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89-521: Classified as spectral type M1.5Iab-Ib , Antares is a red supergiant , a large evolved massive star and one of the largest stars visible to the naked eye. If placed at the center of the Solar System , it would extend out to somewhere in the asteroid belt . Its mass is calculated to be around 13 or 15 to 16 times that of the Sun . Antares appears as a single star when viewed with the naked eye, but it

178-406: A federated unit of Brazil . Antares represents the state of Piauí . The 1995 Oldsmobile Antares concept car is named after the star. Antares is one of the medieval Behenian fixed stars . Stellar classification#Spectral types In astronomy , stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from

267-571: A semi-major axis of about 2.9 ″ . Other recent estimates of the period have ranged from 880 years for a calculated orbit, to 2,562 years for a simple Kepler's Law estimate. Early measurements of the pair found them to be about 3.5″ apart in 1847–49, or 2.5″ apart in 1848. More modern observations consistently give separations around 2.6″  – 2.8″ . The variations in the separation are often interpreted as evidence of orbital motion, but are more likely to be simply observational inaccuracies with very little true relative motion between

356-433: A high-resolution spectrum and comparing the measured wavelengths of known spectral lines to wavelengths from laboratory measurements. A positive radial velocity indicates the distance between the objects is or was increasing; a negative radial velocity indicates the distance between the source and observer is or was decreasing. William Huggins ventured in 1868 to estimate the radial velocity of Sirius with respect to

445-533: A luminosity class of IIIb, while a luminosity class IIIa indicates a star slightly brighter than a typical giant. A sample of extreme V stars with strong absorption in He II λ4686 spectral lines have been given the Vz designation. An example star is HD 93129 B . Additional nomenclature, in the form of lower-case letters, can follow the spectral type to indicate peculiar features of the spectrum. For example, 59 Cygni

534-457: A much smaller planet with an orbital plane on the line of sight. It has been suggested that planets with high eccentricities calculated by this method may in fact be two-planet systems of circular or near-circular resonant orbit. The radial velocity method to detect exoplanets is based on the detection of variations in the velocity of the central star, due to the changing direction of the gravitational pull from an (unseen) exoplanet as it orbits

623-668: A nearby observer. The modern classification system is known as the Morgan–Keenan (MK) classification. Each star is assigned a spectral class (from the older Harvard spectral classification, which did not include luminosity ) and a luminosity class using Roman numerals as explained below, forming the star's spectral type. Other modern stellar classification systems , such as the UBV system , are based on color indices —the measured differences in three or more color magnitudes . Those numbers are given labels such as "U−V" or "B−V", which represent

712-448: A sequence from hotter to cooler). The sequence has been expanded with three classes for other stars that do not fit in the classical system: W , S and C . Some non-stellar objects have also been assigned letters: D for white dwarfs and L , T and Y for Brown dwarfs . In the MK system, a luminosity class is added to the spectral class using Roman numerals . This is based on

801-457: A series of twenty-two types numbered from I–XXII. Because the 22 Roman numeral groupings did not account for additional variations in spectra, three additional divisions were made to further specify differences: Lowercase letters were added to differentiate relative line appearance in spectra; the lines were defined as: Antonia Maury published her own stellar classification catalogue in 1897 called "Spectra of Bright Stars Photographed with

890-518: A star is a short code primarily summarizing the ionization state, giving an objective measure of the photosphere's temperature. Most stars are currently classified under the Morgan–Keenan (MK) system using the letters O , B , A , F , G , K , and M , a sequence from the hottest ( O type) to the coolest ( M type). Each letter class is then subdivided using a numeric digit with 0 being hottest and 9 being coolest (e.g., A8, A9, F0, and F1 form

979-470: A thousand days are analogous to long secondary periods. Research published in 2018 demonstrated that Ngarrindjeri Aboriginal people from South Australia observed the variability of Antares and incorporated it into their oral traditions as Waiyungari (meaning 'red man'). Antares is 4.57 degrees south of the ecliptic , one of four first magnitude stars within 6° of the ecliptic (the others are Spica , Regulus and Aldebaran ), so it can be occulted by

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1068-404: A view of the stellar disc, which is then represented as a limb-darkened disk surrounded by an extended atmosphere. The diameter of the limb-darkened disk was measured as 37.38 ± 0.06 milliarcseconds in 2009 and 37.31 ± 0.09 milliarcseconds in 2010. The linear radius of the star can be calculated from its angular diameter and distance. However, the distance to Antares is not known with

