title: John Dewey

text: Dewey's educational theories were presented in "My Pedagogic Creed" (1897), "The Primary-Education Fetich" (1898), "The School and Society" (1900), "The Child and the Curriculum" (1902), "Democracy and Education" (1916), "Schools of To-morrow" (1915) with Evelyn Dewey, and "Experience and Education" (1938). Several themes recur throughout these writings. Dewey continually argues that education and learning are social and interactive processes, and thus the school itself is a social institution through which social reform can and should take place. In addition, he believed that students thrive in an environment where they are allowed to experience and interact with the curriculum, and all students should have the opportunity to take part in their own learning.


title: John Dewey

text: The ideas of democracy and social reform are continually discussed in Dewey's writings on education. Dewey makes a strong case for the importance of education not only as a place to gain content knowledge, but also as a place to learn how to live. In his eyes, the purpose of education should not revolve around the acquisition of a pre-determined set of skills, but rather the realization of one's full potential and the ability to use those skills for the greater good. He notes that "to prepare him for the future life means to give him command of himself; it means so to train him that he will have the full and ready use of all his capacities" ("My Pedagogic Creed", Dewey, 1897).


title: John Dewey

text: In addition to helping students realize their full potential, Dewey goes on to acknowledge that education and schooling are instrumental in creating social change and reform. He notes that "education is a regulation of the process of coming to share in the social consciousness; and that the adjustment of individual activity on the basis of this social consciousness is the only sure method of social reconstruction".


title: John Dewey

text: In addition to his ideas regarding what education is and what effect it should have on society, Dewey also had specific notions regarding how education should take place within the classroom. In "The Child and the Curriculum" (1902), Dewey discusses two major conflicting schools of thought regarding educational pedagogy. The first is centered on the curriculum and focuses almost solely on the subject matter to be taught. Dewey argues that the major flaw in this methodology is the inactivity of the student; within this particular framework, "the child is simply the immature being who is to be matured; he is the superficial being who is to be deepened" (1902, p. 13). He argues that in order for education to be most effective, content must be presented in a way that allows the student to relate the information to prior experiences, thus deepening the connection with this new knowledge.


title: John Dewey

text: At the same time, Dewey was alarmed by many of the "child-centered" excesses of educational-school pedagogues who claimed to be his followers, and he argued that too much reliance on the child could be equally detrimental to the learning process. In this second school of thought, "we must take our stand with the child and our departure from him. It is he and not the subject-matter which determines both quality and quantity of learning" (Dewey, 1902, pp. 13–14). According to Dewey, the potential flaw in this line of thinking is that it minimizes the importance of the content as well as the role of the teacher.


title: John Dewey

text: In order to rectify this dilemma, Dewey advocated an educational structure that strikes a balance between delivering knowledge while also taking into account the interests and experiences of the student. He notes that "the child and the curriculum are simply two limits which define a single process. Just as two points define a straight line, so the present standpoint of the child and the facts and truths of studies define instruction" (Dewey, 1902, p. 16).


title: John Dewey

text: It is through this reasoning that Dewey became one of the most famous proponents of hands-on learning or experiential education, which is related to, but not synonymous with experiential learning. He argued that "if knowledge comes from the impressions made upon us by natural objects, it is impossible to procure knowledge without the use of objects which impress the mind" (Dewey, 1916/2009, pp. 217–18). Dewey's ideas went on to influence many other influential experiential models and advocates. Problem-Based Learning (PBL), for example, a method used widely in education today, incorporates Dewey's ideas pertaining to learning through active inquiry.


title: John Dewey

text: Dewey not only re-imagined the way that the learning process should take place, but also the role that the teacher should play within that process. Throughout the history of American schooling, education's purpose has been to train students for work by providing the student with a limited set of skills and information to do a particular job. The works of John Dewey provide the most prolific examples of how this limited vocational view of education has been applied to both the K–12 public education system and to the teacher training schools that attempted to quickly produce proficient and practical teachers with a limited set of instructional and discipline-specific skills needed to meet the needs of the employer and demands of the workforce.


title: John Dewey

text: In "The School and Society" (Dewey, 1899) and "Democracy of Education" (Dewey, 1916), Dewey claims that rather than preparing citizens for ethical participation in society, schools cultivate passive pupils via insistence upon mastery of facts and disciplining of bodies. Rather than preparing students to be reflective, autonomous and ethical beings capable of arriving at social truths through critical and intersubjective discourse, schools prepare students for docile compliance with authoritarian work and political structures, discourage the pursuit of individual and communal inquiry, and perceive higher learning as a monopoly of the institution of education (Dewey, 1899; 1916).


title: John Dewey

text: For Dewey and his philosophical followers, education stifles individual autonomy when learners are taught that knowledge is transmitted in one direction, from the expert to the learner. Dewey not only re-imagined the way that the learning process should take place, but also the role that the teacher should play within that process. For Dewey, "The thing needful is improvement of education, not simply by turning out teachers who can do better the things that are not necessary to do, but rather by changing the conception of what constitutes education" (Dewey, 1904, p. 18).


title: John Dewey

text: Dewey's qualifications for teaching—a natural love for working with young children, a natural propensity to inquire about the subjects, methods and other social issues related to the profession, and a desire to share this acquired knowledge with others—are not a set of outwardly displayed mechanical skills. Rather, they may be viewed as internalized principles or habits which "work automatically, unconsciously" (Dewey, 1904, p. 15). Turning to Dewey's essays and public addresses regarding the teaching profession, followed by his analysis of the teacher as a person and a professional, as well as his beliefs regarding the responsibilities of teacher education programs to cultivate the attributes addressed, teacher educators can begin to reimagine the successful classroom teacher Dewey envisioned.


title: John Dewey

text: For many, education's purpose is to train students for work by providing the student with a limited set of skills and information to do a particular job. As Dewey notes, this limited vocational view is also applied to teacher training schools who attempt to quickly produce proficient and practical teachers with a limited set of instructional and discipline skills needed to meet the needs of the employer and demands of the workforce (Dewey, 1904). For Dewey, the school and the classroom teacher, as a workforce and provider of social service, have a unique responsibility to produce psychological and social goods that will lead to both present and future social progress.


title: John Dewey

text: As Dewey notes, "The business of the teacher is to produce a higher standard of intelligence in the community, and the object of the public school system is to make as large as possible the number of those who possess this intelligence. Skill, the ability to act wisely and effectively in a great variety of occupations and situations, is a sign and a criterion of the degree of civilization that a society has reached. It is the business of teachers to help in producing the many kinds of skills needed in contemporary life. If teachers are up to their work, they also aid in the production of character."(Dewey, TAP, 2010, pp. 241–42).


title: John Dewey

text: According to Dewey, the emphasis is placed on producing these attributes in children for use in their contemporary life because it is "impossible to foretell definitely just what civilization will be twenty years from now" (Dewey, MPC, 2010, p. 25). However, although Dewey is steadfast in his beliefs that education serves an immediate purpose (Dewey, DRT, 2010; Dewey, MPC, 2010; Dewey, TTP, 2010), he is not ignorant of the impact imparting these qualities of intelligence, skill, and character on young children in their present life will have on the future society. While addressing the state of educative and economic affairs during a 1935 radio broadcast, Dewey linked the ensuing economic depression to a "lack of sufficient production of intelligence, skill, and character" (Dewey, TAP, 2010, p. 242) of the nation's workforce.


title: John Dewey

text: As Dewey notes, there is a lack of these goods in the present society and teachers have a responsibility to create them in their students, who, we can assume, will grow into the adults who will ultimately go on to participate in whatever industrial or economic civilization awaits them. According to Dewey, the profession of the classroom teacher is to produce the intelligence, skill, and character within each student so that the democratic community is composed of citizens who can think, do and act intelligently and morally.


title: John Dewey

text: Dewey believed that successful classroom teacher possesses a passion for knowledge and intellectual curiosity in the materials and methods they teach. For Dewey, this propensity is an inherent curiosity and love for learning that differs from one's ability to acquire, recite and reproduce textbook knowledge. "No one," according to Dewey, "can be really successful in performing the duties and meeting these demands [of teaching] who does not retain [her] intellectual curiosity intact throughout [her] entire career" (Dewey, APT, 2010, p. 34).


title: John Dewey

text: According to Dewey, it is not that the "teacher ought to strive to be a high-class scholar in all the subjects he or she has to teach," rather, "a teacher ought to have an unusual love and aptitude in some one subject: history, mathematics, literature, science, a fine art, or whatever" (Dewey, APT, 2010, p. 35). The classroom teacher does not have to be a scholar in all subjects; rather, genuine love in one will elicit a feel for genuine information and insight in all subjects taught.


title: John Dewey

text: In addition to this propensity for study into the subjects taught, the classroom teacher "is possessed by a recognition of the responsibility for the constant study of school room work, the constant study of children, of methods, of subject matter in its various adaptations to pupils" (Dewey, PST, 2010, p. 37). For Dewey, this desire for the lifelong pursuit of learning is inherent in other professions (e.g. the architectural, legal and medical fields; Dewey, 1904 & Dewey, PST, 2010), and has particular importance for the field of teaching. As Dewey notes, "this further study is not a sideline but something which fits directly into the demands and opportunities of the vocation" (Dewey, APT, 2010, p. 34).


title: John Dewey

text: According to Dewey, this propensity and passion for intellectual growth in the profession must be accompanied by a natural desire to communicate one's knowledge with others. "There are scholars who have [the knowledge] in a marked degree but who lack enthusiasm for imparting it. To the 'natural born' teacher learning is incomplete unless it is shared" (Dewey, APT, 2010, p. 35). For Dewey, it is not enough for the classroom teacher to be a lifelong learner of the techniques and subject-matter of education; she must aspire to share what she knows with others in her learning community.


title: John Dewey

text: The best indicator of teacher quality, according to Dewey, is the ability to watch and respond to the movement of the mind with keen awareness of the signs and quality of the responses he or her students exhibit with regard to the subject-matter presented (Dewey, APT, 2010; Dewey, 1904). As Dewey notes, "I have often been asked how it was that some teachers who have never studied the art of teaching are still extraordinarily good teachers. The explanation is simple. They have a quick, sure and unflagging sympathy with the operations and process of the minds they are in contact with. Their own minds move in harmony with those of others, appreciating their difficulties, entering into their problems, sharing their intellectual victories" (Dewey, APT, 2010, p. 36).


