Castor, the Star

stars · binary systems · gemini · constellations

Six stars in one. Castor appears as a single point of light to your naked eye, but telescopes reveal it's actually six stars organized into three pairs. Each pair orbits around each other, like a cosmic dance happening far away in space.

Super bright neighbor. Castor is one of the brightest stars visible from Earth, with only a few thousand stars outshining it when you look up at night. It's the second-brightest thing in the Gemini constellation, even though it's labeled as the alpha or primary star.

Binary pairs everywhere. Each of Castor's three binary pairs consists of two stars locked in orbit around their shared center of gravity. This arrangement is common in space, where stars often come in twos or groups rather than existing alone like our Sun.

Ancient constellation star. Castor is a major star in Gemini, one of the 12 zodiac constellations that ancient people used to navigate and tell time. The name Castor comes from Greek mythology, referring to one of the twin brothers in the story of the Gemini twins.