Castor - α Geminorum (alpha Geminorum)
Castor, also designated as α Geminorum (alpha Geminorum), is a variable and multiple main-sequence star in the constellation of Gemini.
Castor visual magnitude is 1.98, making it the 46th brightest star in the sky. Thanks to its high brightness, Castor is clearly visible when observed from locations with dark skyes, and should be also quite easily visible from light polluted areas.
The table below summarizes the key facts about Castor:
Celestial coordinates and finder chart of Castor
Castor is situated north of the celestial equator, as such, it is more easily visible from the northern hemisphere. Celestial coordinates for the J2000 equinox as well as galactic coordinates of Castor are provided in the following table:
The simplified sky map below shows the position of Castor in the sky:
Visibility of Castor from your location
Digitized Sky Survey image of Castor
The image below is a photograph of Castor from the Digitized Sky Survey 2 (DSS2 - see the credits section) taken in the red channel. The area of sky represented in the image is 0.5x0.5 degrees (30x30 arcmins). The proper motion of Castor is -0.171 arcsec per year in Right Ascension and -0.098 arcsec per year in Declination and the associated displacement for the next 1000 years is represented with the red arrow.
Distance of Castor from the Sun and relative movement
Castor is distant 51.53 light years from the Sun and it is moving far from the Sun at the speed of 6 kilometers per second.
Spectral properties of Castor
Castor belongs to spectral class A1 and has a luminosity class of V corresponding to a main-sequence star.
The red dot in the diagram below shows where Castor is situated in the Hertzsprung–Russell diagram.
Castor star system properties
Castor is a visual double star which can be observed with the help of medium or large telescopes. The table below shows key information about the Castor double sysyem: