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Beta Aquarii
Beta Aquarii
Beta Aquarii
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Beta Aquarii
Location of β Aquarii (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aquarius
Right ascension 21h 31m 33.53171s[1]
Declination −05° 34′ 16.2320″[1]
Apparent magnitude (V) 2.87[2]
Characteristics
Evolutionary stage Yellow supergiant
Spectral type G0 Ib[3]
U−B color index +0.58[2]
B−V color index +0.84[2]
Astrometry
Radial velocity (Rv)6.451±0.0627[4] km/s
Proper motion (μ) RA: +18.77[1] mas/yr
Dec.: −8.21[1] mas/yr
Parallax (π)5.9728±0.2147 mas[5]
Distance541.8+18.4
−15.5 ly
(166.12+5.64
−4.75 pc)[6]
Absolute magnitude (MV)−3.04[7]
Details[8]
Mass4.97±0.10[8] – 6.3[9] M☉
Radius47.88+1.68
−1.81 R☉
Luminosity2046±180 L☉
Surface gravity (log g)2.05[10] cgs
Temperature5608±71 K
Metallicity [Fe/H]−0.03[11] dex
Rotational velocity (v sin i)6.3±1.3[12] km/s
Age56[9] – 110±10 Myr
Other designations
Sadalsuud, Saad el Sund, β Aqr, 22 Aqr, BD−06 5770, FK5 808, GC 30137, HD 204867, HIP 106278, HR 8232, SAO 145457, ADS 15050 A, CCDM J21316-0534A[13]
Database references
SIMBADdata

Beta Aquarii is a single[14] yellow supergiant star in the constellation of Aquarius. It has the official name Sadalsuud (/ˌsædəlˈsuːəd/)[15] and the Bayer designation β Aquarii, abbreviated Beta Aqr or β Aqr. Based upon parallax measurements obtained during the Hipparcos mission, this component is located at a distance of approximately 540 light years (165 parsecs) from the Sun.[1] It is drifting further away with a radial velocity of 6.5 km/s.[4] The star serves as an IAU radial velocity standard.[16]

Nomenclature

[edit]

β Aquarii, Latinised to Beta Aquarii, is the star's Bayer designation.

It bore the traditional name Sadalsuud, from an Arabic expression سعد السعود (sa‘d al-su‘ūd), the "luck of lucks". Other spellings that were sometimes encountered were Sad es Saud, Sadalsund, and Saad el Sund. In the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, this star was designated Nir Saad al Saaoud, which was translated into Latin as Lucida Fortunæ Fortunarum (rather identic with R.H. Allen), meaning the brightest of luck of lucks.[17] The International Astronomical Union Working Group on Star Names (WGSN)[18] has approved the name Sadalsuud for the primary or 'A' component.[15]

In Chinese, 虚宿 (Xū Xiù), meaning Emptiness (asterism), refers to an asterism consisting of Beta Aquarii and Alpha Equulei.[19] Consequently, the Chinese name for Beta Aquarii itself is 虛宿一 (Xū Xiù Yī, English: the First Star of Emptiness).[20]

Sadalsuud is found in Hindu texts as Kalpeny and, in the context of the ancient Indian system of astronomy, Jyotisha Veda, is located in the 23rd Nakshatra Shravishthā, a lunar mansion which is ruled by Eight vasus - the "deities of earthly abundance" . On the Euphrates, Sadalsuud was known as Kakkab Nammax, the Star of Mighty Destiny; that may have given origin to the title of the manzil, as well as to the astrologers' name for it — Fortuna Fortunarum.[21]

Properties

[edit]

β Aquarii is the brightest star in Aquarius with an apparent magnitude of 2.87[2] and a stellar classification of G0 Ib.[3] Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.[22] It has an estimated age of 56 million years;[9] old enough for a star of this mass to evolve into a supergiant. The star has about five or six[9] times the mass of the Sun, but it has expanded to 48 times the Sun's radius. It is most likely fusing helium into carbon in its core, and, with insufficient mass to explode as a supernova, will likely end up as a massive white dwarf comparable to Sirius B.[23] It is emitting roughly 2,000 times the Sun's luminosity from its enlarged photosphere at an effective temperature of 5,608 K,[8] giving it the characteristic yellow hue of G-type stars.[24]

X-ray emissions from the corona of this star have been detected using the Chandra X-ray Observatory; among the first such detections of X-rays for a G-type supergiant. A secondary X-ray source discovered near Beta Aquarii probably has an extragalactic origin.[12] This star belongs to a group of three intermediate mass stars with a space velocity that is carrying them perpendicular to the plane of the galaxy. The other members of this grouping are Alpha Aquarii and Eta Pegasi.[12]

