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Alpha Cephei
Alpha Cephei
Alpha Cephei
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α Cephei
Location of α Cephei (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Cepheus
Right ascension 21h 18m 34.7723s[1]
Declination +62° 35′ 08.069″[1]
Apparent magnitude (V) 2.46[2]
Characteristics
Spectral type A8Vn[3] or A7IV-V[4]
U−B color index +0.12[5]
B−V color index +0.21[5]
Variable type suspected δ Sct[6]
Astrometry
Radial velocity (Rv)−15.8±1.1[7] km/s
Proper motion (μ) RA: +150.55[1] mas/yr
Dec.: 49.09[1] mas/yr
Parallax (π)66.50±0.11 mas[1]
Distance49.05 ± 0.08 ly
(15.04 ± 0.02 pc)
Absolute magnitude (MV)1.57[8]
Details[4]
Mass2.00±0.15 M☉
Radius2.175±0.046 (polar)
2.823±0.097 (equator) R☉
Luminosity17[9] L☉
Surface gravity (log g)3.99[9] cgs
Temperature8,440+430
−700 (polar)
7,600 (equator) K
Metallicity [Fe/H]0.09 dex
Rotation12.11±0.26 h
Rotational velocity (v sin i)283±19 km/s
Age820 Myr
Other designations
Alderamin, α Cep, 5 Cep, AG+62°1226, BD+61°2111, FK5 803, GJ 826, HD 203280, HIP 105199, HR 8162, SAO 19302, CCDM J21186+6236A, 2MASS J21183475+6235081[10]
Database references
SIMBADdata

Alpha Cephei (α Cephei, abbreviated Alpha Cep, α Cep), officially named Alderamin /ælˈdɛrəmɪn/,[11][12] is a second magnitude star in the constellation of Cepheus near the northern pole. The star is relatively close to Earth at 49 light years (ly) and drifting closer with a heliocentric radial velocity of about −16 km/s.

Nomenclature

[edit]

α Cephei (Latinised to Alpha Cephei) is the star's Bayer designation. It has a Flamsteed designation of 5 Cephei.

It bore the traditional name Alderamin, a contraction of the Arabic phrase الذراع اليمين al-dhirā‘ al-yamīn, meaning "the right arm". In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[13] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[14] included a table of the first two batches of names approved by the WGSN; which included Alderamin for this star.

Visibility

[edit]

With a declination in excess of 62 degrees north, Alpha Cephei never rises south of −27° latitude, which means for much of South America, Australia, South Africa, and all of New Zealand, the star stays below the horizon. The star is circumpolar throughout all of Europe, northern Asia, Canada, and American cities as far south as San Diego. Since Alpha Cephei has an apparent magnitude of about 2.5, the star is the brightest in the constellation and is easily observable to the naked eye, even in light-polluted cities.

Pole star

[edit]

Alpha Cephei is located near the precessional path traced across the celestial sphere by the Earth's North pole. That means that it periodically comes within 3° of being a pole star,[15] a title currently held by Polaris. Alpha Cephei will next be the North Star in about the year 7500 AD.[16] The north pole of Mars points to the midpoint of the line connecting the star and Deneb.[17]

Preceded by Pole Star Succeeded by
Iota Cephei circa 19,000BC and 7500AD to 8700AD Deneb

Properties

[edit]
A light curve for Alpha Cephei, plotted from TESS data[18]

Alderamin is a white class A star, evolving off the main sequence into a subgiant, probably on its way to becoming a red giant as its hydrogen supply runs low. On average, Alderamin has an apparent magnitude of 2.46.[2] In 2007, the star's parallax was measured at 66.50±0.11 mas yielding a distance of 15 parsecs or approximately 49 light years from Earth.[1]

Interferometry by the CHARA array show that Alderamin has an oblate shape, its equatorial size measures 2.82 R☉ and the polar radius measures 2.18 R☉. The star's temperature varies as well, from 8,440 K in the poles to 7,600 K in the equator.[4] A more recent but less detailed measurement by the Navy Precision Optical Interferometer gives 2.71 R☉, which likely corresponds to the equatorial radius.[19] Like other stars in its class, it is slightly variable with a range in brightness of 0.06 magnitude, and is listed as a Delta Scuti variable.

Alderamin has a very high rotation speed of at least 246 km/s, completing one complete revolution in less than 12 hours, with such a rapid turnover appearing to inhibit the differentiation of chemical elements usually seen in such stars.[20] By comparison, the Sun takes almost a month to turn on its axis. Alpha Cephei is also known to emit an amount of X radiation similar to the Sun, which along with other indicators suggests the existence of considerable magnetic activity—something unexpected (though not at all unusual) for a fast rotator.

