An eclipse is an astronomical event that occurs when an astronomical object is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer. This alignment of three celestial objects is known as a syzygy. Apart from syzygy, the term eclipse is used when a spacecraft reaches a position where it can observe two celestial bodies so aligned. An eclipse is the result of either a transit; the term eclipse is most used to describe either a solar eclipse, when the Moon's shadow crosses the Earth's surface, or a lunar eclipse, when the Moon moves into the Earth's shadow. However, it can refer to such events beyond the Earth–Moon system: for example, a planet moving into the shadow cast by one of its moons, a moon passing into the shadow cast by its host planet, or a moon passing into the shadow of another moon. A binary star system can produce eclipses if the plane of the orbit of its constituent stars intersects the observer's position.
For the special cases of solar and lunar eclipses, these only happen during an "eclipse season", the two times of each year when the plane of the Earth's orbit around the Sun crosses with the plane of the Moon's orbit around the Earth. The type of solar eclipse that happens during each season depends on apparent sizes of the Sun and Moon. If the orbit of the Earth around the Sun, the Moon's orbit around the Earth were both in the same plane with each other eclipses would happen each and every month. There would be a lunar eclipse at every full moon, a solar eclipse at every new moon, and if both orbits were circular each solar eclipse would be the same type every month. It is because of non-circular differences that eclipses are not a common event. Lunar eclipses can be viewed from the entire nightside half of the Earth, but solar eclipses total eclipses occurring at any one particular point on the Earth's surface, are rare events that can be many decades apart. The term is derived from the ancient Greek noun ἔκλειψις, which means "the abandonment", "the downfall", or "the darkening of a heavenly body", derived from the verb ἐκλείπω which means "to abandon", "to darken", or "to cease to exist," a combination of prefix ἐκ-, from preposition ἐκ, "out," and of verb λείπω, "to be absent".
For any two objects in space, a line can be extended from the first through the second. The latter object will block some amount of light being emitted by the former, creating a region of shadow around the axis of the line; these objects are moving with respect to each other and their surroundings, so the resulting shadow will sweep through a region of space, only passing through any particular location in the region for a fixed interval of time. As viewed from such a location, this shadowing event is known as an eclipse; the cross-section of the objects involved in an astronomical eclipse are disk shaped. The region of an object's shadow during an eclipse is divided into three parts: The umbra, within which the object covers the light source. For the Sun, this light source is the photosphere; the antumbra, extending beyond the tip of the umbra, within which the object is in front of the light source but too small to cover it. The penumbra, within which the object is only in front of the light source.
A total eclipse occurs when the observer is within the umbra, an annular eclipse when the observer is within the antumbra, a partial eclipse when the observer is within the penumbra. During a lunar eclipse only the umbra and penumbra are applicable; this is because Earth's apparent diameter from the viewpoint of the Moon is nearly four times that of the Sun. The same terms may be used analogously in describing other eclipses, e.g. the antumbra of Deimos crossing Mars, or Phobos entering Mars's penumbra. The first contact occurs when the eclipsing object's disc first starts to impinge on the light source. For spherical bodies, when the occulting object is smaller than the star, the length of the umbra's cone-shaped shadow is given by: L = r ⋅ R o R s − R o where Rs is the radius of the star, Ro is the occulting object's radius, r is the distance from the star to the occulting object. For Earth, on average L is equal to 1.384×106 km, much larger than the Moon's semimajor axis of 3.844×105 km. Hence the umbral cone of the Earth can envelop the Moon during a lunar eclipse.
If the occulting object has an atmosphere, some of the luminosity of the star can be refracted into the volume of the umbra. This occurs, for example, during an eclipse of the Moon by the Earth—producing a faint, ruddy illumination of the Moon at totality. On Earth, the shadow cast during an eclipse moves approximately at 1 km per sec; this depends on the angle in which it is moving. An eclipse cycle takes place; this happens. A particular instance is the saros, which results in a repetition of a solar or lunar eclipse every 6,585.3 days, or a little over 18 years. Because this is not a
An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, moons and galaxies – in either observational or theoretical astronomy. Examples of topics or fields astronomers study include planetary science, solar astronomy, the origin or evolution of stars, or the formation of galaxies. Related but distinct subjects like physical cosmology. Astronomers fall under either of two main types: observational and theoretical. Observational astronomers analyze the data. In contrast, theoretical astronomers create and investigate models of things that cannot be observed; because it takes millions to billions of years for a system of stars or a galaxy to complete a life cycle, astronomers must observe snapshots of different systems at unique points in their evolution to determine how they form and die. They use these data to create models or simulations to theorize how different celestial objects work.