title: John Dewey

text: Such a teacher is genuinely aware of the complexities of this mind to mind transfer, and she has the intellectual fortitude to identify the successes and failures of this process, as well as how to appropriately reproduce or correct it in the future.


title: John Dewey

text: As a result of the direct influence teachers have in shaping the mental, moral and spiritual lives of children during their most formative years, Dewey holds the profession of teaching in high esteem, often equating its social value to that of the ministry and to parenting (Dewey, APT, 2010; Dewey, DRT, 2010; Dewey, MPC, 2010; Dewey, PST, 2010; Dewey, TTC, 2010; Dewey, TTP, 2010). Perhaps the most important attributes, according to Dewey, are those personal inherent qualities that the teacher brings to the classroom. As Dewey notes, "no amount of learning or even of acquired pedagogical skill makes up for the deficiency" (Dewey, TLS, p. 25) of the personal traits needed to be most successful in the profession.


title: John Dewey

text: According to Dewey, the successful classroom teacher occupies an indispensable passion for promoting the intellectual growth of young children. In addition, they know that their career, in comparison to other professions, entails stressful situations, long hours, and limited financial reward; all of which have the potential to overcome their genuine love and sympathy for their students.


title: John Dewey

text: For Dewey, "One of the most depressing phases of the vocation is the number of careworn teachers one sees, with anxiety depicted on the lines of their faces, reflected in their strained high pitched voices and sharp manners. While contact with the young is a privilege for some temperaments, it is a tax on others and a tax which they do not bear up under very well. And in some schools, there are too many pupils to a teacher, too many subjects to teach, and adjustments to pupils are made in a mechanical rather than a human way. Human nature reacts against such unnatural conditions" (Dewey, APT, 2010, p. 35).


title: John Dewey

text: It is essential, according to Dewey, that the classroom teacher has the mental propensity to overcome the demands and stressors placed on them because the students can sense when their teacher is not genuinely invested in promoting their learning (Dewey, PST, 2010). Such negative demeanors, according to Dewey, prevent children from pursuing their own propensities for learning and intellectual growth. It can therefore be assumed that if teachers want their students to engage with the educational process and employ their natural curiosities for knowledge, teachers must be aware of how their reactions to young children and the stresses of teaching influence this process.


title: John Dewey

text: Dewey's passions for teaching—a natural love for working with young children, a natural propensity to inquire about the subjects, methods and other social issues related to the profession, and a desire to share this acquired knowledge with others—are not a set of outwardly displayed mechanical skills. Rather, they may be viewed as internalized principles or habits which "work automatically, unconsciously" (Dewey, 1904, p. 15). According to Dewey, teacher-education programs must turn away from focusing on producing proficient practitioners because such practical skills related to instruction and discipline (e.g. creating and delivering lesson plans, classroom management, implementation of an assortment of content-specific methods) can be learned over time during their everyday school work with their students (Dewey, PST, 2010).


title: John Dewey

text: As Dewey notes, "The teacher who leaves the professional school with power in managing a class of children may appear to superior advantage the first day, the first week, the first month, or even the first year, as compared with some other teacher who has a much more vital command of the psychology, logic and ethics of development. But later 'progress' may consist only in perfecting and refining skill already possessed. Such persons seem to know how to teach, but they are not students of teaching. Even though they go on studying books of pedagogy, reading teachers' journals, attending teachers' institutes, etc., yet the root of the matter is not in them, unless they continue to be students of subject-matter, and students of mind-activity. Unless a teacher is such a student, he may continue to improve in the mechanics of school management, but he cannot grow as a teacher, an inspirer and director of soul-life" (Dewey, 1904, p. 15).


title: John Dewey

text: For Dewey, teacher education should focus not on producing persons who know how to teach as soon as they leave the program; rather, teacher education should be concerned with producing professional students of education who have the propensity to inquire about the subjects they teach, the methods used, and the activity of the mind as it gives and receives knowledge. According to Dewey, such a student is not superficially engaging with these materials, rather, the professional student of education has a genuine passion to inquire about the subjects of education, knowing that doing so ultimately leads to acquisitions of the skills related to teaching. Such students of education aspire for the intellectual growth within the profession that can only be achieved by immersing one's self in the lifelong pursuit of the intelligence, skills and character Dewey linked to the profession.


title: John Dewey

text: As Dewey notes, other professional fields, such as law and medicine cultivate a professional spirit in their fields to constantly study their work, their methods of their work, and a perpetual need for intellectual growth and concern for issues related to their profession. Teacher education, as a profession, has these same obligations (Dewey, 1904; Dewey, PST, 2010).


title: John Dewey

text: As Dewey notes, "An intellectual responsibility has got to be distributed to every human being who is concerned in carrying out the work in question, and to attempt to concentrate intellectual responsibility for a work that has to be done, with their brains and their hearts, by hundreds or thousands of people in a dozen or so at the top, no matter how wise and skillful they are, is not to concentrate responsibility—it is to diffuse irresponsibility" (Dewey, PST, 2010, p. 39). For Dewey, the professional spirit of teacher education requires of its students a constant study of school room work, constant study of children, of methods, of subject matter in its various adaptations to pupils. Such study will lead to professional enlightenment with regard to the daily operations of classroom teaching.


title: John Dewey

text: As well as his very active and direct involvement in setting up educational institutions such as the University of Chicago Laboratory Schools (1896) and The New School for Social Research (1919), many of Dewey's ideas influenced the founding of Bennington College and Goddard College in Vermont, where he served on the board of trustees. Dewey's works and philosophy also held great influence in the creation of the short-lived Black Mountain College in North Carolina, an experimental college focused on interdisciplinary study, and whose faculty included Buckminster Fuller, Willem de Kooning, Charles Olson, Franz Kline, Robert Duncan, Robert Creeley, and Paul Goodman, among others. Black Mountain College was the locus of the "Black Mountain Poets" a group of avant-garde poets closely linked with the Beat Generation and the San Francisco Renaissance.


title: John Dewey

text: Since the mid-1980s, Dewey's ideas have experienced revival as a major source of inspiration for the public journalism movement. Dewey's definition of "public," as described in "The Public and its Problems", has profound implications for the significance of journalism in society. As suggested by the title of the book, his concern was of the transactional relationship between publics and problems. Also implicit in its name, public journalism seeks to orient communication away from elite, corporate hegemony toward a civic public sphere. "The 'public' of public journalists is Dewey's public."


title: John Dewey

text: Dewey gives a concrete definition to the formation of a public. Publics are spontaneous groups of citizens who share the indirect effects of a particular action. Anyone affected by the indirect consequences of a specific action will automatically share a common interest in controlling those consequences, i.e., solving a common problem.Since every action generates unintended consequences, publics continuously emerge, overlap, and disintegrate.


title: John Dewey

text: In "The Public and its Problems", Dewey presents a rebuttal to Walter Lippmann's treatise on the role of journalism in democracy. Lippmann's model was a basic transmission model in which journalists took information given to them by experts and elites, repackaged that information in simple terms, and transmitted the information to the public, whose role was to react emotionally to the news. In his model, Lippmann supposed that the public was incapable of thought or action, and that all thought and action should be left to the experts and elites.


title: John Dewey

text: Dewey refutes this model by assuming that politics is the work and duty of each individual in the course of his daily routine. The knowledge needed to be involved in politics, in this model, was to be generated by the interaction of citizens, elites, experts, through the mediation and facilitation of journalism. In this model, not just the government is accountable, but the citizens, experts, and other actors as well.


title: John Dewey

text: Dewey also said that journalism should conform to this ideal by changing its emphasis from actions or happenings (choosing a winner of a given situation) to alternatives, choices, consequences, and conditions, in order to foster conversation and improve the generation of knowledge. Journalism would not just produce a static product that told what had already happened, but the news would be in a constant state of evolution as the public added value by generating knowledge. The "audience" would end, to be replaced by citizens and collaborators who would essentially be users, doing more with the news than simply reading it. Concerning his effort to change journalism, he wrote in "The Public and Its Problems": "Till the Great Society is converted in to a Great Community, the Public will remain in eclipse. Communication can alone create a great community" (Dewey, p. 142).


title: John Dewey

text: Dewey believed that communication creates a great community, and citizens who participate actively with public life contribute to that community. "The clear consciousness of a communal life, in all its implications, constitutes the idea of democracy." ("The Public and its Problems", p. 149). This Great Community can only occur with "free and full intercommunication." (p. 211) Communication can be understood as journalism.


title: John Dewey

text: As an atheist and a secular humanist in his later life, Dewey participated with a variety of humanistic activities from the 1930s into the 1950s, which included sitting on the advisory board of Charles Francis Potter's First Humanist Society of New York (1929); being one of the original 34 signatories of the first "Humanist Manifesto" (1933) and being elected an honorary member of the Humanist Press Association (1936).


title: John Dewey

text: His opinion of humanism is summarized in his own words from an article titled "What Humanism Means to Me", published in the June 1930 edition of "Thinker 2":


title: John Dewey

text: While Dewey was at the University of Chicago, his letters to his wife Alice and his colleague Jane Addams reveal that he closely followed the 1894 Pullman Strike, in which the employees of the Pullman Palace Car Factory in Chicago decided to go on strike after industrialist George Pullman refused to lower rents in his company town after cutting his workers’ wages by nearly 30 percent. On May 11, 1894, the strike became official, later gaining the support of the members of the American Railway Union, whose leader Eugene V. Debs called for a nationwide boycott of all trains including Pullman sleeping cars.


title: John Dewey

text: Considering most trains had Pullman cars, the main 24 lines out of Chicago were halted and the mail was stopped as the workers destroyed trains all over the United States. President Grover Cleveland used the mail as a justification to send in the National Guard, and ARU leader Eugene Debs was arrested.


title: John Dewey

text: Dewey wrote to Alice: "The only wonder is that when the 'higher classes' – damn them – take such views there aren't more downright socialists. [...] [T]hat a representative journal of the upper classes – damn them again – can take the attitude of that harper's weekly", referring to headlines such as "Monopoly" and "Repress the Rebellion", which claimed, in Dewey's words, to support the sensational belief that Debs was a "criminal" inspiring hate and violence in the equally "criminal" working classes. He concluded: "It shows what it is to be a higher class. And I fear Chicago Univ. is a capitalistic institution – that is, it too belongs to the higher classes".