Etymology and cultural significance

[edit]

This star, along with Beta Cephei (Alfirk) and Eta Cephei (Alkidr) were al-Kawākib al-Firq (الكواكب الفرق), meaning "the Stars of the Flock" by Ulug Beg.[21][22]

In Chinese, 天鈎 (Tiān Gōu), meaning Celestial Hook, refers to an asterism consisting of α Cephei, 4 Cephei, HD 194298, Eta Cephei, Theta Cephei, Xi Cephei, 26 Cephei, Iota Cephei and Omicron Cephei.[23] Consequently, the Chinese name for Alpha Cephei itself is 天鈎五 (Tiān Gōu wu, English: the Fifth Star of the Celestial Hook.).[24]

Alderamin on the Sky is a Japanese light novel series named after the star.

Namesakes

[edit]

USS Alderamin (AK-116) was a United States Navy Crater class cargo ship named after the star.

See also

[edit]

References

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

Alpha Cephei

View on Grokipedia
from Grokipedia
Alpha Cephei (α Cep), commonly known as Alderamin, is the brightest in the northern constellation Cepheus, representing the right shoulder of the mythological king Cepheus from Greek lore. It is a main-sequence of type A7IVn or A8Vn, with an apparent visual magnitude of 2.45, making it visible to the under . Located at a distance of approximately 49 light-years (15 parsecs) from the Solar System, it exhibits high , traversing the sky at about 150 mas per year in and 49 mas per year in . This star has a mass of 1.92 ± 0.04 solar masses and an of 7510 ± 160 , resulting in a luminosity roughly 18 times that of the Sun. Its is significantly distorted due to rapid rotation: the polar measures 2.162 ± 0.036 solar radii, while the equatorial extends to 2.740 ± 0.044 solar radii, yielding an oblateness of about 1.27. The equatorial rotation reaches approximately 267 km/s, or 94% of the critical breakup speed, with a projected rotational (v i) of 225 km/s at an inclination of 55.7° ± 6.2° to our . This fast spin creates a across its surface, with the polar region at 8588 ± 300 and the equatorial region cooler at 6574 ± 200 . The name Alderamin originates from the Arabic phrase al-dhirāʽ al-yamīn, translating to "the right arm," though it was historically misapplied and refers to the king's in the constellation figure. Observations indicate slight photometric variability of about 0.06 magnitudes, potentially classifying it as a Delta Scuti-type pulsator, though it is not strongly variable. Additionally, it displays magnetic activity and emission akin to solar-like processes, unusual for a star of its type. Positioned at right ascension 21h 18m 35s and +62° 35' in J2000 coordinates, lies near the and has served as a in Earth's distant past, approximately 18,000 years ago. Due to the of Earth's axis, it will become the closest bright star to the again around AD 7500, within 3 degrees, succeeding as a navigational reference.

Nomenclature

Formal Designations

Alpha Cephei, abbreviated as α Cephei or Alf Cep, is the for the brightest star in the constellation Cepheus, assigned by the German astronomer in his 1603 star atlas Uranometria, where Greek letters were used to label stars in order of apparent brightness within each constellation. The star also holds the Flamsteed designation 5 Cephei, introduced by English astronomer in his 1725 Historia Coelestis Britannica, which numbered stars sequentially by within each constellation. Alpha Cephei appears in numerous modern astronomical catalogs, including the Henry Draper Catalogue as HD 203280, the as HR 8162, and the Hipparcos Catalogue as HIP 105199. It is also listed in the astronomical database and the Data Release 3 as source ID 2193192137376175488, providing precise astrometric and photometric data. In 2016, the (IAU) Working Group on Star Names standardized the proper name Alderamin for Alpha Cephei as part of efforts to catalog and approve traditional names for cultural and scientific consistency.

Traditional Names

The primary traditional name for Alpha Cephei is Alderamin, which was officially approved by the (IAU) in 2016 as part of the first batch of proper names standardized by its Working Group on Star Names (WGSN). This name derives from the Arabic phrase al-dhirā' al-yamīn, meaning "the right arm," though it was historically misapplied to the shoulder in the constellation figure. Prior to the widespread adoption of systematic designations like those introduced by in 1603, Alderamin served as the common identifier for the star in medieval Arabic astronomical texts and European translations, reflecting its cultural transmission through Islamic astronomy. In historical star atlases, such as those compiled during the , the name appeared in depictions of the constellation Cepheus, aiding astronomers in mapping the northern sky.

