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75-398: North Star is a name of Polaris in its role as northern pole star. North Star or North Stars may also refer to: North Star As the closest Cepheid variable its distance is used as part of the cosmic distance ladder . The revised Hipparcos stellar parallax gives a distance to Polaris of about 433 light-years (133 parsecs ), while the successor mission Gaia gives

150-423: A 6 fold to 30,000 fold change in luminosity. Mira itself, also known as Omicron Ceti (ο Cet), varies in brightness from almost 2nd magnitude to as faint as 10th magnitude with a period of roughly 332 days. The very large visual amplitudes are mainly due to the shifting of energy output between visual and infra-red as the temperature of the star changes. In a few cases, Mira variables show dramatic period changes over

225-602: A burner or lamp and would reasonably be described as stella polaris from about the High Middle Ages and onwards, both in Greek and Latin. On his first trans-Atlantic voyage in 1492, Christopher Columbus had to correct for the "circle described by the pole star about the pole". In Shakespeare's play Julius Caesar , written around 1599, Caesar describes himself as being "as constant as the northern star", though in Caesar's time there

300-469: A cycle taking 11 months; the star had previously been described as a nova by David Fabricius in 1596. This discovery, combined with supernovae observed in 1572 and 1604, proved that the starry sky was not eternally invariable as Aristotle and other ancient philosophers had taught. In this way, the discovery of variable stars contributed to the astronomical revolution of the sixteenth and early seventeenth centuries. The second variable star to be described

375-463: A day. They are thought to have evolved beyond a red supergiant phase, but the mechanism for the pulsations is unknown. The class was named in 2020 through analysis of TESS observations. Eruptive variable stars show irregular or semi-regular brightness variations caused by material being lost from the star, or in some cases being accreted to it. Despite the name, these are not explosive events. Protostars are young objects that have not yet completed

450-514: A direct line with the Earth's rotational axis "above" the North Pole —the north celestial pole—Polaris stands almost motionless in the sky, and all the stars of the northern sky appear to rotate around it. Therefore, it makes an excellent fixed point from which to draw measurements for celestial navigation and for astrometry . The elevation of the star above the horizon gives the approximate latitude of

525-487: A distance of about 448 light-years (137 parsecs ). Calculations by other methods vary widely. Although appearing to the naked eye as a single point of light, Polaris is a triple star system , composed of the primary, a yellow supergiant designated Polaris Aa, in orbit with a smaller companion, Polaris Ab; the pair is in a wider orbit with Polaris B. The outer pair AB were discovered in August 1779 by William Herschel , where

600-575: A distance of several degrees, in the early medieval period, and numerous names referring to this characteristic as polar star have been in use since the medieval period. In Old English, it was known as scip-steorra ("ship-star") . In the Old English rune poem , the T-rune is apparently associated with "a circumpolar constellation", or the planet Mars. In the Hindu Puranas , it became personified under

675-490: A hiatus in 1963–1965. This was originally thought to be due to secular redward (a long term change in redshift that causes light to stretch into longer wavelengths, causing it to appear red) evolution across the Cepheid instability strip , but it may be due to interference between the primary and the first- overtone pulsation modes. Authors disagree on whether Polaris is a fundamental or first-overtone pulsator and on whether it

750-479: A parallax for Polaris, but a distance inferred from it is 136.6 ± 0.5  pc (445.5 ly) for Polaris B, somewhat further than most previous estimates and several times more accurate. This was further improved to 137.2 ± 0.3  pc (447.6 ly), upon publication of the Gaia Data Release 3 catalog on 13 June 2022 which superseded Gaia Data Release 2. Polaris is depicted in the flag and coat of arms of

825-403: A pardon by saying, "I am as constant as the northern star/Of whose true-fixed and resting quality/There is no fellow in the firmament./The skies are painted with unnumbered sparks,/They are all fire and every one doth shine,/But there's but one in all doth hold his place;/So in the world" (III, i, 65–71). Of course, Polaris will not "constantly" remain as the north star due to precession , but this