title: John Dewey

text: Dewey was an advocate of US participation in the First World War. For this he was criticised by Randolph Bourne, a former student whose essay "Twilight of Idols", was published in the literary journal "Seven Arts" in October 1917. Bourne criticised Dewey's instrumental pragmatist philosophy.


title: John Dewey

text: As a major advocate of academic freedom, in 1935 Dewey, together with Albert Einstein and Alvin Johnson, became a member of the United States section of the International League for Academic Freedom, and in 1940, together with Horace M Kallen, edited a series of articles related to the Bertrand Russell Case.


title: John Dewey

text: He directed the famous Dewey Commission held in Mexico in 1937, which cleared Leon Trotsky of the charges made against him by Joseph Stalin, and marched for women's rights, among many other causes.


title: John Dewey

text: In 1939, Dewey was elected President of the League for Industrial Democracy, an organization with the goal of educating college students about the labor movement. The Student Branch of the L.I.D. would later become Students for a Democratic Society.


title: John Dewey

text: As well as defending the independence of teachers and opposing a communist takeover of the New York Teachers' Union, Dewey was involved in the organization that eventually became the National Association for the Advancement of Colored People, sitting as an executive on the NAACP's early executive board.


title: John Dewey

text: He was an avid supporter of Henry George's proposal for taxing land values. Of George, he wrote, "No man, no graduate of a higher educational institution, has a right to regard himself as an educated man in social thought unless he has some first-hand acquaintance with the theoretical contribution of this great American thinker." As honorary president of the Henry George School of Social Science, he wrote a letter to Henry Ford urging him to support the school.


title: John Dewey

text: Dewey's interests and writings included many topics, and according to the Stanford Encyclopedia of Philosophy, "a substantial part of his published output consisted of commentary on current domestic and international politics, and public statements on behalf of many causes. (He is probably the only philosopher in this encyclopedia to have published both on the Treaty of Versailles and on the value of displaying art in post offices.)"


title: John Dewey

text: In 1917, Dewey met F. M. Alexander in New York City and later wrote introductions to Alexander's "Man's Supreme Inheritance" (1918), "Constructive Conscious Control of the Individual" (1923) and "The Use of the Self" (1932). Alexander's influence is referenced in "Human Nature and Conduct" and "Experience and Nature."


title: John Dewey

text: As well as his contacts with people mentioned elsewhere in the article, he also maintained correspondence with Henri Bergson, William M. Brown, Martin Buber, George S. Counts, William Rainey Harper, Sidney Hook, and George Santayana.


title: John Dewey

text: Historians have examined his religious beliefs. Biographer Steven Clark Rockefeller traced Dewey's democratic convictions to his childhood attendance at the Congregational Church, with its strong proclamation of social ideals and the Social Gospel. Historian Edward A. White suggested in "Science and Religion in American Thought" (1952) that Dewey's work led to the 20th-century rift between religion and science.


title: John Dewey

text: Dewey went through an “evangelical” development as a child. As an adult he was negative, or at most neutral, about theology in education. He instead took a meliorist position with the goal of scientific humanism and educational and social reform without recourse to religion.


title: John Dewey

text: Besides publishing prolifically himself, Dewey also sat on the boards of scientific publications such as "Sociometry" (advisory board, 1942) and "Journal of Social Psychology" (editorial board, 1942), as well as having posts at other publications such as "New Leader" (contributing editor, 1949).


title: John Dewey

text: The following publications by John Dewey are referenced or mentioned in this article. A more complete list of his publications may be found at List of publications by John Dewey.


title: John Dewey

text: Dewey's Complete Writings is available in four multi-volume sets (38 volumes in all) from Southern Illinois University Press:


title: John Dewey

text: "The Collected Works of John Dewey: 1882–1953", "The Correspondence of John Dewey 1871–1952", and "The Lectures of John Dewey" are available online via monographic purchase to academic institutions and via subscription to individuals, and also in TEI format for university servers in the Past Masters series. (The CD-ROM has been discontinued.)


title: Leprechaun

text: A leprechaun () is a diminutive supernatural being in Irish folklore, classed by some as a type of solitary fairy. They are usually depicted as little bearded men, wearing a coat and hat, who partake in mischief. In later times, they have been depicted as shoe-makers who have a hidden pot of gold at the end of the rainbow.


title: Leprechaun

text: Leprechaun-like creatures rarely appear in Irish mythology and only became prominent in later folklore.


title: Leprechaun

text: The Anglo-Irish (Hiberno-English) word "leprechaun" is descended from Old Irish "luchorpán or lupracán", via various (Middle Irish) forms such as "luchrapán, lupraccán", (or var. "luchrupán").


title: Leprechaun

text: John O'Donovan's supplement to O'Reilly's "Irish-English Dictionary" defines as "a sprite, a pigmy; a fairy of a diminutive size, who always carries a purse containing a shilling".


title: Leprechaun

text: The Irish term "leithbrágan" in O'Reilly's Dictionary has also been recognized as an alternative spelling.


title: Leprechaun

text: Other variant spellings in English have included "lubrican", "leprehaun", and "lepreehawn". Some modern Irish books use the spelling "lioprachán". The first recorded instance of the word in the English language was in Dekker's comedy "The Honest Whore, Part 2" (1604): "As for your Irish lubrican, that spirit / Whom by preposterous charms thy lust hath rais'd / In a wrong circle."


title: Leprechaun

text: The word may have been coined as a compound of the roots "lú" or "laghu" (from "small") and "corp" (from "body"), or so it had been suggested by Whitley Stokes. However, research published in 2019 suggests that the word derives from the "Luperci" and the associated Roman festival of Lupercalia.


title: Leprechaun

text: Folk etymology derives the word from "leith" (half) and "bróg" (brogue), because of the frequent portrayal of the leprechaun as working on a single shoe, as evident in the alternative spelling "leithbrágan".


title: Leprechaun

text: The earliest known reference to the leprechaun appears in the medieval tale known as the ("Adventure of Fergus son of Léti"). The text contains an episode in which Fergus mac Léti, King of Ulster, falls asleep on the beach and wakes to find himself being dragged into the sea by three "lúchorpáin". He captures his abductors, who grant him three wishes in exchange for release.


title: Leprechaun

text: The leprechaun is said to be a solitary creature, whose principal occupation is making and cobbling shoes, and who enjoys practical jokes. In McAnally's 1888 account, the Leprechaun was not a professional cobbler, but was frequently seen mending his own shoes, as "he runs about so much he wears them out" with great frequency. This is, he claims, the perfect opportunity for a human being to capture the Leprechaun, refusing to release him until the Leprechaun gives his captor supernatural wealth.


title: Leprechaun

text: The leprechaun has been classed as a "solitary fairy" by the writer and amateur folklorist William Butler Yeats. Yeats was part of the revivalist literary movement greatly influential in "calling attention to the leprechaun" in the late 19th century. This classification by Yeats is derived from D. R. McAnally ("Irish Wonders", 1888) derived in turn from John O'Hanlon (1870).


title: Leprechaun

text: It is stressed that the leprechaun, though some may call it fairy, is clearly to be distinguished from the "Aos Sí" (or the 'good people') of the fairy mounds ("sidhe") and raths. Leprachaun being solitary is one distinguishing characteristic, but additionally, the leprachaun is thought to only engage in pranks on the level of mischief, and requiring special caution, but in contrast, the "Aos Sí" may carry out deeds more menacing to humans, e.g., the spiriting away of children.


title: Leprechaun

text: This identification of leprechaun as a fairy has been consigned to popular notion by modern folklorist Diarmuid Ó Giolláin. Ó Giolláin observes that the dwarf of Teutonic and other traditions as well as the household familiar are more amenable to comparison.


title: Leprechaun

text: According to William Butler Yeats, the great wealth of these fairies comes from the "treasure-crocks, buried of old in war-time", which they have uncovered and appropriated. According to David Russell McAnally the leprechaun is the son of an "evil spirit" and a "degenerate fairy" and is "not wholly good nor wholly evil".


title: Leprechaun

text: The leprechaun originally had a different appearance depending on where in Ireland he was found. Prior to the 20th century, it was generally held that the leprechaun wore red, not green. Samuel Lover, writing in 1831, describes the leprechaun as... quite a beau in his dress, notwithstanding, for he wears a red square-cut coat, richly laced with gold, and inexpressible of the same, cocked hat, shoes and buckles.


title: Leprechaun

text: According to Yeats, the solitary fairies, like the leprechaun, wear red jackets, whereas the "trooping fairies" wear green. The leprechaun's jacket has seven rows of buttons with seven buttons to each row. On the western coast, he writes, the red jacket is covered by a frieze one, and in Ulster the creature wears a cocked hat, and when he is up to anything unusually mischievous, he leaps onto a wall and spins, balancing himself on the point of the hat with his heels in the air.


title: Leprechaun

text: This dress could vary by region, however. In McAnally's account there were differences between leprechauns or Logherymans from different regions:


title: Leprechaun

text: In a poem entitled "The Lepracaun; or, Fairy Shoemaker", 18th century Irish poet William Allingham describes the appearance of the leprechaun as:


title: Leprechaun

text: The modern image of the leprechaun sitting on a toadstool, having a red beard and green hat, etc. is clearly a more modern invention, or borrowed from other strands of European folklore. The most likely explanation for the modern day Leprechaun appearance is that green is a traditional national Irish color dating back as far as 1642. The hat might be derived from the style of outdated fashion still common in Ireland in the 19th century. This style of fashion was commonly worn by Irish immigrants to the United States, since some Elizabethan era clothes were still common in Ireland in the 19th century long after they were out of fashion, as depicted by the Stage Irish. The buckle shoes and other garments also have their origin in the Elizabethan period in Ireland.


title: Leprechaun

text: The leprechaun is related to the "clurichaun" and the "far darrig" in that he is a solitary creature. Some writers even go as far as to substitute these second two less well-known spirits for the leprechaun in stories or tales to reach a wider audience. The clurichaun is considered by some to be merely a leprechaun on a drinking spree.


