The stars of Gemini: Pollux and Castor

Pollux and Castor. Image source: [1]

  Who are Gemini's twins? As for the astronomical objects, the famous constellation is dominated by two bright stars: Pollux (on the left) and Castor (on the right). The two stars stand out because they are similar in angle and brightness, but are very different in color.  

  Pollux is a giant orange star of spectral type K0IIIb. Located 33.7 light years away, it is the giant orange that is closest to the Solar System. With a surface temperature of 4770 K, its radius is 9 or 10 times bigger than the solar radius. Including radiated energy in the infrared, its luminosity, although much superior to Sun's 46 times greater, is low in comparison to other orange giants near like Arturo (α Boötis) or Mentkent (θ Centauri). Its luminosity and temperature allow to estimate a mass 1,8 times greater than the solar mass. As a giant star that is, at its core is the fusion of helium into carbon and oxygen.  

  More details here:  Pollux

  The Sun viewed from the star Pollux (in red circle) in the constellationSagittarius. Made with Celestia. Image source: [2]

  Castor is a giant orange star, which means that it has a luminosity between 60 and 300 times the solar. It is also the star of this type closest to the Solar System and around it orbits an extrasolar planet. It has a visual magnitude of 1.58 and it is curious that in fact the star is a multiple star system of six stars that can only be observed with powerful telescopes. However, Castor does not hold the title of being the most brilliant star of Gemini, since the title belongs to its companion: Póllux.  

  More details here: Castor