Further subcategories under these two main branches of astronomy include planetary astronomy, galactic astronomy, or physical cosmology. Astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using physical laws. Today, that distinction has disappeared and the terms "astronomer" and "astrophysicist" are interchangeable. Professional astronomers are educated individuals who have a Ph. D. in physics or astronomy and are employed by research institutions or universities. They spend the majority of their time working on research, although they quite have other duties such as teaching, building instruments, or aiding in the operation of an observatory; the number of professional astronomers in the United States is quite small. The American Astronomical Society, the major organization of professional astronomers in North America, has 7,000 members; this number includes scientists from other fields such as physics and engineering, whose research interests are related to astronomy.
The International Astronomical Union comprises 10,145 members from 70 different countries who are involved in astronomical research at the Ph. D. beyond. Contrary to the classical image of an old astronomer peering through a telescope through the dark hours of the night, it is far more common to use a charge-coupled device camera to record a long, deep exposure, allowing a more sensitive image to be created because the light is added over time. Before CCDs, photographic plates were a common method of observation. Modern astronomers spend little time at telescopes just a few weeks per year. Analysis of observed phenomena, along with making predictions as to the causes of what they observe, takes the majority of observational astronomers' time. Astronomers who serve as faculty spend much of their time teaching undergraduate and graduate classes. Most universities have outreach programs including public telescope time and sometimes planetariums as a public service to encourage interest in the field.
Those who become astronomers have a broad background in maths and computing in high school. Taking courses that teach how to research and present papers are invaluable. In college/university most astronomers get a Ph. D. in astronomy or physics. While there is a low number of professional astronomers, the field is popular among amateurs. Most cities have amateur astronomy clubs that meet on a regular basis and host star parties; the Astronomical Society of the Pacific is the largest general astronomical society in the world, comprising both professional and amateur astronomers as well as educators from 70 different nations. Like any hobby, most people who think of themselves as amateur astronomers may devote a few hours a month to stargazing and reading the latest developments in research. However, amateurs span the range from so-called "armchair astronomers" to the ambitious, who own science-grade telescopes and instruments with which they are able to make their own discoveries and assist professional astronomers in research.
List of astronomers List of women astronomers List of Muslim astronomers List of French astronomers List of Hungarian astronomers List of Russian astronomers and astrophysicists List of Slovenian astronomers Dallal, Ahmad. "Science and Technology". In Esposito, John; the Oxford History of Islam. Oxford University Press, New York. ISBN 0-300-15911-0. Kennedy, E. S.. "A Survey of Islamic Astronomical Tables. 46. Philadelphia: American Philosophical Society. Toomer, Gerald. "Al-Khwārizmī, Abu Jaʿfar Muḥammad ibn Mūsā". In Gillispie, Charles Coulston. Dictionary of Scientific Biography. 7. New York: Charles Scribner's Sons. ISBN 0-684-16962-2. American Astronomical Society European Astronomical Society International Astronomical Union Astronomical Society of the Pacific Space's astronomy news
Chinese people are the various individuals or ethnic groups associated with China through ancestry, nationality, citizenship or other affiliation. Han Chinese, the largest ethnic group in China, at about 92% of the population, are referred to as "Chinese" or "ethnic Chinese" in English, however there are dozens of other related and unrelated ethnic groups in China. A number of ethnic groups within China, as well as people elsewhere with ancestry in the region, may be referred to as Chinese people. Han Chinese people, the largest ethnic group in China, are referred to as "Chinese" or "ethnic Chinese" in English; the ethnic Chinese form a majority or notable minority in other countries, may comprise as much as 19% of the global human population. Other ethnic groups in China include the related Hui people or "Chinese Muslims", the Zhuang, Manchu and Miao, who make up the five largest ethnic minorities in mainland China with populations exceeding 10 million. In addition, the Yi, Tujia and Mongols each number populations between six and nine million.