title: Leprechaun

text: In the politics of the Republic of Ireland, leprechauns have been used to refer to the twee aspects of the tourism field in Ireland. This can be seen from this example of John A. Costello addressing the Oireachtas in 1963—


title: Leprechaun

text: For many years, we were afflicted with the miserable trivialities of our tourist advertising. Sometimes it descended to the lowest depths, to the caubeen and the shillelagh, not to speak of the leprechaun.


title: Leprechaun

text: Films, television cartoons and advertising have popularised a specific image of leprechauns which bears little resemblance to anything found in the cycles of Irish folklore. It has been argued that the popularised image of a leprechaun is little more than a series of stereotypes based on derogatory 19th-century caricatures.


title: Leprechaun

text: Many Celtic Music groups have used the term Leprechaun LeperKhanz as part of their naming convention or as an album title. Even popular forms of American music have used the mythological character, including heavy metal, celtic metal, punk rock and jazz.


title: Leprechaun

text: Nobel Prize-winning economist Paul Krugman coined the term "leprechaun economics" to describe distorted or unsound economic data, which he first used in a tweet on 12 July 2016 in response to the publication by the Irish Central Statistics Office (CSO) that Irish GDP had grown by 26.3%, and Irish GNP had grown by 18.7%, in the 2015 Irish national accounts. The growth was subsequently shown to be due to Apple restructuring its double Irish tax scheme which the EU Commission had fined €13bn in 2004–2014 Irish unpaid taxes, the largest corporate tax fine in history. The term has been used many times since.


title: Leprechaun

text: In America, Leprechauns are often associated with St. Patrick's Day along with the color green and shamrocks.


title: Leprechaun

text: The Disney film "Darby O'Gill and the Little People" (1959)—based on Herminie Templeton Kavanagh's "Darby O'Gill" books—which features a leprechaun king, is a work in which Fergus mac Léti was "featured parenthetically". In the film, the captured leprechaun king grants three wishes, like Fergus in the saga.


title: Leprechaun

text: While the film project was in development, Walt Disney was in contact with, and consulting Séamus Delargy and the Irish Folklore Commission, but never asked for leprechaun material, even though a large folkloric repository on such subject was housed by the commission.


title: Kapil Sharma

text: Kapil Sharma (born Kapil Punj; 2 April 1981) is an Indian stand-up comedian, television host from Punjab, India, Primarily known for hosting "The Kapil Sharma Show". He won the stand-up comedy reality show, The Great Indian Laughter Challenge season 3 in 2007.


title: Kapil Sharma

text: He previously hosted and produced the television comedy shows such as "Comedy Nights with Kapil," "Family Time with Kapil" on Colors TV and Sony TV channels respectively. He has won multiple seasons of comedy reality show "Comedy circus" of Sony TV along with various partners and in 2011 participated in singing reality show "Star ya rockstar" of Zee TV, where he finished as a second runner up.


title: Kapil Sharma

text: He worked in some films such as "Bhavnao Ko Samjho" (2010)", Kis Kisko Pyaar Karoon" (2015)", Firangi" (2017) and did short appearances in "ABCD 2" (2015)"." He did Hindi dubbing for "The Angry Birds Movie 2" (2019).


title: Kapil Sharma

text: Sharma was born in a Punjabi family in the city of Amritsar of Punjab, India as Kapil Punj. His father Jeetendra Kumar Punj was a head constable in Punjab Police, while his mother Janak Rani is a homemaker. His father was diagnosed with cancer in 1997 and died in 2004 at AIIMS in Delhi. He studied at Shri Ram Ashram Senior Secondary School, Amristar and Hindu College in Amritsar. He is featured in the list of prominent alumni of Apeejay College of Fine Arts, Jalandhar. Sharma has a brother named Ashok Kumar Sharma, who is a Police constable and a sister named Pooja Pawan Devgan.


title: Kapil Sharma

text: Sharma was in relationship with Preeti Simoes for eight years. Simoes also worked as his manager, their affair started from Comedy nights with Kapil and was both together until 2017.


title: Kapil Sharma

text: He married Ginni Chatrath in Jalandhar on 12 December 2018. They had a daughter on 10 December 2019. On 1 February 2021, the couple had another child, a son.


title: Kapil Sharma

text: Sharma rose to fame after winning the comedy reality television show "The Great Indian Laughter Challenge" in 2007, for which he won a cash prize of INR ₹10 lakh. He had previously worked in the Punjabi show "Hasde Hasaande Ravo" on MH One channel. Sharma has stated that he moved to Mumbai in order to become a singer.


title: Kapil Sharma

text: He participated in Sony's "Comedy Circus" and went on to win six seasons of the show. He also hosted the dance reality show "Jhalak Dikhhla Jaa Season 6" and another comedy show "Chhote Miyan". Sharma was seen as a contestant in the show "Ustaadon Ka Ustaad" in 2008. In 2011, he participated as a contestent in Zee TV's singing reality show "Star Ya Rockstar", he fished as runner up. In 2013, Kapil launched his own show, "Comedy Nights with Kapil", under his banner "K9 Productions" on Colors TV.


title: Kapil Sharma

text: At the "CNN-IBN Indian of the Year awards" 2013, Sharma was felicitated with the Indian of the Year award in the entertainment category by veteran actor Amol Palekar. In the same year he did live stage shows in Oman. During the 2014 Lok Sabha Elections, he was appointed the Brand Ambassador by the Delhi Election Commission.


title: Kapil Sharma

text: Sharma was the co-host of the 60th Filmfare Awards in 2015 along with Karan Johar. He was the presenter for the fourth season of Celebrity Cricket League, 2014. He appeared as a guest on the opening episode of the eighth season of the Indian television game show "Kaun Banega Crorepati" and also as a celebrity guest on "The Anupam Kher Show". He also appeared as a guest in Koffee With Karan in 2017.


title: Kapil Sharma

text: Sharma made his Bollywood debut as the male lead in the movie "Kis Kisko Pyaar Karoon", a romantic-comedy directed by Abbas Mustan opposite four actresses, Elli Avram, Manjari Phadnis, Simran Kaur Mundi and Sai Lokur. The film was released on 25 September 2015 to mixed reviews from critics, but did record-breaking opening day business for a debut. In the same year he singed and paid to do six live shows in North America but the event organiser Amit Jaitly alleged that Sharma not did show in one city and thus filed a court case for breach of contract against Sharma in New York's court. Jaitly also accused that Sharma is not taking his phone calls, the case is pending in New York's court.


title: Kapil Sharma

text: His show "Comedy Nights with Kapil" on Colors aired its last episode on 24 January 2016. Sharma then began a new show titled "The Kapil Sharma Show" on Sony Entertainment Television under his "K9 Productions". The Kapil Sharma Show debuted on 23 April 2016 to a positive response from the viewers.


title: Kapil Sharma

text: In 2017, he did not recorded his TV show on multiple times and cancelled shootings, due to it several actors like Ajay Devgn, Shah Rukh Khan and their crew had to return from the sets when Kapil Sharma did not showed up. Later Kapil Sharma admitted in to an Ayurvedic "ashram" in Karnataka to leave his Alcohol addiction but he left the "ashram" before attending full treatment of 40 days, in 12 days. He told to DNA (newspaper) in an interview that he had suffered from high blood pressure and other helth issues. Prior to this Sharma assaulted his employee and fellow comedian on his show, Sunil Grover after drinking alcohol and abused other fellow comedians. After this Grover quite Sharma's TV show.


title: Kapil Sharma

text: His second movie "Firangi" was released on 1 December 2017. Directed by Rajiev Dhingra and produced by Sharma himself, "Firangi" was a period drama film set in the year 1920. Sharma played the role of Manga. Renuka Vyavahare of The Times of India in review wrote, 'Firangi is a boring film', gave 2.0/5 stars and other critics, panned it for bad story, slow speed. It emerged as a big flop at the box-office. The 25 crore film managed to earn 10 crore and Sharma suffered losses.


title: Kapil Sharma

text: His next show was launched on 25 March 2018 stating as "Family Time With Kapil Sharma" which was ended on 1 April after only 3 episodes. In 2018, he produced a Punjabi movie named "Son of Manjeet Singh" which was released on 12 October 2018. His show "The Kapil Sharma Show" was renewed with a new season which started airing on 29 December 2018, produced by Salman Khan.


title: Kapil Sharma

text: In 2020, it was announced he will star in a kids comedy show, titled "The Honey Bunny Show With Kapil Sharma" on Sony Yay. In January 2020, Kapil Sharma - Krushna Abhishek and other members of his Sony TV show did live show in Dubai of United Arab Emirates.


title: Kapil Sharma

text: In January 2022, it was announced that a biopic on his life is under development. Titled as "Funkaar" the film will be directed by Mrighdeep Singh Lamba.


title: Kapil Sharma

text: "The Kapil Sharma Show" initiated airing on Sony from September 10, 2022. The show's one of the main actor Krushna Abhishek left the show after monetary differences. Before the start of shoot in June–July, Sharma did live shows in North America.


title: Kapil Sharma

text: In 2016, Sharma tagged Indian prime minister Narendra Modi in a tweet and alleged that Brihanmumbai Municipal Corporation (BMC) took 5 Lakh rupees bribe from him for construction of his office. “I am paying 15 crores income tax from last five years and still I have to pay 5 lacs bribe to BMC office for making my office Narendra Modi, "Yeh hain aapke achhe din"?", he tweeted. In response chief of BMC's vigilance department asked him names of the people who took bribe and assured to take stringent action against them. But later revealed that Sharma himself was doing illegal activities. BMC issued stop work notice to him and asked to stop illegal extensions work in his two bunglows, ground in Andheri and told to demolish illegal work in next 24 hours. On 4 August 2016, BMC demolished parts of the extensions and their officials alleged that Kapil Sharma did internal changes in his properties and office without leagal permission from BMC.


title: Kapil Sharma

text: In 2018, Sharma did a show for Pakistan Super League in Dubai, United Arab Emirates. It angard people. Maharashtrian party Shiv Sena slammed Sharma and said, "Kapil Sharma is making a mockery of India's honour. He just wants to earn money and doesn't care about the country, we strongly condemn Sharma for performing during PSL", Sena said. Situation of India with its western neighbouring nation is bad from 2008 Mumbai terrorist attack, In it 168 people died and 238 severely injured in an unprecedented terrorist attack.


