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Aldebaran

Alpha Tauribrightest starRohini
(See 88 modern constellations for the genitive forms.) For example, Aldebaran in the constellation Taurus (the Bull) is designated α Tauri (pronounced Alpha Tauri), which means "Alpha of the Bull".
α Tauri is the star's Bayer designation.

HD 117440

d Cend Centauri
Examples include s Carinae (s of the constellation Carina), d Centauri (d of the constellation Centaurus), G Scorpii (G of the constellation Scorpius), and N Velorum (N of the constellation Vela).
HD 117440, also known by its Bayer designation d Centauri (d Cen), is a binary star in the constellation Centaurus.

Puppis

ζ-PuppisPuppusPup
(Constellations with no alpha include Vela and Puppis – both formerly part of Argo Navis, whose alpha is Canopus in Carina.)
Despite the division, Lacaille kept a single set of Bayer designations for the whole constellation Argo.

G Scorpii

G ScoG Sco (Fuyue)
Examples include s Carinae (s of the constellation Carina), d Centauri (d of the constellation Centaurus), G Scorpii (G of the constellation Scorpius), and N Velorum (N of the constellation Vela).
G Scorpii is the star's Bayer designation.

Vela (constellation)

VelaFalse Crossconstellation Vela
Examples include s Carinae (s of the constellation Carina), d Centauri (d of the constellation Centaurus), G Scorpii (G of the constellation Scorpius), and N Velorum (N of the constellation Vela). (Constellations with no alpha include Vela and Puppis – both formerly part of Argo Navis, whose alpha is Canopus in Carina.)
German cartographer Johann Bayer depicted the constellation on his Uranometria of 1603, and gave the stars Bayer designations from Alpha to Omega.

Centaurus

Cena picture of himselfCentaur
Examples include s Carinae (s of the constellation Carina), d Centauri (d of the constellation Centaurus), G Scorpii (G of the constellation Scorpius), and N Velorum (N of the constellation Vela).
It is also the only globular cluster to be designated with a Bayer letter; the globular cluster 47 Tucanae is the only one designated with a Flamsteed number.

Betelgeuse

α OriBetelg'''euseBetelgeuse mass loss
α Orionis (Latinised to Alpha Orionis) is the star's Bayer designation.

Rigel

β Ori (Rigel)B2 IaeBeta Orionis
Beta Orionis is the star's Bayer designation.

Mintaka

δ OriMintaka ABδ Ori (Mintaka)
Delta Orionis is the star's Bayer designation, 34 Orionis its Flamsteed designation.

Castor (star)

CastorCastor Aα Gem
Castor and Pollux of Gemini may be an example of this: Pollux is brighter than Castor, but the latter rises earlier and was assigned alpha.
It appears singular to the naked eye, but it is actually a sextuple star system organized into three binary pairs made up of the stars Castor Aa, Castor Ab, Castor Ba, Castor Bb, Castor Ca, and Castor Cb. Although it has the Bayer designation α (alpha), it is fainter than β (beta) Geminorum, Pollux.

Genitive case

genitivegen.GEN
A Bayer designation is a stellar designation in which a specific star is identified by a Greek or Latin letter followed by the genitive form of its parent constellation's Latin name.
Names of astronomical constellations are Latin, and the genitives of their names are used in naming objects in those constellations, as in the Bayer designation of stars. For example, the brightest star in the constellation Virgo is called Alpha Virginis, which is to say "Alpha of Virgo", as virginis is the genitive of virgō. Note that plural forms and adjectives also decline accordingly: plural Alpha Piscium (Pisces) and Alpha Canum Venaticorum (Canes Venatici) versus singular Alpha Piscis Austrini (Piscis Austrinus) and Alpha Canis Majoris (Canis Major). Astronomy manuals often list the genitive forms, as some are easy to get wrong even with a basic knowledge of Latin, e.g. Vela, which is a neuter plural not a feminine singular: Delta Velorum not *Delta Velae.

Pollux (star)

Polluxβ Gemβ Geminorum
Castor and Pollux of Gemini may be an example of this: Pollux is brighter than Castor, but the latter rises earlier and was assigned alpha.
β Geminorum (Latinised to Beta Geminorum) is the star's Bayer designation.