The People's Republic of China recognizes 56 distinct ethnic groups, many of whom live in the special administrative regions of the country. However, there exists several smaller ethnicities who are "unrecognized" or subsumed as part another ethnic group; the Republic of China recognizes 14 tribes of Taiwanese aborigines, who together with unrecognized tribes comprise about 2% of the country's population. During the Qing dynasty the term "Chinese people" was used by the Qing government to refer to all subjects of the empire, including Han and Mongols. Zhonghua minzu, the "Chinese nation", is a supra-ethnic concept which includes all 56 ethnic groups living in China that are recognized by the government of the People's Republic of China, it includes established ethnic groups who have lived within the borders of China since at least the Qing Dynasty. The term zhonghua minzu was used during the Republic of China from 1911–1949 to refer to a subset of five ethnic groups in China; the term zhongguo renmin, "Chinese people", was the government's preferred term during the life of Mao Zedong.
The Nationality law of the People's Republic of China regulates nationality within the PRC. A person obtains nationality either by birth when at least one parent is of Chinese nationality or by naturalization. All people holding nationality of the People's Republic of China are citizens of the Republic; the Resident Identity Card is the official form of identification for residents of the People's Republic of China. Within the People's Republic of China, a Hong Kong Special Administrative Region passport or Macao Special Administrative Region passport may be issued to permanent residents of Hong Kong or Macao, respectively; the Nationality law of the Republic of China regulates nationality within the Republic of China. A person obtains nationality either by naturalization. A person with at least one parent, a national of the Republic of China, or born in the ROC to stateless parents qualifies for nationality by birth; the National Identification Card is an identity document issued to people who have household registration in Taiwan.
The Resident Certificate is an identification card issued to residents of the Republic of China who do not hold a National Identification Card. The relationship between Taiwanese nationality and Chinese nationality is disputed. Overseas Chinese refers to people of Chinese ethnicity or national heritage who live outside the People's Republic of China or Taiwan as the result of the continuing diaspora. People with one or more Chinese ancestors may consider themselves overseas Chinese; such people vary in terms of cultural assimilation. In some areas throughout the world ethnic enclaves known as Chinatowns are home to populations of Chinese ancestry. In Southeast Asia, Chinese people call themselves 華人, distinguished from or the citizens of the People's Republic of China or the Republic of China; this is so in the Chinese communities of Southeast Asia. The term Zhongguoren has a more ideological aspect in its use. Chinese Ethnic Minorities The Ranking of Ethnic Chinese Population, Overseas Compatriot Affairs Commission, Republic of China, archived from the original on 23 November 2013, retrieved 2008-11-02
Sunspots are temporary phenomena on the Sun's photosphere that appear as spots darker than the surrounding areas. They are regions of reduced surface temperature caused by concentrations of magnetic field flux that inhibit convection. Sunspots appear in pairs of opposite magnetic polarity, their number varies according to the 11-year solar cycle. Individual sunspots or groups of sunspots may last anywhere from a few days to a few months, but decay. Sunspots expand and contract as they move across the surface of the Sun, with diameters ranging from 16 km to 160,000 km; the larger variety are visible from Earth without the aid of a telescope. They may travel at relative speeds, or proper motions, of a few hundred meters per second when they first emerge. Indicating intense magnetic activity, sunspots accompany secondary phenomena such as coronal loops and reconnection events. Most solar flares and coronal mass ejections originate in magnetically active regions around visible sunspot groupings. Similar phenomena indirectly observed on stars other than the Sun are called starspots, both light and dark spots have been measured.