Visibility

Sky Position and Coordinates

Alpha Cephei, the brightest star in the constellation Cepheus and thus bearing the alpha designation in the system, occupies a prominent position in the . Its equatorial coordinates for the J2000.0 epoch are 21ʰ 18ᵐ 34.772ˢ and +62° 35′ 08.07″, placing it near the border with Lacerta to the south and close to the celestial north pole in projection. These coordinates, derived from optical observations integrated in major astronomical catalogs, enable precise targeting with telescopes and are fundamental for astrometric studies. In the , Alpha Cephei lies at longitude 100.999° and latitude +9.172°, positioning it slightly north of the within the of the . This location reflects its proximity to the galactic equator but offset toward higher latitudes, consistent with the distribution of nearby stars in the solar neighborhood. The star demonstrates measurable across the sky, indicating its tangential velocity relative to the Sun. According to Data Release 3, the annual changes are +150.55 mas/yr in and +49.09 mas/yr in , with uncertainties of approximately 0.09 mas/yr for both components. These values, among the higher proper motions for naked-eye stars due to its distance of about 15 parsecs, highlight Alpha Cephei's motion toward the over long timescales. The high declination ensures visibility from latitudes north of about 27° S, though practical observation is limited to northern skies for optimal viewing.

Observational Accessibility

Alpha Cephei, with an apparent visual magnitude of 2.45, is readily visible to the under dark sky conditions, appearing as a prominent in the constellation Cepheus. This brightness allows it to be observed without optical aid from most locations in the where it is above the horizon, though its visibility diminishes in areas affected by , where urban glow can obscure fainter stars but still permits detection of this relatively luminous object. The star is for observers at latitudes north of approximately 27° N, meaning it never sets and remains perpetually visible throughout the night and year from such locations, due to its of about +62.6°. It rises in the northeast and is not visible at all south of 27° S, limiting observations to northern and equatorial regions. From mid-northern latitudes, Alpha Cephei offers optimal viewing during evenings, when it reaches a favorable position high in the sky after sunset, circling the north at a moderate elevation that enhances accessibility without excessive seasonal tilt. significantly impacts its observation in southern urban areas near the visibility limit, where darker rural sites are essential, while its proximity to the celestial pole ensures consistent availability regardless of the time of year in suitable hemispheres.

Prospective Pole Star

Due to Earth's axial precession, which causes the north celestial pole to trace a circle among the stars over a roughly 26,000-year cycle, Alpha Cephei is on track to become the north pole star. Currently, the star lies about 27.4° from the pole, based on its J2000 declination of +62° 35' 08". In approximately 5,500 years, precession will draw Alpha Cephei to its closest approach to the pole around AD 7500, at which point it will be within 3° of the celestial north point—making it the nearest bright star to that position. This development continues the historical succession of pole stars, following in the present era and preceding brighter candidates like in about 12,000 years; intervening roles will be filled by other Cepheus stars such as around AD 4200 and Iota Cephei around AD 5200. For navigators in that distant future, Alpha Cephei's of 2.45 will render it a prominent guide to , much like serves today, though the 3° separation will necessitate complementary methods for high-precision orientation.

Physical Properties

Spectral Classification and Variability

Alpha Cephei is classified as an A7IVn or A8Vn spectral type, denoting a white or main-sequence star exhibiting strong, nebulous absorption lines typical of rapidly rotating A-type stars. This classification, originally revised from an earlier A2n designation, reflects the prominence of broad and metal lines in its spectrum, consistent with an early A-type dwarf transitioning toward subgiant status. The star's chemical composition is characterized by near-solar , with [Fe/H] ≈ 0 dex, and a of log g = 4.0 (cgs), indicating a relatively unevolved atmosphere where and dominate alongside enhanced metal lines. These features align with the spectral peculiarities of A-type stars, where line broadening from rotation contributes to the observed "n" subclassification. The derived from the spectrum and models is 7510 ± 160 K, supporting its placement among white A stars. Alpha Cephei exhibits low-amplitude photometric variability of about 0.06 magnitudes over short periods of hours to days, potentially due to radial or non-radial pulsations in its outer layers, classifying it as a Delta Scuti-type pulsator. This pulsational behavior aligns with its position near the edge of the classical . As an A-type , Alpha Cephei occupies a post-main-sequence evolutionary stage, having depleted in its core and begun expansion off the while still burning in a shell.