1157-403: Is a magnitude 5.5 blue-white main-sequence star of spectral type B2.5V; it also has numerous unusual spectral lines suggesting it has been polluted by matter ejected by Antares. It is assumed to be a relatively normal early-B main sequence star with a mass around 7  M ☉ , a temperature around 18,500  K , and a radius of about 5  R ☉ . As it falls short of

1246-402: Is a red supergiant star with a stellar classification of M1.5Iab-Ib, and is indicated to be a spectral standard for that class. Due to the nature of the star, the derived parallax measurements have large errors, so that the true distance of Antares is approximately 550 light-years (170 parsecs ) from the Sun. The brightness of Antares at visual wavelengths is about 10,000 times that of

1335-407: Is a synonym for hotter , while "late" is a synonym for cooler . Depending on the context, "early" and "late" may be absolute or relative terms. "Early" as an absolute term would therefore refer to O or B, and possibly A stars. As a relative reference it relates to stars hotter than others, such as "early K" being perhaps K0, K1, K2 and K3. "Late" is used in the same way, with an unqualified use of

1424-498: Is actually a binary star system, with its two components called α Scorpii A and α Scorpii B. The brighter of the pair is the red supergiant, while the fainter is a hot main sequence star of magnitude 5.5. They have a projected separation of about 79.1  Tm (529  AU ). Its traditional name Antares derives from the Ancient Greek Ἀντάρης , meaning "rival to Ares ", due to the similarity of its reddish hue to

1513-559: Is based on spectral lines sensitive to stellar temperature and surface gravity , which is related to luminosity (whilst the Harvard classification is based on just surface temperature). Later, in 1953, after some revisions to the list of standard stars and classification criteria, the scheme was named the Morgan–Keenan classification , or MK , which remains in use today. Denser stars with higher surface gravity exhibit greater pressure broadening of spectral lines. The gravity, and hence

1602-532: Is determined by astrometric observations (for example, a secular change in the annual parallax ). Light from an object with a substantial relative radial velocity at emission will be subject to the Doppler effect , so the frequency of the light decreases for objects that were receding ( redshift ) and increases for objects that were approaching ( blueshift ). The radial velocity of a star or other luminous distant objects can be measured accurately by taking

1691-528: Is father of Puanga/Puaka ( Rigel ), an important star in the calculation of the Māori calendar. The Wotjobaluk Koori people of Victoria, Australia, knew Antares as Djuit , son of Marpean-kurrk ( Arcturus ); the stars on each side represented his wives. The Kulin Kooris saw Antares ( Balayang ) as the brother of Bunjil ( Altair ). Antares appears in the flag of Brazil , which displays 27 stars, each representing

1780-545: Is illuminating the Rho Ophiuchi cloud complex in its foreground. The illuminated cloud is sometimes referred to as the Antares Nebula or is otherwise identified as VdB 107. α Scorpii is a double star that is thought to form a binary system . The best calculated orbit for the stars is still considered to be unreliable. It describes an almost circular orbit seen nearly edge-on, with a period of 1,218 years and

1869-512: Is listed as spectral type B1.5Vnne, indicating a spectrum with the general classification B1.5V, as well as very broad absorption lines and certain emission lines. The reason for the odd arrangement of letters in the Harvard classification is historical, having evolved from the earlier Secchi classes and been progressively modified as understanding improved. During the 1860s and 1870s, pioneering stellar spectroscopist Angelo Secchi created

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1958-426: Is near conjunction with the Sun. In higher northern latitudes, Antares is only visible low in the south in summertime. Higher than 64° northern latitude, the star does not rise at all. Antares is easier to see from the southern hemisphere due to its southerly declination. In the whole of Antarctica, the star is circumpolar as the whole continent is above 64° S latitude. Radial velocity variations were observed in

2047-554: The American Association of Variable Star Observers since 1945, and it has been classified as an LC slow irregular variable star, whose apparent magnitude slowly varies between extremes of +0.6 and +1.6, although usually near magnitude +1.0. There is no obvious periodicity, but statistical analyses have suggested periods of 1,733 days or 1650 ± 640 days. No separate long secondary period has been detected, although it has been suggested that primary periods longer than