Optical companions

[edit]
β Aquarii companions
Component Magnitude RA Dec
B 11.0 21h 31m 31.9s −05° 33′ 46″
C 11.6 21h 31m 33.0s −05° 35′ 10″

β Aquarii appears as a solitary star to the naked eye, but when viewed with a telescope is seen to have two faint optical companions. The first has an apparent magnitude of 11.0. In 1947, the position angle was observed at 321 degrees with a separation from Beta Aquarii of 35.4 arcseconds.[25][26] The second star has a magnitude of 11.6. Its position angle is 186 degrees with a separation from Beta Aquarii of 57.2 arcseconds.[25][26] The brighter star is designated component A of this grouping, while the companions are components B and C, respectively. As of 2008, there is no definitive evidence that the three stars form a ternary star system,[14] and Gaia Data Release 2 shows the two companions to be around twice the distance of β Aquarii. All three stars have very different proper motions.[27][28]

In mythology

[edit]
A Gerardus Mercator chart showing Aquarius overlooking Capricorn and pouring water into the mouth of the southern fish (Pisces). β Aquarii is the star in the left shoulder, just above δ Capricorni

In the context of older worldviews (i.e. Egyptian, Persian and Islamic mythology), Sadalsuud relates to the rising of the Sun when winter has passed (March) and the season of gentle, continuous rain has begun.[21] Hence the myth of "luck" or "good fortune" was seen as closely aligned with the essence of spring itself, the burgeoning of new life, and by extension agriculture, which in all societies is the very foundation of prosperity or "good fortune". This mythological view of "the luck of the lucks" also belongs to the 22d Manzil (Arabic Lunar Mansion), which included the two stars Xi Aquarii (Bunda) and 46 Capricorni.[21][a]

β and ξ Aquarii also constitute the Persian lunar mansion Bunda and the similar Coptic mansion Upuineuti, the meaning of which is "the Foundation".

In Chinese mythology, β Aqr alone marks the xiu (Chinese lunar mansion) Heu, Hiu, or Hü, "the Void/Emptiness", anciently Ko, the central one of seven xiu which, taken together, were known as Heung Wu, the Black Warrior, in the northern quarter of the sky.[21] As such, Sadalsuud is an expression of the feminine archetype, the Yin or "Void" (Cosmic Mother), from which, many cultures have believed, creation itself (birth) emanates.

Notes

[edit]

References

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

Beta Aquarii

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from Grokipedia
Beta Aquarii (β Aqr), formally named Sadalsuud, is a star of spectral class G0 Ib in the equatorial constellation of Aquarius. It holds the distinction of being the brightest in Aquarius, with an apparent visual magnitude of 2.89, making it easily visible to the under clear, . The is situated at a distance of approximately 546 light-years (167 parsecs) from the Solar System, as determined by measurements. Sadalsuud exhibits a surface temperature of about 5644 , which imparts a yellowish appearance similar to the Sun but at a much larger scale. As a post-main-sequence evolved , it has a estimated at 4.97 times that of the Sun and has expanded to a of roughly 48 solar radii, resulting in a luminosity approximately 2046 times greater than the Sun's. Its low surface (log g ≈ 1.83) and mild metal enrichment ([Fe/H] = +0.05) are consistent with its status. The rotates slowly, with an equatorial velocity of 9.35 km/s. Although appearing as a solitary point of light to the unaided eye, Beta Aquarii is accompanied by two faint optical companions of around 11th magnitude, separated by 35 and 57 arcseconds from the primary. These companions are not physically bound, as indicated by their differing proper motions. The name Sadalsuud derives from the phrase sa'd al-su'ud, translating to "the luckiest of the lucky," reflecting its auspicious in ancient astronomy.