The earliest extant report of sunspots dates back to the Chinese Book of Changes, c. 800 BC. The first clear mention of a sunspot in Western literature, around 300 BC, was by the ancient Greek scholar Theophrastus, student of Plato and Aristotle and successor to the latter; the earliest surviving record of deliberate sunspot observation dates from 364 BC, based on comments by Chinese astronomer Gan De in a star catalogue. By 28 BC, Chinese astronomers were recording sunspot observations in official imperial records. Sunspots were first observed telescopically in late 1610 by English astronomer Thomas Harriot and Frisian astronomers Johannes and David Fabricius, who published a description in June 1611. Although they are at temperatures of 3,000–4,500 K, the contrast with the surrounding material at about 5,780 K leaves sunspots visible as dark spots; this is because the luminance of a heated black body at these temperatures varies with temperature—considerably more so than the variation in the total black-body radiation at all wavelengths.
Isolated from the surrounding photosphere a sunspot would be brighter than the Moon. Sunspots have two parts: the central umbra, the darkest part, where the magnetic field is vertical and the surrounding penumbra, lighter, where the magnetic field is more inclined. Any given appearance of a sunspot may last anywhere from a few days to a few months, though groups of sunspots and their active regions tend to last weeks or months, but all do decay and disappear. Sunspots expand and contract as they move across the surface of the Sun, with diameters ranging from 16 km to 160,000 km. Although the details of sunspot generation are still a matter of research, it appears that sunspots are the visible counterparts of magnetic flux tubes in the Sun's convective zone that get "wound up" by differential rotation. If the stress on the tubes reaches a certain limit, they puncture the Sun's surface. Convection is inhibited at the puncture points; the Wilson effect implies. Observations using the Zeeman effect show that prototypical sunspots come in pairs with opposite magnetic polarity.
From cycle to cycle, the polarities of leading and trailing sunspots change from north/south to south/north and back. Sunspots appear in groups. Magnetic pressure should tend to remove field concentrations, causing the sunspots to disperse, but sunspot lifetimes are measured in days to weeks. In 2001, observations from the Solar and Heliospheric Observatory using sound waves traveling below the photosphere were used to develop a three-dimensional image of the internal structure below sunspots. Sunspot activity cycles are with some variation in length. Over the solar cycle, sunspot populations rise and fall more slowly; the point of highest sunspot activity during a cycle is known as solar maximum, the point of lowest activity as solar minimum. This period is observed in most other solar activity and is linked to a variation in the solar magnetic field that changes polarity with this period. Early in the cycle, sunspots appear in the higher latitudes and move towards the equator as the cycle approaches maximum, following Spörer's law.
Spots from two adjacent cycles can co-exist for some time. Spots from adjacent cycles can be distinguished by direction of their magnetic field; the Wolf number sunspot index counts the average number of sunspots and groups of sunspots during specific intervals. The 11-year solar cycles are numbered sequentially, starting with the observations made in the 1750s. George Ellery Hale first linked magnetic fields and sunspots in 1908. Hale suggested that the sunspot cycle period is 22 years, covering two periods of increased and decreased sunspot numbers, accompanied by polar reversals of the solar magnetic dipole field. Horace W. Babcock proposed a qualitative model for the dynamics of the solar outer layers; the Babcock Model explains that magnetic fields cause the behavior described by Spörer's law, as well as other effects, whi
Simon & Schuster
Simon & Schuster, Inc. a subsidiary of CBS Corporation, is an American publishing company founded in New York City in 1924 by Richard Simon and Max Schuster. As of 2016, Simon & Schuster was publishing 2,000 titles annually under 35 different imprints. In 1924, Richard Simon's aunt, a crossword puzzle enthusiast, asked whether there was a book of New York World crossword puzzles, which were popular at the time. After discovering that none had been published and Max Schuster decided to launch a company to exploit the opportunity. At the time, Simon was a piano salesman and Schuster was editor of an automotive trade magazine, they pooled US$8,000, equivalent to $117 thousand today, to start a company that published crossword puzzles. The new publishing house used "fad" publishing to publish books that exploited current fads and trends. Simon called this "planned publishing". Instead of signing authors with a planned manuscript, they came up with their own ideas, hired writers to carry them out. In the 1930s, the publisher moved to what has been referred to as "Publisher's Row" on Park Avenue in Manhattan, New York.
In 1939, Simon & Schuster financially backed Robert Fair de Graff to found Pocket Books, America's first paperback publisher. In 1942, Simon & Schuster and Western Printing launched the Little Golden Books series in cooperation with the Artists and Writers Guild. In 1944, Marshall Field III, owner of the Chicago Sun, purchased Pocket Books; the company was sold back to Schuster following his death. In the 1950s and 1960s, many publishers including Simon & Schuster turned toward educational publishing due to the baby boom market. Pocket Books focused on paperbacks for the educational market instead of textbooks and started the Washington Square Press imprint in 1959. By 1964 it had published over 200 titles and was expected to put out another 400 by the end of that year. Books published under the imprint included classic reprints such as Lorna Doone, Tom Sawyer, Huckleberry Finn, Robinson Crusoe. In 1966, Max Schuster sold his half of Simon & Schuster to Leon Shimkin. Shimkin merged Simon & Schuster with Pocket Books under the name of Simon & Schuster.
In 1968, editor-in-chief Robert Gottlieb, who worked at Simon & Schuster since 1955 and edited several bestsellers including Joseph Heller's Catch-22, left abruptly to work at competitor Knopf, taking other influential S&S employees, Nina Bourne, Tony Schulte. In 1979, Richard Snyder was named CEO of the company. Over the next several years he would help grow the company substantially. After the 1983 death of Charles Bluhdorn, head of Gulf+Western who acquired Simon in Schuster in 1976, the company made the decision to diversify. Bluhdorn's successor Martin Davis told The New York Times, "Society was undergoing dramatic changes, so that there was a greater need for textbooks and educational information. We saw the opportunity to diversify into those areas, which are more stable and more profitable than trade publishing."In 1984, Simon & Schuster with CEO Richard E. Snyder acquired Esquire Corporation, buying everything but the magazine for $180 million. Prentice Hall was brought into the company fold in 1985 for over $700 million and was viewed by some executives to be a catalyst for change for the company as a whole.
This acquisition was followed by Silver Burdett in 1986, mapmaker Gousha in 1987 and Charles E. Simon in 1988. Part of the acquisition included educational publisher Allyn & Bacon which, according to editor and chief Michael Korda, became the "nucleus of S&S's educational and informational business." Three California educational companies were purchased between 1988 and 1990—Quercus, Fearon Education and Janus Book Publishers. In all, Simon & Schuster spent more than $1 billion in acquisitions between 1983 and 1991. In the 1980s, Snyder made an unsuccessful bid toward video publishing, believed to have led to the company's success in the audio book business. Snyder was dismayed to realize that Simon & Schuster did not own the video rights to Jane Fonda's Workout Book, a huge bestseller at the time, that the video company producing the VHS was making more money on the video; this prompted Snyder to ask editors to obtain video rights for every new book. Agents were reluctant to give these up—which meant the S&S Video division never took off.
According to Korda, the audio rights expanded into the audio division which by the 1990s would be a major business for Simon & Schuster. In 1989, Gulf and Western Inc. owner of Simon & Schuster, changed its name to Paramount Communications Inc. In 1990, The New York Times described Simon & Schuster as the largest book publisher in the United States with sales of $1.3 billion the previous year. That same year, Schuster acquired the children's publisher Green Tiger Press. In 1994, was fired from S&S and was replaced by the company's president and chief operating officer Jonathan Newcomb; that year, Paramount was sold to Viacom. In 1998, Viacom sold Simon & Schuster's educational operations, including Prentice Hall and Macmillan, to Pearson PLC, the global publisher and owner of Penguin and the Financial Times; the professional and reference operations were sold to Hicks Muse Furst. In 2002, Simon & Schuster acquired its Canadian distributor Distican. Simon & Schuster began publishing in Canada in 2013.
