor planets of the inner Solar System including those co-orbital with Jupiter. There are millions of asteroids, many thought to be the remnants of planetesimals. The large majority of known asteroids orbit in the belt between the orbits of Mars and Jupiter, or are co-orbital with Jupiter. However, other orbital families exist with significant populations, including the near-Earth objects, individual asteroids are classified by their characteristic spectra, with the majority falling into three main groups, C-type, M-type, and S-type. These were named after and are identified with carbon-rich, metallic. The size of asteroids varies greatly, some reaching as much as 1000 km across, asteroids are differentiated from comets and meteoroids. In the case of comets, the difference is one of composition, while asteroids are composed of mineral and rock, comets are composed of dust. In addition, asteroids formed closer to the sun, preventing the development of the aforementioned cometary ice, the difference between asteroids and meteoroids is mainly one of size, meteoroids have a diameter of less than one meter, whereas asteroids have a diameter of greater than one meter. Finally, meteoroids can be composed of either cometary or asteroidal materials, only one asteroid,4 Vesta, which has a relatively reflective surface, is normally visible to the naked eye, and this only in very dark skies when it is favorably positioned. Rarely, small asteroids passing close to Earth may be visible to the eye for a short time. As of March 2016, the Minor Planet Center had data on more than 1.3 million objects in the inner and outer Solar System, the United Nations declared June 30 as International Asteroid Day to educate the public about asteroids. The date of International Asteroid Day commemorates the anniversary of the Tunguska asteroid impact over Siberia, the first asteroid to be discovered, Ceres, was found in 1801 by Giuseppe Piazzi, and was originally considered to be a new planet. In the early half of the nineteenth century, the terms asteroid. Asteroid discovery methods have improved over the past two centuries. This task required that hand-drawn sky charts be prepared for all stars in the band down to an agreed-upon limit of faintness. On subsequent nights, the sky would be charted again and any moving object would, hopefully, the expected motion of the missing planet was about 30 seconds of arc per hour, readily discernible by observers
5.
Ann Arbor, Michigan
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Ann Arbor is a city in the U. S. state of Michigan and the county seat of Washtenaw County. The 2010 census recorded its population to be 113,934, the citys population was estimated at 117,070 as of July 2015 by the U. S. Census Bureau. The Ann Arbor Metropolitan Statistical Area includes all of Washtenaw County, the city is also part of the larger Detroit–Ann Arbor–Flint, MI Combined Statistical Area with a population of 5,318,744. Ann Arbor was founded in 1824, named for wives of the villages founders, the University of Michigan moved from Detroit to Ann Arbor in 1837, and the city grew at a rapid rate in the early to mid-20th century. During the 1960s and 1970s, the city gained a reputation as a center for left-wing politics, Ann Arbor became a focal point for political activism and anti-Vietnam War movement, as well as various student movements. Ann Arbor is home to the University of Michigan, one of the foremost research universities in the United States, the university shapes Ann Arbors economy significantly as it employs about 30,000 workers, including about 12,000 in the medical center. The citys economy is centered on high technology, with several companies drawn to the area by the universitys research and development infrastructure. In about 1774, the Potawatomi founded two villages in the area of what is now Ann Arbor, Ann Arbor was founded in 1824 by land speculators John Allen and Elisha Walker Rumsey. On 25 May 1824, the plat was registered with Wayne County as Annarbour. Allen and Rumsey decided to name it for their wives, both named Ann, and for the stands of Bur Oak in the 640 acres of land purchased for $800 from the federal government at $1.25 per acre. The local Ojibwa named the settlement kaw-goosh-kaw-nick, after the sound of Allens sawmill, Ann Arbor became the seat of Washtenaw County in 1827, and was incorporated as a village in 1833. The Ann Arbor Land Company, a group of speculators, set aside 40 acres of undeveloped land and offered it to the state of Michigan as the site of the state capital, but lost the bid to Lansing. In 1837, the property was accepted instead as the site of the University of Michigan, since the universitys establishment in the city in 1837, the histories of the University of Michigan and Ann Arbor have been closely linked. Throughout the 1840s and the 1850s settlers continued to come to Ann Arbor, while the earlier settlers were primarily of British ancestry, the newer settlers also consisted of Germans, Irish, and African-Americans. In 1851, Ann Arbor was chartered as a city, though the city showed a drop in population during the Depression of 1873. It was not until the early 1880s that Ann Arbor again saw robust growth, with new immigrants coming from Greece, Italy, Russia, Ann Arbor saw increased growth in manufacturing, particularly in milling. Ann Arbors Jewish community also grew after the turn of the 20th century, during the 1960s and 1970s, the city gained a reputation as an important center for liberal politics. Ann Arbor also became a locus for left-wing activism and anti-Vietnam War movement, during the ensuing 15 years, many countercultural and New Left enterprises sprang up and developed large constituencies within the city
6.
Helen of Troy
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In Greek mythology, Helen of Troy, also known as Helen of Sparta, or simply Helen, was the daughter of Zeus and Leda, and was a sister of Castor, Pollux, and Clytemnestra. In Greek myths, she was considered the most beautiful woman in the world, by marriage she was Queen of Laconia, a province within Homeric Greece, the wife of King Menelaus. Her abduction by Prince Paris of Troy brought about the Trojan War, elements of her putative biography come from classical authors such as Aristophanes, Cicero, Euripides and Homer. In her youth, she was abducted by Theseus, a competition between her suitors for her hand in marriage sees Menelaus emerge victorious. An oath sworn beforehand by all the suitors requires them to military assistance in the case of her abduction. When she marries Menelaus she is very young, whether her subsequent involvement with Paris is an abduction or a seduction is ambiguous. The legends recounting Helens fate in Troy are contradictory, Homer depicts her as a wistful figure, even a sorrowful one, who comes to regret her choice and wishes to be reunited with Menelaus. Other accounts have a treacherous Helen who simulates Bacchic rites and rejoices in the carnage, ultimately, Paris was killed in action, and in Homers account Helen was reunited with Menelaus, though other versions of the legend recount her ascending to Olympus instead. A cult associated with her developed in Hellenistic Laconia, both at Sparta and elsewhere, at Therapne she shared a shrine with Menelaus and she was also worshiped in Attica and on Rhodes. Her beauty inspired artists of all time to represent her, frequently as the personification of ideal beauty, Christopher Marlowes lines from his tragedy Doctor Faustus are frequently cited, Was this the face that launchd a thousand ships/And burnt the topless towers of Ilium. However, in the play this meeting and the ensuing temptation are not unambiguously positive, closely preceding death, images of her start appearing in the 7th century BC. In classical Greece, her abduction by—or elopement with—Paris was a popular motif, in medieval illustrations, this event was frequently portrayed as a seduction, whereas in Renaissance painting it is usually depicted as a rape by Paris. The fact that rape and kidnapping were interchangeable terms lends additional ambiguity to the story, the etymology of Helens name continues to be a problem for scholars. Georg Curtius related Helen to the moon, Émile Boisacq considered Ἑλένη to derive from the noun ἑλένη meaning torch. It has also suggested that the λ of Ἑλένη arose from an original ν. Linda Lee Clader, however, says none of the above suggestions offers much satisfaction. Inversely, others have connected this etymology to a hypothetical proto-indo-european sun goddess, in particular, her marriage myth may be connected to a broader indo-european marriage drama of the sun goddess, and she is related to the divine twins, just as many of these goddesses are. The origins of Helens myth date back to the Mycenaean age, the first record of her name appears in the poems of Homer, but scholars assume that such myths invented or received by the Mycenaean Greeks made their way to Homer
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