1.
Variable star
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A variable star is a star whose brightness as seen from Earth fluctuates. Many, possibly most, stars have at least some variation in luminosity, an ancient Egyptian calendar of lucky and unlucky days composed some 3,200 years ago may be the oldest preserved historical document of the discovery of a variable star, the eclipsing binary Algol. This discovery, combined with supernovae observed in 1572 and 1604, proved that the sky was not eternally invariable as Aristotle. In this way, the discovery of variable stars contributed to the revolution of the sixteenth. The second variable star to be described was the eclipsing variable Algol, by Geminiano Montanari in 1669, chi Cygni was identified in 1686 by G. Kirch, then R Hydrae in 1704 by G. D. Maraldi. By 1786 ten variable stars were known, John Goodricke himself discovered Delta Cephei and Beta Lyrae. Since 1850 the number of variable stars has increased rapidly, especially after 1890 when it became possible to identify variable stars by means of photography. The latest edition of the General Catalogue of Variable Stars lists more than 46,000 variable stars in the Milky Way, as well as 10,000 in other galaxies, and over 10,000 suspected variables. The most common kinds of variability involve changes in brightness, but other types of variability also occur, by combining light curve data with observed spectral changes, astronomers are often able to explain why a particular star is variable. Variable stars are generally analysed using photometry, spectrophotometry and spectroscopy, measurements of their changes in brightness can be plotted to produce light curves. Peak brightnesses in the curve are known as maxima, while troughs are known as minima. By estimating the magnitude and noting the time of observation a visual lightcurve can be constructed. The American Association of Variable Star Observers collects such observations from participants around the world, from the light curve the following data are derived, are the brightness variations periodical, semiperiodical, irregular, or unique. What is the period of the brightness fluctuations, what is the shape of the light curve. From the spectrum the following data are derived, what kind of star is it, what is its temperature, is it a single star, or a binary. does the spectrum change with time. In very few cases it is possible to make pictures of a stellar disk and these may show darker spots on its surface. Combining light curves with spectral data often gives a clue as to the changes occur in a variable star. For example, evidence for a star is found in its shifting spectrum because its surface periodically moves toward and away from us
2.
Constellation
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A constellation is formally defined as a region of the celestial sphere, with boundaries laid down by the International Astronomical Union. The constellation areas mostly had their origins in Western-traditional patterns of stars from which the constellations take their names, in 1922, the International Astronomical Union officially recognized the 88 modern constellations, which cover the entire sky. They began as the 48 classical Greek constellations laid down by Ptolemy in the Almagest, Constellations in the far southern sky are late 16th- and mid 18th-century constructions. 12 of the 88 constellations compose the zodiac signs, though the positions of the constellations only loosely match the dates assigned to them in astrology. The term constellation can refer to the stars within the boundaries of that constellation. Notable groupings of stars that do not form a constellation are called asterisms, when astronomers say something is “in” a given constellation they mean it is within those official boundaries. Any given point in a coordinate system can unambiguously be assigned to a single constellation. Many astronomical naming systems give the constellation in which an object is found along with a designation in order to convey a rough idea in which part of the sky it is located. For example, the Flamsteed designation for bright stars consists of a number, the word constellation seems to come from the Late Latin term cōnstellātiō, which can be translated as set of stars, and came into use in English during the 14th century. It also denotes 88 named groups of stars in the shape of stellar-patterns, the Ancient Greek word for constellation was ἄστρον. Colloquial usage does not draw a distinction between constellation in the sense of an asterism and constellation in the sense of an area surrounding an asterism. The modern system of constellations used in astronomy employs the latter concept, the term circumpolar constellation is used for any constellation that, from a particular latitude on Earth, never sets below the horizon. From the North Pole or South Pole, all constellations south or north of the equator are circumpolar constellations. In the equatorial or temperate latitudes, the term equatorial constellation has sometimes been used for constellations that lie to the opposite the circumpolar constellations. They generally include all constellations that intersect the celestial equator or part of the zodiac, usually the only thing the stars in a constellation have in common is that they appear near each other in the sky when viewed from the Earth. In galactic space, the stars of a constellation usually lie at a variety of distances, since stars also travel on their own orbits through the Milky Way, the star patterns of the constellations change slowly over time. After tens to hundreds of thousands of years, their familiar outlines will become unrecognisable, the terms chosen for the constellation themselves, together with the appearance of a constellation, may reveal where and when its constellation makers lived. The earliest direct evidence for the constellations comes from inscribed stones and it seems that the bulk of the Mesopotamian constellations were created within a relatively short interval from around 1300 to 1000 BC
3.