Nomenclature

Proper Names

Beta Aquarii is traditionally known by the proper name Sadalsuud, derived from the phrase saʽd al-suʽūd, meaning "luck of lucks" or "luckiest of the lucky." This name reflects its historical association with good fortune, particularly as its was believed to herald beneficial seasonal changes. The (IAU) formally approved Sadalsuud as the proper name for the star in August 2016 as part of its effort to standardize culturally significant names. Alternative interpretations in ancient Arabic texts occasionally link the name to concepts of prosperity in domestic settings, such as "luck of the homes" or "auspice of tents," tying into the nomadic traditions where the star's appearance signaled favorable conditions for shelter and livelihood. In , Beta Aquarii is designated as 虛宿一 (Xū Xiù Yī), or "First Star of ," serving as the primary star in the Xu Xiu () asterism, one of the 28 lunar mansions that marked celestial divisions for calendrical and seasonal purposes. Hindu astronomical texts refer to the star as Kalpeny, a name associated with themes of fortune and auspiciousness within the ancient Indian sidereal system, where it falls in the 23rd (lunar mansion), Dhanishta (Shravishthā). From ancient Mesopotamian records along the , the star was called Kakkab Nammax (or Nammaḫ), translated as "the Star of Mighty Destiny," emphasizing its role as an omen of powerful fate or prosperity. These proper names collectively underscore Beta Aquarii's position in the constellation Aquarius—the water-bearer—as a celestial marker of abundance and transition, often linked to the onset of rains or fertile seasons in various cultures, symbolizing renewal and good fortune rather than mere astronomical positioning.

Catalog Designations

Beta Aquarii holds the β Aquarii, the brightest star in the constellation Aquarius as assigned by in his star atlas Uranometria published in 1603. It also receives the Flamsteed designation 22 Aquarii, from English astronomer John Flamsteed's catalog in Historia Coelestis Britannica, first compiled around 1712 and published in 1725. In the Henry Draper Catalogue, compiled by and at Harvard College Observatory and published between 1918 and 1924, the star is entry HD 204867, providing its spectral classification G0 Ib. The related , an extension of Harvard's efforts and last revised in 1991 by Dorrit Hoffleit and Wayne H. Warren Jr., lists it as HR 8232. The Hipparcos Catalogue, produced by the European Space Agency's Hipparcos mission and released in 1997, identifies the star as HIP 106278, enabling precise astrometric measurements including parallax. Subsequent Gaia mission data releases refined this further; the second data release (Gaia DR2) in 2018 provided an initial parallax value confirming its distance, while the third (Gaia DR3) in 2022 updated the source identifier to 2671038928727970944 with enhanced precision. Beta Aquarii appears in the Geneva Observatory's photometric database as GEN# +1.00204867, supporting kinematic and metallicity studies, though it is not part of the Geneva-Copenhagen Survey, which focuses on nearby F and G dwarfs. Cross-identifications are compiled in databases such as SIMBAD (main identifier * bet Aqr), which aggregates over 20 catalog entries including BD-06 5770 from the Bonner Durchmusterung, SAO 145457 from the Smithsonian Astrophysical Observatory Star Catalog, and 2MASS J21313352-0534161 from the Two Micron All Sky Survey.
CatalogDesignationReference
Bayerβ AquariiBayer (1603)
Flamsteed22 AquariiFlamsteed (1725)
Henry DraperHD 204867Cannon & Pickering (1918–1924)
Bright StarHR 8232Hoffleit & Warren (1991)
HIP 106278ESA (1997)
DR32671038928727970944Gaia Collaboration (2023)
Geneva PhotometryGEN# +1.00204867Rufener (1988)

Stellar Properties

Fundamental Parameters

Beta Aquarii occupies equatorial coordinates of right ascension 21ʰ 31ᵐ 33.⁵³ˢ and declination −05° 34′ 16.″2 (J2000.0 epoch). Its apparent visual magnitude is 2.89, rendering it the brightest star in the constellation Aquarius. The star's distance is estimated at 167.4 ± 6.0 parsecs (approximately 546 ± 20 light-years), derived from a parallax of 5.973 ± 0.215 milliarcseconds measured by the Gaia mission (DR3). Earlier Gaia DR2 data yielded a parallax of 6.02 ± 0.23 mas, corresponding to 541.8 ± 17 light-years. The star displays proper motion components of +19.21 mas/yr in right ascension and −8.16 mas/yr in declination (Gaia DR3). Beta Aquarii has a radial velocity of +6.45 ± 0.001 km/s, indicating it is receding from the Solar System, and serves as an International Astronomical Union standard for radial velocity measurements. Beta Aquarii's absolute bolometric magnitude implies a luminosity of approximately 2046 L_⊙. Evolutionary models estimate its mass in the range 4.97–6.3 M_⊙. Isochrone fitting suggests an age of 56–110 million years.
ParameterValueSource
Apparent visual magnitude2.89SIMBAD [2002yCat.2237....0D]
Parallax (Gaia DR3)5.973 ± 0.215 masGaia Collaboration (2021)
Distance546 ± 20 lyGaia DR3
Proper motion (RA)+19.21 mas/yrSIMBAD/Gaia DR3
Proper motion (Dec)−8.16 mas/yrSIMBAD/Gaia DR3
Radial velocity+6.45 km/sSIMBAD [2018A&A...616A...7S]
Luminosity~2046 L_⊙Evolutionary models
Mass4.97–6.3 M_⊙Ekström et al. (2012)
Age56–110 MyrIsochrone fitting