title: Kapil Sharma

text: In 2018, Kapil Sharma abused a journalist Vicky Lalwani of SpotboyE in a telephone conversation, later leaked by Lalwani, Sharma used foul language and asked journalist reason for his negative articles about him. After the conversation gone viral on social media, Sharma field a police complaint against Vicky Lalwani, his ex-managers Preeti Simoes and Neeti Simoes for trying to extort INR 25 lakhs from him as well as alleged in police complaint that, both sisters were used to take money from the people who use to arrive in Film City, Mumbai to see his show and Preeti-Neeti manufactured miss understandings between him and his fellow comedians of his show and arriving guests. Simoes said all these alligations are false and made up stories. Preeti Simoes was girlfriend of Kapil Sharma. She and her sister Neeti Simoes worked in Kapil Sharma's production or with him for eight years until 2017. But fault happened between Preeti and Kapil, after later announced his engagement with Ginny Charath in March 2017. Sharma also abused a "Spotboye" and its editor Vicky Lalwani by doing series of tweets, his employees tried it to cover-up by saying his account was hacked but later Sharma confessed that the abusive tweets was done by himself. Twitterati slammed Sharma for foul tweets and some expressed shock. On 8 April 2018, "Spotboye" filed a counter police report against Sharma for doing intimidation, abuse and threats.


title: Kapil Sharma

text: Multiple times various people accused Kapil Sharma for his degrotory comments about women. Once in 2014, he did a joke about a pregnant woman delivering a baby while traveling on his TV show, Comedy nights with Kapil. Women's rights activists filed complaint against him. Many accused him of doing sexiest, vulgar and body shame remarks on women's.


title: Kapil Sharma

text: Sharma has been known for his efforts in promoting animal rights. He and the cast of "Comedy Nights with Kapil" appeared in a PETA campaign to promote adoption of homeless cats and dogs. In July 2014, he adopted a homeless dog, a retired police dog from Mumbai. He has also campaigned to save tortured elephants across the country. Sharma was nominated for the "Swachh Bharat Abhiyan" by the Indian Prime Minister Narendra Modi for which he campaigned and regularly promotes on his show.


title: Kapil Sharma

text: Sharma was nominated in 2014 for the "Swachh Bharat Abhiyan" by the Indian Prime Minister Narendra Modi to spread awareness among people for cleanliness and other hygiene related social issues. For his contribution towards the mission through his show, he was invited to the Rashtrapati Bhavan by President Pranab Mukherjee in September 2015 to acknowledge his contribution.


title: Comet

text: A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena are due to the effects of solar radiation and the solar wind acting upon the nucleus of the comet. Comet nuclei range from a few hundred meters to tens of kilometers across and are composed of loose collections of ice, dust, and small rocky particles. The coma may be up to 15 times Earth's diameter, while the tail may stretch beyond one astronomical unit. If sufficiently bright, a comet may be seen from Earth without the aid of a telescope and may subtend an arc of 30° (60 Moons) across the sky. Comets have been observed and recorded since ancient times by many cultures and religions.


title: Comet

text: Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several millions of years. Short-period comets originate in the Kuiper belt or its associated scattered disc, which lie beyond the orbit of Neptune. Long-period comets are thought to originate in the Oort cloud, a spherical cloud of icy bodies extending from outside the Kuiper belt to halfway to the nearest star. Long-period comets are set in motion towards the Sun from the Oort cloud by gravitational perturbations caused by passing stars and the galactic tide. Hyperbolic comets may pass once through the inner Solar System before being flung to interstellar space. The appearance of a comet is called an apparition.


title: Comet

text: Comets are distinguished from asteroids by the presence of an extended, gravitationally unbound atmosphere surrounding their central nucleus. This atmosphere has parts termed the coma (the central part immediately surrounding the nucleus) and the tail (a typically linear section consisting of dust or gas blown out from the coma by the Sun's light pressure or outstreaming solar wind plasma). However, extinct comets that have passed close to the Sun many times have lost nearly all of their volatile ices and dust and may come to resemble small asteroids. Asteroids are thought to have a different origin from comets, having formed inside the orbit of Jupiter rather than in the outer Solar System. The discovery of main-belt comets and active centaur minor planets has blurred the distinction between asteroids and comets. In the early 21st century, the discovery of some minor bodies with long-period comet orbits, but characteristics of inner solar system asteroids, were called Manx comets. They are still classified as comets, such as C/2014 S3 (PANSTARRS). Twenty-seven Manx comets were found from 2013 to 2017.


title: Comet

text: The word "comet" derives from the Old English from the Latin or . That, in turn, is a romanization of the Greek 'wearing long hair', and the "Oxford English Dictionary" notes that the term () already meant 'long-haired star, comet' in Greek. was derived from () 'to wear the hair long', which was itself derived from () 'the hair of the head' and was used to mean 'the tail of a comet'.


title: Comet

text: The astronomical symbol for comets (represented in Unicode) is , consisting of a small disc with three hairlike extensions.


title: Comet

text: The solid, core structure of a comet is known as the nucleus. Cometary nuclei are composed of an amalgamation of rock, dust, water ice, and frozen carbon dioxide, carbon monoxide, methane, and ammonia. As such, they are popularly described as "dirty snowballs" after Fred Whipple's model. Comets with a higher dust content have been called "icy dirtballs". The term "icy dirtballs" arose after observation of Comet 9P/Tempel 1 collision with an "impactor" probe sent by NASA Deep Impact mission in July 2005. Research conducted in 2014 suggests that comets are like "deep fried ice cream", in that their surfaces are formed of dense crystalline ice mixed with organic compounds, while the interior ice is colder and less dense.


title: Comet

text: The surface of the nucleus is generally dry, dusty or rocky, suggesting that the ices are hidden beneath a surface crust several metres thick. In addition to the gases already mentioned, the nuclei contain a variety of organic compounds, which may include methanol, hydrogen cyanide, formaldehyde, ethanol, ethane, and perhaps more complex molecules such as long-chain hydrocarbons and amino acids. In 2009, it was confirmed that the amino acid glycine had been found in the comet dust recovered by NASA's Stardust mission. In August 2011, a report, based on NASA studies of meteorites found on Earth, was published suggesting DNA and RNA components (adenine, guanine, and related organic molecules) may have been formed on asteroids and comets.


title: Comet

text: The outer surfaces of cometary nuclei have a very low albedo, making them among the least reflective objects found in the Solar System. The Giotto space probe found that the nucleus of Halley's Comet (1P/Halley) reflects about four percent of the light that falls on it, and Deep Space 1 discovered that Comet Borrelly's surface reflects less than 3.0%; by comparison, asphalt reflects seven percent. The dark surface material of the nucleus may consist of complex organic compounds. Solar heating drives off lighter volatile compounds, leaving behind larger organic compounds that tend to be very dark, like tar or crude oil. The low reflectivity of cometary surfaces causes them to absorb the heat that drives their outgassing processes.


title: Comet

text: Comet nuclei with radii of up to have been observed, but ascertaining their exact size is difficult. The nucleus of 322P/SOHO is probably only in diameter. A lack of smaller comets being detected despite the increased sensitivity of instruments has led some to suggest that there is a real lack of comets smaller than across. Known comets have been estimated to have an average density of . Because of their low mass, comet nuclei do not become spherical under their own gravity and therefore have irregular shapes.


title: Comet

text: Roughly six percent of the near-Earth asteroids are thought to be the extinct nuclei of comets that no longer experience outgassing, including 14827 Hypnos and 3552 Don Quixote.


title: Comet

text: Results from the "Rosetta" and "Philae" spacecraft show that the nucleus of 67P/Churyumov–Gerasimenko has no magnetic field, which suggests that magnetism may not have played a role in the early formation of planetesimals. Further, the ALICE spectrograph on "Rosetta" determined that electrons (within above the comet nucleus) produced from photoionization of water molecules by solar radiation, and not photons from the Sun as thought earlier, are responsible for the degradation of water and carbon dioxide molecules released from the comet nucleus into its coma. Instruments on the "Philae" lander found at least sixteen organic compounds at the comet's surface, four of which (acetamide, acetone, methyl isocyanate and propionaldehyde) have been detected for the first time on a comet.


title: Comet

text: The streams of dust and gas thus released form a huge and extremely thin atmosphere around the comet called the "coma". The force exerted on the coma by the Sun's radiation pressure and solar wind cause an enormous "tail" to form pointing away from the Sun.


title: Comet

text: The coma is generally made of water and dust, with water making up to 90% of the volatiles that outflow from the nucleus when the comet is within 3 to 4 astronomical units (450,000,000 to 600,000,000 km; 280,000,000 to 370,000,000 mi) of the Sun. The parent molecule is destroyed primarily through photodissociation and to a much smaller extent photoionization, with the solar wind playing a minor role in the destruction of water compared to photochemistry. Larger dust particles are left along the comet's orbital path whereas smaller particles are pushed away from the Sun into the comet's tail by light pressure.


title: Comet

text: Although the solid nucleus of comets is generally less than across, the coma may be thousands or millions of kilometers across, sometimes becoming larger than the Sun. For example, about a month after an outburst in October 2007, comet 17P/Holmes briefly had a tenuous dust atmosphere larger than the Sun. The Great Comet of 1811 also had a coma roughly the diameter of the Sun. Even though the coma can become quite large, its size can decrease about the time it crosses the orbit of Mars around from the Sun. At this distance the solar wind becomes strong enough to blow the gas and dust away from the coma, and in doing so enlarging the tail. Ion tails have been observed to extend one astronomical unit (150 million km) or more.


title: Comet

text: Both the coma and tail are illuminated by the Sun and may become visible when a comet passes through the inner Solar System, the dust reflects sunlight directly while the gases glow from ionisation. Most comets are too faint to be visible without the aid of a telescope, but a few each decade become bright enough to be visible to the naked eye. Occasionally a comet may experience a huge and sudden outburst of gas and dust, during which the size of the coma greatly increases for a period of time. This happened in 2007 to Comet Holmes.


