Universe Guide

Castor C (Companion Star) Facts

Castor C Facts

Castor C's Alternative Names

(Alpha Geminorum C) is the Bayer Classification for the star. The Bayer Classification was created by Johann Bayer in the early nineteenth century. The brightest star in the constellation is normally given the Alpha designation although there are exceptions such as Pollux which is Beta Geminorum.

Castor C has alternative name(s) :- YY Geminorum.

More details on objects' alternative names can be found at Star Names .

Location of Castor C

The location of the main sequence star in the night sky is determined by the Right Ascension (R.A.) and Declination (Dec.), these are equivalent to the Longitude and Latitude on the Earth. The Right Ascension is how far expressed in time (hh:mm:ss) the star is along the celestial equator. If the R.A. is positive then its eastwards. The Declination is how far north or south the object is compared to the celestial equator and is expressed in degrees. For Castor C, the location is 07h 34m 37.584 and +31 ° 53` 17.81 .

Radial Velocity and Proper Motion of Castor C

Proper Motion

All stars like planets orbit round a central spot, in the case of planets, its the central star such as the Sun. In the case of a star, its the galactic centre. The constellations that we see today will be different than they were 50,000 years ago or 50,000 years from now. Proper Motion details the movements of these stars and are measured in milliarcseconds. The star is moving -96.00 milliarcseconds/year towards the north and -207.60 milliarcseconds/year east if we saw them in the horizon.

Radial Velocity

The Radial Velocity, that is the speed at which the star is moving away/towards the Sun is 2.50 km/s . When the value is negative then the star and the Sun are getting closer to one another, likewise, a positive number means that two stars are moving away. Its nothing to fear as the stars are so far apart, they won't collide in our life-time, if ever.

Physical Properties (Colour) of Castor C

Castor C Colour and Temperature

Castor C has a spectral type of M0.5VeFe-2 C. This means the star is a red main sequence star.

Castor C Apparent and Absolute Magnitudes

Magnitude, whether it be apparent/visual or absolute magnitude is measured by a number, the smaller the number, the brighter the Star is. Our own Sun is the brightest star and therefore has the lowest of all magnitudes, -26.74. A faint star will have a high number.

Variable Type of Castor C

The star is a rotating BY Draconis variable type which means that its size changes over time. The Variable Type is usually named after the first star of that type to be spotted.

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Additional Castor C Facts and Figures

Visual Facts

Primary / Proper / Traditional NameCastor C
Alternative NamesAlpha Geminorum C, YY Geminorum
Spectral TypeM0.5VeFe-2 C
Constellation's Main StarNo
Multiple Star SystemYes
Star Type Main Sequence Dwarf Star
GalaxyMilky Way
Right Ascension (R.A.)07h 34m 37.584
Declination (Dec.)+31 ° 53` 17.81
Proper Motion Dec.-96.00 milliarcseconds/year
Proper Motion RA.-207.60 milliarcseconds/year
Radial Velocity2.50 km/s
Associated / Clustered StarsCastor
Castor B

Companions (Multi-Star and Exoplanets) Facts

Exoplanet CountNone/Unaware

Variable Star Details

Variable Star ClassRotating
Variable Star TypeBY Draconis

Sources and Links


Location of Castor C in Gemini

Castor C Location in Gemini

The map was generated using Night Vision, an awesome free application by Brian Simpson.

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