2136-681: The Arab warrior-hero celebrated in the pre-Islamic poems Mu'allaqat . However, the name "Antares" is already proven in the Greek culture, e.g. in Ptolemy's Almagest and Tetrabiblos. In 2016, the International Astronomical Union organised a Working Group on Star Names (WGSN) to catalog and standardise proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by

2225-589: The He  II λ4541 disappears. However, with modern equipment, the line is still apparent in the early B-type stars. Today for main-sequence stars, the B class is instead defined by the intensity of the He ;I violet spectrum, with the maximum intensity corresponding to class B2. For supergiants, lines of silicon are used instead; the Si ;IV λ4089 and Si III λ4552 lines are indicative of early B. At mid-B,

2314-604: The Hipparcos satellite's trigonometric parallax of 5.89 ± 1.00 mas with modern angular diameter estimates lead to a radius of about 680  R ☉ . Older radii estimates exceeding 850  R ☉ were derived from older measurements of the diameter, but those measurements are likely to have been affected by asymmetry of the atmosphere and the narrow range of infrared wavelengths observed; Antares has an extended shell which radiates strongly at those particular wavelengths. Despite its large size compared to

2403-612: The Infrared Astronomical Satellite (IRAS) Sky Survey Atlas catalogue as IRAS 16262–2619. It is also catalogued as a double star WDS J16294-2626 and CCDM J16294-2626. Antares is a variable star and is listed in the General Catalogue of Variable Stars , but as a Bayer-designated star it does not have a separate variable star designation . Its traditional name Antares derives from the Ancient Greek Ἀντάρης , meaning "rival to Ares ", due to

2492-591: The Kelvin–Helmholtz mechanism , which is now known to not apply to main-sequence stars . If that were true, then stars would start their lives as very hot "early-type" stars and then gradually cool down into "late-type" stars. This mechanism provided ages of the Sun that were much smaller than what is observed in the geologic record , and was rendered obsolete by the discovery that stars are powered by nuclear fusion . The terms "early" and "late" were carried over, beyond

2581-567: The Moon . The occultation of 31 July 2009 was visible in much of southern Asia and the Middle East. Every year around December 2 the Sun passes 5° north of Antares. Lunar occultations of Antares are fairly common, depending on the 18.6-year cycle of the lunar nodes . The last cycle ended in 2010 and the next begins in 2023. Shown at right is a video of a reappearance event, clearly showing events for both components. Antares can also be occulted by

2670-505: The Secchi classes in order to classify observed spectra. By 1866, he had developed three classes of stellar spectra, shown in the table below. In the late 1890s, this classification began to be superseded by the Harvard classification, which is discussed in the remainder of this article. The Roman numerals used for Secchi classes should not be confused with the completely unrelated Roman numerals used for Yerkes luminosity classes and

2759-496: The Sun is then G2V, indicating a main-sequence star with a surface temperature around 5,800 K. The conventional colour description takes into account only the peak of the stellar spectrum. In actuality, however, stars radiate in all parts of the spectrum. Because all spectral colours combined appear white, the actual apparent colours the human eye would observe are far lighter than the conventional colour descriptions would suggest. This characteristic of 'lightness' indicates that

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2848-498: The Sun , but because the star radiates a considerable part of its energy in the infrared part of the spectrum , the true bolometric luminosity is around 100,000 times that of the Sun. There is a large margin of error assigned to values for the bolometric luminosity, typically 30% or more. There is also considerable variation between values published by different authors, for example 75,900  L ☉ and 97,700  L ☉ published in 2012 and 2013. The mass of

2937-450: The barycentric radial-velocity measure or spectroscopic radial velocity. However, due to relativistic and cosmological effects over the great distances that light typically travels to reach the observer from an astronomical object, this measure cannot be accurately transformed to a geometric radial velocity without additional assumptions about the object and the space between it and the observer. By contrast, astrometric radial velocity

3026-639: The 11 inch Draper Telescope as Part of the Henry Draper Memorial", which included 4,800 photographs and Maury's analyses of 681 bright northern stars. This was the first instance in which a woman was credited for an observatory publication. In 1901, Annie Jump Cannon returned to the lettered types, but dropped all letters except O, B, A, F, G, K, M, and N used in that order, as well as P for planetary nebulae and Q for some peculiar spectra. She also used types such as B5A for stars halfway between types B and A, F2G for stars one fifth of