Atmospheric and Evolutionary Characteristics

Beta Aquarii is classified as a G0 Ib , featuring broad absorption lines due to its expanded envelope and low . This spectral type places it among , with an of 5644 that imparts a yellow-white hue to its . Atmospheric modeling from high-resolution yields a of log g ≈ 1.83 (in cgs units), consistent with the low-pressure environment of a 's outer layers. The star's is nearly solar, with [Fe/H] ≈ +0.05 and no notable deviations in abundances, suggesting a similar to that of the Sun despite its advanced evolutionary state. Its radius measures 47.88 R☉, determined from interferometric measurements of approximately 1.07 mas combined with the distance estimate. As a post-main-sequence object, Beta Aquarii is interpreted as being in the core helium-burning phase, having evolved off the and contracted toward hotter temperatures in a typical of intermediate-mass . Chandra X-ray Observatory observations have detected coronal X-ray emissions from Beta Aquarii, with luminosities indicating plasma temperatures around 6–10 MK, likely arising from magnetic activity in the or interactions within a . The star exhibits no significant intrinsic photometric variability, maintaining a stable that qualifies it as an IAU standard and a reference for calibration in astronomical observations.

Apparent Companions

Component B

Component B is one of two apparent optical companions to Beta Aquarii A, with an of 11.0 in the V-band, located 39.3 arcseconds southeast of the primary. According to the Washington Double Star Catalog (WDS), this companion is at a position angle of 137° relative to the primary, confirming its non-physical, line-of-sight nature rather than a gravitationally bound member of the system. Astrometric measurements show a significant proper motion difference between Component B and the primary: +15 mas/yr in and +10 mas/yr in (Gaia DR2), precluding orbital binding. This discrepancy corresponds to a relative tangential of approximately 10 km/s (assuming primary ), supporting the unbound status. Photometric data from Gaia DR2 indicate colors consistent with an A-type star, though the estimated and precise remain uncertain due to the companion's faintness and quality.

Component C

Component C is a faint, unrelated optical companion to the primary star Beta Aquarii, cataloged as β Aqr C in the Washington Double Star Catalog (WDS). It has an of 11.6 in the V-band and is located 94.5 arcseconds northwest of the primary at a position angle of 323° . The of Component C is −5 mas/yr in and −8 mas/yr in , differing from the primary's DR3 values of +19.21 mas/yr in RA and −8.16 mas/yr in Dec, indicating independent trajectories.; Hipparcos Catalogue Astrometric data from the and missions confirm this as a line-of-sight alignment, with no evidence of physical association.; Gaia Data Release 3 Photometric data suggest colors consistent with an F-type star, but the estimated distance from DR3 is uncertain given the faint magnitude.; SIMBAD Astronomical Database This companion has been documented in observations since the 19th century, with no reported variability in photometric surveys. Given the primary's apparent magnitude of 2.91, Component C requires a telescope of at least 4-inch aperture for reliable detection under dark skies.

Cultural Significance

Mythological Associations

In Greek mythology, Beta Aquarii marks the left shoulder of Aquarius, the water-bearer constellation often identified with the Trojan youth Ganymede, who was abducted by Zeus in the form of an eagle to serve as cup-bearer to the gods on Olympus. Alternatively, Aquarius represents Deucalion, son of Prometheus, who survived a great deluge sent by Zeus and repopulated the earth with his wife Pyrrha by casting stones that became humans. This positioning of Beta Aquarii emphasizes the figure's role in dispensing life-giving waters, symbolizing renewal and divine favor in classical tales. In Arabic astronomical traditions, forms a key part of the lunar Al Sa'd al Su'ud, or "Luck of the Lucks," whose heralded the end of winter and the onset of gentle spring rains, promising prosperity and agricultural bounty. Astrologically, this was deemed highly fortunate, conferring marital happiness, military victories, and social alliances, though it was thought to obstruct official decrees. In Chinese imperial astronomy, Beta Aquarii anchors the Xu asterism, or "Emptiness," within the Ershibasu Xiu system of lunar mansions and part of the broader "Emptiness" enclosure, evoking concepts of void, transition, and the contemplative emptiness of midautumn skies. This asterism, paired with Alpha Equulei, represented a liminal space in the celestial order, reflecting philosophical ideas of impermanence and balance in the cosmic structure observed by ancient astronomers. Beta Aquarii holds no prominent specific role in Egyptian traditions, where the broader Aquarius figure occasionally evokes the Nile god Hapi but without direct stellar attribution. Similarly, Native American astronomical narratives do not feature notable associations with this star, as indigenous sky lore typically emphasizes local seasonal markers over zodiacal imports.