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900-474: A period of 29.59 ± 0.02 years and an eccentricity of 0.608 ± 0.005 . In 2019, a study by R. I. Anderson gave a period of 29.32 ± 0.11 years with an eccentricity of 0.620 ± 0.008 . There were once thought to be two more widely separated components—Polaris C and Polaris D—but these have been shown not to be physically associated with the Polaris system. Polaris Aa, the supergiant primary component,

975-419: A period of 0.01–0.2 days. Their spectral type is usually between A0 and F5. These stars of spectral type A2 to F5, similar to δ Scuti variables, are found mainly in globular clusters. They exhibit fluctuations in their brightness in the order of 0.7 magnitude (about 100% change in luminosity) or so every 1 to 2 hours. These stars of spectral type A or occasionally F0, a sub-class of δ Scuti variables found on

1050-684: A period of 0.1–1 day and an amplitude of 0.1 magnitude on average. Their spectra are peculiar by having weak hydrogen while on the other hand carbon and helium lines are extra strong, a type of extreme helium star . These are yellow supergiant stars (actually low mass post-AGB stars at the most luminous stage of their lives) which have alternating deep and shallow minima. This double-peaked variation typically has periods of 30–100 days and amplitudes of 3–4 magnitudes. Superimposed on this variation, there may be long-term variations over periods of several years. Their spectra are of type F or G at maximum light and type K or M at minimum brightness. They lie near

1125-477: A period of decades, thought to be related to the thermal pulsing cycle of the most advanced AGB stars. These are red giants or supergiants . Semiregular variables may show a definite period on occasion, but more often show less well-defined variations that can sometimes be resolved into multiple periods. A well-known example of a semiregular variable is Betelgeuse , which varies from about magnitudes +0.2 to +1.2 (a factor 2.5 change in luminosity). At least some of

1200-419: A pulsation is caused by the blocking of the internal energy flow by material with a high opacity, but this must occur at a particular depth of the star to create visible pulsations. If the expansion occurs below a convective zone then no variation will be visible at the surface. If the expansion occurs too close to the surface the restoring force will be too weak to create a pulsation. The restoring force to create

1275-406: A single well-defined period, but often they pulsate simultaneously with multiple frequencies and complex analysis is required to determine the separate interfering periods. In some cases, the pulsations do not have a defined frequency, causing a random variation, referred to as stochastic . The study of stellar interiors using their pulsations is known as asteroseismology . The expansion phase of

1350-461: A slightly offset period versus luminosity relationship, so it is always important to know which type of star is being observed. These stars are somewhat similar to Cepheids, but are not as luminous and have shorter periods. They are older than type I Cepheids, belonging to Population II , but of lower mass than type II Cepheids. Due to their common occurrence in globular clusters , they are occasionally referred to as cluster Cepheids . They also have

1425-446: A table of the first two batches of names approved by the WGSN; which included Polaris for the star α Ursae Minoris Aa. In antiquity, Polaris was not yet the closest naked-eye star to the celestial pole, and the entire constellation of Ursa Minor was used for navigation rather than any single star. Polaris moved close enough to the pole to be the closest naked-eye star, even though still at

1500-493: A very close F6 main-sequence star with a mass of 1.26  M ☉ . Polaris B can be resolved with a modest telescope. William Herschel discovered the star in August 1779 using a reflecting telescope of his own, one of the best telescopes of the time. In January 2006, NASA released images, from the Hubble telescope , that showed the three members of the Polaris ternary system. The variable radial velocity of Polaris A

1575-593: A well established period-luminosity relationship, and so are also useful as distance indicators. These A-type stars vary by about 0.2–2 magnitudes (20% to over 500% change in luminosity) over a period of several hours to a day or more. Delta Scuti (δ Sct) variables are similar to Cepheids but much fainter and with much shorter periods. They were once known as Dwarf Cepheids . They often show many superimposed periods, which combine to form an extremely complex light curve. The typical δ Scuti star has an amplitude of 0.003–0.9 magnitudes (0.3% to about 130% change in luminosity) and