3115-453: The B2 subclass, and moderate hydrogen lines. As O- and B-type stars are so energetic, they only live for a relatively short time. Thus, due to the low probability of kinematic interaction during their lifetime, they are unable to stray far from the area in which they formed, apart from runaway stars . The transition from class O to class B was originally defined to be the point at which

3204-567: The Heart"), because it was the second star of the mansion Xin (心). It was the national star of the Shang dynasty , and it was sometimes referred to as ( Chinese : 火星 ; pinyin : Huǒxīng ; lit. 'fiery star') because of its reddish appearance. The Māori people of New Zealand call Antares Rēhua , and regard it as the chief of all the stars especially the Matariki . Rēhua

3293-583: The LOS direction. Equivalently, radial speed equals the norm of the radial velocity, modulo the sign. In astronomy, the point is usually taken to be the observer on Earth, so the radial velocity then denotes the speed with which the object moves away from the Earth (or approaches it, for a negative radial velocity). Given a differentiable vector r ∈ R 3 {\displaystyle \mathbf {r} \in \mathbb {R} ^{3}} defining

3382-478: The Sun, Antares is dwarfed by even larger red supergiants, such as VY Canis Majoris , WOH G64 , RW Cephei or Mu Cephei . Antares, like the similarly sized red supergiant Betelgeuse in the constellation Orion , will almost certainly explode as a supernova , probably in 1.0 to 1.4 million years. For a few months, the Antares supernova could be as bright as the full moon and be visible in daytime. Antares B

3471-572: The Sun, based on observed redshift of the star's light. In many binary stars , the orbital motion usually causes radial velocity variations of several kilometres per second (km/s). As the spectra of these stars vary due to the Doppler effect, they are called spectroscopic binaries . Radial velocity can be used to estimate the ratio of the masses of the stars, and some orbital elements , such as eccentricity and semimajor axis . The same method has also been used to detect planets around stars, in

3560-536: The WGSN, which included Antares for the star α Scorpii A. It is now so entered in the IAU Catalog of Star Names. Antares is visible all night around May 31 of each year, when the star is at opposition to the Sun . Antares then rises at dusk and sets at dawn as seen at the equator. For two to three weeks on either side of November 30, Antares is not visible in the night sky from mid-northern latitudes, because it

3649-519: The alphabet. This classification system was later modified by Annie Jump Cannon and Antonia Maury to produce the Harvard spectral classification scheme. In 1897, another astronomer at Harvard, Antonia Maury , placed the Orion subtype of Secchi class I ahead of the remainder of Secchi class I, thus placing the modern type B ahead of the modern type A. She was the first to do so, although she did not use lettered spectral types, but rather

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3738-697: The appearance of the planet Mars . α Scorpii (Latinised to Alpha Scorpii ) is the star's Bayer designation . Antares has the Flamsteed designation 21 Scorpii, as well as catalogue designations such as HR 6134 in the Bright Star Catalogue and HD 148478 in the Henry Draper Catalogue . As a prominent infrared source, it appears in the Two Micron All-Sky Survey catalogue as 2MASS J16292443-2625549 and

3827-433: The brighter stars of the constellation Orion . About 1 in 800 (0.125%) of the main-sequence stars in the solar neighborhood are B-type main-sequence stars . B-type stars are relatively uncommon and the closest is Regulus, at around 80 light years. Radial velocity The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between

3916-520: The classes indicate the temperature of the star's atmosphere and are normally listed from hottest to coldest. A common mnemonic for remembering the order of the spectral type letters, from hottest to coolest, is " O h, B e A F ine G uy/ G irl: K iss M e!", or another one is " O ur B right A stronomers F requently G enerate K iller M nemonics!" . The spectral classes O through M, as well as other more specialized classes discussed later, are subdivided by Arabic numerals (0–9), where 0 denotes

4005-637: The colors passed by two standard filters (e.g. U ltraviolet, B lue and V isual). The Harvard system is a one-dimensional classification scheme by astronomer Annie Jump Cannon , who re-ordered and simplified the prior alphabetical system by Draper (see History ). Stars are grouped according to their spectral characteristics by single letters of the alphabet, optionally with numeric subdivisions. Main-sequence stars vary in surface temperature from approximately 2,000 to 50,000  K , whereas more-evolved stars – in particular, newly-formed white dwarfs – can have surface temperatures above 100,000 K. Physically,

