Although Pollux is slightly brighter, the star designated as Kastor (the 23rd brightest star in the sky) is represented by the Greek letter alpha. It has a magnitude of 1.5 and is located 51 light-years away from Earth. In addition, it is known as a multiple star system. The primary component has a magnitude of 1.9 and is overall 22 times more luminous than the Sun, while the companion reaches a magnitude of 2.9. They orbit each other around a common center of gravity every 445 years. The angular separation of the pair has been relatively small in recent years, reaching a minimum of 1.9" in 1970. Since then, it has gradually increased, allowing these blue components to be resolved even with a small telescope. In 1985, their separation was 2.6", and by 2017, it had increased to 6".