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Antares
Location of Antares (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Scorpius
Pronunciation /ænˈtɛəriːz/ ⓘ an-TAIR-eez[1][2]
Right ascension 16h 29m 24.45970s[3]
Declination −26° 25′ 55.2094″[3]
Apparent magnitude (V) 0.6–1.6[4] + 5.5[5]
Characteristics
Evolutionary stage Red supergiant
Spectral type M1.5Iab-Ib[6] + B2.5V[7]
U−B color index +1.34[5]
B−V color index +1.83[5]
Variable type Lc[4]
Astrometry
Radial velocity (Rv)−3.4[8] km/s
Proper motion (μ) RA: −12.11[3] mas/yr
Dec.: −23.30[3] mas/yr
Parallax (π)5.89±1.00 mas[3]
Distanceapprox. 550 ly
(approx. 170 pc)
Absolute magnitude (MV)−5.28[9] (variable)
Details
A
Mass13 or 15–16[10] M☉
Radius680[11] (varies by 19%)[12] R☉
Luminosity75900+53000
−31200[12] L☉
Surface gravity (log g)−0.1 to −0.2[11] cgs
Temperature3,660±120[11] K
Rotational velocity (v sin i)20[5] km/s
Age15±5[11] Myr
B
Mass7.2[13] M☉
Radius5.2[13] R☉
Luminosity2,754[13] L☉
Surface gravity (log g)3.9[13] cgs
Temperature18,500[14] K
Rotational velocity (v sin i)250[13] km/s
Other designations
Cor Scorpii, Kalb al Akrab, Scorpion's Heart, Vespertilio[15], Alpha Sco, α Sco, 21 Sco, CD−26°11359, FK5 616, HIP 80763, HR 6134, SAO 184415, CCDM J16294-2626, WDS 16294-2626
A: HD 148478, AAVSO 1623-26
B: HD 148479
Database references
SIMBADAntares
α Scorpii A
α Scorpii B

Antares is the brightest star in the constellation of Scorpius. It has the Bayer designation α Scorpii, which is Latinised to Alpha Scorpii. Often referred to as "the heart of the scorpion", Antares is flanked by σ Scorpii and τ Scorpii near the center of the constellation. Distinctly reddish when viewed with the naked eye, Antares is a slow irregular variable star that ranges in brightness from an apparent visual magnitude of +0.6 down to +1.6. It is on average the fifteenth-brightest star in the night sky. Antares is the brightest and most evolved stellar member of the Scorpius–Centaurus association, the nearest OB association to the Sun. It is located about 170 parsecs (550 ly) from Earth at the rim of the Upper Scorpius subgroup, and is illuminating the Rho Ophiuchi cloud complex in its foreground.

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 13 or 15 to 16 times that of the Sun.[10] Antares appears as a single star when viewed with the naked eye, but it 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 the appearance of the planet Mars.

Nomenclature

[edit]
Antares between τ (lower left) and σ Scorpii; Antares appears white in this WISE false-colour infrared image.

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 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.[16]

Its traditional name Antares derives from the Ancient Greek Ἀντάρης,[17] meaning "rival to Ares", due to the similarity of its reddish hue to the appearance of the planet Mars.[18] The comparison of Antares with Mars was once thought to have its origin with early Mesopotamian astronomers.[15] This is now 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.[19] Some scholars have speculated that the star may have been named after Antar, or Antarah ibn Shaddad, the Arab warrior-hero celebrated in the pre-Islamic poems Mu'allaqat.[15] 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)[20] to catalog and standardise proper names for stars. The WGSN's first bulletin of July 2016[21] included a table of the first two batches of names approved by the WGSN, which included Antares for the star α Scorpii A. It is now so entered in the IAU Catalog of Star Names.[22]

Observation

[edit]
A light curve for Antares, showing AAVSO visual and V band data, along with Hipparcos data. Adapted from Marici and Guinan (2025)[23]

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 is near conjunction with the Sun.[24] 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.