Alphabet
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An alphabet is a standard set of letters that is used to write one or more languages based upon the general principle that the letters represent phonemes of the spoken language. This is in contrast to other types of writing systems, such as syllabaries and logographies, the Proto-Canaanite script, later known as the Phoenician alphabet, is the first fully phonemic script. Thus the Phoenician alphabet is considered to be the first alphabet, the Phoenician alphabet is the ancestor of most modern alphabets, including Arabic, Greek, Latin, Cyrillic, Hebrew, and possibly Brahmic. Under a terminological distinction promoted by Peter T. Daniels, an alphabet is a script that represents both vowels and consonants as letters equally. In this narrow sense of the word the first true alphabet was the Greek alphabet, in other alphabetic scripts such as the original Phoenician, Hebrew or Arabic, letters predominantly or exclusively represent consonants, such a script is also called an abjad. A third type, called abugida or alphasyllabary, is one where vowels are shown by diacritics or modifications of consonantal letters, as in Devanagari. The Khmer alphabet is the longest, with 74 letters, there are dozens of alphabets in use today, the most popular being the Latin alphabet. Many languages use modified forms of the Latin alphabet, with additional letters formed using diacritical marks, while most alphabets have letters composed of lines, there are also exceptions such as the alphabets used in Braille. Alphabets are usually associated with an ordering of letters. This makes them useful for purposes of collation, specifically by allowing words to be sorted in alphabetical order and it also means that their letters can be used as an alternative method of numbering ordered items, in such contexts as numbered lists and number placements. The English word alphabet came into Middle English from the Late Latin word alphabetum, the Greek word was made from the first two letters, alpha and beta. The names for the Greek letters came from the first two letters of the Phoenician alphabet, aleph, which also meant ox, and bet, in the alphabet song in English, the term ABCs is used instead of the word alphabet. Knowing ones ABCs, in general, can be used as a metaphor for knowing the basics about anything, the history of the alphabet started in ancient Egypt. These glyphs were used as guides for logograms, to write grammatical inflections. Based on letter appearances and names, it is believed to be based on Egyptian hieroglyphs and this script had no characters representing vowels, although originally it probably was a syllabary, but unneeded symbols were discarded. An alphabetic cuneiform script with 30 signs including three that indicate the vowel was invented in Ugarit before the 15th century BC. This script was not used after the destruction of Ugarit, the Proto-Sinaitic script eventually developed into the Phoenician alphabet, which is conventionally called Proto-Canaanite before ca.1050 BC. The oldest text in Phoenician script is an inscription on the sarcophagus of King Ahiram and this script is the parent script of all western alphabets
4.
Serpens
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Serpens is a constellation of the northern hemisphere. One of the 48 constellations listed by the 2nd-century astronomer Ptolemy and it is unique among the modern constellations in being split into two non-contiguous parts, Serpens Caput to the west and Serpens Cauda to the east. Between these two lies the constellation of Ophiuchus, the Serpent-Bearer. In figurative representations, the body of the serpent is represented as passing behind Ophiuchus between Mu Serpentis in Serpens Caput and Nu Serpentis in Serpens Cauda. The brightest star in Serpens is the red giant star Alpha Serpentis, or Unukalhai, in Serpens Caput, also located in Serpens Caput are the naked-eye globular cluster Messier 5 and the naked-eye variables R Serpentis and Tau4 Serpentis. Part of the Milky Ways galactic plane passes through Serpens Cauda, the nebula measures 70 light-years by 50 light-years and contains the Pillars of Creation, three dust clouds that became famous for the image taken by the Hubble Space Telescope. In Greek mythology, Serpens represents a snake held by the healer Asclepius, represented in the sky by the constellation Ophiuchus, Asclepius once killed a snake, but the animal was subsequently resurrected after a second snake placed a revival herb on it before its death. As snakes shed their skin every year, they were