4094-525: The demise of the model they were based on. O-type stars are very hot and extremely luminous, with most of their radiated output in the ultraviolet range. These are the rarest of all main-sequence stars. About 1 in 3,000,000 (0.00003%) of the main-sequence stars in the solar neighborhood are O-type stars. Some of the most massive stars lie within this spectral class. O-type stars frequently have complicated surroundings that make measurement of their spectra difficult. O-type spectra formerly were defined by

4183-536: The derivative of the right-hand-side by the chain rule using ( 1 ) the expression becomes By reciprocity, ⟨ v , r ⟩ = ⟨ r , v ⟩ {\displaystyle \langle \mathbf {v} ,\mathbf {r} \rangle =\langle \mathbf {r} ,\mathbf {v} \rangle } . Defining the unit relative position vector r ^ = r / r {\displaystyle {\hat {r}}=\mathbf {r} /{r}} (or LOS direction),

4272-719: The extreme velocity of their stellar wind , which may reach 2,000 km/s. Because they are so massive, O-type stars have very hot cores and burn through their hydrogen fuel very quickly, so they are the first stars to leave the main sequence . When the MKK classification scheme was first described in 1943, the only subtypes of class O used were O5 to O9.5. The MKK scheme was extended to O9.7 in 1971 and O4 in 1978, and new classification schemes that add types O2, O3, and O3.5 have subsequently been introduced. Spectral standards: B-type stars are very luminous and blue. Their spectra have neutral helium lines, which are most prominent at

4361-627: The help of the Harvard computers , especially Williamina Fleming , the first iteration of the Henry Draper catalogue was devised to replace the Roman-numeral scheme established by Angelo Secchi. The catalogue used a scheme in which the previously used Secchi classes (I to V) were subdivided into more specific classes, given letters from A to P. Also, the letter Q was used for stars not fitting into any other class. Fleming worked with Pickering to differentiate 17 different classes based on

4450-404: The hottest stars of a given class. For example, A0 denotes the hottest stars in class A and A9 denotes the coolest ones. Fractional numbers are allowed; for example, the star Mu Normae is classified as O9.7. The Sun is classified as G2. The fact that the Harvard classification of a star indicated its surface or photospheric temperature (or more precisely, its effective temperature )

4539-418: The inner product is either +1 or -1, for parallel and antiparallel vectors , respectively. A singularity exists for coincident observer target, i.e., r = 0 {\displaystyle r=0} ; in this case, range rate is undefined. In astronomy, radial velocity is often measured to the first order of approximation by Doppler spectroscopy . The quantity obtained by this method may be called

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4628-518: The instantaneous relative position of a target with respect to an observer. Let the instantaneous relative velocity of the target with respect to the observer be The magnitude of the position vector r {\displaystyle \mathbf {r} } is defined as in terms of the inner product The quantity range rate is the time derivative of the magnitude ( norm ) of r {\displaystyle \mathbf {r} } , expressed as Substituting ( 2 ) into ( 3 ) Evaluating

4717-408: The intensity of hydrogen spectral lines, which causes variation in the wavelengths emanated from stars and results in variation in color appearance. The spectra in class A tended to produce the strongest hydrogen absorption lines while spectra in class O produced virtually no visible lines. The lettering system displayed the gradual decrease in hydrogen absorption in the spectral classes when moving down

4806-484: The intensity of the latter relative to that of Si II λλ4128-30 is the defining characteristic, while for late B, it is the intensity of Mg II λ4481 relative to that of He I λ4471. These stars tend to be found in their originating OB associations , which are associated with giant molecular clouds . The Orion OB1 association occupies a large portion of a spiral arm of the Milky Way and contains many of

4895-419: The main sequence). Nominal luminosity class VII (and sometimes higher numerals) is now rarely used for white dwarf or "hot sub-dwarf" classes, since the temperature-letters of the main sequence and giant stars no longer apply to white dwarfs. Occasionally, letters a and b are applied to luminosity classes other than supergiants; for example, a giant star slightly less luminous than typical may be given