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1650-483: Is 2.5 times brighter today than when Ptolemy observed it, changing from third to second magnitude. Astronomer Edward Guinan considers this to be a remarkable change and is on record as saying that "if they are real, these changes are 100 times larger than [those] predicted by current theories of stellar evolution ". In 2024, researchers led by Nancy Evans at the Harvard & Smithsonian , have studied with more accuracy

1725-450: Is a low-amplitude Population I classical Cepheid variable , although it was once thought to be a type II Cepheid due to its high galactic latitude . Cepheids constitute an important standard candle for determining distance, so Polaris, as the closest such star, is heavily studied. The variability of Polaris had been suspected since 1852; this variation was confirmed by Ejnar Hertzsprung in 1911. The range of brightness of Polaris

1800-506: Is crossing the instability strip for the first time or not. The temperature of Polaris varies by only a small amount during its pulsations, but the amount of this variation is variable and unpredictable. The erratic changes of temperature and the amplitude of temperature changes during each cycle, from less than 50  K to at least 170 K, may be related to the orbit with Polaris Ab. Research reported in Science suggests that Polaris

1875-523: Is given as 1.86–2.13, but the amplitude has changed since discovery. Prior to 1963, the amplitude was over 0.1 magnitude and was very gradually decreasing. After 1966, it very rapidly decreased until it was less than 0.05 magnitude; since then, it has erratically varied near that range. It has been reported that the amplitude is now increasing again, a reversal not seen in any other Cepheid. The period, roughly 4 days, has also changed over time. It has steadily increased by around 4.5 seconds per year except for

1950-421: Is named after Beta Cephei . Classical Cepheids (or Delta Cephei variables) are population I (young, massive, and luminous) yellow supergiants which undergo pulsations with very regular periods on the order of days to months. On September 10, 1784, Edward Pigott detected the variability of Eta Aquilae , the first known representative of the class of Cepheid variables. However, the namesake for classical Cepheids

2025-718: Is often much smaller, with the more rapid primary variations are superimposed. The reasons for this type of variation are not clearly understood, being variously ascribed to pulsations, binarity, and stellar rotation. Beta Cephei (β Cep) variables (sometimes called Beta Canis Majoris variables, especially in Europe) undergo short period pulsations in the order of 0.1–0.6 days with an amplitude of 0.01–0.3 magnitudes (1% to 30% change in luminosity). They are at their brightest during minimum contraction. Many stars of this kind exhibits multiple pulsation periods. Slowly pulsating B (SPB) stars are hot main-sequence stars slightly less luminous than

2100-495: Is only noticeable over centuries. In Inuit astronomy , Polaris is known as Nuutuittuq ( syllabics : ᓅᑐᐃᑦᑐᖅ ). In traditional Lakota star knowledge, Polaris is named "Wičháȟpi Owáŋžila". This translates to "The Star that Sits Still". This name comes from a Lakota story in which he married Tȟapȟúŋ Šá Wíŋ, "Red Cheeked Woman". However, she fell from the heavens, and in his grief Wičháȟpi Owáŋžila stared down from "waŋkátu" (the above land) forever. The Plains Cree call

2175-471: Is the closest Cepheid variable to Earth so its physical parameters are of critical importance to the whole astronomical distance scale . It is also the only one with a dynamically measured mass. The Hipparcos spacecraft used stellar parallax to take measurements from 1989 and 1993 with the accuracy of 0.97  milliarcseconds (970 microarcseconds), and it obtained accurate measurements for stellar distances up to 1,000 pc away. The Hipparcos data

2250-495: Is the star Delta Cephei , discovered to be variable by John Goodricke a few months later. Type II Cepheids (historically termed W Virginis stars) have extremely regular light pulsations and a luminosity relation much like the δ Cephei variables, so initially they were confused with the latter category. Type II Cepheids stars belong to older Population II stars, than do the type I Cepheids. The Type II have somewhat lower metallicity , much lower mass, somewhat lower luminosity, and

