Universe Guide


Castor B, Alpha Geminorum B

Castor B (Alpha Geminorum B) is a blue star that can be located in the constellation of Gemini. Castor B is the brightest star in Gemini based on the Hipparcos 2007 apparent magnitude. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.

Alpha Geminorum B is the Bayer Classification for the star.

Location of Castor B

The location of the star in the galaxy 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 star is compared to the celestial equator and is expressed in degrees. For Castor B, the location is 07h 34m 36.10 and +31 d 53 ` 18.57 .

Physical Properties (Colour, Radius) of Castor B

Castor B has a spectral type of Am. This means the star is a blue star.

The star has a companion star which is in orbit close by, it has at least the following companions in close orbit, .

Castor B Apparent and Absolute Magnitudes

Castor B has an apparent magnitude of 2.97 which is how bright we see the star from Earth. Apparent Magnitude is also known as Visual Magnitude. 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.

Source of Information

The source of the information if it has a Hip I.D. is from Simbad, the Hipparcos data library based at the University at Strasbourg, France. Hipparcos was a E.S.A. satellite operation launched in 1989 for four years. The items in red are values that I've calculated so they could well be wrong. Information regarding Metallicity and/or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.

Castor B Facts

Alternative Names

Traditional/Proper NameCastor B
Bayer DesignationAlpha Geminorum B

Visual Facts

Star Type star
Visual / Apparent Magnitude2.97
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)07h 34m 36.10
Declination (Dec.)+31 d 53 ` 18.57
Spectral TypeAm
Colour(A) blue

Estimated Facts

Related Stars

Location of Castor B in Gemini

Castor B (Alpha Geminorum B) Location in Gemini

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

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