known as the symbol of rebirth in ancient Greek society, although this is likely the logic for Serpens presence with Ophiuchus, the true reason is still not fully known. Sometimes, Serpens was depicted as coiling around Ophiuchus, but the majority of atlases showed Serpens passing either behind Ophiuchus body or between his legs. In some ancient atlases, the constellations Serpens and Ophiuchus were depicted as two separate constellations, although often they were shown as a single constellation. One notable figure to depict Serpens separately was Johann Bayer, thus, when Eugène Delporte established modern constellation boundaries in the 1920s, he elected to depict the two separately. However, this posed the problem of how to disentangle the two constellations, with Deporte deciding to split Serpens into two areas—the head and the tail—separated by the continuous Ophiuchus. These two areas known as Serpens Caput and Serpens Cauda, caput being the Latin word for head. In Chinese astronomy, most of the stars of Serpens represented part of a wall surrounding a marketplace, known as Tianshi, Serpens also contains a few Chinese constellations. Two stars in the tail represented part of Shilou, the tower with the market office, another star in the tail represented Liesi, jewel shops. One star in the head marked Tianru, the crown princes wet nurse, there were two serpent constellations in Babylonian astronomy, known as Mušḫuššu and Bašmu. It appears that Mušḫuššu was depicted as a hybrid of a dragon, a lion and a bird, Bašmu was a horned serpent and roughly corresponds to the Ὄφις constellation of Eudoxus of Cnidus on which the Ὄφις of Ptolemy is based. Serpens is the one of the 88 modern constellations to be split into two disconnected regions in the sky, Serpens Caput and Serpens Cauda
5.
Germany
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Germany, officially the Federal Republic of Germany, is a federal parliamentary republic in central-western Europe. It includes 16 constituent states, covers an area of 357,021 square kilometres, with about 82 million inhabitants, Germany is the most populous member state of the European Union. After the United States, it is the second most popular destination in the world. Germanys capital and largest metropolis is Berlin, while its largest conurbation is the Ruhr, other major cities include Hamburg, Munich, Cologne, Frankfurt, Stuttgart, Düsseldorf and Leipzig. Various Germanic tribes have inhabited the northern parts of modern Germany since classical antiquity, a region named Germania was documented before 100 AD. During the Migration Period the Germanic tribes expanded southward, beginning in the 10th century, German territories formed a central part of the Holy Roman Empire. During the 16th century, northern German regions became the centre of the Protestant Reformation, in 1871, Germany became a nation state when most of the German states unified into the Prussian-dominated German Empire. After World War I and the German Revolution of 1918–1919, the Empire was replaced by the parliamentary Weimar Republic, the establishment of the national socialist dictatorship in 1933 led to World War II and the Holocaust. After a period of Allied occupation, two German states were founded, the Federal Republic of Germany and the German Democratic Republic, in 1990, the country was reunified. In the 21st century, Germany is a power and has the worlds fourth-largest economy by nominal GDP. As a global leader in industrial and technological sectors, it is both the worlds third-largest exporter and importer of goods. Germany is a country with a very high standard of living sustained by a skilled. It upholds a social security and universal health system, environmental protection. Germany was a member of the European Economic Community in 1957. It is part of the Schengen Area, and became a co-founder of the Eurozone in 1999, Germany is a member of the United Nations, NATO, the G8, the G20, and the OECD. The national military expenditure is the 9th highest in the world, the English word Germany derives from the Latin Germania, which came into use after Julius Caesar adopted it for the peoples east of the Rhine. This in turn descends from Proto-Germanic *þiudiskaz popular, derived from *þeudō, descended from Proto-Indo-European *tewtéh₂- people, the discovery of the Mauer 1 mandible shows that ancient humans were present in Germany at least 600,000 years ago. The oldest complete hunting weapons found anywhere in the world were discovered in a mine in Schöningen where three 380, 000-year-old wooden javelins were unearthed
6.