2325-471: Is true north; the rest of the time it is displaced eastward or westward, and the bearing must be corrected using tables or a rule of thumb . The best approximation is made using the leading edge of the " Big Dipper " asterism in the constellation Ursa Major. The leading edge (defined by the stars Dubhe and Merak ) is referenced to a clock face, and the true azimuth of Polaris worked out for different latitudes. The apparent motion of Polaris towards and, in

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2400-454: Is used to describe oscillations in other stars that are excited in the same way and the study of these oscillations is one of the main areas of active research in the field of asteroseismology . A Blue Large-Amplitude Pulsator (BLAP) is a pulsating star characterized by changes of 0.2 to 0.4 magnitudes with typical periods of 20 to 40 minutes. A fast yellow pulsating supergiant (FYPS) is a luminous yellow supergiant with pulsations shorter than

2475-466: The Canadian Inuit territory of Nunavut , the flag of the U.S. states of Alaska and Minnesota , and the flag of the U.S. city of Duluth, Minnesota . Variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude ) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking

2550-485: The instability strip , that swell and shrink very regularly caused by the star's own mass resonance , generally by the fundamental frequency . Generally the Eddington valve mechanism for pulsating variables is believed to account for cepheid-like pulsations. Each of the subgroups on the instability strip has a fixed relationship between period and absolute magnitude, as well as a relation between period and mean density of

2625-410: The period of variation and its amplitude can be very well established; for many variable stars, though, these quantities may vary slowly over time, or even from one period to the next. Peak brightnesses in the light curve are known as maxima, while troughs are known as minima. Amateur astronomers can do useful scientific study of variable stars by visually comparing the star with other stars within

2700-489: The 'A' refers to what is now known to be the Aa/Ab pair. Polaris Aa is an evolved yellow supergiant of spectral type F7Ib with 5.4 solar masses ( M ☉ ). It is the first classical Cepheid to have a mass determined from its orbit. The two smaller companions are Polaris B, a 1.39  M ☉ F3 main-sequence star orbiting at a distance of 2,400  astronomical units (AU), and Polaris Ab (or P),

2775-525: The Beta Cephei stars, with longer periods and larger amplitudes. The prototype of this rare class is V361 Hydrae , a 15th magnitude subdwarf B star . They pulsate with periods of a few minutes and may simultaneous pulsate with multiple periods. They have amplitudes of a few hundredths of a magnitude and are given the GCVS acronym RPHS. They are p-mode pulsators. Stars in this class are type Bp supergiants with

2850-520: The Marian Polar Star"), a collection of Marian poetry published by Nicolaus Lucensis (Niccolo Barsotti de Lucca) in 1655. Its name in traditional pre-Islamic Arab astronomy was al-Judayy الجدي ("the kid", in the sense of a juvenile goat ["le Chevreau"] in Description des Etoiles fixes), and that name was used in medieval Islamic astronomy as well. In those times, it was not yet as close to

2925-642: 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, in particular changes in the spectrum . 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 . For regular variables,

3000-574: The Polaris' smaller companion orbit using the CHARA Array . During this observation campaign they have succeeded in shooting Polaris features on its surface; large bright places and dark ones have appeared in close-up images, changing over time. Further, Polaris diameter size has been re-measured to 46  R ☉ , using the Gaia distance of 446 ± 1 light-years, and its mass was determined at 5.13  M ☉ . Because Polaris lies nearly in

3075-479: The book The Stars of High Luminosity, in which she made numerous observations of variable stars, paying particular attention to Cepheid variables . Her analyses and observations of variable stars, carried out with her husband, Sergei Gaposchkin, laid the basis for all subsequent work on the subject. The latest edition of the General Catalogue of Variable Stars (2008) lists more than 46,000 variable stars in

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3150-402: The constellation Ursa Minor, Cynosura (from the Greek κυνόσουρα "the dog's tail"), became associated with the pole star in particular by the early modern period. An explicit identification of Mary as stella maris with the polar star ( Stella Polaris ), as well as the use of Cynosura as a name of the star, is evident in the title Cynosura seu Mariana Stella Polaris (i.e. "Cynosure, or

