A report on Castor (star)

A visual band light curve for YY Geminorum (Castor C), adapted from Butler et al. (2015)

Second-brightest object in the zodiac constellation of Gemini.

- Castor (star)
A visual band light curve for YY Geminorum (Castor C), adapted from Butler et al. (2015)

8 related topics with Alpha

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Gemini (constellation)

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One of the constellations of the zodiac and is located in the northern celestial hemisphere.

One of the constellations of the zodiac and is located in the northern celestial hemisphere.

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The constellation Gemini as it can be seen with the unaided eye, with added connecting lines.
AFGL 5180 - Through the Clouds.
An animation of the constellation Gemini (center), "the twins", shows two parallel stick figures. Gemini is associated with the myth of Castor and Polydeuces (also known as Pollux), collectively known as the Dioscuri.
Gemini as depicted in Urania's Mirror, a set of constellation cards published in London c.1825.
Sculpture showing Castor and Pollux, the legend behind the third astrological sign in the Zodiac and the constellation of Gemini
Diagram of H. A. Rey's alternative way to connect the stars of the constellation Gemini. Twins are shown holding hands.

The easiest way to locate the constellation is to find its two brightest stars Castor and Pollux eastward from the familiar V-shaped asterism (the open cluster Hyades) of Taurus and the three stars of Orion's Belt (Alnitak, Alnilam, and Mintaka).

Detail of Bayer's chart for Orion showing the belt stars and Orion Nebula region, with both Greek and Latin letter labels visible

Bayer designation

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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.

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.

Detail of Bayer's chart for Orion showing the belt stars and Orion Nebula region, with both Greek and Latin letter labels visible
Orion constellation map

A good example is the constellation Gemini, where Pollux is Beta Geminorum and the slightly dimmer Castor is Alpha Geminorum.

Pollux is one of the two brightest stars in the constellation of Gemini (lower left).

Pollux (star)

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Brightest star in constellation of Gemini.

Brightest star in constellation of Gemini.

Pollux is one of the two brightest stars in the constellation of Gemini (lower left).
The Sun viewed from Pollux (in red circle) in the constellation Sagittarius. Made with Celestia.
Size comparison of Pollux (left) and the Sun (right)

Castor and Pollux are the two "heavenly twin" stars giving the constellation Gemini (Latin, 'the twins') its name.

Binary system of two stars

Binary star

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System of two stars that are gravitationally bound to and in orbit around each other.

System of two stars that are gravitationally bound to and in orbit around each other.

Binary system of two stars
Edge-on disc of gas and dust present around the binary star system HD 106906
Algol B orbits Algol A. This animation was assembled from 55 images of the CHARA interferometer in the near-infrared H-band, sorted according to orbital phase.
Artist's conception of a cataclysmic variable system
Artist's impression of the binary star system AR Scorpii
Artist rendering of plasma ejections from V Hydrae
Artist's impression of the sight from a (hypothetical) moon of planet HD 188753 Ab (upper left), which orbits a triple star system. The brightest companion is just below the horizon.
Schematic of a binary star system with one planet on an S-type orbit and one on a P-type orbit
The two visibly distinguishable components of Albireo
Luhman 16, the third closest star system, contains two brown dwarfs.
Planet Lost in the Glare of Binary Stars (illustration)

There are also examples of systems beyond ternaries: Castor is a sextuple star system, which is the second-brightest star in the constellation Gemini and one of the brightest stars in the nighttime sky.

Star system named DI Cha. While only two stars are apparent, it is actually a quadruple system containing two sets of binary stars.

Star system

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Small number of stars that orbit each other, bound by gravitational attraction.

Small number of stars that orbit each other, bound by gravitational attraction.

Star system named DI Cha. While only two stars are apparent, it is actually a quadruple system containing two sets of binary stars.
Orbits of the HR 6819 hierarchical triple star system: an inner binary with one star (orbit in blue) and a black hole (orbit in red), encircled by another star in a wider orbit (also in blue).
Subsystem notation in Tokovinin's Multiple Star Catalogue
Sirius A (center), with its white dwarf companion, Sirius B (lower left) taken by the Hubble Space Telescope.
HD 98800 is a quadruple star system located in the TW Hydrae association.

A real example of a system with hierarchy 3 is Castor, also known as Alpha Geminorum or α Gem. It consists of what appears to be a visual binary star which, upon closer inspection, can be seen to consist of two spectroscopic binary stars. By itself, this would be a quadruple hierarchy 2 system as in (d), but it is orbited by a fainter more distant component, which is also a close red dwarf binary. This forms a sextuple system of hierarchy 3.

Astronomers have mistakenly reported observations of a double star in place of J 900 and a faint star in the constellation of Gemini.

Double star

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Pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes.

Pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes.

Astronomers have mistakenly reported observations of a double star in place of J 900 and a faint star in the constellation of Gemini.
Artist's impression of the discs around the young stars HK Tauri A and B.

Castor system (Aa/Ab/Ba/Bb) and YY Geminorum (thus Castor Ca/Cb) is generally considered a physical system

Statues of Castor and Pollux (3rd century AD)

Castor and Pollux

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Castor and Pollux (or Polydeukes) are twin half-brothers in Greek and Roman mythology, known together as the Dioscuri.

Castor and Pollux (or Polydeukes) are twin half-brothers in Greek and Roman mythology, known together as the Dioscuri.

Statues of Castor and Pollux (3rd century AD)
Castor depicted on a calyx krater of c. 460–450 BC, holding a horse's reins and spears and wearing a pilos-style helmet
Pair of Roman statuettes (3rd century AD) depicting the Dioscuri as horsemen, with their characteristic skullcaps (Metropolitan Museum of Art)
The Rape of the Daughters of Leucippus by Rubens, c. 1618
Coin of Antiochus VI with Dioskouroi
Robert Fagan Castor and Pollux (between 1793 and 1795)
Fragmentary remains of the Temple of Castor and Pollux in Rome.
Relief (2nd century BC) depicting the Dioskouroi galloping above a winged Victory, with a banquet (theoxenia) laid out for them below
Funerary stele from Alba Iulia; it reads Invicto/ Mythrae / Diosco/rus Marci/ v(otum) s(olvit) l(ibens) m(erito) Dioscorus pays the vows of Marcus to the invincible Mythras and willingly deserves it.
Etruscan inscription to the Dioskouroi as "sons of Zeus" at the bottom of an Attic red-figure kylix (c. 515–510 BC)
Zeus, Hera, and Amor observe the birth of Helen and Dioscuri (Dutch majolica, 1550).

The brothers became the two brightest stars in the constellation Gemini ("the twins"): Castor (Alpha Geminorum) and Pollux (Beta Geminorum).

Diagram of Rho Geminorum and the four companions listed in the WDS

Rho Geminorum

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Diagram of Rho Geminorum and the four companions listed in the WDS
The positions of the three stars in the Rho Geminorum system on the Hertzsprung-Russell diagram. As Rho Geminorum B does not have a known B-V or temperature, a line through its absolute magnitude is drawn instead.
A light curve for V376 Geminorum (ρ Geminorum C), plotted from TESS data covering a single 11.63 day period.

Rho Geminorum (ρ Gem) is a star system that lies approximately 59 light-years away in the constellation of Gemini, about 5 arcminutes east of Castor.