description Castor Overview
Castor, designated Alpha Geminorum, is the second-brightest star system in the constellation of Gemini, located approximately 51 light-years from Earth. Despite its Bayer designation implying it is the brightest, it is fainter than its neighbor Pollux. Astronomically, Castor is a complex system composed of six individual stars arranged into three binary pairs that orbit a common center of mass.
insights Ranking position
Castor ranks #34 of 221 in the Star ranking, behind Fomalhaut, ahead of V838 Monocerotis.
help Castor FAQ
Why is Castor called one star if it is actually six?
Castor appears as a single point to the unaided eye, but observations resolve it into three gravitationally associated binary pairs. The system is therefore described as sextuple rather than as one isolated star.
Is Castor brighter than Pollux in Gemini?
No. Castor is designated Alpha Geminorum, but Pollux is the constellation's brightest star, while Castor is second-brightest at about apparent magnitude 1.6.
Can Castor's components be separated with an amateur telescope?
A suitable telescope can separate the bright Castor A and Castor B pair under good conditions. The complete six-star architecture cannot be visually resolved so simply because each major component is itself a close binary.
How far away is the Castor star system?
Castor is roughly 51 light-years from the Solar System. Its third visible component is also known as YY Geminorum, an eclipsing pair of red dwarf stars.
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