Letter case
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Letter case is the distinction between the letters that are in larger upper case and smaller lower case in the written representation of certain languages. The writing systems that distinguish between the upper and lower case have two sets of letters, with each letter in one set usually having an equivalent in the other set. Basically, the two variants are alternative representations of the same letter, they have the same name and pronunciation. Letter case is generally applied in a fashion, with both upper- and lower-case letters appearing in a given piece of text. The choice of case is often prescribed by the grammar of a language or by the conventions of a particular discipline, in mathematics, letter case may indicate the relationship between objects, with upper-case letters often representing superior objects. In some contexts, it is conventional to use only one case, the terms upper case and lower case can be written as two consecutive words, connected with a hyphen, or as a single word. These terms originated from the layouts of the shallow drawers called type cases used to hold the movable type for letterpress printing. Traditionally, the letters were stored in a separate case that was located above the case that held the small letters. Majuscule, for palaeographers, is technically any script in which the letters have very few or very short ascenders and descenders, or none at all. By virtue of their impact, this made the term majuscule an apt descriptor for what much later came to be more commonly referred to as uppercase letters. The word is often spelled miniscule, by association with the word miniature. This has traditionally been regarded as a mistake, but is now so common that some dictionaries tend to accept it as a nonstandard or variant spelling. Miniscule is still less likely, however, to be used in reference to lower-case letters, the glyphs of lower-case letters can resemble smaller forms of the upper-case glyphs restricted to the base band or can look hardly related. There is more variation in the height of the minuscules, as some of them have higher or lower than the typical size. In Times New Roman, for instance, b, d, f, h, k, l, t are the letters with ascenders, and g, j, p, q, y are the ones with descenders. In addition, with old-style numerals still used by traditional or classical fonts,6 and 8 make up the ascender set. Writing systems using two separate cases are bicameral scripts, languages that use the Latin, Cyrillic, Greek, Coptic, Armenian, Adlam, Varang Kshiti, Cherokee, and Osage scripts use letter cases in their written form as an aid to clarity. Other bicameral scripts, which are not used for any modern languages, are Old Hungarian, Glagolitic, the Georgian alphabet has several variants, and there were attempts to use them as different cases, but the modern written Georgian language does not distinguish case
7.
Fraktur
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Fraktur is a calligraphic hand of the Latin alphabet and any of several blackletter typefaces derived from this hand. From this, Fraktur is sometimes contrasted with the Latin alphabet in northern European texts, similarly, the term Fraktur or Gothic is sometimes applied to all of the blackletter typefaces. Besides the 26 letters of the Latin alphabet, Fraktur includes the ß, vowels with umlauts, and the ſ. Some Fraktur typefaces also include a variant form of the letter r known as the r rotunda, most older Fraktur typefaces make no distinction between the majuscules I and J, even though the minuscules i and j are differentiated. One difference between the Fraktur and other blackletter scripts is that in the lower case o, the part of the bow is broken. In Danish texts composed in Fraktur, the letter ø was already preferred to the German, Fraktur types for printing were established by the Augsburg publisher Johann Schönsperger at the issuance of a series of Maximilians works such as his Prayer Book or the illustrated Theuerdank poem. In the 18th century, the German Theuerdank Fraktur was further developed by the Leipzig typographer Johann Gottlob Immanuel Breitkopf to create the typeset Breitkopf Fraktur, while over the succeeding centuries, most Central Europeans switched to Antiqua, German-speakers remained a notable holdout. Some books at that time used related blackletter fonts such as Schwabacher, however, the predominant typeface was the Normalfraktur and this move was hotly debated in Germany, where it was known as the Antiqua–Fraktur dispute. The shift affected mostly scientific writing in Germany, whereas most belletristic literature, the press was scolded for its frequent use of Roman characters under Jewish influence and German émigrés were urged to use only German script. This radically changed on January 3,1941, when Martin Bormann issued a circular to all public offices which declared Fraktur to be Judenlettern, German historian Albert Kapr has speculated that the régime had realized that Fraktur would inhibit communication in the territories occupied during World War II. Even with the abolition of Fraktur, some publications include elements of it in headlines, very occasionally, academic works still used Fraktur in the text itself. Notably, Joachim Jeremiass work Die Briefe an Timotheus und Titus was published in 1963 using Fraktur, more often, some ligatures ch, ck from Fraktur were used in antiqua-typed editions. That continued mostly up to the offset type period, Fraktur saw a brief resurgence after the War, but quickly disappeared in a Germany keen on modernising its appearance. In this modern decorative use, the rules about the use of long s and short s. Individual Fraktur letters are used in mathematics, which often denotes associated or parallel concepts by the same letter in different fonts. For example, a Lie group is denoted by G. A ring ideal might be denoted by a while an element is a ∈ a, the Fraktur c is also used to denote the cardinality of the continuum, that is, the cardinality of the real line. In model theory, A is used to denote an arbitrary model, in Unicode, Fraktur is treated as a font of the Latin alphabet, and is not encoded separately
8.