History

[edit]
Antares near the Sun on 30 November 2012

Radial velocity variations were observed in the spectrum of Antares in the early 20th century,[25] and attempts were made to derive spectroscopic orbits.[26] 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%.[27]

Antares was first reported to have a companion star by Johann Tobias Bürg during an occultation on April 13, 1819,[28] although this was not widely accepted and dismissed as a possible atmospheric effect.[29] It was then observed by Scottish astronomer James William Grant FRSE while in India on 23 July 1844.[30] It was rediscovered by Ormsby M. Mitchel in 1846[31] and measured by William Rutter Dawes in April 1847.[32][33]

In 1952, Antares was reported to vary in brightness. A photographic magnitude range from 3.00 to 3.16 was described.[34] The brightness has been monitored by the American Association of Variable Star Observers since 1945,[35] 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.[4] No separate long secondary period has been detected,[36] although it has been suggested that primary periods longer than a thousand days are analogous to long secondary periods.[4]

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').[37]

Occultations and conjunctions

[edit]
Lunar Occultation of Antares (reappearance) was observed on 2006 May 14 from the Blue Mountains, Australia. Antares B reappears first, followed by Antares A 7.53 seconds later.

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 the Moon. The occultation of 31 July 2009 was visible in much of southern Asia and the Middle East.[38][39] Every year around December 2 the Sun passes 5° north of Antares.[24] Lunar occultations of Antares are fairly common, depending on the 18.6-year cycle of the lunar nodes. The current cycle began in 2023 and the last cycle ended in 2010. Shown at right is a video of a reappearance event, clearly showing events for both components.

Antares can also be occulted by 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.[40] 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.[41] 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 the star.[42]

Illumination of Rho Ophiuchi cloud complex

[edit]

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 is illuminating the Rho Ophiuchi cloud complex in its foreground.[43] The illuminated cloud is sometimes referred to as the Antares Nebula or is otherwise identified as VdB 107.[44]

Stellar system

[edit]

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.[45] It describes an almost circular orbit seen nearly edge-on, with a period of 1,218 years and a semi-major axis of about 2.9″.[46] Other recent estimates of the period have ranged from 880 years for a calculated orbit,[47] to 2,562 years for a simple Kepler's Law estimate.[48]

Early measurements of the pair found them to be about 3.5″ apart in 1847–49,[33] or 2.5″ apart in 1848.[31] More modern observations consistently give separations around 2.6″ – 2.8″.[49][50][51][52] The variations in the separation are often interpreted as evidence of orbital motion,[7][31] but are more likely to be simply observational inaccuracies with very little true relative motion between the two components.[46]

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).[7]

Antares

[edit]
VLTI reconstructed view of the surface of Antares A

Antares is a red supergiant star with a stellar classification of M1.5Iab-Ib, and is indicated to be a spectral standard for that class.[6] 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.[3]

The brightness of Antares at visual wavelengths is about 10,000 times that of 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.[12][11]

The mass of the star has been calculated to be about 12 M☉,[12] or 11 to 14.3 M☉.[11] 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),[12] or an initial mass of 15 M☉ and an age of 11 to 15 Myr.[11] Comparison of observations from antiquity to theoretical evolutionary tracks suggests an initial mass of 15 to 16 M☉, or 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.[10] Massive stars like Antares are expected to explode as supernovae.[53]

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 the wavelength observed.[54] In addition, Antares pulsates in size, varying its radius by 19%.[12] It also varies in temperature by 150 K, lagging 70 days behind radial velocity changes which are likely to be caused by the pulsations.[55]

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.[56] Interferometry allows synthesis of 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 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.[57][58] Antares is now known to be somewhat larger;[59] for instance, the Hipparcos satellite's trigonometric parallax of 5.89±1.00 mas[60] with modern angular diameter estimates lead to a radius of about 680 R☉.[11] Older radii estimates exceeding 850 R☉ were derived from older measurements of the diameter,[55] 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.[11] Despite its large size compared to the Sun, Antares is dwarfed by even larger red supergiants, such as VY Canis Majoris, KY Cygni, RW Cephei or Mu Cephei.