3225-436: The contraction phase of a pulsation can be pressure if the pulsation occurs in a non-degenerate layer deep inside a star, and this is called an acoustic or pressure mode of pulsation, abbreviated to p-mode . In other cases, the restoring force is gravity and this is called a g-mode . Pulsating variable stars typically pulsate in only one of these modes. This group consists of several kinds of pulsating stars, all found on

3300-566: The distance. The next major step in high precision parallax measurements comes from Gaia , a space astrometry mission launched in 2013 and intended to measure stellar parallax to within 25 microarcseconds (μas). Although it was originally planned to limit Gaia's observations to stars fainter than magnitude 5.7, tests carried out during the commissioning phase indicated that Gaia could autonomously identify stars as bright as magnitude 3. When Gaia entered regular scientific operations in July 2014, it

3375-399: The eclipsing binary Algol . Aboriginal Australians are also known to have observed the variability of Betelgeuse and Antares , incorporating these brightness changes into narratives that are passed down through oral tradition. Of the modern astronomers, the first variable star was identified in 1638 when Johannes Holwarda noticed that Omicron Ceti (later named Mira) pulsated in

3450-443: The entire star expands and shrinks as a whole; and non-radial , where one part of the star expands while another part shrinks. Depending on the type of pulsation and its location within the star, there is a natural or fundamental frequency which determines the period of the star. Stars may also pulsate in a harmonic or overtone which is a higher frequency, corresponding to a shorter period. Pulsating variable stars sometimes have

3525-473: The future, away from the celestial pole, is due to the precession of the equinoxes . The celestial pole will move away from α UMi after the 21st century, passing close by Gamma Cephei by about the 41st century , moving towards Deneb by about the 91st century . The celestial pole was close to Thuban around 2750 BC, and during classical antiquity it was slightly closer to Kochab (β UMi) than to Polaris, although still about 10 ° from either star. It

3600-509: The gas more opaque, and radiation temporarily becomes captured in the gas. This heats the gas further, leading it to expand once again. Thus a cycle of expansion and compression (swelling and shrinking) is maintained. The pulsation of cepheids is known to be driven by oscillations in the ionization of helium (from He to He and back to He ). In a given constellation, the first variable stars discovered were designated with letters R through Z, e.g. R Andromedae . This system of nomenclature

3675-447: The instability strip, cooler than type I Cepheids more luminous than type II Cepheids. Their pulsations are caused by the same basic mechanisms related to helium opacity, but they are at a very different stage of their lives. Alpha Cygni (α Cyg) variables are nonradially pulsating supergiants of spectral classes B ep to A ep Ia. Their periods range from several days to several weeks, and their amplitudes of variation are typically of

3750-450: The light, so variable stars are classified as either: Many, possibly most, stars exhibit at least some oscillation in luminosity: the energy output of the Sun , for example, varies by about 0.1% over an 11-year solar cycle . 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,

3825-406: The main sequence. They have extremely rapid variations with periods of a few minutes and amplitudes of a few thousandths of a magnitude. The long period variables are cool evolved stars that pulsate with periods in the range of weeks to several years. Mira variables are Asymptotic giant branch (AGB) red giants. Over periods of many months they fade and brighten by between 2.5 and 11 magnitudes ,

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3900-636: The name Dhruva ("immovable, fixed"). In the later medieval period, it became associated with the Marian title of Stella Maris "Star of the Sea" (so in Bartholomaeus Anglicus , c. 1270s), due to an earlier transcription error. An older English name, attested since the 14th century, is lodestar "guiding star", cognate with the Old Norse leiðarstjarna , Middle High German leitsterne . The ancient name of

3975-434: The north celestial pole as it is now, and used to rotate around the pole. It was invoked as a symbol of steadfastness in poetry, as "steadfast star" by Spenser . Shakespeare 's sonnet 116 is an example of the symbolism of the north star as a guiding principle: "[Love] is the star to every wandering bark / Whose worth's unknown, although his height be taken." In Julius Caesar , he has Caesar explain his refusal to grant