Nicolas-Louis de Lacaille
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Abbé Nicolas Louis de La Caille, sometimes spelled Lacaille, was a French astronomer. Born at Rumigny, he attended school in Mantes-sur-Seine, afterwards, he studied rhetoric and philosophy at the Collège de Lisieux and then theology at the Collège de Navarre. He was left destitute in 1731 by the death of his father, however, he was supported in his studies by the Duc de Bourbon, his fathers former patron. After he graduated, he did not accept ordination as a priest but took deacons orders and he was the author of a number of influential textbooks and a firm advocate of Newtonian gravitational theory. Among his students were Antoine Lavoisier and Jean Sylvain Bailly, both of whom were guillotined during the Revolution. His desire to determine the distances of the planets trigonometrically, using the longest possible baseline, led him to propose, in 1750 and this was officially sanctioned by Roland-Michel Barrin de La Galissonière. There, he constructed an observatory on the shore of Table Bay with the support of the Dutch Governor Ryk Tulbagh. The primary result of his stay was a catalogue of nearly 10,000 southern stars. In the course of his survey he took note of 42 nebulous objects and he also achieved his aim of determining the lunar and solar parallaxes. This work required near-simultaneous observations from Europe which were carried out by Jérôme Lalande and his southern catalogue, called Coelum Australe Stelliferum, was published posthumously in 1763. He found it necessary to introduce 14 new constellations which have become standard. One of these was Mons Mensa, the only named after a terrestrial feature. While at the Cape, La Caille determined the radius of the earth in the southern hemisphere and he set out a baseline in the Swartland plain north of present-day Darling. Using triangulation he then measured a 137 km arc of meridian between Cape Town and Aurora, determining the latitudes of the end points by means of astronomical observations, there is a memorial to his work at a location near Aurora, pictured here. His result suggested that the earth was more flattened towards the pole than towards the north. In 1838, Thomas Maclear, who was Astronomer Royal at the Cape, repeated the measurements over a longer baseline, La Caille was in fact an indefatigable calculator. Apart from constructing astronomical ephemerides and mathematical tables, he calculated a table of eclipses for 1800 years, Lalande said of him that, during a comparatively short life, he had made more observations and calculations than all the astronomers of his time put together. The quality of his work rivalled its quantity, while the disinterestedness, on his return to Paris in 1754, following a diversion to Mauritius, La Caille was distressed to find himself an object of public attention
9.
International Astronomical Union
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The International Astronomical Union is an international association of professional astronomers, at the PhD level and beyond, active in professional research and education in astronomy. Among other activities, it acts as the recognized authority for assigning designations to celestial bodies. The IAU is a member of the International Council for Science and its main objective is to promote and safeguard the science of astronomy in all its aspects through international cooperation. The IAU maintains friendly relations with organizations that include amateur astronomers in their membership, the IAU has its head office on the second floor of the Institut dAstrophysique de Paris in the 14th arrondissement of Paris. The IAU is also responsible for the system of astronomical telegrams which are produced and distributed on its behalf by the Central Bureau for Astronomical Telegrams, the Minor Planet Center also operates under the IAU, and is a clearinghouse for all non-planetary or non-moon bodies in the Solar System. The Working Group for Meteor Shower Nomenclature and the Meteor Data Center coordinate the nomenclature of meteor showers, the IAU was founded on July 28,1919, at the Constitutive Assembly of the International Research Council held in Brussels, Belgium. The 7 initial member states were Belgium, Canada, France, Great Britain, Greece, Japan, the first executive committee consisted of Benjamin Baillaud, Alfred Fowler, and four vice presidents, William Campbell, Frank Dyson, Georges Lecointe, and Annibale Riccò. Thirty-two Commissions were appointed at the Brussels meeting and focused on topics ranging from relativity to minor planets, the reports of these 32 Commissions formed the main substance of the first General Assembly, which took place in Rome, Italy, May 2–10,1922. By the end of the first General Assembly, ten nations had joined the Union. Although the Union was officially formed eight months after the end of World War I, the first 50 years of the Unions history are well documented. Subsequent history is recorded in the form of reminiscences of past IAU Presidents, twelve of the fourteen past General Secretaries in the period 1964-2006 contributed their recollections of the Unions history in IAU Information Bulletin No.100. Six past IAU Presidents in the period 1976–2003 also contributed their recollections in IAU Information Bulletin No.104, the IAU includes a total of 12,664 individual members who are professional astronomers from 96 countries worldwide. 83% of all members are male, while 17% are female, among them the unions current president. Membership also includes 79 national members, professional astronomical communities representing their countrys affiliation with the IAU, the sovereign body of the IAU is its General Assembly, which comprises all members. The Assembly determines IAU policy, approves the Statutes and By-Laws of the Union, the right to vote on matters brought before the Assembly varies according to the type of business under discussion. On budget matters, votes are weighted according to the subscription levels of the national members. A second category vote requires a turnout of at least two-thirds of national members in order to be valid, an absolute majority is sufficient for approval in any vote, except for Statute revision which requires a two-thirds majority. An equality of votes is resolved by the vote of the President of the Union, since 1922, the IAU General Assembly meets every three years, with the exception of the period between 1938 and 1948, due to World War II
10.