4984-409: The mass limit required for stars to undergo a supernova , it will likely expand into a red giant before dying as a massive white dwarf similar to Sirius B . Antares B is normally difficult to see in small telescopes due to glare from Antares, but can sometimes be seen in apertures over 150 millimetres (5.9 inches). It is often described as green, but this is probably either a contrast effect , or

5073-485: The modern definition uses the ratio of the nitrogen line N IV λ4058 to N III λλ4634-40-42. O-type stars have dominant lines of absorption and sometimes emission for He  II lines, prominent ionized ( Si  IV, O  III, N  III, and C  III) and neutral helium lines, strengthening from O5 to O9, and prominent hydrogen Balmer lines , although not as strong as in later types. Higher-mass O-type stars do not retain extensive atmospheres due to

5162-508: The planets, e.g. Venus , but these events are rare. The last occultation of Antares by Venus took place on September 17, 525 BC; the next one will be November 17, 2400. Other planets have been calculated not to have occulted Antares over the last millennium, nor will they in the next millennium, as most planets stay near the ecliptic and pass north of Antares. Venus will be extremely near Antares on October 19, 2117, and every eight years thereafter through to October 29, 2157, it will pass south of

5251-473: The possibility that Antares is on a blue loop with an initial mass of 13  M ☉ (while excluding 14  M ☉ as a possible mass estimate). These correspond to ages from 11.8 to 17.3 MYr. These initial mass estimates mean that Antares may have once resembled massive blue stars like the members of the Acrux system, which have similar initial masses (both Antares and Acrux are members of

5340-401: The pressure, on the surface of a giant star is much lower than for a dwarf star because the radius of the giant is much greater than a dwarf of similar mass. Therefore, differences in the spectrum can be interpreted as luminosity effects and a luminosity class can be assigned purely from examination of the spectrum. A number of different luminosity classes are distinguished, as listed in

5429-638: The proposed neutron star classes. In the 1880s, the astronomer Edward C. Pickering began to make a survey of stellar spectra at the Harvard College Observatory , using the objective-prism method. A first result of this work was the Draper Catalogue of Stellar Spectra , published in 1890. Williamina Fleming classified most of the spectra in this catalogue and was credited with classifying over 10,000 featured stars and discovering 10 novae and more than 200 variable stars. With

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5518-408: The pyramidal ceremonies). It was called t ms n h ntt "the red one of the prow". In Persia , Antares was known as one of the four " royal stars ". In India , it with σ Scorpii and τ Scorpii were Jyeshthā (the eldest or biggest, probably attributing its huge size), one of the nakshatra ( Hindu lunar mansions ). The ancient Chinese called Antares 心宿二 ( Xīnxiù'èr , "second star of

5607-436: The range rate is simply expressed as i.e., the projection of the relative velocity vector onto the LOS direction. Further defining the velocity direction v ^ = v / v {\displaystyle {\hat {v}}=\mathbf {v} /{v}} , with the relative speed v = ‖ v ‖ {\displaystyle v=\|\mathbf {v} \|} , we have: where

5696-428: The ratio of the strength of the He  II λ4541 relative to that of He I λ4471, where λ is the radiation wavelength . Spectral type O7 was defined to be the point at which the two intensities are equal, with the He I line weakening towards earlier types. Type O3 was, by definition, the point at which said line disappears altogether, although it can be seen very faintly with modern technology. Due to this,

5785-569: The result of the mixing of light from the two stars when they are seen together through a telescope and are too close to be completely resolved. Antares B can sometimes be observed with a small telescope for a few seconds during lunar occultations while Antares is hidden by the Moon. Antares B appears a profound blue or bluish-green color, in contrast to the orange-red Antares. In the Babylonian star catalogues dating from at least 1100 BCE, Antares

5874-486: The same accuracy as modern measurements of its diameter. An estimate obtained by interferometry in 1925 by Francis G. Pease at the Mount Wilson Observatory gave Antares a diameter of 400 to 430 million mi (640 to 690 million km), equal to approximately 463-497  R ☉ , making it the then largest star known . Antares is now known to be somewhat larger; for instance,

5963-518: The similarity of its reddish hue to the appearance of the planet Mars . The comparison of Antares with Mars may have originated with early Mesopotamian astronomers which is considered an outdated speculation, because the name of this star in Mesopotamian astronomy has always been "heart of Scorpion" and it was associated with the goddess Lisin . Some scholars have speculated that the star may have been named after Antar , or Antarah ibn Shaddad,