title: Comet

text: In 1996, comets were found to emit X-rays. This greatly surprised astronomers because X-ray emission is usually associated with very high-temperature bodies. The X-rays are generated by the interaction between comets and the solar wind: when highly charged solar wind ions fly through a cometary atmosphere, they collide with cometary atoms and molecules, "stealing" one or more electrons from the atom in a process called "charge exchange". This exchange or transfer of an electron to the solar wind ion is followed by its de-excitation into the ground state of the ion by the emission of X-rays and far ultraviolet photons.


title: Comet

text: Bow shocks form as a result of the interaction between the solar wind and the cometary ionosphere, which is created by the ionization of gases in the coma. As the comet approaches the Sun, increasing outgassing rates cause the coma to expand, and the sunlight ionizes gases in the coma. When the solar wind passes through this ion coma, the bow shock appears.


title: Comet

text: The first observations were made in the 1980s and 1990s as several spacecraft flew by comets 21P/Giacobini–Zinner, 1P/Halley, and 26P/Grigg–Skjellerup. It was then found that the bow shocks at comets are wider and more gradual than the sharp planetary bow shocks seen at, for example, Earth. These observations were all made near perihelion when the bow shocks already were fully developed.


title: Comet

text: The "Rosetta" spacecraft observed the bow shock at comet 67P/Churyumov–Gerasimenko at an early stage of bow shock development when the outgassing increased during the comet's journey toward the Sun. This young bow shock was called the "infant bow shock". The infant bow shock is asymmetric and, relative to the distance to the nucleus, wider than fully developed bow shocks.


title: Comet

text: In the outer Solar System, comets remain frozen and inactive and are extremely difficult or impossible to detect from Earth due to their small size. Statistical detections of inactive comet nuclei in the Kuiper belt have been reported from observations by the Hubble Space Telescope but these detections have been questioned. As a comet approaches the inner Solar System, solar radiation causes the volatile materials within the comet to vaporize and stream out of the nucleus, carrying dust away with them.


title: Comet

text: The streams of dust and gas each form their own distinct tail, pointing in slightly different directions. The tail of dust is left behind in the comet's orbit in such a manner that it often forms a curved tail called the type II or dust tail. At the same time, the ion or type I tail, made of gases, always points directly away from the Sun because this gas is more strongly affected by the solar wind than is dust, following magnetic field lines rather than an orbital trajectory. On occasions—such as when Earth passes through a comet's orbital plane, the antitail, pointing in the opposite direction to the ion and dust tails, may be seen.


title: Comet

text: The observation of antitails contributed significantly to the discovery of solar wind. The ion tail is formed as a result of the ionization by solar ultra-violet radiation of particles in the coma. Once the particles have been ionized, they attain a net positive electrical charge, which in turn gives rise to an "induced magnetosphere" around the comet. The comet and its induced magnetic field form an obstacle to outward flowing solar wind particles. Because the relative orbital speed of the comet and the solar wind is supersonic, a bow shock is formed upstream of the comet in the flow direction of the solar wind. In this bow shock, large concentrations of cometary ions (called "pick-up ions") congregate and act to "load" the solar magnetic field with plasma, such that the field lines "drape" around the comet forming the ion tail.


title: Comet

text: If the ion tail loading is sufficient, the magnetic field lines are squeezed together to the point where, at some distance along the ion tail, magnetic reconnection occurs. This leads to a "tail disconnection event". This has been observed on a number of occasions, one notable event being recorded on 20 April 2007, when the ion tail of Encke's Comet was completely severed while the comet passed through a coronal mass ejection. This event was observed by the STEREO space probe.


title: Comet

text: In 2013, ESA scientists reported that the ionosphere of the planet Venus streams outwards in a manner similar to the ion tail seen streaming from a comet under similar conditions."


title: Comet

text: Uneven heating can cause newly generated gases to break out of a weak spot on the surface of comet's nucleus, like a geyser. These streams of gas and dust can cause the nucleus to spin, and even split apart. In 2010 it was revealed dry ice (frozen carbon dioxide) can power jets of material flowing out of a comet nucleus. Infrared imaging of Hartley 2 shows such jets exiting and carrying with it dust grains into the coma.


title: Comet

text: Most comets are small Solar System bodies with elongated elliptical orbits that take them close to the Sun for a part of their orbit and then out into the further reaches of the Solar System for the remainder. Comets are often classified according to the length of their orbital periods: The longer the period the more elongated the ellipse.


title: Comet

text: Periodic comets or short-period comets are generally defined as those having orbital periods of less than 200 years. They usually orbit more-or-less in the ecliptic plane in the same direction as the planets. Their orbits typically take them out to the region of the outer planets (Jupiter and beyond) at aphelion; for example, the aphelion of Halley's Comet is a little beyond the orbit of Neptune. Comets whose aphelia are near a major planet's orbit are called its "family". Such families are thought to arise from the planet capturing formerly long-period comets into shorter orbits.


title: Comet

text: At the shorter orbital period extreme, Encke's Comet has an orbit that does not reach the orbit of Jupiter, and is known as an Encke-type comet. Short-period comets with orbital periods less than 20 years and low inclinations (up to 30 degrees) to the ecliptic are called traditional Jupiter-family comets (JFCs). Those like Halley, with orbital periods of between 20 and 200 years and inclinations extending from zero to more than 90 degrees, are called Halley-type comets (HTCs). , 94 HTCs have been observed, compared with 744 identified JFCs.


title: Comet

text: Recently discovered main-belt comets form a distinct class, orbiting in more circular orbits within the asteroid belt.


title: Comet

text: Because their elliptical orbits frequently take them close to the giant planets, comets are subject to further gravitational perturbations. Short-period comets have a tendency for their aphelia to coincide with a giant planet's semi-major axis, with the JFCs being the largest group. It is clear that comets coming in from the Oort cloud often have their orbits strongly influenced by the gravity of giant planets as a result of a close encounter. Jupiter is the source of the greatest perturbations, being more than twice as massive as all the other planets combined. These perturbations can deflect long-period comets into shorter orbital periods.


title: Comet

text: Based on their orbital characteristics, short-period comets are thought to originate from the centaurs and the Kuiper belt/scattered disc —a disk of objects in the trans-Neptunian region—whereas the source of long-period comets is thought to be the far more distant spherical Oort cloud (after the Dutch astronomer Jan Hendrik Oort who hypothesized its existence). Vast swarms of comet-like bodies are thought to orbit the Sun in these distant regions in roughly circular orbits. Occasionally the gravitational influence of the outer planets (in the case of Kuiper belt objects) or nearby stars (in the case of Oort cloud objects) may throw one of these bodies into an elliptical orbit that takes it inwards toward the Sun to form a visible comet. Unlike the return of periodic comets, whose orbits have been established by previous observations, the appearance of new comets by this mechanism is unpredictable. When flung into the orbit of the sun, and being continuously dragged towards it, tons of matter are stripped from the comets which greatly influence their lifetime; the more stripped, the shorter they live and vice versa.


title: Comet

text: Long-period comets have highly eccentric orbits and periods ranging from 200 years to thousands or even millions of years. An eccentricity greater than 1 when near perihelion does not necessarily mean that a comet will leave the Solar System. For example, Comet McNaught had a heliocentric osculating eccentricity of 1.000019 near its perihelion passage epoch in January 2007 but is bound to the Sun with roughly a 92,600-year orbit because the eccentricity drops below 1 as it moves farther from the Sun. The future orbit of a long-period comet is properly obtained when the osculating orbit is computed at an epoch after leaving the planetary region and is calculated with respect to the center of mass of the Solar System. By definition long-period comets remain gravitationally bound to the Sun; those comets that are ejected from the Solar System due to close passes by major planets are no longer properly considered as having "periods". The orbits of long-period comets take them far beyond the outer planets at aphelia, and the plane of their orbits need not lie near the ecliptic. Long-period comets such as C/1999 F1 and C/2017 T2 (PANSTARRS) can have aphelion distances of nearly with orbital periods estimated around 6 million years.


title: Comet

text: Single-apparition or non-periodic comets are similar to long-period comets because they also have parabolic or slightly hyperbolic trajectories when near perihelion in the inner Solar System. However, gravitational perturbations from giant planets cause their orbits to change. Single-apparition comets have a hyperbolic or parabolic osculating orbit which allows them to permanently exit the Solar System after a single pass of the Sun. The Sun's Hill sphere has an unstable maximum boundary of . Only a few hundred comets have been seen to reach a hyperbolic orbit (e > 1) when near perihelion that using a heliocentric unperturbed two-body best-fit suggests they may escape the Solar System.


title: Comet

text: , only two objects have been discovered with an eccentricity significantly greater than one: 1I/ʻOumuamua and 2I/Borisov, indicating an origin outside the Solar System. While ʻOumuamua, with an eccentricity of about 1.2, showed no optical signs of cometary activity during its passage through the inner Solar System in October 2017, changes to its trajectory—which suggests outgassing—indicate that it is probably a comet. On the other hand, 2I/Borisov, with an estimated eccentricity of about 3.36, has been observed to have the coma feature of comets, and is considered the first detected interstellar comet. Comet C/1980 E1 had an orbital period of roughly 7.1 million years before the 1982 perihelion passage, but a 1980 encounter with Jupiter accelerated the comet giving it the largest eccentricity (1.057) of any known solar comet with a reasonable observation arc.<ref name="C/1980E1-jpl"></ref> Comets not expected to return to the inner Solar System include C/1980 E1, C/2000 U5, C/2001 Q4 (NEAT), C/2009 R1, C/1956 R1, and C/2007 F1 (LONEOS).


title: Comet

text: Some authorities use the term "periodic comet" to refer to any comet with a periodic orbit (that is, all short-period comets plus all long-period comets), whereas others use it to mean exclusively short-period comets. Similarly, although the literal meaning of "non-periodic comet" is the same as "single-apparition comet", some use it to mean all comets that are not "periodic" in the second sense (that is, to also include all comets with a period greater than 200 years).