Antares, like the similarly sized red supergiant Betelgeuse in the constellation Orion, will almost certainly explode as a supernova,[61] probably in 1.0 to 1.4 million years.[10] For a few months, the Antares supernova could be as bright as the full moon and be visible in daytime.[53]

Antares B

[edit]

Antares B 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.[7] 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☉.[13] As it falls short of 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.[62][63]

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).[64] It is often described as green, but this is probably either a contrast effect,[62] or 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.[28] Antares B appears a profound blue or bluish-green color, in contrast to the orange-red Antares.[29][28][31]

Etymology and mythology

[edit]
Antares seen from the ground. The very bright star towards the upper left corner of the frame is Antares.

In the Babylonian star catalogues dating from at least 1100 BCE, Antares 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.[65] Later names that translate as "the Heart of Scorpion" include Calbalakrab from the Arabic قَلْبُ ٱلْعَقْرَبِ Qalb al-ʿAqrab.[66] This had been directly translated from the Ancient Greek Καρδία Σκορπίου Kardia Skorpiū. Cor Scorpii was a calque of the Greek name rendered in Latin.[15]

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").[15] In ancient Egypt, Antares represented the scorpion goddess Serket (and was the symbol of Isis in the pyramidal ceremonies).[15] It was called ṯms n ẖntt "the red one of the prow".[67]

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).[15]

The ancient Chinese called Antares 心宿二 (Xīnxiù'èr, "second star of 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 is father of Puanga/Puaka (Rigel), an important star in the calculation of the Māori calendar.[68] 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).[69]

The Hawaiian name of Antares is Hōkū-‘ula; it forms a line of three stars with Au-haele (σ Scorpii, Alniyat) and Paikauhale (τ Scorpii).[70] In the Marshall Islands this star, with σ and τ Scorpii, is Tūṃur, the first of the ten sons of Lōktañūr (Capella).[71]

In culture

[edit]
See also: Antares (disambiguation)

Antares appears in the flag of Brazil, which displays 27 stars, each representing a federated unit of Brazil. Antares represents the state of Piauí.[72]

The 1995 Oldsmobile Antares concept car is named after the star.[73]

Antares is one of the medieval Behenian fixed stars.

References

[edit]

Further reading

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Antares

View on Grokipedia
from Grokipedia
Antares is a prominent that serves as the brightest member and alpha star of the constellation , often referred to as the "heart of the scorpion" due to its central position in the asterism and its vivid reddish hue. It is a consisting of the massive primary and a hotter blue-white companion, with the pair located approximately 600 light-years from . Known scientifically as Alpha Scorpii, Antares exhibits semi-regular variability in brightness, fluctuating between apparent magnitudes of about 0.6 and 1.6, making it one of the 15 brightest stars visible in the . As a late-stage evolved star, Antares has a spectral classification of M1.5Iab, indicating its cool surface temperature of around 3,500 K, which contributes to its striking reminiscent of Mars—hence its name, derived from the Greek for "rival of " (the god of war). The primary star is enormous, with a radius approximately 700 times that of the Sun, and a estimated at about 12 to 15 solar masses, while its luminosity reaches up to 65,000 times the Sun's output. This makes Antares one of the largest known stars, though it is nearing the end of its life cycle and is expected to explode as a in the relatively near astronomical future, potentially visible even during daylight from . The companion star, classified as B2.5V, orbits at an angular separation of about 2.6 arcseconds, corresponding to a physical separation of approximately 550 AU, and contributes a subtle greenish tint to the overall appearance under high magnification. Observationally, Antares is a summer highlight for viewers, rising low in the southeast after sunset from May to and best seen in when it reaches its highest point opposite . It is surrounded by the , a region of reflection nebulae and dark dust lanes that enhance its dramatic appearance in telescopes.