4050-602: The observer. In 2018 Polaris was 0.66° (39.6 arcminutes) away from the pole of rotation (1.4 times the Moon disc) and so revolves around the pole in a small circle 1.3° in diameter. It will be closest to the pole (about 0.45 degree, or 27 arcminutes) soon after the year 2100. Because it is so close to the celestial north pole, its right ascension is changing rapidly due to the precession of Earth's axis , going from 2.5h in AD 2000 to 6h in AD 2100. Twice in each sidereal day Polaris's azimuth

4125-448: The order of 0.1 magnitudes. These non-radially pulsating stars have short periods of hundreds to thousands of seconds with tiny fluctuations of 0.001 to 0.2 magnitudes. Known types of pulsating white dwarf (or pre-white dwarf) include the DAV , or ZZ Ceti , stars, with hydrogen-dominated atmospheres and the spectral type DA; DBV , or V777 Her , stars, with helium-dominated atmospheres and

4200-405: The order of 0.1 magnitudes. The light changes, which often seem irregular, are caused by the superposition of many oscillations with close periods. Deneb , in the constellation of Cygnus is the prototype of this class. Gamma Doradus (γ Dor) variables are non-radially pulsating main-sequence stars of spectral classes F to late A. Their periods are around one day and their amplitudes typically of

4275-529: The prefixed V335 onwards. Variable stars may be either intrinsic or extrinsic . These subgroups themselves are further divided into specific types of variable stars that are usually named after their prototype. For example, dwarf novae are designated U Geminorum stars after the first recognized star in the class, U Geminorum . Examples of types within these divisions are given below. Pulsating stars swell and shrink, affecting their brightness and spectrum. Pulsations are generally split into: radial , where

4350-426: The same telescopic field of view of which the magnitudes are known and constant. By estimating the variable's 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 and shares the data with the scientific community. From the light curve the following data are derived: From

4425-419: The same frequency as its changing brightness. About two-thirds of all variable stars appear to be pulsating. In the 1930s astronomer Arthur Stanley Eddington showed that the mathematical equations that describe the interior of a star may lead to instabilities that cause a star to pulsate. The most common type of instability is related to oscillations in the degree of ionization in outer, convective layers of

4500-500: The semi-regular variables are very closely related to Mira variables, possibly the only difference being pulsating in a different harmonic. These are red giants or supergiants with little or no detectable periodicity. Some are poorly studied semiregular variables, often with multiple periods, but others may simply be chaotic. Many variable red giants and supergiants show variations over several hundred to several thousand days. The brightness may change by several magnitudes although it

4575-501: The spectral type DB; and GW Vir stars, with atmospheres dominated by helium, carbon, and oxygen. GW Vir stars may be subdivided into DOV and PNNV stars. The Sun oscillates with very low amplitude in a large number of modes having periods around 5 minutes. The study of these oscillations is known as helioseismology . Oscillations in the Sun are driven stochastically by convection in its outer layers. The term solar-like oscillations

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4650-418: The spectrum the following data are derived: In very few cases it is possible to make pictures of a stellar disk. These may show darker spots on its surface. Combining light curves with spectral data often gives a clue as to the changes that occur in a variable star. For example, evidence for a pulsating star is found in its shifting spectrum because its surface periodically moves toward and away from us, with

4725-511: The star had approached the celestial pole to within a few degrees. Gemma Frisius , writing in 1547, referred to it as stella illa quae polaris dicitur ("that star which is called 'polar'"), placing it 3° 8' from the celestial pole. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included

4800-516: The star in Nehiyawewin : acâhkos êkâ kâ-âhcît "the star that does not move" ( syllabics : ᐊᒑᐦᑯᐢ ᐁᑳ ᑳ ᐋᐦᒌᐟ ). In Mi'kmawi'simk the star is named Tatapn . In the ancient Finnish worldview, the North Star has also been called taivaannapa and naulatähti ("the nailstar") because it seems to be attached to the firmament or even to act as a fastener for the sky when other stars orbit it. Since