Friedrich Wilhelm Argelander
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Friedrich Wilhelm August Argelander was a German astronomer. He is known for his determinations of stellar brightnesses, positions, Argelander was born in Memel in the Kingdom of Prussia, the son of a father of Finnish descent, Johann Gottfried Argelander, and German mother, Wilhelmina Dorothea Grünhagen. He studied with Friedrich Bessel, and obtained his Ph. D. in 1822 at University of Königsberg, from 1823 until 1837, Argelander was the head of the Finnish observatory, first in Turku and then in Helsinki. He then moved to Bonn, Germany, there he designed and built a new observatory at the University of Bonn with funding approved directly by King Frederick William IV whom Argelander had become friends with in his childhood. Argelander excelled in developing effective, simple and fast methods for measuring star positions and magnitudes and he also measured star distances with heliometers. His, and his collaborators, great works of star cataloging. Argelander was the first astronomer to begin a study of variable stars. Only a handful were known when he began, and he was responsible for introducing the system of identifying them. He also made a determination of the direction in which the Sun was moving. In 1842, he discovered that Groombridge 1830 had a high proper motion. For many decades its proper motion was the highest known, today it still occupies third place, for a time, it was known as Argelanders Star. This was the last star map to be published without the use of photography, in 1863, Argelander helped lead in the founding an international organization of astronomers named the Astronomische Gesellschaft. Elected a foreign member of the Royal Swedish Academy of Sciences in 1846, elected a Foreign Honorary Member of the American Academy of Arts and Sciences in 1855. Was awarded the Gold Medal of the Royal Astronomical Society in 1863, orden Pour le Mérite für Wissenschaften und Künste in 1874. The three astronomical institutes of the Bonn University were merged and renamed as the Argelander-Institut für Astronomie in 2006, the crater Argelander on the Moon and the asteroid 1551 Argelander are named for him. Untersuchung über die Bahn des grossen Cometen vom Jahre 1811,4, Königsberg Asimov, asimovs Biographical Encyclopedia of Science and Technology. Monthly Notices of the Royal Astronomical Society, neue Uranometrie,1843 - Full digital facsimile, Linda Hall Library
11.