Historical and Observational Context

Beta Aquarii was first recorded in ancient astronomical catalogs as part of the constellation Aquarius. In the 2nd century AD, Claudius Ptolemy included it in his as the star marking the left shoulder of the water-bearer's figure, assigning it a magnitude of 2 based on naked-eye observations. During the , al-Sufi documented the star in his around 964 AD, confirming Ptolemy's position while adding notes on its brightness and visibility from the , drawing from both Greek and Persian traditions. The star received its modern , β Aquarii, in Johann Bayer's influential star atlas Uranometria published in 1603, where it was mapped as the second-brightest in Aquarius. In 1725, cataloged it as 22 Aquarii in his Historia Coelestis Britannica, the first comprehensive star catalog from Greenwich Observatory, establishing its Flamsteed number based on . These early modern designations facilitated more precise positional astronomy amid the transition to telescopic observations. In the , spectroscopic studies advanced the understanding of Beta Aquarii's nature. Angelo Secchi, a pioneer in stellar , observed its spectrum in the 1860s. By the mid-20th century, the star played a key role in establishing observational standards. It was also incorporated into the Morgan-Keenan (MK) spectral classification system developed in the 1940s, confirming its G0 status through standardized spectral analysis. Space-based missions marked a new era of precision for Beta Aquarii's observations. The Hipparcos satellite, launched by the European Space Agency, provided the first trigonometric parallax measurement in 1997, yielding a distance estimate of approximately 165 parsecs and refining its proper motion. In the 2000s, X-ray observations from the Chandra X-ray Observatory detected emissions from the star, indicating coronal activity typical of evolved giants, though limited follow-up has explored its implications. More recently, the Gaia mission delivered highly accurate astrometry: Data Release 2 in 2018 and Data Release 3 in 2022 improved parallax to about 167 parsecs and proper motions, enabling kinematic analysis. Despite these advances, observational gaps persist in contemporary research. As of 2025, post-2020 studies on Beta Aquarii remain sparse, with limited investigations into potential planetary debris disks or detailed modeling of its stellar winds, leaving opportunities for future missions like the to address these aspects.

References

  1. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=Beta+Aquarii
  2. http://stars.astro.illinois.edu/sow/sadalsuud.html
  3. https://noirlab.edu/public/education/constellations/aquarius/
  4. https://www.stellarcatalog.com/stars/beta-aquarii
  5. https://www.astronomytrek.com/stars/sadalsuud/
  6. https://www.constellationsofwords.com/sadalsuud/
  7. http://judy-volker.com/StarLore/Index/Aquarius.html
  8. https://www.star-facts.com/sadalsuud/
  9. https://astrologyking.com/sadalsuud-star/
  10. https://www.lindahall.org/about/news/scientist-of-the-day/johann-bayer/
  11. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=Beta+Aqr
  12. https://pbarbier.com/flamsteed/flamsteed.html
  13. https://www.cosmos.esa.int/web/hipparcos/catalogues
  14. https://www.cosmos.esa.int/web/gaia/dr3
  15. https://ui.adsabs.harvard.edu/abs/2004A&A...418..989N/abstract
  16. https://www.aanda.org/articles/aa/full_html/2018/08/aa32964-18/aa32964-18.html
  17. https://www.cosmos.esa.int/documents/596853/1145435/Gaia_DR3_summary.pdf
  18. https://ui.adsabs.harvard.edu/abs/2005ApJ...627L..53A/abstract
  19. https://iopscience.iop.org/article/10.1086/431977
  20. https://www.usno.navy.mil/USNO/astrometry/optical-ir-prod/wds
  21. https://vizier.cds.unistra.fr/viz-bin/VizieR?-source=J/A+A/616/A2
  22. https://gea.esac.esa.int/archive/
  23. http://simbad.u-strasbg.fr/simbad/
  24. https://www.constellation-guide.com/constellation-list/aquarius-constellation/
  25. https://www.constellationsofwords.com/aquarius/
  26. https://www.chinasage.info/stars.htm
  27. https://www.lehigh.edu/~dwp0/Assets/images/reader.pdf
  28. https://www.nativestargazers.org/constellations
  29. http://www.ianridpath.com/startales/aquarius.html
  30. https://www.atlascoelestis.com/Zagrebelsky/28854_Hafez_2010_Chapters_1_to_4_thesis.pdf
  31. https://digital.sciencehistory.org/works/v979v309v
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