At the end of 2005, Viacom split into two companies: CBS Corporation, the other retaining the Viacom name. In 2005, Simon & Schuster acquired Strebor Books International, founded in 1999 by author Kristina Laferne Roberts, who has written under the pseudonym "Zane." A year in 2006, Simon & Schuster launched the conservative imprint Threshold Editions. In 2009, Simon & Schuster
Hipparchus of Nicaea was a Greek astronomer and mathematician. He is considered the founder of trigonometry but is most famous for his incidental discovery of precession of the equinoxes. Hipparchus was born in Nicaea and died on the island of Rhodes, Greece, he is known to have been a working astronomer at least from 162 to 127 BC. Hipparchus is considered the greatest ancient astronomical observer and, by some, the greatest overall astronomer of antiquity, he was the first whose accurate models for the motion of the Sun and Moon survive. For this he made use of the observations and the mathematical techniques accumulated over centuries by the Babylonians and by Meton of Athens, Aristyllus, Aristarchus of Samos and Eratosthenes, among others, he developed trigonometry and constructed trigonometric tables, he solved several problems of spherical trigonometry. With his solar and lunar theories and his trigonometry, he may have been the first to develop a reliable method to predict solar eclipses.
His other reputed achievements include the discovery and measurement of Earth's precession, the compilation of the first comprehensive star catalog of the western world, the invention of the astrolabe of the armillary sphere, which he used during the creation of much of the star catalogue. There is a strong tradition that Hipparchus was born in Nicaea, in the ancient district of Bithynia, in what today is the country Turkey; the exact dates of his life are not known, but Ptolemy attributes astronomical observations to him in the period from 147–127 BC, some of these are stated as made in Rhodes. His birth date was calculated by Delambre based on clues in his work. Hipparchus must have lived some time after 127 BC because he analyzed and published his observations from that year. Hipparchus obtained information from Alexandria as well as Babylon, but it is not known when or if he visited these places, he is believed to have died on the island of Rhodes, where he seems to have spent most of his life.
It is not known what Hipparchus's economic means were nor how he supported his scientific activities. His appearance is unknown: there are no contemporary portraits. In the 2nd and 3rd centuries coins were made in his honour in Bithynia that bear his name and show him with a globe. Little of Hipparchus's direct work survives into modern times. Although he wrote at least fourteen books, only his commentary on the popular astronomical poem by Aratus was preserved by copyists. Most of what is known about Hipparchus comes from Strabo's Geography and Pliny's Natural History in the 1st century. Hipparchus was amongst the first to calculate a heliocentric system, but he abandoned his work because the calculations showed the orbits were not circular as believed to be mandatory by the science of the time. Although a contemporary of Hipparchus', Seleucus of Seleucia, remained a proponent of the heliocentric model, Hipparchus' rejection of heliocentrism, supported by ideas from Aristotle, remained dominant for nearly 2000 years until Copernican heliocentrism turned the tide of the debate.
Hipparchus's only preserved work is Τῶν Ἀράτου καὶ Εὐδόξου φαινομένων ἐξήγησις. This is a critical commentary in the form of two books on a popular poem by Aratus based on the work by Eudoxus. Hipparchus made a list of his major works, which mentioned about fourteen books, but, only known from references by authors, his famous star catalog was incorporated into the one by Ptolemy, may be perfectly reconstructed by subtraction of two and two thirds degrees from the longitudes of Ptolemy's stars. The first trigonometric table was compiled by Hipparchus, now known as "the father of trigonometry". Hipparchus was in the international news in 2005, when it was again proposed that the data on the celestial globe of Hipparchus or in his star catalog may have been preserved in the only surviving large ancient celestial globe which depicts the constellations with moderate accuracy, the globe carried by the Farnese Atlas. There are a variety of mis-steps in the more ambitious 2005 paper, thus no specialists in the area accept its publicized speculation.
Lucio Russo has said that Plutarch, in his work On the Face in the Moon, was reporting some physical theories that we consider to be Newtonian and that these may have come from Hipparchus. According to one book review, both of these claims have been rejected by other scholars. A line in Plutarch's Table Talk states that Hipparchus counted 103049 compound propositions that can be formed from ten simple propositions. 103049 is the tenth Schröder–Hipparchus number, which counts the number of ways of adding one or more pairs of parentheses around consecutive subsequences of two or more items in any sequence of ten symbols. This has led to speculation that Hipparchus knew about enumerative combinatorics, a field of mathematics that developed independently in modern mathematics. Earlier Greek astronomers and mathematicians were influenced by Babylonian astronomy to some extent, for instance the period relations of the Metonic cycle and Saros cycle may have come from Babylonian sources (see "Babylonian astron