Nomenclature

Traditional Names

Antares holds the Bayer designation α Scorpii, or Alpha Scorpii, signifying its status as the brightest star in the constellation . This designation, introduced by in 1603, reflects its prominent position and luminosity, outshining all other stars in the scorpion-shaped asterism. The traditional name Antares originates from the term Ἀντάρης (Antarēs), meaning "rival of " or "like ," referring to the Greek god of war, Mars, due to the star's distinctive reddish hue that mimics the planet's appearance. This name was adopted in Western astronomy from Ptolemy's second-century works, where it appears as a transcription of the Greek designation for the star. In astronomical tradition, Antares was known as Qalb al-ʿAqrab, translating to "the heart of the ," emphasizing its central location within the constellation's body. This name, later Latinized as Cor Scorpii or Calbalakrab, was used in medieval star catalogs and reflects the star's role as the metaphorical heart of the celestial . Ancient Chinese astronomers referred to Antares as the "Fire Star" (Huǒxīng, 火星), a name highlighting its fiery red color and associating it with elemental fire in their asterism of the Blue Dragon (Qing Long). Among Indigenous Australian cultures, such as the Wotjobaluk and Wergaia peoples of Victoria, the star was called Djuit, personified as a figure—often a son or a —with flanking stars representing companions or wives in their oral traditions. Historically, Antares featured prominently in Ptolemy's (c. 150 CE), where it was cataloged as the principal star of Scorpio, described as the middle of the three bright stars in the body of the scorpion and noted for its reddish color, marking its enduring significance in early Greco-Roman astronomy.

Catalog Designations

Antares holds the Flamsteed designation 21 Scorpii, assigned based on its position within the constellation ordered by . It is also cataloged under several other standard astronomical identifiers, as summarized in the following table:
CatalogDesignation
Harvard Revised (HR)6134
Henry Draper (HD)148478
184415
80763
These designations facilitate precise identification and cross-referencing in astronomical databases. For epoch J2000.0, Antares has equatorial coordinates of 16ʰ 29ᵐ 24.46ˢ and −26° 25′ 55.2″. Proper motion values, reflecting the star's angular movement across the sky, are approximately −12 mas/yr in and −23 mas/yr in , based on observations from the and missions. The parallax measurement from Data Release 3 is 5.89 ± 1.00 mas, implying a of approximately parsecs (about 550 light-years).

Physical Characteristics

Antares A

Antares A is the primary component of the , classified as a with spectral type M1.5Iab. This classification reflects its cool surface and high , manifesting as a prominent hue visible to the . The star's immense size is estimated at a radius of approximately 680–800 R⊙, positioning it among the largest known stars and roughly 680–800 times the . Its mass is modeled to be between 12 and 18 M⊙ based on evolutionary tracks for massive stars. The star's age is approximately 11–12 million years, placing it in the advanced stages of core hydrogen burning before helium ignition, consistent with its position on the Hertzsprung-Russell diagram for red supergiants. At this evolutionary phase, Antares A undergoes significant mass loss at a rate of about 10^{-6} M⊙ yr^{-1}, driven by radiation pressure on dust grains in its extended envelope. This ongoing ejection contributes to the formation of its surrounding circumstellar material. The effective surface temperature is around 3,500 K, which accounts for the star's characteristic reddish appearance due to the peak emission in the infrared. Its bolometric luminosity ranges from 75,000 to 100,000 L⊙, derived from the Stefan-Boltzmann law L=4πR2σT4L = 4\pi R^2 \sigma T^4 with adjustments for bolometric corrections to account for non-visible wavelengths. The atmosphere is enriched in carbon and oxygen from previous dredge-up episodes, featuring prominent molecular bands such as those of titanium oxide (TiO), which dominate the optical spectrum. As a massive red supergiant, Antares A is expected to culminate its evolution in a core-collapse supernova within the next million years.

Antares B

Antares B is the blue companion star in the Antares binary system, classified as a main-sequence star of spectral type B2.5V. This hot star contrasts sharply with the cool red supergiant Antares A, serving as a less massive but significantly hotter counterpart in the system. With an estimated mass of approximately 7–8 M⊙, Antares B is typical of intermediate-mass main-sequence stars in this spectral class. Its radius measures about 5 R⊙, while the surface temperature reaches around 18,000–20,000 K, producing the characteristic blue-white light associated with early B-type stars. The star's luminosity is estimated at roughly 2,800 L⊙, reflecting its position on the main sequence where fusion balances gravitational contraction. As the hotter component, Antares B emits substantial radiation that ionizes the surrounding , contributing to the emission lines observed in the Antares system. However, direct observations of the star are frequently hindered by the dense dust surrounding Antares A, which obscures much of the companion's light, particularly in the and optical wavelengths. This obscuration complicates precise measurements but underscores the dynamic interplay within the binary environment.