title: Comet

text: Early observations have revealed a few genuinely hyperbolic (i.e. non-periodic) trajectories, but no more than could be accounted for by perturbations from Jupiter. Comets from interstellar space are moving with velocities of the same order as the relative velocities of stars near the Sun (a few tens of km per second). When such objects enter the Solar System, they have a positive specific orbital energy resulting in a positive velocity at infinity (formula_1) and have notably hyperbolic trajectories. A rough calculation shows that there might be four hyperbolic comets per century within Jupiter's orbit, give or take one and perhaps two orders of magnitude.


title: Comet

text: The Oort cloud is thought to occupy a vast space starting from between to as far as from the Sun. This cloud encases the celestial bodies that start at the middle of our solar system—the sun, all the way to outer limits of the Kuiper Belt. The Oort cloud consists of viable materials necessary for the creation of celestial bodies. The planets we have today, exist only because of the planetesimals (chunks of leftover space that assisted in the creation of planets) that were condensed and formed by the gravity of the sun. The eccentric made from these trapped planetesimals is why the Oort Cloud even exists. Some estimates place the outer edge at between . The region can be subdivided into a spherical outer Oort cloud of , and a doughnut-shaped inner cloud, the Hills cloud, of . The outer cloud is only weakly bound to the Sun and supplies the long-period (and possibly Halley-type) comets that fall to inside the orbit of Neptune. The inner Oort cloud is also known as the Hills cloud, named after J. G. Hills, who proposed its existence in 1981. Models predict that the inner cloud should have tens or hundreds of times as many cometary nuclei as the outer halo; it is seen as a possible source of new comets that resupply the relatively tenuous outer cloud as the latter's numbers are gradually depleted. The Hills cloud explains the continued existence of the Oort cloud after billions of years.


title: Comet

text: Exocomets beyond the Solar System have also been detected and may be common in the Milky Way. The first exocomet system detected was around Beta Pictoris, a very young A-type main-sequence star, in 1987. A total of 11 such exocomet systems have been identified , using the absorption spectrum caused by the large clouds of gas emitted by comets when passing close to their star. For ten years the Kepler space telescope was responsible for searching for planets and other forms outside of the solar system. The first transiting exocomets were found in February 2018 by a group consisting of professional astronomers and citizen scientists in light curves recorded by the Kepler Space Telescope. After Kepler Space Telescope retired in October 2018, a new telescope called TESS Telescope has taken over Kepler's mission. Since the launch of TESS, astronomers have discovered the transits of comets around the star Beta Pictoris using a light curve from TESS. Since TESS has taken over, astronomers have since been able to better distinguish exocomets with the spectroscopic method. New planets are detected by the white light curve method which is viewed as a symmetrical dip in the charts readings when a planet overshadows its parent star. However, after further evaluation of these light curves, it has been discovered that the asymmetrical patterns of the dips presented are caused by the tail of a comet or of hundreds of comets.


title: Comet

text: As a comet is heated during close passes to the Sun, outgassing of its icy components also releases solid debris too large to be swept away by radiation pressure and the solar wind. If Earth's orbit sends it through that trail of debris, which is composed mostly of fine grains of rocky material, there is likely to be a meteor shower as Earth passes through. Denser trails of debris produce quick but intense meteor showers and less dense trails create longer but less intense showers. Typically, the density of the debris trail is related to how long ago the parent comet released the material. The Perseid meteor shower, for example, occurs every year between 9 and 13 August, when Earth passes through the orbit of Comet Swift–Tuttle. Halley's Comet is the source of the Orionid shower in October.


title: Comet

text: Many comets and asteroids collided with Earth in its early stages. Many scientists think that comets bombarding the young Earth about 4 billion years ago brought the vast quantities of water that now fill Earth's oceans, or at least a significant portion of it. Others have cast doubt on this idea. The detection of organic molecules, including polycyclic aromatic hydrocarbons, in significant quantities in comets has led to speculation that comets or meteorites may have brought the precursors of life—or even life itself—to Earth. In 2013 it was suggested that impacts between rocky and icy surfaces, such as comets, had the potential to create the amino acids that make up proteins through shock synthesis. The speed at which the comets entered the atmosphere, combined with the magnitude of energy created after initial contact, allowed smaller molecules to condense into the larger macro-molecules that served as the foundation for life. In 2015, scientists found significant amounts of molecular oxygen in the outgassings of comet 67P, suggesting that the molecule may occur more often than had been thought, and thus less an indicator of life as has been supposed.


title: Comet

text: It is suspected that comet impacts have, over long timescales, also delivered significant quantities of water to Earth's Moon, some of which may have survived as lunar ice. Comet and meteoroid impacts are also thought to be responsible for the existence of tektites and australites.


title: Comet

text: Fear of comets as acts of God and signs of impending doom was highest in Europe from AD 1200 to 1650. The year after the Great Comet of 1618, for example, Gotthard Arthusius published a pamphlet stating that it was a sign that the Day of Judgment was near. He listed ten pages of comet-related disasters, including "earthquakes, floods, changes in river courses, hail storms, hot and dry weather, poor harvests, epidemics, war and treason and high prices".


title: Comet

text: By 1700 most scholars concluded that such events occurred whether a comet was seen or not. Using Edmond Halley's records of comet sightings, however, William Whiston in 1711 wrote that the Great Comet of 1680 had a periodicity of 574 years and was responsible for the worldwide flood in the Book of Genesis, by pouring water on Earth. His announcement revived for another century fear of comets, now as direct threats to the world instead of signs of disasters. Spectroscopic analysis in 1910 found the toxic gas cyanogen in the tail of Halley's Comet, causing panicked buying of gas masks and quack "anti-comet pills" and "anti-comet umbrellas" by the public.


title: Comet

text: If a comet is traveling fast enough, it may leave the Solar System. Such comets follow the open path of a hyperbola, and as such, they are called hyperbolic comets. Solar comets are only known to be ejected by interacting with another object in the Solar System, such as Jupiter. An example of this is Comet C/1980 E1, which was shifted from an orbit of 7.1 million years around the Sun, to a hyperbolic trajectory, after a 1980 close pass by the planet Jupiter. Interstellar comets such as 1I/ʻOumuamua and 2I/Borisov never orbited the Sun and therefore do not require a 3rd-body interaction to be ejected from the Solar System.


title: Comet

text: Jupiter-family comets and long-period comets appear to follow very different fading laws. The JFCs are active over a lifetime of about 10,000 years or ~1,000 orbits whereas long-period comets fade much faster. Only 10% of the long-period comets survive more than 50 passages to small perihelion and only 1% of them survive more than 2,000 passages. Eventually most of the volatile material contained in a comet nucleus evaporates, and the comet becomes a small, dark, inert lump of rock or rubble that can resemble an asteroid. Some asteroids in elliptical orbits are now identified as extinct comets. Roughly six percent of the near-Earth asteroids are thought to be extinct comet nuclei.


title: Comet

text: The nucleus of some comets may be fragile, a conclusion supported by the observation of comets splitting apart. A significant cometary disruption was that of Comet Shoemaker–Levy 9, which was discovered in 1993. A close encounter in July 1992 had broken it into pieces, and over a period of six days in July 1994, these pieces fell into Jupiter's atmosphere—the first time astronomers had observed a collision between two objects in the Solar System. Other splitting comets include 3D/Biela in 1846 and 73P/Schwassmann–Wachmann from 1995 to 2006. Greek historian Ephorus reported that a comet split apart as far back as the winter of 372–373 BC. Comets are suspected of splitting due to thermal stress, internal gas pressure, or impact.


title: Comet

text: Comets 42P/Neujmin and 53P/Van Biesbroeck appear to be fragments of a parent comet. Numerical integrations have shown that both comets had a rather close approach to Jupiter in January 1850, and that, before 1850, the two orbits were nearly identical.


title: Comet

text: Some comets have been observed to break up during their perihelion passage, including great comets West and Ikeya–Seki. Biela's Comet was one significant example when it broke into two pieces during its passage through the perihelion in 1846. These two comets were seen separately in 1852, but never again afterward. Instead, spectacular meteor showers were seen in 1872 and 1885 when the comet should have been visible. A minor meteor shower, the Andromedids, occurs annually in November, and it is caused when Earth crosses the orbit of Biela's Comet.


title: Comet

text: Some comets meet a more spectacular end – either falling into the Sun or smashing into a planet or other body. Collisions between comets and planets or moons were common in the early Solar System: some of the many craters on the Moon, for example, may have been caused by comets. A recent collision of a comet with a planet occurred in July 1994 when Comet Shoemaker–Levy 9 broke up into pieces and collided with Jupiter.


title: Comet

text: The names given to comets have followed several different conventions over the past two centuries. Prior to the early 20th century, most comets were referred to by the year when they appeared, sometimes with additional adjectives for particularly bright comets; thus, the "Great Comet of 1680", the "Great Comet of 1882", and the "Great January Comet of 1910".


title: Comet

text: After Edmond Halley demonstrated that the comets of 1531, 1607, and 1682 were the same body and successfully predicted its return in 1759 by calculating its orbit, that comet became known as Halley's Comet. Similarly, the second and third known periodic comets, Encke's Comet and Biela's Comet, were named after the astronomers who calculated their orbits rather than their original discoverers. Later, periodic comets were usually named after their discoverers, but comets that had appeared only once continued to be referred to by the year of their appearance.


title: Comet

text: In the early 20th century, the convention of naming comets after their discoverers became common, and this remains so today. A comet can be named after its discoverers or an instrument or program that helped to find it. For example, in 2019, astronomer Gennadiy Borisov observed a comet that appeared to have originated outside of the solar system; the comet was named 2I/Borisov after him.


title: Comet

text: From ancient sources, such as Chinese oracle bones, it is known that comets have been noticed by humans for millennia. Until the sixteenth century, comets were usually considered bad omens of deaths of kings or noble men, or coming catastrophes, or even interpreted as attacks by heavenly beings against terrestrial inhabitants.


title: Comet

text: Aristotle (384–322 BC) was the first known scientist to use various theories and observational facts to employ a consistent, structured cosmological theory of comets. He believed that comets were atmospheric phenomena, due to the fact that they could appear outside of the zodiac and vary in brightness over the course of a few days. Aristotle's cometary theory arose from his observations and cosmological theory that everything in the cosmos is arranged in a distinct configuration. Part of this configuration was a clear separation between the celestial and terrestrial, believing comets to be strictly associated with the latter. According to Aristotle, comets must be within the sphere of the moon and clearly separated from the heavens. Also in the 4th century BC, Apollonius of Myndus supported the idea that comets moved like the planets. Aristotelian theory on comets continued to be widely accepted throughout the Middle Ages, despite several discoveries from various individuals challenging aspects of it.