Fundamental Parameters

Alpha Cephei possesses well-determined fundamental parameters derived from astrometric, interferometric, and spectroscopic observations. Its distance from the Solar System is 49.05 ± 0.08 light-years, calculated from the Data Release 3 of 66.50 ± 0.11 mas, confirming earlier measurements while providing higher precision. This proximity allows for detailed study of the star's properties. The heliocentric is -15.8 ± 1.1 km/s, signifying motion toward the Solar System at approximately 16 km/s. The star's mass is 1.92 ± 0.04 solar masses, estimated through comparison with models that account for its spectral type and observed . Due to its shape from rapid rotation, the effective radius averages approximately 2.45 solar radii, with polar and equatorial values detailed below. The effective surface temperature is 7510 ± 160 K, consistent with its A7 IVn classification and contributing to its white color in the sky. Alpha Cephei's bolometric is 18.1 ± 1.8 solar luminosities, computed from the integrated flux over its distance and , with age ~820 million years from evolutionary models.
ParameterValueUnitReference
Distance49.05 ± 0.08light-yearsGaia DR3
Radial velocity-15.8 ± 1.1km/s[2006AstL...32..759G]
Mass1.92 ± 0.04M⊙[2009ApJ...701..209Z]
Radius (effective)~2.45R⊙[2009ApJ...701..209Z]
Luminosity18.1 ± 1.8L⊙[2009ApJ...701..209Z]
Effective temperature7510 ± 160K[2009ApJ...701..209Z]
Age~820 millionyears[2009ApJ...701..209Z]
These parameters position Alpha Cephei as a key example of an intermediate-mass A-type star, with its and age consistent with expectations from its spectral type and effects.

Rotation and Stellar Structure

Alpha Cephei exhibits rapid , with an equatorial rotational velocity of approximately 267 km/s and a projected rotational velocity v sin i of 225 km/s as measured spectroscopically. This corresponds to a rotational period of approximately 12.5 hours, derived from the star's geometry and velocity profile. The star's is near its critical breakup velocity, reaching about 94% of the limit for , which distorts its shape into an spheroid. Interferometric observations with the CHARA Array reveal a significantly flattened stellar disk, with an equatorial radius of 2.740 ± 0.044 solar radii and a polar radius of 2.162 ± 0.036 solar radii, yielding an oblateness ratio of about 1.27. This oblateness, combined with darkening, produces a temperature contrast across the surface: the equatorial regions are cooler at 6574 ± 200 , while the poles reach 8588 ± 300 . The darkening exponent is measured at 0.216 ± 0.021, indicating a profile consistent with the star's . The star's high rotation rate induces hydrodynamical instabilities that enhance internal mixing of and chemical elements processed via the , thereby altering its evolutionary path and potentially extending its main-sequence lifetime compared to non-rotating models. The axis is inclined at 55.7° ± 6.2° to our . No resolved companion has been detected in high-resolution interferometric , supporting the interpretation of the observed properties as arising solely from the primary star's .

Etymology and Cultural Significance

Name Origins

The traditional name Alderamin for Alpha Cephei derives from the Arabic phrase al-dhirāʿ al-yamīn, meaning "the right arm," a designation reflecting its position in the constellation Cepheus, depicted as an enthroned king in ancient astronomy. This name was documented in astronomical texts during the , contributing to the preservation and transmission of Arabic stellar . The name's application has a complex history, with some scholars noting its possible misattribution; Alpha Cephei actually marks the right shoulder of Cepheus, leading to alternative derivations linking it to phrases denoting the "right shoulder," such as potential variants emphasizing the constellation figure's anatomy over strict arm placement. By the medieval period, the name appeared in Western astronomy as Al Deraimin in the Alfonsine Tables of 1521, a key astronomical reference compiled under , which adapted Arabic sources for European use and solidified Alderamin's place in Latin star catalogs. In 2016, the International Astronomical Union's Working Group on Star Names (WGSN) formally approved Alderamin as the proper name for Alpha Cephei, drawing on historical origins documented in seminal works like Paul Kunitzsch and Tim Smart's A Dictionary of Modern Star Names (2006), to standardize nomenclature and honor traditional etymologies. This approval process ensured the name's official recognition in modern astronomical databases, bridging ancient astronomy with contemporary practice.