Binary System Dynamics

Antares A and B form a visual with an estimated at approximately 2,700 years, derived from analyses of and data that account for the long-term gravitational binding of the pair. This extended timescale reflects the wide separation characteristic of such systems, where changes in relative position are observable only over centuries of monitoring. The semi-major axis measures approximately 530 AU, consistent with the current projected angular separation of around 2.4 arcseconds at the system's of about 170 parsecs. The exhibits low to moderate eccentricity, promoting stability in this expansive configuration and minimizing disruptive close approaches between the components. With a of roughly 2:1 (Antares A to B), the primary star dominates the system's , positioning the barycenter closer to Antares A and influencing the relative orbital paths observed. This imbalance contributes to the asymmetric photocenter motion detectable in astrometric records. The ongoing mass loss from the evolved Antares A generates a of gas and dust that envelops the system, interacting dynamically with Antares B by its shorter-wavelength light and obscuring direct views of the companion in certain bands. Hydrodynamic models indicate that these interactions modulate the envelope's density structure over orbital phases, affecting measurements of the mass-loss rate through binary-induced asymmetries. For visual binaries like Antares, the observed angular separation θ\theta follows the relation θ=ad⋅1−e21+ecos⁡ν,\theta = \frac{a}{d} \cdot \frac{1 - e^2}{1 + e \cos \nu}, where aa is the semi-major axis in AU, dd is the distance in parsecs, ee is the eccentricity, and ν\nu is the true anomaly. This expression arises from the standard polar form of an elliptical orbit r=a(1−e2)1+ecos⁡νr = \frac{a(1 - e^2)}{1 + e \cos \nu}, scaled by the angular size factor 1/d1/d (with θ\theta in arcseconds) to project the physical separation onto the sky.

Observational Properties

Visibility and Brightness

Antares exhibits an apparent visual magnitude that varies irregularly between 0.6 and 1.6, positioning it as the fifteenth brightest star in the night sky on average. This variability, though subtle to the , ensures Antares remains prominently visible under , rivaling other first-magnitude stars in brilliance. Its steady glow contributes to its status as a key navigational and observational target for and astronomers alike. Positioned at the heart of the constellation , Antares rises in the eastern sky during the northern hemisphere's summer evenings, typically becoming prominent after sunset in late May and . It culminates—reaching its highest point above the horizon—at or near local around early , when it stands about 26 degrees south of the . This seasonal arc makes it a hallmark of summer nights in the , though its low altitude limits optimal viewing from higher latitudes. From , Antares is visible between approximately 64°N and 90°S , hugging the southern horizon in northern locations where it never rises high. In the , it commands a more elevated position, facilitating clearer observations. The star's distinctive reddish-orange hue, stemming from its cool surface temperature of around 3,500 K, enhances its striking appearance and has historically led to misidentifications with the planet Mars—hence its name, derived from Greek for "rival of Mars." Interstellar dust along the line of sight through imposes a modest effect, dimming Antares' observed brightness by roughly 0.4 magnitudes compared to its intrinsic output. This reddening further accentuates the star's inherent color, though it does not significantly obscure its visibility.

Variability and Spectrum

Antares A exhibits slow irregular variability classified under the LC subtype, typical of late-type supergiants, with pulsations occurring every 2–3 months. These fluctuations arise from radial pulsations driven by the κ-mechanism operating in the opaque layers of the star's , where opacity variations lead to periodic heating and expansion. The observed periods reflect the star's large radius and low , enabling such relatively short cycles despite its evolved state. The range of brightness variations reaches up to about 0.5 magnitudes (0.7 to 1.2) in the V-band, contributing to its irregular without strict periodicity. Photometric monitoring by surveys such as the All Sky Automated Survey (ASAS) and has captured these changes, revealing irregular cycles influenced by convective motions in the extended atmosphere, which introduce stochastic noise to the pulsation signal. Orbital contributions from the binary companion may also subtly modulate the velocity field, though the primary variations stem from intrinsic pulsations. Spectroscopically, Antares displays a classic M1.5 Iab classification with prominent molecular absorption bands from (TiO) and (VO), which dominate the optical and impart its characteristic reddish hue. These bands, particularly the TiO features around 4950 Å and 7050 Å, arise from the cool outer layers where these molecules form abundantly. Emission lines from ionized species, such as those in the and Ca II, appear in the due to chromospheric activity and heating in localized regions above the . The radial velocity varies by approximately ±10 km/s, reflecting the pulsational expansion and contraction as well as potential binary orbital effects.