title: Comet

text: In the 1st century AD, Seneca the Younger questioned Aristotle's logic concerning comets. Because of their regular movement and imperviousness to wind, they cannot be atmospheric, and are more permanent than suggested by their brief flashes across the sky. He pointed out that only the tails are transparent and thus cloudlike, and argued that there is no reason to confine their orbits to the zodiac. In criticizing Apollonius of Myndus, Seneca argues, "A comet cuts through the upper regions of the universe and then finally becomes visible when it reaches the lowest point of its orbit." While Seneca did not author a substantial theory of his own, his arguments would spark much debate among Aristotle's critics in the 16th and 17th centuries.


title: Comet

text: Also in the 1st century, Pliny the Elder believed that comets were connected with political unrest and death. Pliny observed comets as "human like", often describing their tails with "long hair" or "long beard". His system for classifying comets according to their color and shape was used for centuries.


title: Comet

text: In India, by the 6th century astronomers believed that comets were celestial bodies that re-appeared periodically. This was the view expressed in the 6th century by the astronomers Varāhamihira and Bhadrabahu, and the 10th-century astronomer Bhaṭṭotpala listed the names and estimated periods of certain comets, but it is not known how these figures were calculated or how accurate they were. In 1301, the Italian painter Giotto was the first person to accurately and anatomically portray a comet. In his work "Adoration of the Magi," Giotto's depiction of Halley's Comet in the place of the Star of Bethlehem would go unmatched in accuracy until the 19th century and be bested only with the invention of photography.


title: Comet

text: Astrological interpretations of comets proceeded to take precedence clear into the 15th century, despite the presence of modern scientific astronomy beginning to take root. Comets continued to forewarn of disaster, as seen in the "Luzerner Schilling" chronicles and in the warnings of Pope Callixtus III. In 1578, German Lutheran bishop Andreas Celichius defined comets as "the thick smoke of human sins ... kindled by the hot and fiery anger of the Supreme Heavenly Judge". The next year, Andreas Dudith stated that "If comets were caused by the sins of mortals, they would never be absent from the sky."


title: Comet

text: Crude attempts at a parallax measurement of Halley's Comet were made in 1456, but were erroneous. Regiomontanus was the first to attempt to calculate diurnal parallax by observing the great comet of 1472. His predictions were not very accurate, but they were conducted in the hopes of estimating the distance of a comet from the Earth.


title: Comet

text: In the 16th century, Tycho Brahe and Michael Maestlin demonstrated that comets must exist outside of Earth's atmosphere by measuring the parallax of the Great Comet of 1577. Within the precision of the measurements, this implied the comet must be at least four times more distant than from Earth to the Moon. Based on observations in 1664, Giovanni Borelli recorded the longitudes and latitudes of comets that he observed, and suggested that cometary orbits may be parabolic. Galileo Galilei, one of the most renowned astronomers to date, even attempted writings on comets in "The Assayer". He rejected Brahe's theories on the parallax of comets and claimed that they may be a mere optical illusion. Intrigued as early scientists were about the nature of comets, Galileo could not help but throw about his own theories despite little personal observation. Maestlin's student Johannes Kepler responded to these unjust criticisms in his work "Hyperaspistes." Jakob Bernoulli published another attempt to explain comets (Conamen Novi Systematis Cometarum) in 1682.


title: Comet

text: Also occurring in the early modern period was the study of comets and their astrological significance in medical disciplines. Many healers of this time considered medicine and astronomy to be inter-disciplinary and employed their knowledge of comets and other astrological signs for diagnosing and treating patients.


title: Comet

text: Isaac Newton, in his "Principia Mathematica" of 1687, proved that an object moving under the influence of gravity by an inverse square law must trace out an orbit shaped like one of the conic sections, and he demonstrated how to fit a comet's path through the sky to a parabolic orbit, using the comet of 1680 as an example.


title: Comet

text: He describes comets as compact and durable solid bodies moving in oblique orbit and their tails as thin streams of vapor emitted by their nuclei, ignited or heated by the Sun. He suspected that comets were the origin of the life-supporting component of air. He also pointed out that comets usually appear near the Sun, and therefore most likely orbit it. On their luminosity, he stated, "The comets shine by the Sun's light, which they reflect," with their tails illuminated by "the Sun's light reflected by a smoke arising from [the coma]".


title: Comet

text: In 1705, Edmond Halley (1656–1742) applied Newton's method to 23 cometary apparitions that had occurred between 1337 and 1698. He noted that three of these, the comets of 1531, 1607, and 1682, had very similar orbital elements, and he was further able to account for the slight differences in their orbits in terms of gravitational perturbation caused by Jupiter and Saturn. Confident that these three apparitions had been three appearances of the same comet, he predicted that it would appear again in 1758–9. Halley's predicted return date was later refined by a team of three French mathematicians: Alexis Clairaut, Joseph Lalande, and Nicole-Reine Lepaute, who predicted the date of the comet's 1759 perihelion to within one month's accuracy. When the comet returned as predicted, it became known as Halley's Comet.


title: Comet

text: As early as the 18th century, some scientists had made correct hypotheses as to comets' physical composition. In 1755, Immanuel Kant hypothesized in his "Universal Natural History" that comets were condensed from "primitive matter" beyond the known planets, which is "feebly moved" by gravity, then orbit at arbitrary inclinations, and are partially vaporized by the Sun's heat as they near perihelion. In 1836, the German mathematician Friedrich Wilhelm Bessel, after observing streams of vapor during the appearance of Halley's Comet in 1835, proposed that the jet forces of evaporating material could be great enough to significantly alter a comet's orbit, and he argued that the non-gravitational movements of Encke's Comet resulted from this phenomenon.


title: Comet

text: In the 19th century, the Astronomical Observatory of Padova was an epicenter in the observational study of comets. Led by Giovanni Santini (1787–1877) and followed by Giuseppe Lorenzoni (1843–1914), this observatory was devoted to classical astronomy, mainly to the new comets and planets orbit calculation, with the goal of compiling a catalog of almost ten thousand stars. Situated in the Northern portion of Italy, observations from this observatory were key in establishing important geodetic, geographic, and astronomical calculations, such as the difference of longitude between Milan and Padua as well as Padua to Fiume. In addition to these geographic observations, correspondence within the observatory, particularly between Santini and another astronomer Giuseppe Toaldo, about the importance of comet and planetary orbital observations.


title: Comet

text: In 1950, Fred Lawrence Whipple proposed that rather than being rocky objects containing some ice, comets were icy objects containing some dust and rock. This "dirty snowball" model soon became accepted and appeared to be supported by the observations of an armada of spacecraft (including the European Space Agency's "Giotto" probe and the Soviet Union's "Vega 1" and "Vega 2") that flew through the coma of Halley's Comet in 1986, photographed the nucleus, and observed jets of evaporating material.


title: Comet

text: On 22 January 2014, ESA scientists reported the detection, for the first definitive time, of water vapor on the dwarf planet Ceres, the largest object in the asteroid belt. The detection was made by using the far-infrared abilities of the Herschel Space Observatory. The finding is unexpected because comets, not asteroids, are typically considered to "sprout jets and plumes". According to one of the scientists, "The lines are becoming more and more blurred between comets and asteroids." On 11 August 2014, astronomers released studies, using the Atacama Large Millimeter/Submillimeter Array (ALMA) for the first time, that detailed the distribution of HCN, HNC, , and dust inside the comae of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON).


title: Comet

text: Approximately once a decade, a comet becomes bright enough to be noticed by a casual observer, leading such comets to be designated as great comets. Predicting whether a comet will become a great comet is notoriously difficult, as many factors may cause a comet's brightness to depart drastically from predictions. Broadly speaking, if a comet has a large and active nucleus, will pass close to the Sun, and is not obscured by the Sun as seen from Earth when at its brightest, it has a chance of becoming a great comet. However, Comet Kohoutek in 1973 fulfilled all the criteria and was expected to become spectacular but failed to do so. Comet West, which appeared three years later, had much lower expectations but became an extremely impressive comet.


title: Comet

text: The Great Comet of 1577 is a well-known example of a great comet. It passed near Earth as a non-periodic comet and was seen by many, including well-known astronomers Tycho Brahe and Taqi ad-Din. Observations of this comet led to several significant findings regarding cometary science, especially for Brahe.


title: Comet

text: The late 20th century saw a lengthy gap without the appearance of any great comets, followed by the arrival of two in quick succession—Comet Hyakutake in 1996, followed by Hale–Bopp, which reached maximum brightness in 1997 having been discovered two years earlier. The first great comet of the 21st century was C/2006 P1 (McNaught), which became visible to naked eye observers in January 2007. It was the brightest in over 40 years.


title: Comet

text: A sungrazing comet is a comet that passes extremely close to the Sun at perihelion, generally within a few million kilometers. Although small sungrazers can be completely evaporated during such a close approach to the Sun, larger sungrazers can survive many perihelion passages. However, the strong tidal forces they experience often lead to their fragmentation.


title: Comet

text: About 90% of the sungrazers observed with SOHO are members of the Kreutz group, which all originate from one giant comet that broke up into many smaller comets during its first passage through the inner Solar System. The remainder contains some sporadic sungrazers, but four other related groups of comets have been identified among them: the Kracht, Kracht 2a, Marsden, and Meyer groups. The Marsden and Kracht groups both appear to be related to Comet 96P/Machholz, which is also the parent of two meteor streams, the Quadrantids and the Arietids.


title: Comet

text: Of the thousands of known comets, some exhibit unusual properties. Comet Encke (2P/Encke) orbits from outside the asteroid belt to just inside the orbit of the planet Mercury whereas the Comet 29P/Schwassmann–Wachmann currently travels in a nearly circular orbit entirely between the orbits of Jupiter and Saturn. 2060 Chiron, whose unstable orbit is between Saturn and Uranus, was originally classified as an asteroid until a faint coma was noticed. Similarly, Comet Shoemaker–Levy 2 was originally designated asteroid .