Role in Mythology

In , Cepheus was the king of , a legendary realm encompassing parts of ancient and the eastern , renowned as the husband of the vain queen Cassiopeia and father of the princess Andromeda. His lineage traced back to the nymph Io, one of Zeus's lovers, through four generations, granting him divine favor that ultimately led to his celestial placement alongside his family after their tragic fates involving a sent by . The constellation Cepheus, immortalizing the king, was included among the 48 ancient constellations cataloged by in his 2nd-century , where it was depicted as a robed figure near the north . Within the ancient Greek asterism, Alpha Cephei, known traditionally as Alderamin, marked the king's right shoulder, emphasizing his regal posture in the starry figure. This positioning highlighted Cepheus's role as a constellation, always visible in the northern sky, symbolizing enduring royalty and serving as a for ancient observers. In northern cultures, Cepheus held symbolic importance in related to kingship and the heavens, with its nature reinforcing themes of stability and guidance. For instance, in , parts of the constellation were interpreted as the stag , one of four deer feeding on the Yggdrasil, with as its rear foot, blending royal and natural motifs in sky lore.

Namesakes in Culture

In nautical history, the name Alderamin has been used for vessels honoring the star. The USS Alderamin (AK-116), a Crater-class of the , was commissioned during on April 3, 1944, and served in the Pacific Theater, transporting troops and supplies across over 100 ports until its decommissioning on April 10, 1946. The name Alderamin appears prominently in modern media, particularly in and . It serves as the title for the series Nejimaki Seirei Senki: Tenkyō no Alderamin (translated as ), written by Bokuto Uno and first published in , which follows a young strategist in a fictional empire at war; the series spans 14 volumes and inspired a adaptation and a 2016 television series produced by , comprising 13 episodes. This work blends and fantasy elements, with the title evoking and imperial ambition. In gaming, Alderamin influences science fiction role-playing systems. Alpha Cephei is a tabletop RPG released in , designed as an accessible entry into space adventure narratives, featuring advanced mechanics for interstellar exploration and while drawing its name directly from the star's astronomical designation. Beyond these, Alderamin has no confirmed namesakes in or surveys, though its prominence as a navigational suggests potential future use in such contexts. No asteroids bear the name, and while indirect cultural inspirations appear in art and festivals tied to celestial themes, none are verifiably linked to Alderamin specifically.

References

  1. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=alf+cep
  2. http://stars.astro.illinois.edu/sow/alderamin.html
  3. https://arxiv.org/abs/0906.2241
  4. https://earthsky.org/brightest-stars/alderamin-the-kings-brightest-star/
  5. https://www.star-facts.com/alderamin/
  6. https://www.lindahall.org/about/news/scientist-of-the-day/johann-bayer/
  7. https://www.pas.rochester.edu/~emamajek/WGSN/WGSN_bulletin1.pdf
  8. https://astrologyking.com/alderamin-star/
  9. http://www.ianridpath.com/starnames.html
  10. https://simbad.cds.unistra.fr/simbad/sim-id?Ident=Alpha+Cep
  11. https://simbad.cds.unistra.fr/simbad/sim-ref?bibcode=2022yCat.1352....0G
  12. https://www.universeguide.com/star/105199/alderamin
  13. https://theskylive.com/sky/stars/alderamin-alpha-cephei-star
  14. https://nightsky.jpl.nasa.gov/news/198/
  15. https://simbad.cds.unistra.fr/simbad/sim-basic?Ident=Alpha+Cep
  16. https://www.skyatnightmagazine.com/advice/alderamin-alpha-cephei
  17. https://www.space.com/stargazing/has-polaris-always-been-the-north-star-how-earths-26-000-year-cycle-changes-the-pole-star
  18. https://www.astronomy.com/science/earths-axis-precesses-bright-stars-become-the-north-star/
  19. https://www.aanda.org/articles/aa/full_html/2013/07/aa20689-12/aa20689-12.html
  20. https://simbad.cds.unistra.fr/simbad/sim-basic?Ident=alf+cep
  21. https://iopscience.iop.org/article/10.1088/0004-637X/701/1/209
  22. https://www.glyphweb.com/esky/stars/alderamin.html
  23. https://arxiv.org/abs/2405.19388
  24. https://www.stellarcatalog.com/stars/alpha-cephei
  25. https://www.constellationsofwords.com/alderamin/
  26. https://muslimheritage.com/arabic-star-names/
  27. https://journals.sagepub.com/doi/10.1177/002182868601700104
  28. http://www.ianridpath.com/startales/cepheus.html
  29. https://www.constellationsofwords.com/cepheus/
  30. https://englishhistoryauthors.blogspot.com/2013/12/what-did-vikings-and-saxons-call-stars.html
  31. https://www.ibiblio.org/hyperwar/USN/ships/AK/AK-116_Alderamin.html
  32. https://myanimelist.net/anime/31764/Nejimaki_Seirei_Senki__Tenkyou_no_Alderamin
  33. https://rafael.lv/introducing-alpha-cephei-rpg-a-new-fully-featured-tabletop-space-adventure/
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