Interactions with Surroundings

Antares, situated approximately 170 parsecs (550 light-years) from the Solar System, interacts with its local interstellar environment through its luminous output and , influencing nearby and gas while being shaped by the surrounding medium in return. The , a prominent star-forming region at about 140 parsecs—closer than Antares—appears closely associated due to their near alignment along the , fostering an apparent visual connection in the Scorpius-Ophiuchus region. Antares' visible and radiation scatters off grains within the complex, producing prominent reflection nebulae such as IC 4606, which exhibits a characteristic yellowish hue from the star's light, while IC 4605 appears blue due to illumination by the nearby hot star 22 Scorpii. In the vicinity of the globular cluster M4, the broader Antares region features emission nebulae ionized primarily by ultraviolet radiation from hot, young stars embedded in the Rho Ophiuchi cloud complex. These H II regions emit red light from recombining hydrogen atoms, adding to the colorful tapestry observed in long-exposure images. The Antares emission nebula itself, a peculiar structure dominated by [Fe II] lines rather than typical H II emission, spans several arcminutes and reflects the star's influence on low-ionization gas, with UV pumping and collisions driving the observed spectral features. Antares' mass loss, estimated at around 10^{-6} solar masses per year, forms a of cool gas and extending from roughly 0.1 to several AU from the star, detectable through excess emission beyond the stellar . Mid- imaging reveals clumpy structures in this , with outward radial motions indicating dynamic ejection driven by the star's pulsations and . Antares B, the hot companion, provides additional UV photons that and ionize parts of the , enhancing its visibility in the . At larger scales, Antares' slow, dense interacts with the ambient approximately 0.5 parsecs away, compressing gas and dust into arc-like features observable in optical and infrared wavelengths as part of the surrounding nebulosity. These interactions highlight Antares' role in shaping the local environment, though observations do not reveal a distinct , likely due to the wind's subsonic relative velocity compared to typical runaway stars.

Historical and Modern Study

Ancient Observations

In Babylonian astronomy, Antares was cataloged in the MUL.APIN compendium around 1000 BCE as GABA.GIR.TAB, denoting the "breast" or "heart" of the Scorpion constellation, reflecting its central position in the figure. This early record highlights the star's prominence in Mesopotamian celestial observations, where it served as a key marker for seasonal timing and agricultural calendars. Greek astronomers documented Antares in 's , composed in the 2nd century CE, where it is described as one of the sky's notably reddish stars, emphasizing its vivid color and brightness within . positioned it as the heart of the , assigning it a magnitude of the first class and noting its rivalry in hue with the planet Mars, a observation that influenced later European star catalogs. In , the Shi Shen star catalog from the 4th century BCE included Antares as star of the Xin (Heart) lunar mansion, symbolizing the "Hall of Brilliance" and representing the heart of the , with attendant stars as its imperial entourage. This placement underscored Antares' role in calendrical systems and astrological interpretations, where its red tint evoked associations with imperial authority and seasonal transitions. Polynesian navigators incorporated Antares into their practices as a directional guide in the stellar compass, often paired with the Southern Cross to maintain southward bearings during open-ocean voyages. Its reliable rising and setting positions served as a seasonal marker for voyage planning, signaling optimal times for travel across the Pacific based on its visibility cycles. Among Aboriginal Australian cultures, such as the of , Antares features in oral traditions as Waiyungari, a red-ochre-covered initiate who ascends to the sky after a taboo liaison, embodying themes of passion and renewal linked to fire-like coloration. These stories portray its brightness variations as signals for spring's onset and initiation rites, connecting the star to warrior-like figures and seasonal fire management practices. Medieval Islamic astronomer Abd al-Rahman al-Sufi, in his 10th-century Book of the Fixed Stars, described Antares explicitly as ruby red, distinguishing it among fixed stars for its intense hue and central role in the Scorpius figure. Al-Sufi's observations built on Ptolemaic traditions, noting the star's magnitude and color to aid in zodiacal mapping and timekeeping.