Star catalogue
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A star catalogue or star catalog, is an astronomical catalogue that lists stars. In astronomy, many stars are referred to simply by catalogue numbers, there are a great many different star catalogues which have been produced for different purposes over the years, and this article covers only some of the more frequently quoted ones. Star catalogues were compiled by many different ancient peoples, including the Babylonians, Greeks, Chinese, Persians, most modern catalogues are available in electronic format and can be freely downloaded from space agencies data center. Completeness and accuracy is described by the weakest apparent magnitude V, from their existing records, it is known that the ancient Egyptians recorded the names of only a few identifiable constellations and a list of thirty-six decans that were used as a star clock. They are better known by their Assyrian-era name Three Stars Each and these star catalogues, written on clay tablets, listed thirty-six stars, twelve for Anu along the celestial equator, twelve for Ea south of that, and twelve for Enlil to the north. In Ancient Greece, the astronomer and mathematician Eudoxus laid down a set of the classical constellations around 370 BC. His catalogue Phaenomena, rewritten by Aratus of Soli between 275 and 250 BC as a poem, became one of the most consulted astronomical texts in antiquity. It contains descriptions of the positions of the stars, the shapes of the constellations, approximately in the 3rd century BC, the Greek astronomers Timocharis of Alexandria and Aristillus created another star catalogue. Hipparchus completed his star catalogue in 129 BC, which he compared to Timocharis and this led him to determine the first value of the precession of the equinoxes. In the 2nd century, Ptolemy of Roman Egypt published a star catalogue as part of his Almagest, ptolemys catalogue was based almost entirely on an earlier one by Hipparchus. It remained the star catalogue in the Western and Arab worlds for over eight centuries. The earliest known inscriptions for Chinese star names were written on oracle bones, sources dating from the Zhou Dynasty which provide star names include the Zuo Zhuan, the Shi Jing, and the Canon of Yao in the Book of Documents. The Lüshi Chunqiu written by the Qin statesman Lü Buwei provides most of the names for the twenty-eight mansions, an earlier lacquerware chest found in the Tomb of Marquis Yi of Zeng contains a complete list of the names of the twenty-eight mansions. Star catalogues are traditionally attributed to Shi Shen and Gan De, the Shi Shen astronomy is attributed to Shi Shen, and the Astronomic star observation to Gan De. It was not until the Han Dynasty that astronomers started to observe and record names for all the stars that were apparent in the night sky, not just those around the ecliptic. A star catalogue is featured in one of the chapters of the late 2nd-century-BC history work Records of the Grand Historian by Sima Qian and contains the schools of Shi Shen and Gan Des work. For his Spiritual Constitution of the Universe of 120 AD, the astronomer Zhang Heng compiled a star catalogue comprising 124 constellations, Chinese constellation names were later adopted by the Koreans and Japanese. A large number of star catalogues were published by Muslim astronomers in the medieval Islamic world and these were mainly Zij treatises, including Arzachels Tables of Toledo, the Maragheh observatorys Zij-i Ilkhani and Ulugh Begs Zij-i-Sultani
12.
R Coronae Borealis
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R Coronae Borealis is a peculiar low-mass yellow supergiant star, and is the prototype of the rare RCB class of variable stars, which fade by several magnitudes at irregular intervals. Over successive months it gradually returns to its brightness, giving it the nickname Fade-Out star. The variability of R CrB was discovered by the English astronomer Edward Pigott in 1795 and it was known as Variabilis Coronae, Variable of Corona. In 1935 it was the first star shown to have a different chemical composition than the sun via spectral analysis, R Coronae Borealis is a variable star and the prototype of its class. It is one of only two R Coronae Borealis variables bright enough to be seen with the eye, along with RY Sagittarii. Much of the time it shows variations of around a tenth of a magnitude with poorly defined periods that have reported as 40 and 51 days. These correspond to the first overtone and fundamental radial pulsation modes for an extreme helium star slightly under one M☉, at irregular intervals a few years or decades apart R Coronae Borealis fades from its normal brightness near 6th magnitude for a period of months or sometimes years. There is no fixed minimum, but the star can become fainter than 15th magnitude in the visual range, the fading is less pronounced at longer wavelengths. Typically the star starts to return to maximum brightness almost immediately from its minimum and this irregular fading is the defining characteristic of the R Coronae Borealis variables and is thought to be due to the condensation of carbon into soot surrounding the star. In August 2007, R Coronae Borealis began a fade to an unprecedented minimum and it fell to 14th magnitude in 33 days, then continued to fade slowly, dropping below 15th magnitude in June 2009. It then began a slow rise, not reaching 12th magnitude until late 2011. This was a deep and exceptional long minimum, longer even than the deep five year minimum of 1962-7. However, R Coronae Borealis then faded again to near 15th magnitude, in late 2014, R Coronae Borealis brightened quickly to 7th magnitude but then began to fade again. As of May 2015 it is around 8th magnitude, R Coronae Borealis at maximum light shows the spectrum clearly of a late F or early G yellow supergiant, but with marked peculiarities. Hydrogen lines are weak or absent, while carbon lines and molecular bands of cyanogen, helium lines and metals such as calcium are also present as expected. The spectrum is variable, most obviously during the brightness fades, the normal absorption spectrum is replaced by emission lines, especially HeI, CaII, NaI, and other metals. The lines are very narrow at this stage. Helium emission lines sometimes show P Cygni profiles, in deep minima, many of the metal lines disappear although the Ca doublet remains strong
