Alpha or Castor which means the Horseman, the 23rd brightest star in the sky at magnitude 1.9 is the second brightest star in Gemini lying 51 light years from Earth, Castor is an A 1 class star with a temperature of around 10,000’c much hotter the Sun at 5,800’C. Although it appears to the naked eye as a single star there are in fact 6 stars that make up the Castor system.