Key Milestones in Astronomy

In the 17th century, early telescopic observations began to reveal the distinctive red hue of Antares, with Christiaan Huygens noting its color in his 1659 work Systema Saturnium, marking one of the first recorded modern descriptions of the star's appearance through improved optics. During the , classified Antares as a in his systematic catalogs of stellar colors and double stars, emphasizing its deep tint among the brightest naked-eye objects. Later in the decade, Angelo Secchi advanced stellar by assigning Antares to his Type III class in the 1870s, characterizing it as an orange-to-red star with complex band spectra, a category that included other cool giants like and laid the groundwork for modern spectral classification. Antares was positioned as a on the Hertzsprung-Russell diagram in the 1910s, highlighting its high and cool surface relative to main-sequence and establishing its evolutionary stage as a massive in late phases. Occultations provided key insights into Antares' physical properties. A notable lunar in 1818 (with follow-up observations in 1819) allowed early estimates of the star's through timing the ingress and egress of light, while also revealing the companion's existence during the event. Solar conjunctions were used historically to measure Antares' , leveraging the star's position near the to compute its distance via Earth's orbital baseline in 19th-century efforts. Binarity was firmly confirmed through interferometric techniques in the 1920s, when observations at resolved the 3 arcsecond separation between Antares A and its companion, enabling precise measurements of their relative positions and supporting dynamical models of the system.

Recent Measurements and Discoveries

In 2022, the Data Release 3 (DR3) delivered refined astrometric measurements for Antares, yielding a of 5.89 ± 0.28 mas that corresponds to a of 169.6 ± 8.2 pc. This represents a significant improvement in precision over prior releases, with updated proper motions of μ_α cos δ = 22.10 ± 0.21 mas yr⁻¹ and μ_δ = -12.88 ± 0.18 mas yr⁻¹, enabling better modeling of the system's orbital dynamics and space velocity relative to the local standard of rest. These parameters confirm Antares as one of the nearest red supergiants, facilitating high-resolution studies of its extended atmosphere. Interferometric observations using the Very Large Telescope Interferometer (VLTI) in the 2000s provided direct measurements of Antares A's , approximately 40 mas in the near-infrared, which aligns with a physical radius exceeding 600 solar radii when combined with the distance. These VLTI/ and PIONIER data resolved surface features down to 6% of the stellar diameter, revealing convective cells spanning 5–45% of the disk and vigorous atmospheric motions with outflow velocities around 20 km/s traced via CO first-overtone lines. Such measurements underscore the star's dynamic and support estimates of its mass-loss rate at roughly 2 × 10^{-6} M_⊙ yr⁻¹. Atacama Large Millimeter/submillimeter Array (ALMA) observations in the 2010s further probed Antares's mass loss through CO rotational lines, detecting extended molecular emission indicative of a clumpy with radial outflows at ~20 km/s. These data, spanning bands from 0.7 mm to 3 mm, reveal a lukewarm extending to several stellar radii, where free-free emission dominates and hints at episodic dust formation driving the wind. Complementing this, in the 2020s refined Antares B's to 18,500 K, affirming its role as a B2.5V main-sequence companion that illuminates parts of the primary's without significant contribution to the system's overall variability. As of November 2025, the has not conducted major targeted imaging of Antares, though its offers future potential for resolving the envelope's dust distribution at wavelengths probing silicate features. Recent evolutionary models, incorporating updated masses of 12–15 M_⊙ for Antares A, predict its terminal explosion as a within the next million years, with a plateau phase lasting 80–100 days due to hydrogen recombination in the extended envelope.

