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an ancient Egyptian calendar of lucky and unlucky days composed some 3,200 years ago may be the oldest preserved historical document of the discovery of a variable star, the eclipsing binary Algol.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.
Bayer designation
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A Bayer designation is a stellar designation in which a specific star is identified by a Greek letter, followed by the genitive form of its parent constellations Latin name. The original list of Bayer designations contained 1,564 stars, most of the brighter stars were assigned their first systematic names by the German astronomer Johann Bayer in 1603, in his star atlas Uranometria. Bayer assigned a lower-case Greek letter, such as alpha, beta, gamma, for example, Aldebaran is designated α Tauri, which means Alpha of the constellation Taurus. A single constellation may contain fifty or more stars, but the Greek alphabet has only twenty-four letters, when these ran out, Bayer began using Latin letters, upper case A, followed by lower case b through z, for a total of another 24 letters. Bayer never went beyond z, but later added more designations using both upper and lower case Latin letters, the upper case letters following the lower case ones in general. Examples include s Carinae, d Centauri, G Scorpii, and N Velorum, the last upper-case letter used in this way was Q. Bayer catalogued only a few stars too far south to be seen from Germany, in most constellations, Bayer assigned Greek and Latin letters to stars within a constellation in rough order of apparent brightness, from brightest to dimmest. Since the brightest star in a majority of constellations is designated Alpha, in Bayers day, however, stellar brightness could not be measured precisely. Within each magnitude class, Bayer made no attempt to arrange stars by relative brightness, as a result, the brightest star in each class did not always get listed first in Bayers order. Occasionally the order looks quite arbitrary, of the 88 modern constellations, there are at least 30 in which Alpha is not the brightest star, and four of those lack an alpha star altogether. Orion provides an example of Bayers method. Bayer first designated Betelgeuse and Rigel, the two 1st-magnitude stars, as Alpha and Beta from north to south, with Betelgeuse coming ahead of Rigel, Bayer then repeated the procedure for the stars of the 2nd magnitude, labeling them from gamma through zeta in top-down order. The First to Rise in the East order is used in a number of instances, Castor and Pollux of Gemini may be an example of this, Pollux is brighter than Castor, but the latter rises earlier and was assigned alpha. In this case, Bayer may also have influenced by the traditional order of the mythological names Castor and Pollux. Although the brightest star in Draco is Eltanin, Thuban was assigned alpha by Bayer because, due to precession, sometimes there is no apparent order, as exemplified by the stars in Sagittarius, where Bayers designations appear almost random to the modern eye. Alpha and Beta Sagittarii are perhaps the most anomalously designated stars in the sky, the order of the letters assigned in Sagittarius does correspond to the magnitudes as illustrated on Bayers chart, but the latter do not agree with modern determinations of the magnitudes. Bayer designations added by later astronomers generally were ordered by magnitude, in Libra, for example, the new designations sigma, tau, and upsilon were chosen to avoid conflict with Bayers earlier designations, even though several stars with earlier letters are not as bright. In Cygnus, for example, Bayers fixed stars run through g, Bayer did not intend such labels as catalog designations, but some have survived to refer to astronomical objects, P Cygni for example is still used as a designation for Nova Cyg 1600
3.
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
4.
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
5.
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
6.
YZ Ceti
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YZ Ceti is a red dwarf star in the constellation Cetus. Although it is close to the Sun at just 12 light years. It is classified as a star that undergoes intermittent fluctuations in luminosity. YZ Ceti is about 8.5 percent the mass of the Sun and this star is unusually close to Tau Ceti, a star of spectral class G8. The two are only about 1.6 light years apart, a more than a third of the distance from the Sun to the Solar Systems nearest neighbor
7.
Latin script
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Latin script is used as the standard method of writing in most Western and Central European languages, as well as in many languages in other parts of the world. Latin script is the basis for the largest number of alphabets of any writing system and is the most widely adopted writing system in the world, Latin script is also the basis of the International Phonetic Alphabet. The 26 most widespread letters are the contained in the ISO basic Latin alphabet. The script is either called Roman script or Latin script, in reference to its origin in ancient Rome, in the context of transliteration, the term romanization or romanisation is often found. Unicode uses the term Latin as does the International Organization for Standardization, the numeral system is called the Roman numeral system, and the collection of the elements, Roman numerals. The numbers 1,2,3. are Latin/Roman script numbers for the Hindu–Arabic numeral system, the Latin alphabet spread, along with Latin, from the Italian Peninsula to the lands surrounding the Mediterranean Sea with the expansion of the Roman Empire. The Latin script also came into use for writing the West Slavic languages and several South Slavic languages, the speakers of East Slavic languages generally adopted Cyrillic along with Orthodox Christianity. The Serbian language uses both scripts, with Cyrillic predominating in official communication and Latin elsewhere, as determined by the Law on Official Use of the Language and Alphabet. As late as 1500, the Latin script was limited primarily to the languages spoken in Western, Northern, the Orthodox Christian Slavs of Eastern and Southeastern Europe mostly used Cyrillic, and the Greek alphabet was in use by Greek-speakers around the eastern Mediterranean. The Arabic script was widespread within Islam, both among Arabs and non-Arab nations like the Iranians, Indonesians, Malays, and Turkic peoples, most of the rest of Asia used a variety of Brahmic alphabets or the Chinese script. It is used for many Austronesian languages, including the languages of the Philippines, Latin letters served as the basis for the forms of the Cherokee syllabary developed by Sequoyah, however, the sound values are completely different. In the late 19th century, the Romanians returned to the Latin alphabet, under French rule and Portuguese missionary influence, a Latin alphabet was devised for the Vietnamese language, which had previously used Chinese characters. In 1928, as part of Mustafa Kemal Atatürks reforms, the new Republic of Turkey adopted a Latin alphabet for the Turkish language, kazakhstan, Kyrgyzstan, Iranian-speaking Tajikistan, and the breakaway region of Transnistria kept the Cyrillic alphabet, chiefly due to their close ties with Russia. In the 1930s and 1940s, the majority of Kurds replaced the Arabic script with two Latin alphabets, although the only official Kurdish government uses an Arabic alphabet for public documents, the Latin Kurdish alphabet remains widely used throughout the region by the majority of Kurdish-speakers. In 2015, the Kazakh government announced that the Latin alphabet would replace Cyrillic as the system for the Kazakh language by 2025. In the course of its use, the Latin alphabet was adapted for use in new languages, sometimes representing phonemes not found in languages that were written with the Roman characters. These new forms are given a place in the alphabet by defining an alphabetical order or collation sequence, a digraph is a pair of letters used to write one sound or a combination of sounds that does not correspond to the written letters in sequence. Examples are ⟨ch⟩, ⟨ng⟩, ⟨rh⟩, ⟨sh⟩ in English, a trigraph is made up of three letters, like the German ⟨sch⟩, the Breton ⟨c’h⟩ or the Milanese ⟨oeu⟩