Johann Bayer

Bayer Johann BayerBayer, Johann
Most of the brighter stars were assigned their first systematic names by the German astronomer Johann Bayer in 1603, in his star atlas Uranometria.
The Uranometria introduced a new system of star designation which has become known as the Bayer designation.

Gemini (constellation)

Geminiconstellation GeminiGem
Castor and Pollux of Gemini may be an example of this: Pollux is brighter than Castor, but the latter rises earlier and was assigned alpha.
Castor's Bayer designation as "Alpha" arose because Johann Bayer did not carefully distinguish which of the two was the brighter when he assigned his eponymous designations in 1603.

Thuban

α DraconisAdibAlpha Draconians
Although the brightest star in Draco is Eltanin (Gamma Draconis), Thuban was assigned alpha by Bayer because, due to precession, Thuban was the north pole star 4,000 years ago.
α Draconis (Latinised to Alpha Draconis) is the star's Bayer designation.

Uranometria

Uranometria Omnium Asterismorum1603Uranometria atlas
Most of the brighter stars were assigned their first systematic names by the German astronomer Johann Bayer in 1603, in his star atlas Uranometria.
Uranometria introduced the convention of labelling stars by Greek and Latin letters, known as Bayer star designations, a system which is still used today.

P Cygni

P CygP Cygni profileP-Cygni Profile
Bayer did not intend such labels as catalog designations, but some have survived to refer to astronomical objects: P Cygni for example is still used as a designation for Nova Cyg 1600.
The designation "P" was originally assigned by Johann Bayer in Uranometria as a nova.

Argo Navis

ArgoArgosSouth Pole Star
(Constellations with no alpha include Vela and Puppis – both formerly part of Argo Navis, whose alpha is Canopus in Carina.)
Lacaille replaced Bayer's designations with new ones that followed stellar magnitudes more closely, but used only a single Greek-letter sequence and described the constellation for those stars as "Argûs".

Canopus

α Carinaea first magnitude starCanopean
(Constellations with no alpha include Vela and Puppis – both formerly part of Argo Navis, whose alpha is Canopus in Carina.)
α Carinae (Latinised to Alpha Carinae) is the star's Bayer designation.

Upsilon Librae

υ Lib
Bayer's Gamma and Omicron Scorpii, for example, were later reassigned from Scorpius to Libra and given the new names Sigma and Upsilon Librae.
Upsilon Librae (υ Lib, υ Librae) is the Bayer designation for a double star in the zodiac constellation Libra.

Bellatrix

γ Oria star in the Orion constellationγ Ori (Bellatrix)
γ Orionis is the star's Bayer designation.

Orion (constellation)

Orionconstellation of OrionOrion constellation
Orion provides a good example of Bayer's method.
Betelgeuse, alternatively by its Bayer designation Alpha Orionis, is a massive M-type red supergiant star nearing the end of its life. When it explodes it will even be visible during the day. It is the second brightest star in Orion, and is a semiregular variable star. It serves as the "right shoulder" of the hunter it represents (assuming that he is facing the observer), and is the eighth brightest star in the night sky.

HR 3803

N VelN Velorum
Examples include s Carinae (s of the constellation Carina), d Centauri (d of the constellation Centaurus), G Scorpii (G of the constellation Scorpius), and N Velorum (N of the constellation Vela).
In 1752, French astronomer Nicolas Louis de Lacaille divided the former constellation Argo Navis into three separate constellations, and then referenced its stars by extending Bayer's system of star nomenclature; this star was given the designation N Velorum.

Alnitak

ζ OriAlnitahAlnitak (ζ Ori)
ζ Orionis (Latinised as Zeta Orionis) is the star system's Bayer designation and 50 Orionis its Flamsteed designation.

Cygnus (constellation)

Cygnusconstellation of CygnusCygnus constellation
In Cygnus, for example, Bayer's fixed stars run through g, and on this chart Bayer employs H through P as miscellaneous labels, mostly for neighboring constellations.
Bayer catalogued many stars in the constellation, giving them the Bayer designations from Alpha to Omega and then using lowercase Roman letters to g. John Flamsteed added the Roman letters h, i, k, l and m (these stars were considered informes by Bayer as they lay outside the asterism of Cygnus), but were dropped by Francis Baily.