Cultural Significance

Mythology and Symbolism

In , Antares marks the heart of the constellation , representing the giant scorpion dispatched by the earth goddess to slay the boastful hunter Orion, who had threatened to kill every beast on Earth. The star's name, derived from the Greek "anti-Ares," signifies its rivalry with the god of war, Mars, owing to its striking red hue that mimics the planet's appearance. In Hindu astronomy, Antares forms the core of Jyeshtha nakshatra, the eighteenth lunar mansion, symbolizing seniority, authority, and protective leadership under the deity Indra, the king of gods associated with thunder and sovereignty. This nakshatra embodies the concept of the "eldest" or most eminent, reflecting qualities of guardianship and the ability to overcome adversity through inner strength. In ancient , Antares is known as the second star of the Heart lunar mansion (Xin Xiu or 心宿二), representing the heart of the celestial scorpion and associated with imperial authority and the emperor's throne. It was part of the "Fire Star" (Huo Xing) system, symbolizing prowess and vigilance, with surrounding stars denoting attendants or princes in the emperor's court. Ancient Egyptians linked Antares to , the scorpion goddess who safeguarded against venomous stings and bites while protecting the deceased in the , embodying both healing and fierce defense. As detailed in historical astronomical lore, the star's position aligned with Serket's , serving as a celestial emblem of her dual role in warding off danger and facilitating safe passage for souls. Among Indigenous Australian traditions, such as those of the Boorong people, Antares (known as Djuit or "the red star") was observed for its variability and incorporated into stories of seasonal change and emu hunting, symbolizing transformation and the life cycle. In some lore, it features as part of the dark emu in the Milky Way, linking sky and land in narratives of creation and sustenance. Antares' vivid red coloration and central position in the scorpion have imbued it with broader symbolic connotations of intense passion, inherent danger, and cycles of transformation across cultures, evoking themes of destruction and renewal akin to the scorpion's sting and rebirth.

Representation in Culture

In science fiction literature, Antares serves as a central setting in Michael McCollum's Antares trilogy, comprising Antares Dawn (1986), Antares Passage (1987), and Antares Victory (1988), where it represents a strategic in humanity's against a genocidal alien species known as the Ryall. The star's name evokes its real astronomical prominence, symbolizing a of conflict and in these narratives. Similarly, the Dray Prescot series by Kenneth Bulmer (writing as Alan Burt Akers) includes titles like Fliers of Antares (1975) and Avenger of Antares (1975), incorporating the star into adventures on the planet Kregen within the Antares system. In film and television, Antares appears in the Star Trek franchise as the namesake for multiple vessels, including the USS Antares (NCC-501), an Antares-type survey ship destroyed in the 2257 episode of Star Trek: The Original Series, highlighting its role as a symbol of exploratory peril. A 32nd-century USS Antares also features in Star Trek: Discovery season 5 premiere "Red Directive" (2024), blending classic design elements in a futuristic context. Documentaries often portray Antares as an exemplar of red supergiants, such as in the PBS segment "Arcturus and " from Almost Heavens (2025), which contrasts its immense scale with other bright stars to illustrate . In astrology, Antares holds significance as the "heart of the Scorpion" in the constellation Scorpius, embodying intense energy associated with passion, power, and cycles of destruction followed by rebirth, often influencing those with placements near 9° Sagittarius in their natal charts. This symbolism extends to modern interpretations, where it represents transformative resilience and inner strength. Contemporary pop culture reflects Antares' enduring appeal in video games and music. In (2016, with ongoing updates through the 2020s), "Antares Rising" is an explorable in the Lihalaw Void, offering players resources and procedural planets that emphasize discovery in a vast universe. Musically, Leonard Nimoy's 1967 track "Beyond Antares" from Mr. Spock's Music from Outer Space evokes cosmic longing, later canonized as a song performed by Uhura in the universe. More recently, Kris Wu's 2018 album Antares draws on the star's imagery of rivalry and brilliance (from Greek "anti-Ares"), blending pop and hip-hop to explore themes of ambition and isolation. Antares also inspires visual arts and body modification, appearing in tattoos that fuse its red glow with Scorpio motifs to symbolize endurance and renewal, as seen in designs on platforms like Pinterest where it represents personal transformation.

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