6052-410: The simplified assignment of colours within the spectrum can be misleading. Excluding colour-contrast effects in dim light, in typical viewing conditions there are no green, cyan, indigo, or violet stars. "Yellow" dwarfs such as the Sun are white, "red" dwarfs are a deep shade of yellow/orange, and "brown" dwarfs do not literally appear brown, but hypothetically would appear dim red or grey/black to

6141-462: The solar chromosphere, then to stellar spectra. Harvard astronomer Cecilia Payne then demonstrated that the O-B-A-F-G-K-M spectral sequence is actually a sequence in temperature. Because the classification sequence predates our understanding that it is a temperature sequence, the placement of a spectrum into a given subtype, such as B3 or A7, depends upon (largely subjective) estimates of

6230-472: The spectrum of Antares in the early 20th century, and attempts were made to derive spectroscopic orbits. It became apparent that the small variations could not be due to orbital motion, and they were actually caused by pulsation of the star's atmosphere. Even in 1928, it was calculated that the size of the star must vary by about 20%. Antares was first reported to have a companion star by Johann Tobias Bürg during an occultation on April 13, 1819, although this

6319-536: The star has been calculated to be about 12  M ☉ , or 11 to 14.3  M ☉ . Comparison of the effective temperature and luminosity of Antares to theoretical evolutionary tracks for massive stars suggest a progenitor mass of 17  M ☉ and an age of 12 million years (MYr), or an initial mass of 15  M ☉ and an age of 11 to 15 MYr. Comparison of observations from antiquity to theoretical evolutionary tracks suggests an initial mass of 15 to 16  M ☉ , or

6408-485: The star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the rainbow of colors interspersed with spectral lines . Each line indicates a particular chemical element or molecule , with the line strength indicating the abundance of that element. The strengths of the different spectral lines vary mainly due to the temperature of the photosphere , although in some cases there are true abundance differences. The spectral class of

6497-524: The star. Antares is the brightest and most evolved stellar member of the Scorpius–Centaurus association , the nearest OB association to the Sun. It is a member of the Upper Scorpius subgroup of the association, which contains thousands of stars with a mean age of 11 million years. Antares is located about 170 parsecs (550  ly ) from Earth at the rim of the Upper Scorpius subgroup, and

6586-420: The star. When the star moves towards us, its spectrum is blueshifted, while it is redshifted when it moves away from us. By regularly looking at the spectrum of a star—and so, measuring its velocity—it can be determined if it moves periodically due to the influence of an exoplanet companion. From the instrumental perspective, velocities are measured relative to the telescope's motion. So an important first step of

6675-630: The strengths of absorption features in stellar spectra. As a result, these subtypes are not evenly divided into any sort of mathematically representable intervals. The Yerkes spectral classification , also called the MK, or Morgan-Keenan (alternatively referred to as the MKK, or Morgan-Keenan-Kellman) system from the authors' initials, is a system of stellar spectral classification introduced in 1943 by William Wilson Morgan , Philip C. Keenan , and Edith Kellman from Yerkes Observatory . This two-dimensional ( temperature and luminosity ) classification scheme

6764-463: The table below. Marginal cases are allowed; for example, a star may be either a supergiant or a bright giant, or may be in between the subgiant and main-sequence classifications. In these cases, two special symbols are used: For example, a star classified as A3-4III/IV would be in between spectral types A3 and A4, while being either a giant star or a subgiant. Sub-dwarf classes have also been used: VI for sub-dwarfs (stars slightly less luminous than

6853-483: The term indicating stars with spectral types such as K and M, but it can also be used for stars that are cool relative to other stars, as in using "late G" to refer to G7, G8, and G9. In the relative sense, "early" means a lower Arabic numeral following the class letter, and "late" means a higher number. This obscure terminology is a hold-over from a late nineteenth century model of stellar evolution , which supposed that stars were powered by gravitational contraction via

6942-406: The two components. The pair have a projected separation of about 529 astronomical units (AU) (≈ 80 billion km) at the estimated distance of Antares, giving a minimum value for the distance between them. Spectroscopic examination of the energy states in the outflow of matter from the companion star suggests that the latter is over 220  AU beyond the primary (about 33 billion km). Antares

