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Castor is a bright star located in the constellation Gemini, one of the zodiac constellations visible in the night sky. It matters to astronomy because it is actually a complex multiple star system rather than a single star, making it scientifically valuable for understanding stellar properties and interactions.
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Castor is the second-brightest object in the zodiac constellation of Gemini. It has the Bayer designation α Geminorum, which is Latinised to Alpha Geminorum and abbreviated Alpha Gem or α Gem. With an apparent visual magnitude of 1.58, it is one of the brightest stars in the night sky. Castor appears singular to the naked eye, but it is actually a sextuple star system organized into three binary pairs. Although it is the 'α' (alpha) member of the constellation, it is half a magnitude fainter than 'β' (beta) Geminorum, Pollux.
Stellar system