4875-427: The star. When the star is in the swelling phase, its outer layers expand, causing them to cool. Because of the decreasing temperature the degree of ionization also decreases. This makes the gas more transparent, and thus makes it easier for the star to radiate its energy. This in turn makes the star start to contract. As the gas is thereby compressed, it is heated and the degree of ionization again increases. This makes

4950-541: The star. The period-luminosity relationship was first established for Delta Cepheids by Henrietta Leavitt , and makes these high luminosity Cepheids very useful for determining distances to galaxies within the Local Group and beyond. Edwin Hubble used this method to prove that the so-called spiral nebulae are in fact distant galaxies. The Cepheids are named only for Delta Cephei , while a completely separate class of variables

5025-584: The starry sky seemed to rotate around it, the firmament is thought of as a wheel, with the star as the pivot on its axis. The names derived from it were sky pin and world pin . Many recent papers calculate the distance to Polaris at about 433 light-years (133 parsecs), based on parallax measurements from the Hipparcos astrometry satellite. Older distance estimates were often slightly less, and research based on high resolution spectral analysis suggests it may be up to 110 light years closer (323 ly/99 pc). Polaris

5100-427: The system in 1929, giving an orbital period of about 29.7 years with an eccentricity of 0.63. This period was confirmed by proper motion studies performed by B. P. Gerasimovič in 1939. As part of her doctoral thesis, in 1955 E. Roemer used radial velocity data to derive an orbital period of 30.46 y for the Polaris A system, with an eccentricity of 0.64. K. W. Kamper in 1996 produced refined elements with

5175-439: Was about the same angular distance from β UMi as to α UMi by the end of late antiquity . The Greek navigator Pytheas in ca. 320 BC described the celestial pole as devoid of stars. However, as one of the brighter stars close to the celestial pole, Polaris was used for navigation at least from late antiquity, and described as ἀεί φανής ( aei phanēs ) "always visible" by Stobaeus (5th century), also termed Λύχνος ( Lychnos ) akin to

5250-430: Was configured to routinely process stars in the magnitude range 3 – 20. Beyond that limit, special procedures are used to download raw scanning data for the remaining 230 stars brighter than magnitude 3; methods to reduce and analyse these data are being developed; and it is expected that there will be "complete sky coverage at the bright end" with standard errors of "a few dozen μas". Gaia Data Release 2 does not include

5325-466: Was developed by Friedrich W. Argelander , who gave the first previously unnamed variable in a constellation the letter R, the first letter not used by Bayer . Letters RR through RZ, SS through SZ, up to ZZ are used for the next discoveries, e.g. RR Lyrae . Later discoveries used letters AA through AZ, BB through BZ, and up to QQ through QZ (with J omitted). Once those 334 combinations are exhausted, variables are numbered in order of discovery, starting with

5400-434: Was examined again with more advanced error correction and statistical techniques. Despite the advantages of Hipparcos astrometry , the uncertainty in its Polaris data has been pointed out and some researchers have questioned the accuracy of Hipparcos when measuring binary Cepheids like Polaris. The Hipparcos reduction specifically for Polaris has been re-examined and reaffirmed but there is still not widespread agreement about

5475-521: Was no constant northern star. Despite its relative brightness, it is not, as is popularly believed, the brightest star in the sky. Polaris was referenced in Nathaniel Bowditch 's 1802 book, American Practical Navigator , where it is listed as one of the navigational stars . The modern name Polaris is shortened from Neo-Latin stella polaris " polar star ", coined in the Renaissance when

5550-420: Was reported by W. W. Campbell in 1899, which suggested this star is a binary system. Since Polaris A is a known cepheid variable, J. H. Moore in 1927 demonstrated that the changes in velocity along the line of sight were due to a combination of the four-day pulsation period combined with a much longer orbital period and a large eccentricity of around 0.6. Moore published preliminary orbital elements of

5625-562: Was the eclipsing variable Algol, by Geminiano Montanari in 1669; John Goodricke gave the correct explanation of its variability in 1784. 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 known variable stars has increased rapidly, especially after 1890 when it became possible to identify variable stars by means of photography. In 1930, astrophysicist Cecilia Payne published

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