7031-409: The two points. It is formulated as the vector projection of the target-observer relative velocity onto the relative direction or line-of-sight (LOS) connecting the two points. The radial speed or range rate is the temporal rate of the distance or range between the two points. It is a signed scalar quantity , formulated as the scalar projection of the relative velocity vector onto

7120-474: The wavelength observed. In addition, Antares pulsates in size, varying its radius by 19%. It also varies in temperature by 150 K, lagging 70 days behind radial velocity changes which are likely to be caused by the pulsations. The diameter of Antares can be measured most accurately using interferometry or observing lunar occultations events. An apparent diameter from occultations 41.3 ± 0.1 milliarcseconds has been published. Interferometry allows synthesis of

7209-482: The way from F to G, and so on. Finally, by 1912, Cannon had changed the types B, A, B5A, F2G, etc. to B0, A0, B5, F2, etc. This is essentially the modern form of the Harvard classification system. This system was developed through the analysis of spectra on photographic plates, which could convert light emanated from stars into a readable spectrum. A luminosity classification known as the Mount Wilson system

7298-399: The way that the movement's measurement determines the planet's orbital period, while the resulting radial-velocity amplitude allows the calculation of the lower bound on a planet's mass using the binary mass function . Radial velocity methods alone may only reveal a lower bound, since a large planet orbiting at a very high angle to the line of sight will perturb its star radially as much as

7387-450: The wider Scorpius–Centaurus association ). Massive stars like Antares are expected to explode as supernovae . Like most cool supergiants, Antares's size has much uncertainty due to the tenuous and translucent nature of the extended outer regions of the star. Defining an effective temperature is difficult due to spectral lines being generated at different depths in the atmosphere, and linear measurements produce different results depending on

7476-533: The width of certain absorption lines in the star's spectrum, which vary with the density of the atmosphere and so distinguish giant stars from dwarfs. Luminosity class  0 or Ia+ is used for hypergiants , class  I for supergiants , class  II for bright giants , class  III for regular giants , class  IV for subgiants , class  V for main-sequence stars , class  sd (or VI ) for subdwarfs , and class  D (or VII ) for white dwarfs . The full spectral class for

7565-791: Was a calque of the Greek name rendered in Latin . In ancient Mesopotamia , Antares may have been known by various names: Urbat, Bilu-sha-ziri ("the Lord of the Seed"), Kak-shisa ("the Creator of Prosperity"), Dar Lugal ("The King"), Masu Sar ("the Hero and the King"), and Kakkab Bir ("the Vermilion Star"). In ancient Egypt , Antares represented the scorpion goddess Serket (and was the symbol of Isis in

7654-632: Was called GABA GIR.TAB, "the Breast of the Scorpion". In MUL.APIN , which dates between 1100 and 700 BC, it is one of the stars of Ea in the southern sky and denotes the breast of the Scorpion goddess Ishhara . Later names that translate as "the Heart of Scorpion" include Calbalakrab from the Arabic قَلْبُ ٱلْعَقْرَبِ Qalb al-Άqrab . This had been directly translated from the Ancient Greek Καρδία Σκορπίου Kardia Skorpiū . Cor Scorpii

7743-461: Was not fully understood until after its development, though by the time the first Hertzsprung–Russell diagram was formulated (by 1914), this was generally suspected to be true. In the 1920s, the Indian physicist Meghnad Saha derived a theory of ionization by extending well-known ideas in physical chemistry pertaining to the dissociation of molecules to the ionization of atoms. First he applied it to

7832-542: Was not widely accepted and dismissed as a possible atmospheric effect. It was then observed by Scottish astronomer James William Grant FRSE while in India on 23 July 1844. It was rediscovered by Ormsby M. Mitchel in 1846 and measured by William Rutter Dawes in April 1847. In 1952, Antares was reported to vary in brightness. A photographic magnitude range from 3.00 to 3.16 was described. The brightness has been monitored by

7921-488: Was used to distinguish between stars of different luminosities. This notation system is still sometimes seen on modern spectra. The stellar classification system is taxonomic , based on type specimens , similar to classification of species in biology : The categories are defined by one or more standard stars for each category and sub-category, with an associated description of the distinguishing features. Stars are often referred to as early or late types. "Early"

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